European Journal of Mechanics A-Solids最新文献

This study addresses ductile fracture of single grains in metals by modeling of the formation and propagation of transgranular cracks. A proposed model integrates gradient-extended hardening, phase-field modeling for fracture, and crystal plasticity. It is presented in a thermodynamical framework in large deformation kinematics and accounts for damage irreversibility. A micromorphic approach for variationally and thermodynamically consistent damage irreversibility is adopted. The main objective of this work is to analyze the capability of the proposed model to describe transgranular crack propagation. Further, the micromorphic approach for damage irreversibility is evaluated in the context of the presented ductile phase-field model. This is done by analyzing the impact of gradient-enhanced hardening considering micro-free and micro-hard boundary conditions, studying the effect of the micromorphic regularization parameter, evaluating the performance of the model in ratcheting loading and testing its capability to predict three-dimensional crack propagation. In order to solve the fully coupled global and local equation systems, a staggered solution scheme that extends to the local level is presented.

The present study is aimed to develop an ad hoc four-steps procedure, based on the use of Digital Image Processing (DIP) techniques, homogenization methods and micro-modelling approaches, able to provide an effective tool for characterizing the mechanical properties of non-periodic masonry. More in detail, after creating, through a DIP technique and automated procedures, a finite element mesh from the Red-Green-Blue (RGB) image of a real masonry wall with non-periodic texture (Step 1 and Step 2), a homogenization method, which considers the properties of each masonry constituent (stone units and mortar joints), is used to derive the main elastic characteristics of a homogeneous continuum equivalent to the random masonry (Step 3). Specifically, this estimate can be achieved following the test-windows method based on the use of least-sized partitions subjected to boundary conditions in terms of displacements or stresses until a chosen convergence criterion is fulfilled. The non-linear response is then accomplished by means of a micro-modelling approach (Step 4). To this end, a three-dimensional finite element (FE) analysis can be therefore developed to characterize the main inelastic material parameters of the random masonry. Lastly, as a benchmark of the method, the proposed procedure has been validated against the laboratory outcomes obtained from a previous experimental campaign on non-periodic masonry walls.

Unlike the shear band development of metals generally regarded as the precursor to failure, the shear banding process in amorphous glassy polymers is known to influence both the strengthening and fracturing behaviors. Complementary to the previous experimental work in the literature on the shear band development under torsion under limited cases, the finite element (FE) analysis has been conducted to investigate the general shear banding behaviors in terms of the initiation and propagation in more detail. The FE model has been established by incorporating the Boyce-Parks-Argon (BPA) constitutive model with the full-network modification via a user material subroutine in ABAQUS. A series of nondimensional quantities were used to discuss the mesh sensitivity and the effects of predefined imperfections, specimen geometry, and torsion mode. Besides, by altering the extents of the intrinsic material softening and the strain hardening, the shear banding behaviors of typical materials under typical temperature and strain rate conditions are equivalently investigated. The validity of the simulation has been qualitatively validated by directly comparing with the experimental results from the literature.

Fracture analysis of orthotropic materials presents a persistent challenge in computational mechanics, particularly in bond–based peridynamics (BB–PD) framework. This challenge arises from the special material properties of orthotropic materials, presenting difficulties in accurately simulating the mechanical behavior and discerning fracture modes. In particular, the neglect of fracture parameters that profoundly affect the fracture behavior has resulted in an insufficient study of the fracture mechanisms for orthotropic materials. To address this issue, a novel BB–PD model for orthotropic materials was proposed, accompanied by the development of an energy–based failure criterion. The presented BB–PD model has no material parameter limitations and can accurately capture the deformation of orthotropic materials. The energy–based failure criterion considers the variation of fracture energy in different directions and fracture modes, ensuring that the PD calculated fracture energies align with their corresponding theoretical values. To validate the effectiveness of the developed BB–PD model and failure criterion, several numerical examples were performed, including convergence analysis, deformation analysis, and three quasi-static fracture analyses. The results demonstrate that the presented model and failure criterion can accurately predict material deformation and fracture. Furthermore, analysis of fracture modes indicates that the ratio of mode I and mode II fracture energies significantly influences crack paths and fracture modes in orthotropic materials.

High-entropy alloys (HEAs) have garnered considerable attention for their exceptional mechanical properties, positioning them as promising candidates for diverse industrial applications. This study investigates the mechanical properties of CoCrFeMnNi HEAs over a wide range of strain rates. Based on a novel electromagnetic loading device equipped with high-speed photography, intermediate strain rate tests of the HEAs are conducted. The intermediate strain rate test results show the effectiveness of the experiments. Experimental results exhibit a remarkable strain rate sensitivity of the HEA during tension tests. Microstructural analysis reveals the collaborative interplay between deformation twins and dislocations, enhancing strength-plasticity relationships under tension loading. Finally, a constitutive model (M-JCK) integrated by Johnson-cook model and KHL model is proposed to describe the mechanical behavior of HEAs. The results demonstrate that the M-JCK model outperforms traditional models, providing enhanced accuracy in capturing the complex responses of HEAs across varying strain rates.

Both theoretical and experimental studies are performed to investigate the impact properties of composite hexagonal auxetic honeycomb cylindrical shells subjected to an internal high-velocity projectile impact. Firstly, an analytical model of composite cylindrical shells with two fiber-reinforced polymer (FRP) skins and a hexagonal auxetic honeycomb core (HAHC) is built to anticipate the high-velocity impact properties, with the delamination and fracture energy absorption mechanisms of the skin and the core being considered. A strain-rate fitting function method is proposed to determine the material properties of the FRP skins and the core considering the strain-rate effect. Reddy's higher-order shear deformation theory is utilized to define the displacement of any point of the structure. Also, an improved Gibson theory is applied to derive the equivalent elastic moduli and Poisson's ratios of the HAHC. A detailed experimental validation is conducted on such shell specimens based on a high-velocity impact experimental system to validate the analytical model, in which comprehensive error analysis is discussed. Finally, the influence of critical geometric parameters of the projectile and the studied shell on its impact characteristics is evaluated and some crucial conclusions are provided to enhance impact resistance.

The micromechanical damage model has been developed to better describe multiscale fracture behavior in quasi-brittle rocks. While the deduced yield criterion under tension and compression has been carefully investigated in different stress spaces, it fails to capture a smooth transition from extension to shear fracture and overestimates the tensile strength of the rock. This paper introduces a unified nonlinear yield criterion based on a stress-dependent fracture energy parameter. In particular, the effect of the intermediate principal stress is encapsulated. The proposed yield criterion is then validated in the principal stress space based on a detailed parameter calibration procedure. Subsequently, four verification examples corresponding to Beishan granite, Lac du Bonnect granite, Carrara marble and Berea sandstone are carried out to show a desirable predictive capacity of the proposed yield criterion on progressive failure, extension to compressive-shear fracture transition and fault slip in quasi-brittle rocks.

This paper presents a variational modeling framework for investigating the flexoelectricity-driven evolution of remanent polarization in piezoceramics. In small-scale electromechanical systems, strain gradients can exhibit polarization in dielectric materials via the direct flexoelectric effect. In ferroelectrics, it is reasonable to expect that a sufficiently large magnitude of the flexoelectricity leads to a switching of the domain structure and thus the material becomes remanently polarized. It is interesting to note that this means that poling would be able to occur in the absence of any external electrical source. This provides the motivation to gain a better understanding of this effect for a possible technical use in e.g. sensor applications. For this purpose, a macroscopic model is presented that couples flexoelectricity and ferroelectric domain switching processes. By embedding the model in the variational framework of the generalized standard materials (GSM), a minimum-type potential structure and thus a stable and efficient numerical treatment is obtained. A mixed finite element formulation based on the Helmholtz free energy is introduced to solve the higher-order flexoelectric boundary value problem. In order to realistically predict the flexoelectric material behavior, the model response is adapted to experimental results in literature obtained for a piezoceramic in a bending test. By simulations based on the adapted model the evolution of the flexoelectricity-driven remanent polarization in the vicinity of a notch is shown.

Hierarchical designs have exhibited great potential in reducing structural weight and improving mechanical properties. However, the hierarchical design of perforated auxetic metamaterials with curved holes is rarely investigated and the choice of self-similar hierarchical design or not still confuses us. In this study, two types of hierarchical designs with self-similar and non-self-similar features for the auxetic metamaterial with peanut-shaped perforations are realized and compared. First, the printed hierarchical auxetic metamaterials via additive manufacturing technology are tested by quasi-static tension to explore their mechanical performance in different directions. Correspondingly, the computational homogenization model is established to characterize their full elastic properties and its effectiveness is verified by the experimental results. Subsequently, the deformation mechanisms of the proposed hierarchical metamaterials are numerically analyzed to address the superiority of self-similar design over the non-self-similar design. Finally, the influences of microstructural parameters and hierarchy order on the effective elastic constants of the proposed hierarchical metamaterial are considered and the optimal topology with extreme auxetic behavior is recommended. The results indicate that the proposed self-similar hierarchical design exhibits significant anisotropic feature, which can serve the multidirectional mechanical requirements, and the remarkable enhancement in auxeticity can be attributed to the synergistic deformation of tetrachiral sub-elements. Besides, the increase of hierarchy order does not continuously enhance the auxetic behavior of hierarchical metamaterial, although it can effectively change the porosity of structure. Through such investigations, a meaningful guidance of property map is provided for the hierarchical design of auxetic metamaterial perforated by curved cuts.

Among the various models presented so far to describe the nonlinear viscoelastic behavior of materials, the model proposed by Schapery in the 1960s stands out for its wide acceptance and significant contributions to the field. Through a detailed inspection of the main articles presented by Schapery and other related studies, the present paper reviews the Schapery nonlinear viscoelastic model. One-dimensional and three-dimensional formulations of the model for both isotropic and anisotropic materials, along with model accuracy, are discussed. The present article highlights the challenges of material characterization methods, such as creep-recovery testing, stress relaxation testing, and dynamic mechanical analysis. The article also addresses the issues of characterizing the material's behavior under non-recoverable strain and varying temperatures. Finally, the future research needs in this field are outlined, emphasizing the potential for further advancements in our understanding of nonlinear viscoelasticity.