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工程力学
Engineering Mechanics
Since 1984 Monthly
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Chief Editor: Xinzheng LU
Editor & Publisher: 《工程力学》杂志社
ISSN 1000-4750 CN 11-2595/O3
Articles online first have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
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2023 No. 9, Publish Date: 2023-09-06
Display Method:
2023, 40(9): 1-12.
doi: 10.6052/j.issn.1000-4750.2022.01.0032
Abstract:
Closed-form expressions considering the influence of single or multiple rectangular holes on the critical elastic buckling stress of plates under bending, compression, shearing and combined bending shear are developed, validated and summarized. The expression forms are based on classical plate stability approximations, and are developed and verified by parametric studies employing shell finite elements. The expressions serve as a convenient alternative to shell finite element eigen-buckling analysis. The finite element parameter studies show that holes may produce unique buckling modes, and the change of hole spacing may reduce or increase the critical elastic buckling stress of the plate. When the spacing between holes is long enough, the buckling stress equation of single-hole plate can be used for multiple-hole plate. The validated closed-form expressions and their associated limitations are intended to be versatile enough to accommodate the range of hole sizes and spacings commonly found in engineering practice.
Closed-form expressions considering the influence of single or multiple rectangular holes on the critical elastic buckling stress of plates under bending, compression, shearing and combined bending shear are developed, validated and summarized. The expression forms are based on classical plate stability approximations, and are developed and verified by parametric studies employing shell finite elements. The expressions serve as a convenient alternative to shell finite element eigen-buckling analysis. The finite element parameter studies show that holes may produce unique buckling modes, and the change of hole spacing may reduce or increase the critical elastic buckling stress of the plate. When the spacing between holes is long enough, the buckling stress equation of single-hole plate can be used for multiple-hole plate. The validated closed-form expressions and their associated limitations are intended to be versatile enough to accommodate the range of hole sizes and spacings commonly found in engineering practice.
2023, 40(9): 13-19.
doi: 10.6052/j.issn.1000-4750.2021.12.0005
Abstract:
High-resolution flow field data has a great significance to the study of fluid induced vibration and vortex induced vibration mechanism. Limited by measurement methods and calculation efficiency, it is still difficult to obtain high-resolution flow fields. Thusly, the low-dimensional representation model of flow time history data is adopted, and a deep learning method is proposed for the reconstruction of unsteady flow time history data. A low-dimensional representation model is established for the unsteady flow field based on the one-dimensional convolution method; The mapping relationship is developed between the physical space and the encoding space; The decoder in the representation model is utilized to generate the flow field time history data at any position. The problem of unsteady flow around bridge deck is verified, and the accuracy of the method is proved. The method proposed is a high-precision flow field data reconstruction method in the time dimension, and it is an unsupervised training method. It is a brand-new method that can be widely used in point-based sensor data processing.
High-resolution flow field data has a great significance to the study of fluid induced vibration and vortex induced vibration mechanism. Limited by measurement methods and calculation efficiency, it is still difficult to obtain high-resolution flow fields. Thusly, the low-dimensional representation model of flow time history data is adopted, and a deep learning method is proposed for the reconstruction of unsteady flow time history data. A low-dimensional representation model is established for the unsteady flow field based on the one-dimensional convolution method; The mapping relationship is developed between the physical space and the encoding space; The decoder in the representation model is utilized to generate the flow field time history data at any position. The problem of unsteady flow around bridge deck is verified, and the accuracy of the method is proved. The method proposed is a high-precision flow field data reconstruction method in the time dimension, and it is an unsupervised training method. It is a brand-new method that can be widely used in point-based sensor data processing.
2023, 40(9): 20-28.
doi: 10.6052/j.issn.1000-4750.2022.01.0022
Abstract:
Fracture is the main failure form of marine structures due to the action of ocean waves. It is necessary to monitor the initiation and extension of the crack timely and accurately, and the SIF (Stress Intensity Factor) is an important indicator for judging the propagation of cracks. Based on the existing research, this study combines the calculation method for SIF based on single strain gauge (SSG) and maximum crack opening displacement (CMOD) and, proposes a method based on Kalman filter (KF). Numerical simulation and experimental verifications of this method have been carried out. The results show that the method can be used for a variety of configurations of pre-cracked specimens. And compared with the SSG-based and CMOD-based methods, the KF-based method can obtain more accurate results, the relative errors (RE) is not more than 1.2%.
Fracture is the main failure form of marine structures due to the action of ocean waves. It is necessary to monitor the initiation and extension of the crack timely and accurately, and the SIF (Stress Intensity Factor) is an important indicator for judging the propagation of cracks. Based on the existing research, this study combines the calculation method for SIF based on single strain gauge (SSG) and maximum crack opening displacement (CMOD) and, proposes a method based on Kalman filter (KF). Numerical simulation and experimental verifications of this method have been carried out. The results show that the method can be used for a variety of configurations of pre-cracked specimens. And compared with the SSG-based and CMOD-based methods, the KF-based method can obtain more accurate results, the relative errors (RE) is not more than 1.2%.
2023, 40(9): 29-36.
doi: 10.6052/j.issn.1000-4750.2021.12.1012
Abstract:
Proposed is a theory-aided few-shot learning algorithm applicable to any material elastoplastic relationships utilized in civil engineering. The new algorithm can effectively alleviate the paucity of data in real applications when applying large-scale deep learning models. The framework of the classical elastoplasticity theory is briefly recapped. On this basis, the paper elaborates on how to incorporate the elastoplastic equations into the ordinary deep learning models, wherein the entire processes require neither the concrete form of the underlying models nor its complicated numerical implementation, thus maintaining the simple, direct, and efficient advantages of data-driven techniques. To address the divergence issue caused by the complicated optimization target, a novel training strategy named overfitting-correction method is invented, which is able to stabilize the training and accelerate the convergence. A numerical experiment is performed upon a sophisticated elastoplastic constitutive model of structural steel. The results demonstrate that the theory-aided few-shot learning algorithm succeeds in realizing excellent generalization performance of a large-scale deep learning model on small training datasets. Quantitatively, the new algorithm overwhelms the pure data-driven model by 38.9%. The philosophy of theory-aided driven mode proposed can extend to the structural level in the future, facilitating the introduction of more advanced intelligent technologies into civil engineering.
Proposed is a theory-aided few-shot learning algorithm applicable to any material elastoplastic relationships utilized in civil engineering. The new algorithm can effectively alleviate the paucity of data in real applications when applying large-scale deep learning models. The framework of the classical elastoplasticity theory is briefly recapped. On this basis, the paper elaborates on how to incorporate the elastoplastic equations into the ordinary deep learning models, wherein the entire processes require neither the concrete form of the underlying models nor its complicated numerical implementation, thus maintaining the simple, direct, and efficient advantages of data-driven techniques. To address the divergence issue caused by the complicated optimization target, a novel training strategy named overfitting-correction method is invented, which is able to stabilize the training and accelerate the convergence. A numerical experiment is performed upon a sophisticated elastoplastic constitutive model of structural steel. The results demonstrate that the theory-aided few-shot learning algorithm succeeds in realizing excellent generalization performance of a large-scale deep learning model on small training datasets. Quantitatively, the new algorithm overwhelms the pure data-driven model by 38.9%. The philosophy of theory-aided driven mode proposed can extend to the structural level in the future, facilitating the introduction of more advanced intelligent technologies into civil engineering.
2023, 40(9): 37-47.
doi: 10.6052/j.issn.1000-4750.2021.12.1017
Abstract:
The cold regions at high altitude have the characteristics of high altitude, low temperature and large temperature difference between day and night. Under the action of freeze-thaw cycle, the concrete structure is prone to damage in the high altitude and cold regions, which affects the service life of buildings and even threatens the safety of buildings when the damage is serious. To study the working performance, mechanical properties, frost resistance durability and freeze-thaw damage mechanism of concrete in the high altitude and cold regions, four kinds of concrete specimens were produced in a bridge construction project, and the freeze-thaw cycle tests were carried out. At the same time, the Nuclear Magnetic Resonance (NMR) tests of concrete under different freeze-thaw cycles were carried out. The results show that the alpine air-entraining and water-reducing concrete has the best frost resistance durability from the perspective of macroscopic mechanical properties. At the same time, the frost resistance durability of the four alpine concrete specimens is closely related to the proportion of mesopores (<0.01 μm) and micropores (0.01 μm-0.05 μm) inside the concrete, i.e., the proportion of small pores and mesopores in the alpine concrete. A larger proportion leads to a better frost resistance of concrete.
The cold regions at high altitude have the characteristics of high altitude, low temperature and large temperature difference between day and night. Under the action of freeze-thaw cycle, the concrete structure is prone to damage in the high altitude and cold regions, which affects the service life of buildings and even threatens the safety of buildings when the damage is serious. To study the working performance, mechanical properties, frost resistance durability and freeze-thaw damage mechanism of concrete in the high altitude and cold regions, four kinds of concrete specimens were produced in a bridge construction project, and the freeze-thaw cycle tests were carried out. At the same time, the Nuclear Magnetic Resonance (NMR) tests of concrete under different freeze-thaw cycles were carried out. The results show that the alpine air-entraining and water-reducing concrete has the best frost resistance durability from the perspective of macroscopic mechanical properties. At the same time, the frost resistance durability of the four alpine concrete specimens is closely related to the proportion of mesopores (<0.01 μm) and micropores (0.01 μm-0.05 μm) inside the concrete, i.e., the proportion of small pores and mesopores in the alpine concrete. A larger proportion leads to a better frost resistance of concrete.
2023, 40(9): 48-60.
doi: 10.6052/j.issn.1000-4750.2022.01.0018
Abstract:
To study the shear behaviors of steel-concrete composite beams after experiencing high temperatures, Material performance tests on normal concrete and steel after high temperature and static load tests on steel-concrete composite beams after high temperatures were carried out involving experimental parameters of heating temperature and cooling regime. The mechanical properties of concrete and steel after high temperatures and two cooling regimes were studied, and the microstructure of concrete after high temperatures was observed by using the scanning electron microscope. Then, seven steel-concrete composite beams were designed according to 'strong bending and weak shear'. The distribution of the section temperature field during temperature rise and fall was measured. Loading failure tests on composite beams at room temperature and after experiencing high temperatures were carried out. The ultimate bearing capacity, mid-span deflection and strain of composite beams at room temperature and after high temperatures were compared and analyzed. Furthermore, the effects of heating temperature and cooling regime on mechanical performance of composite beams were analyzed, and the calculation method for ultimate shear capacity of composite beams after high temperatures was discussed. The results show that the loose cement compound in concrete and the crack at the wrapping interface between cement and aggregate are the main factors causing the deterioration of macro mechanical properties of concrete after experiencing high temperatures. The failure modes of steel-concrete composite beams at room temperature and after high temperatures are penetrating oblique cracks in concrete slab. The bearing capacity, stiffness and ductility of composite beams decrease with the increasing heating temperature. When the temperature is lower than 400 ℃, the cooling regime has little effect on the bearing capacity. When the temperature is 600 ℃, the bearing capacity of composite beams after water spray cooling is greater than that of natural cooling. Compared with the natural cooling specimens, the stiffness of the specimens after water spray cooling is large and the ultimate deflection is small. Based on the experimental data and regression analysis, the calculation formulas between concrete compressive strength, steel yield strength and heating temperature are established. The calculated values of the revised AS/NZS 2327 specification formula are in good agreement with the test values.
To study the shear behaviors of steel-concrete composite beams after experiencing high temperatures, Material performance tests on normal concrete and steel after high temperature and static load tests on steel-concrete composite beams after high temperatures were carried out involving experimental parameters of heating temperature and cooling regime. The mechanical properties of concrete and steel after high temperatures and two cooling regimes were studied, and the microstructure of concrete after high temperatures was observed by using the scanning electron microscope. Then, seven steel-concrete composite beams were designed according to 'strong bending and weak shear'. The distribution of the section temperature field during temperature rise and fall was measured. Loading failure tests on composite beams at room temperature and after experiencing high temperatures were carried out. The ultimate bearing capacity, mid-span deflection and strain of composite beams at room temperature and after high temperatures were compared and analyzed. Furthermore, the effects of heating temperature and cooling regime on mechanical performance of composite beams were analyzed, and the calculation method for ultimate shear capacity of composite beams after high temperatures was discussed. The results show that the loose cement compound in concrete and the crack at the wrapping interface between cement and aggregate are the main factors causing the deterioration of macro mechanical properties of concrete after experiencing high temperatures. The failure modes of steel-concrete composite beams at room temperature and after high temperatures are penetrating oblique cracks in concrete slab. The bearing capacity, stiffness and ductility of composite beams decrease with the increasing heating temperature. When the temperature is lower than 400 ℃, the cooling regime has little effect on the bearing capacity. When the temperature is 600 ℃, the bearing capacity of composite beams after water spray cooling is greater than that of natural cooling. Compared with the natural cooling specimens, the stiffness of the specimens after water spray cooling is large and the ultimate deflection is small. Based on the experimental data and regression analysis, the calculation formulas between concrete compressive strength, steel yield strength and heating temperature are established. The calculated values of the revised AS/NZS 2327 specification formula are in good agreement with the test values.
2023, 40(9): 61-73.
doi: 10.6052/j.issn.1000-4750.2022.01.0019
Abstract:
Concrete-filled steel tubular (CFST) members combine the advantages of steel tube and core concrete, which has been gradually employed in bridge piers, and the impact resistance is a key issue to promote its application. For this purpose, a total of 56 finite element (FE) models of double-column CFST piers subjected to vehicle collision were established using LS-DYNA software, and mechanism analysis as well as parameter studies of impact resistance were performed. The FE models were verified by comparing with the data of the drop-hammer impact and the actual vehicle-impact test. The impact force, the plastic strain development, internal force distribution and energy conversion of typical CFST piers were investigated. The effects of steel ratio, axial-load ratio, cargo stiffness, vehicle mass and speed on the impact force and lateral-displacement distribution were analyzed. The equivalent static force method was used to calculate the 25 ms equivalent vehicle impact force (ESF25), and then the recommended value of AASHTO code was evaluated. The equation for the impact force of CFST piers was proposed. The results showed that steel tubes and concrete can work together well under vehicle impact, and steel tubes are the main energy-absorbing component. Due to the existence of the upper mass and the inertial force, the internal force distribution of the piers corresponding to different impact phases is significantly different. Parametric studies indicated that the vehicle mass and speed have significant influences on the evolution of impact force, while the effects of steel ratio and axial load ratio are marginal. In addition, the Young’s modulus of cargo has an obvious effect when it varies within 2000 MPa. The proposed equation could well predict the impact force of CFST piers considering the influence of the upper mass.
Concrete-filled steel tubular (CFST) members combine the advantages of steel tube and core concrete, which has been gradually employed in bridge piers, and the impact resistance is a key issue to promote its application. For this purpose, a total of 56 finite element (FE) models of double-column CFST piers subjected to vehicle collision were established using LS-DYNA software, and mechanism analysis as well as parameter studies of impact resistance were performed. The FE models were verified by comparing with the data of the drop-hammer impact and the actual vehicle-impact test. The impact force, the plastic strain development, internal force distribution and energy conversion of typical CFST piers were investigated. The effects of steel ratio, axial-load ratio, cargo stiffness, vehicle mass and speed on the impact force and lateral-displacement distribution were analyzed. The equivalent static force method was used to calculate the 25 ms equivalent vehicle impact force (ESF25), and then the recommended value of AASHTO code was evaluated. The equation for the impact force of CFST piers was proposed. The results showed that steel tubes and concrete can work together well under vehicle impact, and steel tubes are the main energy-absorbing component. Due to the existence of the upper mass and the inertial force, the internal force distribution of the piers corresponding to different impact phases is significantly different. Parametric studies indicated that the vehicle mass and speed have significant influences on the evolution of impact force, while the effects of steel ratio and axial load ratio are marginal. In addition, the Young’s modulus of cargo has an obvious effect when it varies within 2000 MPa. The proposed equation could well predict the impact force of CFST piers considering the influence of the upper mass.
2023, 40(9): 74-80.
doi: 10.6052/j.issn.1000-4750.2022.01.0021
Abstract:
Based on a theoretical analysis, a new functionally graded flexural concrete member (FGFCM) is proposed. Through the combined reinforcement of graded FRP bars and steel bars, the distribution gradient of the flexural load-bearing capacity along the member is adapted to the load distribution gradient. Then multiple functionally graded segments in the FGFCMs reach their plastic state, and the functional gradient is formed to more utilize the seismic capacity of the members. The distribution and development degree of the plasticity in the FGFCMs can be effectively controlled to achieve the ductile failure mode and better recoverability. The functional gradient greatly improves the deformation capacity, increases the lateral bearing capacity, reduces the ultimate stiffness, and enhances the seismic performance of the members. The model experiment proved the feasibility of the FGFCMs and their mechanical effects, and verified the effectiveness and engineering practicability of the proposed construction scheme to form the functional gradient.
Based on a theoretical analysis, a new functionally graded flexural concrete member (FGFCM) is proposed. Through the combined reinforcement of graded FRP bars and steel bars, the distribution gradient of the flexural load-bearing capacity along the member is adapted to the load distribution gradient. Then multiple functionally graded segments in the FGFCMs reach their plastic state, and the functional gradient is formed to more utilize the seismic capacity of the members. The distribution and development degree of the plasticity in the FGFCMs can be effectively controlled to achieve the ductile failure mode and better recoverability. The functional gradient greatly improves the deformation capacity, increases the lateral bearing capacity, reduces the ultimate stiffness, and enhances the seismic performance of the members. The model experiment proved the feasibility of the FGFCMs and their mechanical effects, and verified the effectiveness and engineering practicability of the proposed construction scheme to form the functional gradient.
2023, 40(9): 81-97.
doi: 10.6052/j.issn.1000-4750.2022.01.0024
Abstract:
To reveal the coupling dynamic characteristics of pile-soil systems under vertical seismic loads, the pile foundation was firstly regarded as a three-dimensional axisymmetric bar with radial and vertical deformation, and its motion equation was established by using a Hamiltonan variational principle. The soil around the pile was treated as a three-dimensional fluid-filled porous continuous medium, and its dynamic behavior was described by using Boer’s poroelastic media model. Without the introduction of potential functions, the volumetric strain of soil skeleton and pore fluid pressure were taken as intermediate variables to deal with the soil motion equation, and then the motion equations of soil and pile were solved by the method of variable separation. Combined with the boundary and continuity conditions of the pile-soil system, the analytical solutions of the kinematic amplification factor and kinematic response factor of the pile top were derived. The correctness of the proposed solution was verified by comparing the numerical results of the corresponding finite element model with the existing solutions. Finally, the influence of the main pile-soil parameters on the dynamic characteristics of the pile-soil coupling system was analyzed, and some meaningful conclusions were obtained, which can provide a reference for related engineering practice. The results show that: when the pile length-radius ratio is small, the radial deformation of pile foundation has a significant effect on the dynamic response of saturated soil-pile system. If the radial deformation of the pile foundation could be ignored, the resonance behavior of the pile-soil system might be overestimated. For single-phase soil, in the low frequency range, the response of a pile top is smaller than that of a free field surface and, in the high frequency range, it is larger with the increase of pile length-radius ratio. The resonance behavior of a pile-soil system occurs when the excitation frequency is close to the natural frequency of a soil free field. As the length-radius ratio of piles increases, the magnifying effect of a pile-soil system on bedrock movement tends to increase. For saturated soil, the response of saturated soil surface is basically the same as the movement of bedrock. With the increase of pile length-radius ratio, the magnifying effect of a pile-soil system on bedrock movement tends to decrease.
To reveal the coupling dynamic characteristics of pile-soil systems under vertical seismic loads, the pile foundation was firstly regarded as a three-dimensional axisymmetric bar with radial and vertical deformation, and its motion equation was established by using a Hamiltonan variational principle. The soil around the pile was treated as a three-dimensional fluid-filled porous continuous medium, and its dynamic behavior was described by using Boer’s poroelastic media model. Without the introduction of potential functions, the volumetric strain of soil skeleton and pore fluid pressure were taken as intermediate variables to deal with the soil motion equation, and then the motion equations of soil and pile were solved by the method of variable separation. Combined with the boundary and continuity conditions of the pile-soil system, the analytical solutions of the kinematic amplification factor and kinematic response factor of the pile top were derived. The correctness of the proposed solution was verified by comparing the numerical results of the corresponding finite element model with the existing solutions. Finally, the influence of the main pile-soil parameters on the dynamic characteristics of the pile-soil coupling system was analyzed, and some meaningful conclusions were obtained, which can provide a reference for related engineering practice. The results show that: when the pile length-radius ratio is small, the radial deformation of pile foundation has a significant effect on the dynamic response of saturated soil-pile system. If the radial deformation of the pile foundation could be ignored, the resonance behavior of the pile-soil system might be overestimated. For single-phase soil, in the low frequency range, the response of a pile top is smaller than that of a free field surface and, in the high frequency range, it is larger with the increase of pile length-radius ratio. The resonance behavior of a pile-soil system occurs when the excitation frequency is close to the natural frequency of a soil free field. As the length-radius ratio of piles increases, the magnifying effect of a pile-soil system on bedrock movement tends to increase. For saturated soil, the response of saturated soil surface is basically the same as the movement of bedrock. With the increase of pile length-radius ratio, the magnifying effect of a pile-soil system on bedrock movement tends to decrease.
2023, 40(9): 98-107.
doi: 10.6052/j.issn.1000-4750.2022.01.0037
Abstract:
In order to study the section classification of stainless steel flexural members, the finite element (FE) software ABAQUS was used to establish the FE model of stainless steel welded I-section and box-section members, and the validity of the FE models was verified by the experimental results. Using the FE model, a large number of parameter analyses were carried out, and the rationality and applicability of the classification limit of the width-to-thickness ratio of section plates in European stainless steel code EN 1993-1-4+A2 and standard for design of steel structures GB 50017−2017 were evaluated. By considering the correlation of section components, the paper proposed the section classification method, width-to-thickness ratio grade and limit value of section plates for austenitic stainless steel flexural members.
In order to study the section classification of stainless steel flexural members, the finite element (FE) software ABAQUS was used to establish the FE model of stainless steel welded I-section and box-section members, and the validity of the FE models was verified by the experimental results. Using the FE model, a large number of parameter analyses were carried out, and the rationality and applicability of the classification limit of the width-to-thickness ratio of section plates in European stainless steel code EN 1993-1-4+A2 and standard for design of steel structures GB 50017−2017 were evaluated. By considering the correlation of section components, the paper proposed the section classification method, width-to-thickness ratio grade and limit value of section plates for austenitic stainless steel flexural members.
2023, 40(9): 108-116, 189.
doi: 10.6052/j.issn.1000-4750.2022.01.0038
Abstract:
To improve the evaluation accuracy of flexural capacity of corroded reinforced concrete (RC) structures, a method for the model parameter updating and prediction of flexural capacity is proposed based on the improved particle filter (PF) algorithm. The proposed model comprehensively considers the geometric size of corroded RC structures, steel cross-sectional area and mechanical properties, concrete strength, bond performance and other factors. A large number of particles are generated to represent the uncertainty of model parameters during the degradation process of flexural capacity. The PF algorithm is improved from the perspective of selecting different proposal density functions to solve the problem of particle degradation in traditional PF algorithm. The PF, the extended particle filter (EPF) and the unscented particle filter (UPF) algorithm are employed to estimate and update the model parameters, which can effectively predict the flexural capacity of corroded RC structures. The results show that the flexural capacity of RC beams decreases gradually with the increase of steel corrosion loss. The prediction method of the flexural capacity of corroded RC structures based on the improved PF algorithm considers the updating of model parameters, which makes the prediction results closer to the reality. The improved PF algorithm based on EKF and UKF can effectively constrain the degradation of the particle, and the prediction accuracy is better than that of the PF algorithm. The prediction accuracy of the flexural capacity of corroded RC structures increases with the increase of training data and particle number.
To improve the evaluation accuracy of flexural capacity of corroded reinforced concrete (RC) structures, a method for the model parameter updating and prediction of flexural capacity is proposed based on the improved particle filter (PF) algorithm. The proposed model comprehensively considers the geometric size of corroded RC structures, steel cross-sectional area and mechanical properties, concrete strength, bond performance and other factors. A large number of particles are generated to represent the uncertainty of model parameters during the degradation process of flexural capacity. The PF algorithm is improved from the perspective of selecting different proposal density functions to solve the problem of particle degradation in traditional PF algorithm. The PF, the extended particle filter (EPF) and the unscented particle filter (UPF) algorithm are employed to estimate and update the model parameters, which can effectively predict the flexural capacity of corroded RC structures. The results show that the flexural capacity of RC beams decreases gradually with the increase of steel corrosion loss. The prediction method of the flexural capacity of corroded RC structures based on the improved PF algorithm considers the updating of model parameters, which makes the prediction results closer to the reality. The improved PF algorithm based on EKF and UKF can effectively constrain the degradation of the particle, and the prediction accuracy is better than that of the PF algorithm. The prediction accuracy of the flexural capacity of corroded RC structures increases with the increase of training data and particle number.
2023, 40(9): 117-129.
doi: 10.6052/j.issn.1000-4750.2022.01.0039
Abstract:
A statistical damage constitutive model of concrete under uniaxial compression is proposed to consider the impact of freeze-thaw. The entire compression process is divided into two stages: uniform damage and local failure, considering two mesoscopic damage modes of yield and fracture. Under the freeze-thaw environment, the internal pore structure and the mechanical characteristics of the microstructure will change significantly, which can be reflected by the initial elastic modulus E. In the process of further bearing the compressive load, the shape, path and quantity of microcracks initiation and propagation in the microstructure will also change due to the influence of the initial freeze-thaw degradation, which could be characterized by damage parameters εa, εh, εb and H. Assuming that under different number of freeze-thaw cycles, the evolution trend of the mechanical properties of the microstructure and the meso-damage process obey a certain regularity, thusly define the above 5 characteristic parameters as functions of the number of freeze-thaw cyclesN. To verify the rationality of the model, the uniaxial compression test was carried out, and the stress-strain full curves of concrete were obtained when the number of freeze-thaw cycles N changed from 0 to 150. Meanwhile, five groups of experimental data in the literature were also analyzed. The results show that: prediction curves are in a good agreement with the test curves, and the characteristic parameters in the model show obvious regularity as the number of freeze-thaw cycles increases. This model provides an effective tool for both the analysis and predicting damage mechanism of concrete in the freeze-thaw environment.
A statistical damage constitutive model of concrete under uniaxial compression is proposed to consider the impact of freeze-thaw. The entire compression process is divided into two stages: uniform damage and local failure, considering two mesoscopic damage modes of yield and fracture. Under the freeze-thaw environment, the internal pore structure and the mechanical characteristics of the microstructure will change significantly, which can be reflected by the initial elastic modulus E. In the process of further bearing the compressive load, the shape, path and quantity of microcracks initiation and propagation in the microstructure will also change due to the influence of the initial freeze-thaw degradation, which could be characterized by damage parameters εa, εh, εb and H. Assuming that under different number of freeze-thaw cycles, the evolution trend of the mechanical properties of the microstructure and the meso-damage process obey a certain regularity, thusly define the above 5 characteristic parameters as functions of the number of freeze-thaw cyclesN. To verify the rationality of the model, the uniaxial compression test was carried out, and the stress-strain full curves of concrete were obtained when the number of freeze-thaw cycles N changed from 0 to 150. Meanwhile, five groups of experimental data in the literature were also analyzed. The results show that: prediction curves are in a good agreement with the test curves, and the characteristic parameters in the model show obvious regularity as the number of freeze-thaw cycles increases. This model provides an effective tool for both the analysis and predicting damage mechanism of concrete in the freeze-thaw environment.
2023, 40(9): 130-141.
doi: 10.6052/j.issn.1000-4750.2022.01.0040
Abstract:
To study the seismic performance and replaceable capacity of energy dissipation beams with bolted end plates, four replaceable energy dissipation beam specimens were designed and fabricated. The effects of length ratio on seismic performance and replaceable capacity of the replaceable energy dissipation beams were investigated through quasi-static test. The results show that specimens with small length ratio present a shear dominated behavior including web-to-stiffener weld fracture, web buckling and web tear. Whereas the failure features of shear and flexure dominate the behavior of specimens with large length ratio, manifested as flange buckling and end plate-to-flange weld fracture. All tested specimens exhibit stable hysteresis behavior, excellent deformation ability and energy dissipation capacity. In addition, the bearing capacity of replaceable energy dissipation beams is strengthened significantly, and the average value of the overstrength factor is about 1.9. The replaceable energy dissipation beams with bolted end plates can be replaced after the earthquake. Moreover, the energy dissipation beams can be replaced conveniently after the earthquake when the residual angle at the beam end is 0.0020 rad-0.0046 rad. Meanwhile, the main stress development of replaceable beams can be divided into three stages of serviceability, non-essential and mandatory replaceability according to the deformation relationship between the replaceable link beams and the proposed frame structure system.
To study the seismic performance and replaceable capacity of energy dissipation beams with bolted end plates, four replaceable energy dissipation beam specimens were designed and fabricated. The effects of length ratio on seismic performance and replaceable capacity of the replaceable energy dissipation beams were investigated through quasi-static test. The results show that specimens with small length ratio present a shear dominated behavior including web-to-stiffener weld fracture, web buckling and web tear. Whereas the failure features of shear and flexure dominate the behavior of specimens with large length ratio, manifested as flange buckling and end plate-to-flange weld fracture. All tested specimens exhibit stable hysteresis behavior, excellent deformation ability and energy dissipation capacity. In addition, the bearing capacity of replaceable energy dissipation beams is strengthened significantly, and the average value of the overstrength factor is about 1.9. The replaceable energy dissipation beams with bolted end plates can be replaced after the earthquake. Moreover, the energy dissipation beams can be replaced conveniently after the earthquake when the residual angle at the beam end is 0.0020 rad-0.0046 rad. Meanwhile, the main stress development of replaceable beams can be divided into three stages of serviceability, non-essential and mandatory replaceability according to the deformation relationship between the replaceable link beams and the proposed frame structure system.
2023, 40(9): 142-152.
doi: 10.6052/j.issn.1000-4750.2022.01.0044
Abstract:
Particle shape plays an essential role in deformation characteristics of railway ballast bed. The numerical reconstruction of ballast morphological features, including overall shape and angular distribution, remains a hot issue in research on ballast mechanical behavior simulation. A novel shape reconstruction method was adopted to generate ballast particles that met the desired probability density distribution of morphological indices. On this basis, the numerical model of ballast triaxial tests were established under different confining pressures. The results were compared with those obtained from indoor tests and simulations whose particles were generated from 3D scanning or non-statistical random generation. The results show that the particle shape has a growing effect on the mechanical response of ballast, with an increase in confining pressure. The relation between deviatoric stress and axial strain in the specimen which meets the probability density distribution is more consistent with the experimental results than that of the non-statistical randomly generated specimen. The lateral deformation of ballast is correlated with the adjustment of the packing structure. For non-statistical randomly generated specimen, both the lateral deformation and the particle adjustment are larger than those generated by 3D scanning. The ballast contact force evolution is less influenced by its morphological features. Nevertheless, the difference in the maximum contact force of specimens with various particle shapes is nearly 50%.
Particle shape plays an essential role in deformation characteristics of railway ballast bed. The numerical reconstruction of ballast morphological features, including overall shape and angular distribution, remains a hot issue in research on ballast mechanical behavior simulation. A novel shape reconstruction method was adopted to generate ballast particles that met the desired probability density distribution of morphological indices. On this basis, the numerical model of ballast triaxial tests were established under different confining pressures. The results were compared with those obtained from indoor tests and simulations whose particles were generated from 3D scanning or non-statistical random generation. The results show that the particle shape has a growing effect on the mechanical response of ballast, with an increase in confining pressure. The relation between deviatoric stress and axial strain in the specimen which meets the probability density distribution is more consistent with the experimental results than that of the non-statistical randomly generated specimen. The lateral deformation of ballast is correlated with the adjustment of the packing structure. For non-statistical randomly generated specimen, both the lateral deformation and the particle adjustment are larger than those generated by 3D scanning. The ballast contact force evolution is less influenced by its morphological features. Nevertheless, the difference in the maximum contact force of specimens with various particle shapes is nearly 50%.
2023, 40(9): 153-160.
doi: 10.6052/j.issn.1000-4750.2022.01.0056
Abstract:
To investigate the application of the novel composite material 'high-strength stainless steel wire mesh/ECC confined concrete' in engineering practice, based on the axial compression test results of high-strength stainless steel wire mesh/ECC confined high strength concrete (referred to as HSME confined high strength concrete) components, the effects of ECC's strength, strength of core concrete and transverse steel strand reinforcement ratio on the compressive performance are investigated and analyzed. The test results indicate that the HSME can effectively constrain the core concrete, and the specimens exhibit ductile failure pattern. The compressive stress-strain curves of the HSME confined high strength concrete are obtained based on the test results, which include three stages: elastic stage, elastoplastic stage and descending stage. According to the mathematical characteristics of the stress-strain curve at each stage, the constitutive model of HSME confined high strength concrete under the whole loading process is established. The ECC characteristic value and the transverse steel strand characteristic value are introduced to analyze various parameters of the proposed constitutive model. Then, the formulas of cracking strain under compression, peak stress, strain at the peak stress and the ultimate compressive strain, et al, are proposed. The stress-strain curves are obtained by substituting parameters into the proposed compressive constitutive relationship, which are in good agreement with the stress-strain curves obtained from the test results. The ratios of calculated value to the test value for the cracking strain under compression and the ultimate compressive strain are within 0.949-1.068 and 0.938-1.039, respectively. It demonstrates that the proposed compression constitutive model could accurately describe the stress-strain relationship of the HSME confined high strength concrete.
To investigate the application of the novel composite material 'high-strength stainless steel wire mesh/ECC confined concrete' in engineering practice, based on the axial compression test results of high-strength stainless steel wire mesh/ECC confined high strength concrete (referred to as HSME confined high strength concrete) components, the effects of ECC's strength, strength of core concrete and transverse steel strand reinforcement ratio on the compressive performance are investigated and analyzed. The test results indicate that the HSME can effectively constrain the core concrete, and the specimens exhibit ductile failure pattern. The compressive stress-strain curves of the HSME confined high strength concrete are obtained based on the test results, which include three stages: elastic stage, elastoplastic stage and descending stage. According to the mathematical characteristics of the stress-strain curve at each stage, the constitutive model of HSME confined high strength concrete under the whole loading process is established. The ECC characteristic value and the transverse steel strand characteristic value are introduced to analyze various parameters of the proposed constitutive model. Then, the formulas of cracking strain under compression, peak stress, strain at the peak stress and the ultimate compressive strain, et al, are proposed. The stress-strain curves are obtained by substituting parameters into the proposed compressive constitutive relationship, which are in good agreement with the stress-strain curves obtained from the test results. The ratios of calculated value to the test value for the cracking strain under compression and the ultimate compressive strain are within 0.949-1.068 and 0.938-1.039, respectively. It demonstrates that the proposed compression constitutive model could accurately describe the stress-strain relationship of the HSME confined high strength concrete.
2023, 40(9): 161-171.
doi: 10.6052/j.issn.1000-4750.2022.01.0058
Abstract:
For a tubed concrete column, the tube gaps are usually arranged at the column ends to avoid the steel tube carrying loads directly. Two type square tubed steel reinforced concrete (TSRC) columns, i.e., a column with two gaps at the column ends and another column with an additional gap at the mid-height, are discussed in this paper. Experimental studies on the compression behavior of TSRC slender columns were conducted to investigate the effects of the width-to-thickness ratio of steel tube and the load eccentricity ratio. The failure modes, the ultimate strengths, and the load to tube stress curves were analyzed. The results indicated that the two type columns shown similar failure modes. The axial strength of column with additional gap at the mid-height was slightly higher than that of column with two gaps, while the eccentric strength of column exhibited opposite tendency. Parametric analysis were carried out based on the precise finite element (FE) models. Based on the test and FE results, the stiffness reduction coefficient to calculate the moment amplification effect was proposed by regression analysis, and the design method of square TSRC column with additional gap at the mid-height under eccentric compression was proposed.
For a tubed concrete column, the tube gaps are usually arranged at the column ends to avoid the steel tube carrying loads directly. Two type square tubed steel reinforced concrete (TSRC) columns, i.e., a column with two gaps at the column ends and another column with an additional gap at the mid-height, are discussed in this paper. Experimental studies on the compression behavior of TSRC slender columns were conducted to investigate the effects of the width-to-thickness ratio of steel tube and the load eccentricity ratio. The failure modes, the ultimate strengths, and the load to tube stress curves were analyzed. The results indicated that the two type columns shown similar failure modes. The axial strength of column with additional gap at the mid-height was slightly higher than that of column with two gaps, while the eccentric strength of column exhibited opposite tendency. Parametric analysis were carried out based on the precise finite element (FE) models. Based on the test and FE results, the stiffness reduction coefficient to calculate the moment amplification effect was proposed by regression analysis, and the design method of square TSRC column with additional gap at the mid-height under eccentric compression was proposed.
2023, 40(9): 172-189.
doi: 10.6052/j.issn.1000-4750.2022.04.0291
Abstract:
Far-field long-period harmonic-like ground motion characterized with long-period acceleration harmonic-like pulses in the late stage of vibration has adverse effects on the long-period structures. However, there still lacks of far-field ground motion records that could be directly used for seismic analysis due to limited records of ground motions. A synthetic method for far-filed harmonic-like ground motion based on Ensemble Empirical Mode Decomposition Method (EEMD) was proposed to solve the problem of shortage of available far-field ground motions, and its accuracy and feasibility was verified. The recorded far-field long-period harmonic-like ground motions were decomposed through EEMD to obtain the main-pulse composition and attenuation of low-frequency component, which were fitted and reconstructed to generate harmonic-like main-pulse component. Then the identification and simplification of characteristic parameters for the synthetic harmonic-like main-pulse components were conducted to obtain the main-pulse velocity model, which composed of harmonic-like main-pulse function with attenuation function. The synthetic method for far-filed harmonic-like ground motion was proposed based on combination of the main-pulse velocity model and high-frequency IMF components. In addition, the synthesis of three arbitrary harmonic-like ground motions according to selected characteristics parameters was carried out, and the comparisons with the original far-field long-period harmonic-like ground motions was conducted. The results demonstrated that the low-frequency component of original ground motion could be effectively extracted with EEMD and the velocity-time history obtained from the proposed main-pulse velocity model fitted well with the velocity-time history of the original ground motion. The proposed synthetic method could generate artificial harmonic-like ground motion that retained the non-stationary characteristics of the far-field harmonic-like ground motion, and fit well with the original ground motion.
Far-field long-period harmonic-like ground motion characterized with long-period acceleration harmonic-like pulses in the late stage of vibration has adverse effects on the long-period structures. However, there still lacks of far-field ground motion records that could be directly used for seismic analysis due to limited records of ground motions. A synthetic method for far-filed harmonic-like ground motion based on Ensemble Empirical Mode Decomposition Method (EEMD) was proposed to solve the problem of shortage of available far-field ground motions, and its accuracy and feasibility was verified. The recorded far-field long-period harmonic-like ground motions were decomposed through EEMD to obtain the main-pulse composition and attenuation of low-frequency component, which were fitted and reconstructed to generate harmonic-like main-pulse component. Then the identification and simplification of characteristic parameters for the synthetic harmonic-like main-pulse components were conducted to obtain the main-pulse velocity model, which composed of harmonic-like main-pulse function with attenuation function. The synthetic method for far-filed harmonic-like ground motion was proposed based on combination of the main-pulse velocity model and high-frequency IMF components. In addition, the synthesis of three arbitrary harmonic-like ground motions according to selected characteristics parameters was carried out, and the comparisons with the original far-field long-period harmonic-like ground motions was conducted. The results demonstrated that the low-frequency component of original ground motion could be effectively extracted with EEMD and the velocity-time history obtained from the proposed main-pulse velocity model fitted well with the velocity-time history of the original ground motion. The proposed synthetic method could generate artificial harmonic-like ground motion that retained the non-stationary characteristics of the far-field harmonic-like ground motion, and fit well with the original ground motion.
2023, 40(9): 190-202.
doi: 10.6052/j.issn.1000-4750.2022.05.0423
Abstract:
Establishes a numerical model using ABAQUS/Implicit for analyzing the progressive collapse of concrete-filled steel tubular (CFST) column to flat web H-shaped steel beam joint. In the joint configuration, a corrugated web steel beam and a welded haunch were employed to improve the anti-collapse capacity. The failure mode and failure mechanism of the joints under vertical loading and the folding effect of the corrugated web are analyzed. The results show that the failure of CFST column to flat web beam joint (J-WB-O) started at the connection between the ring plate and the beam, while the initial failure of the CFST column-corrugated web beam haunch joint (J-CW-AP) appeared at the end of the welded haunch, which delayed the fracture of the lower flange of the beam. Moreover, for the specimen J-WB-O, the entire beam section contributed to anti-collapse capacity. For the specimen J-CW-AP, the corrugated web seldom contributed to anti-collapse capacity in the initial loading stage. After the fracture of the bottom flange of the specimen J-CW-AP, the corrugated web began to contribute to anti-collapse capacity. As the cracks propagated upwards, the sections of the corrugated web were under tension gradually. The fracture and local buckling of the web were delayed due to the folding effect of the corrugated web. Compared with the specimen J-WB-O, the bearing capacity and ductility of the specimen J-CW-AP increased by 67.2% and 62.3%, respectively. Furthermore, a simplified calculation method of anti-collapse capacity is proposed based on the analysis of resistance mechanism.
Establishes a numerical model using ABAQUS/Implicit for analyzing the progressive collapse of concrete-filled steel tubular (CFST) column to flat web H-shaped steel beam joint. In the joint configuration, a corrugated web steel beam and a welded haunch were employed to improve the anti-collapse capacity. The failure mode and failure mechanism of the joints under vertical loading and the folding effect of the corrugated web are analyzed. The results show that the failure of CFST column to flat web beam joint (J-WB-O) started at the connection between the ring plate and the beam, while the initial failure of the CFST column-corrugated web beam haunch joint (J-CW-AP) appeared at the end of the welded haunch, which delayed the fracture of the lower flange of the beam. Moreover, for the specimen J-WB-O, the entire beam section contributed to anti-collapse capacity. For the specimen J-CW-AP, the corrugated web seldom contributed to anti-collapse capacity in the initial loading stage. After the fracture of the bottom flange of the specimen J-CW-AP, the corrugated web began to contribute to anti-collapse capacity. As the cracks propagated upwards, the sections of the corrugated web were under tension gradually. The fracture and local buckling of the web were delayed due to the folding effect of the corrugated web. Compared with the specimen J-WB-O, the bearing capacity and ductility of the specimen J-CW-AP increased by 67.2% and 62.3%, respectively. Furthermore, a simplified calculation method of anti-collapse capacity is proposed based on the analysis of resistance mechanism.
2023, 40(9): 203-213, 256.
doi: 10.6052/j.issn.1000-4750.2022.09.0813
Abstract:
To evaluate the effects of corrosion and aftershock on structural seismic resistance. Two seismic designed reinforced-concrete frame buildings located in a coastal city were selected for study. Four corrosion conditions were considered, i.e., uncorroded and corrosion ratios of 5%, 10% and 15%. A set of 662 mainshock-aftershock sequences were taken as the inputs for time history analysis. Then the damage analysis and fragility assessment were conducted to the corroded and uncorroded buildings subjected to mainshock-aftershock sequences. Results show that the increment of corrosion ratio exacerbates structural cumulative damage under mainshock-aftershock sequences. The increment ratio of the structural cumulative damage is even over 30%. The corrosion effect can lead to an increase in fragility curves, and the influence of the corrosion effect on mainshock fragility curves under heavy corrosion condition is close to that under aftershocks. The coupling effect of corrosion and aftershock can cause a significant elevating in mainshock fragility curve. Therefore, it is necessary to consider the effect of corrosion in seismic performance assessment subjected to mainshock-aftershock sequences.
To evaluate the effects of corrosion and aftershock on structural seismic resistance. Two seismic designed reinforced-concrete frame buildings located in a coastal city were selected for study. Four corrosion conditions were considered, i.e., uncorroded and corrosion ratios of 5%, 10% and 15%. A set of 662 mainshock-aftershock sequences were taken as the inputs for time history analysis. Then the damage analysis and fragility assessment were conducted to the corroded and uncorroded buildings subjected to mainshock-aftershock sequences. Results show that the increment of corrosion ratio exacerbates structural cumulative damage under mainshock-aftershock sequences. The increment ratio of the structural cumulative damage is even over 30%. The corrosion effect can lead to an increase in fragility curves, and the influence of the corrosion effect on mainshock fragility curves under heavy corrosion condition is close to that under aftershocks. The coupling effect of corrosion and aftershock can cause a significant elevating in mainshock fragility curve. Therefore, it is necessary to consider the effect of corrosion in seismic performance assessment subjected to mainshock-aftershock sequences.
2023, 40(9): 214-223.
doi: 10.6052/j.issn.1000-4750.2021.12.0010
Abstract:
The leakage of radioactive, flammable and other dangerous gases from the pressure-bearing shell would pose a major threat to the environment, and the leakage assessment is a necessary prerequisite for the optimization of emergency measures. Aiming at the micro-cracking of the thick shell wall under severe accidents, an efficient and quantitative analysis numerical model for the leakage rate is established. Based on the principle of flow conservation, an improved model is proposed for calculating the leakage rate through a variable cross-section channel formed by multi-segment micro-cracks in a thick-walled structure. The concrete plastic damage model is applied to simulate the nonlinear damage of the structure under its ultimate load, and the model for calculating the scale of smeared micro-cracks is improved by the transformation between the geometric irregular element and the regular space realized through an isoparametric function. Through numerical examples, the research results were compared with those in the literature. The stability and validity of the above two sub-models are verified separately, and the feasibility of the model is further verified by the leakage rate analysis of the damaged shear wall. Finally, the model is applied to a prestressed concrete complex pressure-bearing shell resisting high temperature and internal pressure damage. The results show that the improved model is suitable for the leakage rate analysis of thick-walled, porous and, other complex pressure-bearing structures, which has a certain practical engineering significance.
The leakage of radioactive, flammable and other dangerous gases from the pressure-bearing shell would pose a major threat to the environment, and the leakage assessment is a necessary prerequisite for the optimization of emergency measures. Aiming at the micro-cracking of the thick shell wall under severe accidents, an efficient and quantitative analysis numerical model for the leakage rate is established. Based on the principle of flow conservation, an improved model is proposed for calculating the leakage rate through a variable cross-section channel formed by multi-segment micro-cracks in a thick-walled structure. The concrete plastic damage model is applied to simulate the nonlinear damage of the structure under its ultimate load, and the model for calculating the scale of smeared micro-cracks is improved by the transformation between the geometric irregular element and the regular space realized through an isoparametric function. Through numerical examples, the research results were compared with those in the literature. The stability and validity of the above two sub-models are verified separately, and the feasibility of the model is further verified by the leakage rate analysis of the damaged shear wall. Finally, the model is applied to a prestressed concrete complex pressure-bearing shell resisting high temperature and internal pressure damage. The results show that the improved model is suitable for the leakage rate analysis of thick-walled, porous and, other complex pressure-bearing structures, which has a certain practical engineering significance.
2023, 40(9): 224-237.
doi: 10.6052/j.issn.1000-4750.2022.01.0015
Abstract:
Adhesive connection is a traditional connecting technique in the manufacturing of lightweight bodies of vehicles. The modeling of adhesive joints is a crucial precondition for the crash safety design of lightweight vehicles. To fully capture the mechanical response of epoxy-based structural adhesive with high tenacity and improve the accuracy of existing models of joint failure under impact loading, a constitutive model that considers the stress state effect, strain rate effect, and damage accumulation simultaneously is introduced in this study. Based on the constitutive model, this paper presents a method to recognize the model parameters and a corresponding parameter calibration process. Then, two material models for different epoxy-based adhesives are established. The constitutive model and characterization approach introduced in this study are verified through a result comparison between FE simulations and multi-level impact tests. The bulk specimen tests, adhesive joints tests, and structural impact tests are included in this study.
Adhesive connection is a traditional connecting technique in the manufacturing of lightweight bodies of vehicles. The modeling of adhesive joints is a crucial precondition for the crash safety design of lightweight vehicles. To fully capture the mechanical response of epoxy-based structural adhesive with high tenacity and improve the accuracy of existing models of joint failure under impact loading, a constitutive model that considers the stress state effect, strain rate effect, and damage accumulation simultaneously is introduced in this study. Based on the constitutive model, this paper presents a method to recognize the model parameters and a corresponding parameter calibration process. Then, two material models for different epoxy-based adhesives are established. The constitutive model and characterization approach introduced in this study are verified through a result comparison between FE simulations and multi-level impact tests. The bulk specimen tests, adhesive joints tests, and structural impact tests are included in this study.
2023, 40(9): 238-246.
doi: 10.6052/j.issn.1000-4750.2021.12.1013
Abstract:
In order to explore the damage failure mechanism of glass fiber-reinforced flexible pipes under internal pressure, the theory of three-dimensional (3D) elasticity is adopted to carry out the theoretical analysis on 3D constitutive relationship of a flexible tube. Combined with a 3D Hashin-Yeh failure criterion and a nonlinear stiffness degradation model, considering the nonlinear mechanical behavior of matrix materials, a 3D progressive failure model of the flexible tube is established. The hydrostatic burst experiments are used to verify the theoretical model. And on this basis, the influence of winding angle and diameter thickness ratio on the failure load and failure mode of the flexible tube is analyzed. The analysis results show that: the theoretical model is in a good agreement with the experimental results. The winding angle has an obvious effect on the stress distribution of the flexible pipe under internal pressure; with the increase of the winding angle, the first layer failure load and the final burst failure load of the flexible pipe all present a tendency of increasing; with the increase of diameter thickness ratio, the pressure capacity of the flexible pipe decreases rapidly, but the failure mode does not change.
In order to explore the damage failure mechanism of glass fiber-reinforced flexible pipes under internal pressure, the theory of three-dimensional (3D) elasticity is adopted to carry out the theoretical analysis on 3D constitutive relationship of a flexible tube. Combined with a 3D Hashin-Yeh failure criterion and a nonlinear stiffness degradation model, considering the nonlinear mechanical behavior of matrix materials, a 3D progressive failure model of the flexible tube is established. The hydrostatic burst experiments are used to verify the theoretical model. And on this basis, the influence of winding angle and diameter thickness ratio on the failure load and failure mode of the flexible tube is analyzed. The analysis results show that: the theoretical model is in a good agreement with the experimental results. The winding angle has an obvious effect on the stress distribution of the flexible pipe under internal pressure; with the increase of the winding angle, the first layer failure load and the final burst failure load of the flexible pipe all present a tendency of increasing; with the increase of diameter thickness ratio, the pressure capacity of the flexible pipe decreases rapidly, but the failure mode does not change.
2023, 40(9): 247-256.
doi: 10.6052/j.issn.1000-4750.2022.01.0011
Abstract:
High temperature superconducting materials have attracted many attentions in the field of science and technology due to their outstanding advantages such as high current carrying capacity and low AC loss, etc. However, a series of electromagnetic mechanical problems in practical applications seriously hinder its development in the field of engineering technology. Thusly, a superconducting thin rectangular strip is considered to transport current. The influence of the inhomogeneous critical current density on the electrical and mechanical properties are analyzed. The critical current density is assumed to distribute nonuniformly along the width of the superconducting thin strip, then the analytical expressions for the induced current and magnetic field in the thin strip are developed. Based on a superconducting critical Bean model, the analytical expression of the flux pinning force is obtained. The plane stress method of the elastic theory is adopted to calculate the flux pinning stress and strain, then the magnetostriction in the superconducting thin strip are obtained. The simulating results show that: the nonuniformity of the critical current density has no influence on the distribution law of the flux pinning force induced in the superconducting thin strip, the same as the flux pinning stress and strain do. However, the nonuniformly distributed critical current density increases the penetration depth of the trapped magnetic flux. The value of the maximum compressive stress is also increased, and its position approaches to the center of the thin strip when the transport current increases. The maximum tensile stress appears in the thin strip when reducing the transport current from its maximum value, and its value decreases with the decrement of the transport current. The shape of the magnetostriction curve changes when the distribution of the critical current density is inhomogeneous, and its maximum value is less to that with homogeneous critical current density. All in all, the influence of the inhomogeneous critical current density cannot be neglected during the study of the superconducting materials.
High temperature superconducting materials have attracted many attentions in the field of science and technology due to their outstanding advantages such as high current carrying capacity and low AC loss, etc. However, a series of electromagnetic mechanical problems in practical applications seriously hinder its development in the field of engineering technology. Thusly, a superconducting thin rectangular strip is considered to transport current. The influence of the inhomogeneous critical current density on the electrical and mechanical properties are analyzed. The critical current density is assumed to distribute nonuniformly along the width of the superconducting thin strip, then the analytical expressions for the induced current and magnetic field in the thin strip are developed. Based on a superconducting critical Bean model, the analytical expression of the flux pinning force is obtained. The plane stress method of the elastic theory is adopted to calculate the flux pinning stress and strain, then the magnetostriction in the superconducting thin strip are obtained. The simulating results show that: the nonuniformity of the critical current density has no influence on the distribution law of the flux pinning force induced in the superconducting thin strip, the same as the flux pinning stress and strain do. However, the nonuniformly distributed critical current density increases the penetration depth of the trapped magnetic flux. The value of the maximum compressive stress is also increased, and its position approaches to the center of the thin strip when the transport current increases. The maximum tensile stress appears in the thin strip when reducing the transport current from its maximum value, and its value decreases with the decrement of the transport current. The shape of the magnetostriction curve changes when the distribution of the critical current density is inhomogeneous, and its maximum value is less to that with homogeneous critical current density. All in all, the influence of the inhomogeneous critical current density cannot be neglected during the study of the superconducting materials.
