Search Results (132)

This paper proposes an improved wave function asperity elastic–plastic model. A cosine function that could better fit the geometric morphology was selected to construct the asperity, the elastic phase was controlled by the Hertz contact theory, the elastoplastic transition phase was corrected by the hyperbolic tangent function, and the fully plastic phase was improved by the projected area theory. The model broke through the limitations of the spherical assumption and was able to capture the stress concentration and plastic flow phenomena. The results show that the contact pressure in the elastic phase was 22% higher than that of the spherical shape, the plastic strain in the elastoplastic phase was 52% lower than that of the spherical shape, and the fully plastic phase reduced the contact area error by 20%. The improved hyperbolic tangent function eliminated the unphysical oscillation phenomenon in the elastoplastic phase and ensured the continuity and monotonicity of the contact variables, with an error of <5% from the finite element analysis. Meanwhile, extending the proposed model, we developed a rough surface contact model, and it was verified that the wavy asperity could better match the mechanical properties of the real rough surface and exhibited progressive stiffness reduction during the plastic flow process. The model in this paper can provide a theoretical basis for predicting stress distribution, plastic evolution, and multi-scale mechanical behavior in the connection interface. Full article

Tunnel deformation induced by excavation in brittle and quasi-brittle rock masses involves complex interactions among stress redistribution, plastic deformation, and fracture evolution. Existing numerical approaches often struggle to capture these coupled mechanisms, particularly under varying material properties such as Poisson’s ratio. This study aims to analyze tunnel deformation using an elastoplastic Discretized Virtual Internal Bond (DVIB) method embedded in a modified Stillinger–Weber (SW) potential. In this framework, plastic deformation is introduced through the two-body component, whereas the three-body angular potential governs Poisson’s ratio. A fracture-energy-based regularization strategy was implemented to reduce the mesh sensitivity and ensure energy consistency during bond failure. The model was evaluated through numerical simulations, including pre-cracked plates, center-split circular Brazilian discs, and tunnel models, under various in situ stress conditions and Poisson ratios. The findings indicate that higher Poisson’s ratios lead to increased deformation, with tunnel wall displacements rising from 0.45 mm at $\nu =0.17 \mathrm{to} 1.32 \mathrm{mm}$ at $\nu =0.35$. The deformation patterns and failure zones are consistent with theoretical expectations, confirming the applicability of the model to tunnel stability analysis in brittle geomaterials. Full article

To overcome the limitation of traditional elastic phase field models that neglect plastic deformation in rock compressive-shear failure, this study developed an elastoplastic phase field fracture model incorporating plastic strain energy and established a coupling framework for plastic deformation and crack evolution. By introducing the non-associated flow rule and plastic damage variable, an energy functional comprising elastic strain energy, plastic work, and crack surface energy was constructed. The phase field governing equation considering plastic-damage coupling was obtained, enabling the simulation of the energy evolution in rock from the elastic stage to plastic damage and unstable failure. Validation was carried out through single-edge notch tension tests and uniaxial compression tests with prefabricated cracks. Results demonstrate that the model accurately captures characteristics such as the linear propagation of tensile cracks, the initiation of wing-like cracks under compressive-shear conditions, and the evolution of mixed-mode failure modes, which are highly consistent with classical experimental observations. Specifically, the model provides a more detailed description of local damage evolution and residual strength caused by stress concentration in compressive-shear scenarios, thereby quantifying the influence of plastic deformation on crack driving force. These findings offer theoretical support for crack propagation analysis in rock engineering applications, including hydraulic fracturing and the construction of underground energy storage caverns. The proposed plastic phase field model can be effectively utilized to simulate rock failure processes under complex stress states. Full article

To overcome the limitations of rigid body limit equilibrium methods in earth rock dam slope stability analysis, this study develops a system reliability framework using the finite element strength reduction method (FEM-SRM). An elastoplastic finite element model simulates dam construction and impoundment, identifying potential slip pathways. Each pathway, treated as a parallel system of shear-failed elements, is analyzed via the response surface method to derive explicit limit state functions. Reliability indices are computed using an improved first-order second-moment method, while interdependencies are assessed through stepwise equivalent linearization. System reliability is determined using Ditlevsen’s narrow bound method. Applied to a 314 m earth rockfill dam, three critical slip pathways were identified: upstream shallow (reliability index is 6.94), upstream deep (reliability index is 6.87), and downstream deep (reliability index is 7.44), with correlation coefficients between 0.26 and 0.89. The system reliability index (6.81) significantly exceeds the code target (4.2), highlighting the method’s ability to integrate material randomness, stress-strain nonlinearity, and multi-slip interactions. This framework provides a robust probabilistic approach for high earth rock dam stability assessment, enhancing engineering safety evaluations. Full article

The construction of an elastoplastic constitutive model for energy dissipation and crack evolution in rocks is crucial for accurately predicting their failure processes. This study first constructs a theoretical elastoplastic constitutive model by analyzing the mechanical properties of rocks, energy dissipation, and crack evolution under conventional triaxial compression. Subsequently, a three-dimensional finite difference scheme for the theoretical model is derived to implement a numerical algorithm. Finally, using argillaceous siltstone as an example, the validity of the theoretical model and its algorithmic implementation is verified through experimental testing, result analysis, model construction, secondary development, and numerical simulation. The research indicates that the dissipated energy is equal to the integral of the stress–strain curve minus the elastic strain energy, which can be quantitatively described using strength parameters. The volumetric strain of cracks is equal to the plastic volumetric strain, which can be indirectly quantified using the dilation angle. The simulated stress–strain curves closely align with the experimental data, and the simulated dissipated energy and crack volumetric strain are consistent with the theoretical calculations, confirming that the theoretical model effectively captures the nonlinear mechanical behavior, energy dissipation, and crack evolution of rocks. Full article

Seabed foundations consisting of interbedded layers of saturated soft clay and sand deposited during the Quaternary period are widely distributed in the coastal areas of Southeastern China. These soil foundations are prone to significant settlement under seismic loading. The study of the seismic dynamic response characteristics of saturated foundations with interbedded soft clay–sand and the development of rapid prediction models are essential for controlling settlement and ensuring the service safety of marine structures. A total of 4000 sets of seabed foundation models are randomly generated, with layers of saturated soft clay and sand and with a random distribution of layer thickness and burial depth. The mechanical behavior of saturated soft clay is described using the Soft Clay model based on the boundary surface theory, and the generalized elastoplastic constitutive model PZIII is used to characterize the mechanical behavior of sandy soil. The finite element platform FssiCAS is employed for a computational analysis to study the characteristics of seismic subsidence in saturated seabed foundations with interbedded soft clay–sand. A machine learning model is implemented based on the Random Forest algorithm, in which 3200 sets of numerical simulation results are used for model training, and 800 sets are used for validating the model’s reliability. The results show that under seismic excitation, the pore water pressure within the saturated seabed foundation with interbedded soft clay–sand accumulates, effective stress decreases, and the seabed foundation softens, to a certain extent. During the post-seismic consolidation phase, significant settlement of the seabed foundation occurs. The fast prediction model based on the Random Forest algorithm could reliably predict the settlement characteristics of submarine foundations. This research provides a new technological avenue for the rapid prediction of the seismic settlement of submarine foundations, which could be of use in engineering design, assessment, and prediction. Full article

Bistable microstructures are promising for implementation in many mictroelectromechanical system (MEMS)-based applications due to their ability to stay in several equilibrium states, high tunability and unprecedented sensitivity to external stimuli. As opposed to the extensively investigated one-dimensional curved beam-type devices of this kind, microfabrication of non-planar two-dimensional bistable structures, such as plates or shells, represents a remarkable challenge. Recently reported by us, a new moldless stamping procedure, based on pressing a soft stamp over a thin suspended metallic film, was demonstrated to be a feasible direction for the fabrication of initially curved micro plates. However, reliable implementation of this fabrication paradigm and its further development requires better understanding of the role of the process parameters, and of the effect of both the plate and the stamp material properties on the shape of the formed shell and on the postfabrication residual stresses, and therefore on the shell behavior. The need for an appropriate choice of these parameters requires the development of a systematic modeling approach to the stamping process. Here, we report on a finite element (FE)-based methodology for modeling the processing sequences of a successfully fabricated aluminum (Al) micro shell of realistic geometry. The model accounts for the elasto-plastic behavior of the plate material, the nonlinear material behavior of the foam and the contact between them. It was found that the stamping pressure and the plate material parameters are the key parameters affecting the residual shell curvature as well as its shape. Consistently with previously presented experimental results, we show that the fabrication procedure partially relieves the prestresses emerging during preceding fabrication steps, leaving a nontrivial distribution of residual stresses in the formed shell. The presented analysis approach and results provide tools for designers and manufacturers of systems including micro structural elements of shell type. Full article

High-strength steel (HSS) plates are widely used due to their superior performance. However, residual stresses generated during welding can exacerbate the initiation of fatigue cracks, and the accurate prediction of residual stresses is crucial. Therefore, thermo-mechanical behavior analysis of the EH40 joints was completed based on the proposed new heat source model. The thermo-elastoplastic finite element analysis was determined via thermo-mechanical coupling with fully parametric programming. The influence of laser welding power and joint thickness on peak temperature and gradient was clarified. Meanwhile, it was found that when the laser welding power increased from 9 kW to 22.5 kW and the joint thickness increased from 6 mm to 15 mm, the distribution trend of longitudinal residual stress in the weld zone was gradually altered from a “U” shape to a “W” shape, while the transverse stress was transformed from a “U” shape to an “M” shape. It was determined that the amplitude of longitudinal and transverse stress changed along the thickness direction of nodes and was directly proportional to the peak temperature. The above results imply that the peak temperature, maximum temperature gradient longitudinal, and transverse residual stress distribution in the weld zone and its vicinity were remarkably affected by laser welding power and joint thickness. Full article

A numerical tool for simulating the detection signals of electromagnetic nondestructive testing technology (ENDT) is of great significance for studying detection mechanisms and improving detection efficiency. However, the quantitative analysis methods for ENDT have not yet been sufficiently studied due to the absence of an effective constitutive model. This paper proposed a new magneto–mechanical model that can reflect the dependence of relative permeability on elasto–plastic deformation and proposed a finite element–infinite element coupling method that can replace the traditional finite element truncation boundary. The validity of the finite element–infinite element coupling method is verified by the experimental result of testing electromagnetic analysis methods using TEAM Problem 7. Then, the reliability and accuracy of the proposed model are verified by comparing the simulation results under elasto–plastic deformation with experimental results. This paper also investigates the effect of elasto–plastic deformation on the transient magnetic flux signal, a quantitative hyperbolic tangent model between Bz_pp (peak–peak value of the normal component of magnetic flux signal) and elastic stress, and the exponential function relationship between Bz_pp and plastic deformation is established. In addition, the difference and mechanism of a magnetic flux signal under elasto–plastic deformations are analyzed. The results reveal that the variation of the transient magnetic flux signal is mainly due to domain wall pinning, which is significantly affected by elasto–plastic deformation. The results of this paper are important for improving the accuracy of quantitative ENDT for elasto–plastic deformation. Full article

A top-chord-free Vierendeel-truss composite slab (TVCS) comprises a concrete slab, several vertical webs, and a steel bottom chord. In this study, static tests and finite element analyses were conducted based on an actual project to investigate the deformation, crack characteristics, ultimate bearing capacity, and failure mode of the composite slab. The findings indicated that the loading process of this type of floor can be divided into elastic, elastoplastic, and failure stages. The section stress distribution in the elastic stage was further analyzed. The crack development pattern exhibited a fine density in the pure bending sections of the concrete slabs, while demonstrating good overall flexural bearing capacity and ductility for the composite slab. Experimental results were compared with the ANSYS finite element model simulation to validate the accuracy of the simulation. Parametric analysis was conducted to assess the impact of concrete strength, steel strength, vertical web width, and distance ratios on the mechanical characteristics of the composite slab. By introducing an adjustment coefficient for the vertical web distance ratio, a revised calculation formula for flexural bearing capacity was proposed, which aligned well with the finite element analysis. Full article

This paper aims to predict the damage and fracture behavior of thermoplastic fiber-reinforced metal laminates (TFMLs) under ballistic impact loadings. A dynamic metal constitutive model has been employed and implemented in Abaqus/Explicit through a vectorized user material subroutine (VUMAT). The effects of the Lode angle, temperature, and strain rate are considered in the strength model, while the effects of stress triaxiality, Lode angle, temperature, and strain rate are taken into account in the failure criteria. To assess the validity and superiority of the proposed model, the numerically predicted responses of polypropylene fiber-reinforced metal laminates subjected to varying impact energies were systematically compared with corresponding experimental results. Additionally, a comparative analysis was performed between the numerical simulation results predicted by the present model and those obtained using other constitutive models, such as the Johnson–Cook (JC) constitutive model and the elastoplastic constitutive model. Furthermore, the effect of projectile types on the ballistic performance of TFMLs have been systematically investigated. The findings demonstrate that the failure pattern predicted by the current model closely aligns with the experimental observations, while both the Johnson–Cook (JC) constitutive model and the elastoplastic constitutive model were unable to accurately replicate the experimentally observed failure behavior. This study also reveals that the projectile’s nose shape plays a significant role in influencing the perforation behavior of TFMLs, affecting both the residual velocity and damage. Full article

To advance the technology of Certification by Analysis (CbA), as called for by the aerospace industry, the fatigue problems of SAE keyhole specimens are analyzed to demonstrate a subcase of CbA. First, phenomena identification and ranking table (PIRT) analysis is performed. Second, modeling of the key phenomena is conducted, and finally, verification and validation with the experimental results are achieved. In particular, the elastic/elastoplastic stress distributions in the keyhole specimens are obtained using the finite element method (FEM). Plasticity correction for stress/strain at the notch root is made using the modified Neuber’s rule along with the Ramberg–Osgood equation. The low cycle fatigue (LCF) crack nucleation life is analytically predicted using the modified Tanaka–Mura model, a.k.a. the TMW model, given the material’s elastic modulus, Poisson’s ratio, Burgers vector, and surface energy, without the need for coupon fatigue data regression. The Tomkins equation is used to simulate plastic crack growth within the notch plastic zone. The above analytical life predictions are validated against the SAE keyhole specimen tests, becoming the first successful case of fatigue CbA at a sub-element level. Full article

The plastic properties for the jellyroll of lithium-ion batteries showed different behavior in tension and compression, showing the yield strength in compression being several times higher than in tension. The crushable foam models were widely used to predict the mechanical responses to compressive loadings. However, since the compressive characteristic is dominant in this model, it is difficult to identify distributions of the yield strength in tension. In this study, a simplified jellyroll model consisting of double-layer windings was devised to reflect different plastic characteristics of a jellyroll, and the proposed model was applied to an 18650 cylindrical battery under compressive loading conditions. One winding adopted the crushable foam model for representing the compressive plastic behavior, and the other winding adopted the elastoplastic models for tracking the tensile plastic behavior. The material parameters in the crushable foam model were calibrated by comparing the simulated force–displacement curve with the experimental one for the case where the cell was crushed between two plates when the punch was displaced by 7 mm. A specific cut-off value (10 MPa) was assigned to a yield stress limit in the elastoplastic model. Further, the computational model was validated with two more loading cases, a cylindrical rod indentation and a spherical punch indentation, as the punch was displaced by 6.3 mm and 6.5 mm, respectively. For three loading cases, deformed configurations and plastic strain distributions were investigated by finite element analysis. It was found that the proposed model clearly provides the plastic behavior both in compression and tension. For the crush simulation, the maximum compressive stress approached 222 MPa in the middle of the jellyroll, and the maximum effective plastic strain approached 60% in the middle of the layered roll. For indentation with the cylindrical and the spherical punch, the maximum effective plastic strain approached 52% and 277% in the layered roll, respectively. The local crack or location of a short circuit could be predicted from the maximum effective plastic strain. Full article

Due to their excellent mechanical properties, the carbon fiber-reinforced polymer composites (CFRPs) of thermoplastic resins are widely used, and an accurate constitutive model plays a pivotal role in structural design and service safety. A two-parameter three-dimensional (3D) plastic potential was obtained by considering both the deviatoric deformation and the dilatation deformation associated with hydrostatic stress. The Langmuir function was first adopted to model the plastic hardening behavior of composites. The two-parameter 3D plastic potential, connected to the Langmuir function of plastic hardening, was thus proposed to model the constitutive behavior of the CFRPs of thermoplastic resins. Also, T700/PEEK specimens with different off-axis angles were subjected to tensile loading to obtain the corresponding fracture surface angles of specimens and the load–displacement curves. The two unknown plastic parameters in the proposed 3D plastic potential were obtained by using the quasi-Newton algorithm programmed in MATLAB, and the unknown hardening parameters in the Langmuir function were determined by fitting the effective stress-plastic strain curve in different off-axis angles. Meanwhile, the user material subroutine VUMAT, following the proposed constitutive model, was developed in terms of the maximum stress criterion for fiber failure and the LaRC05 criterion for matrix failure to simulate the 3D elastoplastic damage behavior of T700/PEEK. Finally, comparisons between the experimental tests and the numerical analysis were made, and a fairly good agreement was found, which validated the correctness of the proposed constitutive model in this work. Full article

This study reveals the essential load-bearing characteristics of the steel–concrete composite floor system under fire conditions applying the structural stressing state theory. Firstly, the strain data in the entire process of the fire test are modeled as state variables which can present the slab’s stressing state evolution characteristics. Then, the state variables are used to build the stressing state mode and the parameter characterizing the mode. Further, the Mann–Kendall criterion is adopted to detect the leap points in the evolution curves of the characteristic parameters during the entire fire exposure process. Also, the evolution curves of the stressing state modes are investigated to verify the leap profiles around the leap/characteristic points. Finally, the detected leap points are defined as the failure starting points and elastoplastic branching points, which is unseen in past research focusing on the failure endpoint defined at the ultimate load-bearing state of the composite floor system. The failure starting point and the elastoplastic branching point are the embodiment of natural law from quantitative change to quality change in a system rather than an empirical and statistical judgment. Hence, both characteristic points avoidably exist in the strain data of the composite floor system undergoing the fire process, which can be revealed through the proper modeling methods and update the existing theories and methods on structural analysis and design in fire. Full article