Mechanics of Materials最新文献

The inclusions in a high-temperature resistant matrix can significantly influence the radiative heat transfer of composite materials at elevated temperatures; therefore, the microstructure design of composites for thermal protection during atmospheric re-entry require a more accurate prediction of thermal insulation performance. In this paper, the Rosseland approximation was used to investigate the radiative heat transfer within thermal protection materials, e.g., porous carbon-based material and ultra-high-temperature ceramics (e.g., ZrB₂-SiC), and the discrete dipole scattering method was used to evaluate the extinction efficiency across the inclusions with different types of microstructures. The effect of inclusion parameters, such as inclusion size, shape coefficient, volume fraction, orientation, and size distribution, on the radiative and effective thermal conductivity (ETC) at various temperatures was analyzed in detail. Test results obtained from the existing literature were used to validate the ETC of porous ceramics predicted by the proposed model. The results indicated that the microstructures in thermal protection materials play a fundamental role in improving the heat-shielding properties. The present study deepens the understanding of the relationship between microstructures and thermal radiation properties and provides theoretical design guidelines for thermal protection materials with improved thermal insulation properties.

In this work, a hybrid physics-based data-driven surrogate model for the microscale analysis of heterogeneous material is investigated. The proposed model benefits from the physics-based knowledge contained in the constitutive models used in the full-order micromodel by embedding the material models in a neural network. Following previous developments, this paper extends the applicability of the physically recurrent neural network (PRNN) by introducing an architecture suitable for rate-dependent materials in a finite strain framework. In this model, the homogenized deformation gradient of the micromodel is encoded into a set of deformation gradients serving as input to the embedded constitutive models. These constitutive models compute stresses, which are combined in a decoder to predict the homogenized stress, such that the internal variables of the history-dependent constitutive models naturally provide physics-based memory for the network. To demonstrate the capabilities of the surrogate model, we consider a unidirectional composite micromodel with transversely isotropic elastic fibers and elasto-viscoplastic matrix material. The extrapolation properties of the surrogate model trained to replace such micromodel are tested on loading scenarios unseen during training, ranging from different strain-rates to cyclic loading and relaxation. Speed-ups of three orders of magnitude with respect to the runtime of the original micromodel are obtained.

Theoretical models have been developed to explore the electrodeposition stability between Li metal and salt-doped polymer electrolytes. However, there is still limited investigation on the coupling behavior between mechanics and electrochemistry in those novel nano-structured polymers with immobilized anions. In this work, we employ a multiphysics modeling framework to predict the electro-chemo-mechanical behavior of polymer electrolytes containing immobilized anions. We analyze the impacts of charging conditions, stress coupling and the immobilization of anions on their ion transport, electrical and mechanical properties during charging. Strengthening stress coupling is demonstrated to improve the diffusion-driven stability of electrodeposition, by enhancing limiting applied current densities. Compared with stress coupling, immobilizing anions surprisingly sustains the non-zero interfacial Li⁺-ion concentrations even at high applied currents, thereby mitigating the potential diffusion-driven instability of electrodeposition. Both stress/strain and overpotentials also get reduces with increasing the concentrations of immobilized anions. This theoretical work provides insights into the strategy of redesigning polymer electrolytes, and also lays foundation for the multiphysics modeling of electrodes and full-cell battery systems.

Recent advances have prominently highlighted physics informed neural networks (PINNs) as an efficient methodology for solving partial differential equations (PDEs). The present paper proposes a proof of concept exploring the use of PINNs as an alternative to finite element (FE) solvers in both classical and gradient-enhanced solid mechanics. To this end, spatio-temporal PINNs are designed to represent continuous solutions of boundary value problems within spatio-temporal space. These PINNs directly incorporate the equilibrium and constitutive equations in their differential and rate forms, bypassing the requirement for incremental implementation. This simplifies application of PINNs to solve complex mechanical problems, particularly those involved in the context of gradient-enhanced continua. Moreover, traditional meshing is no longer required as it is replaced by a point cloud, making it possible to overcome meshing drawbacks. The results of this investigation prove the effectiveness of the proposed methodology, especially with regards to non-monotonic loading conditions and irreversible plastic deformation. Compared to classical FE approaches, the proposed spatio-temporal PINNs are more readily applied to complex problems, which are tackled in their raw form. This is especially true for gradient-enhanced continuum problems, where there is no need to introduce additional degrees of freedom as in classical FE approaches. However, PINNs training generally requires more computation time, a challenge that can be mitigated by employing the concept of transfer learning as shown in this paper. This concept, which is very useful when performing parametric studies, involves applying knowledge grained from solving one problem to another different but related one. The use of PINNs as mechanical solvers is shown to be highly promising in the forthcoming era, where advancements in GPU technology can further enhance their performance in terms of computation time.

The unit size effect of 316L diamond lattice structures was systematically investigated through experiments, theory, and simulations. Experimental tests demonstrated that reducing the cell size to 5 mm and 2.5 mm enhances the load carrying capacity and energy absorption of the structures. Additionally, analytical solutions were developed to acceptably estimate the elastic modulus and yield strength of diamond lattice structures. Finite element simulations, incorporating elastic, plastic, and ductile damage models, were utilized to depict the entire deformation evolution at different strain levels. These simulations were found to be precisely consistent with experimental observations. The results confirmed a transition from non-uniform deformation to uniform large-scale plastic deformation. This transition is attributed to either locally fractured struts caused by longer struts in structures with large cell sizes or largely deformed, non-ruptured short beams in structures with smaller cell sizes. Comparisons with previous reports indicated that the current structures with a cell size of 2.5 mm exhibit outstanding mechanical performance, making them desirable candidates for engineering applications.

The emergence of artificial metamaterials not only enables many physical and mechanical properties that are not accessible by natural materials but also provides people with new opportunities to break down particular limitations in engineering. In this work, a new metamaterial characterized by unusual sign-switching Poisson's ratio is introduced. Different from all conventional and auxetic materials that exhibit reversed lateral deformation under tension and compression, the new metamaterial proposed here always expands in the direction orthogonal to the applied load. Our design relies on a planar construction perforated with periodically distributed self-contact slits. The mechanical responses of the proposed metamaterial subjected to uniaxially tensile, compressive, and bending loads are systematically investigated using a combination of numerical simulations and experimental tests. It is found that a lateral expansion effect is also induced for the bending test. Based on its unique property, a new concept of implant is developed to reduce the risk of loosening after total hip replacement. The demonstrative example highlights the potential applications of the new metamaterial in various fastening systems.

In this paper, we propose a novel three-dimensional micromechanics-based failure criterion to assess the load-bearing capacity of quasi-brittle materials under complex multiaxial stress conditions. This criterion not only inherits benefits of the multi-scale friction-damage coupling modeling approach but also accounts for the effect of the intermediate principal stress. Physically, the initiation and propagation of microcracks contribute to the damage, and the failure of the material ultimately occurs due to the unstable growth of microcracks. Simultaneously, plastic deformation, which results from frictional sliding along microcracks, is intimately coupled with the damage process. Employing friction-damage coupling up-scale analyses and introducing a novel parabolic local frictional law, we derive a new nonlinear compression meridian criterion within the upscaling framework. Moreover, by incorporating a Lode dependence function, this criterion effectively addresses variations in strength induced by the intermediate principal stress. To validate this criterion, we utilize data from triaxial compression, triaxial extension, and true triaxial tests conducted on various rock materials and concrete, all of which demonstrate excellent agreement.

Active fault zones have complex structural and geometric features that are expected to affect earthquake nucleation, rupture propagation with shear and volumetric deformation, and arrest. Earthquakes, in turn, dynamically activate co-seismic off-fault damage that may be both distributed and localized, affecting fault zone geometry and rheology, and further influencing post-seismic deformation and subsequent earthquake sequences. Understanding this co-evolution of fault zones and earthquakes is a fundamental challenge in computational rupture dynamics with consequential implications for earthquake physics, seismic hazard and risk. Here, we implement a continuum damage-breakage (CDB) rheology model in our MOOSE-FARMS dynamic rupture simulator to investigate the interplay between bulk damage and fault motion on the evolution of dynamic rupture, energy partitioning, and ground motion characteristics. We demonstrate several effects of damage (accounting for distributed cracking) and breakage (accounting for granulation) on rupture dynamics in the context of two prototype problems addressed currently in the 2D plane-strain setting: (1) a single planar fault and (2) a fracture network. We quantify the spatio-temporal reduction in wave speeds associated with dynamic ruptures in each of these cases and track the evolution of the original fault zone geometry. The results highlight the growth and coalescence of localization bands as well as competition between localized slip on the pre-existing faults vs. inelastic deformation in the bulk. We analyze the differences between off-fault dissipation through damage-breakage vs. plasticity and show that damage-induced softening increases the slip and slip rate, suggesting enhanced energy radiation and reduced energy dissipation. These results have important implications for long-standing problems in earthquake and fault physics as well as near-fault seismic hazard, and they motivate continuing towards 3D simulations and detailed near-fault observations to uncover the processes occurring in earthquake rupture zones.

Post Forming Electro Plastic Effect (PFEPE) has been proposed as a promising technology for mitigating forming forces and addressing springback challenges in the metal forming industry. However, several research gaps remain unaddressed for the industrialization of this technology. Firstly, there is a lack of experimental validation regarding the impact of stress reduction on springback. Secondly, the potential effect of the skin-effect on the current metrics of stress reduction needs to be evaluated. Additionally, a post-forming electrically assisted elastoplastic material model is necessary for further technology development in stamping processes. This study tackles these challenges by utilizing AA5754H22 as a reference material and integrating a comprehensive experimental campaign with finite element numerical models and empirical material model developments. Our findings confirm that PFEPE facilitates a significant reduction in springback, achieving approximately a 100% reduction. Although the skin-effect introduces non-uniform current flux density distribution, its impact at the macroscopic level is negligible for the studied thin samples. While the numerical results of springback fails to accurately replicate experimental results, the developed material model aligns well with experimental trends.

Thermo-oxidative aging (TOA) significantly impacts the fatigue life of rubbers by reducing the fatigue strength and modifying the slope of the Wöhler curve, rendering traditional time-temperature superposition methods inadequate. In this work, we aim to develop a model capable of predicting the effect of TOA on the fatigue properties of rubbers. For this purpose, dumbbell specimens of natural rubber (NR) were subjected to aging in an air-vented oven at different temperatures prior to mechanical testing. Tensile tests were conducted to quantify the aging effects on a microscale network parameter known as elastically active chains (EAC) density, along with determining ultimate properties such as the stress and strain at break. By using a time-temperature equivalence and the Arrhenius shift factor, master curves were constructed for both EAC density and ultimate properties. Subsequently, the fracture properties of the aged material were predicted using an energy limiter approach whose evolution follows that of EAC density. Furthermore, a relationship between the parameters of the continuum damage mechanics (CDM) approach (specifically, the power law parameters of the Wöhler curve) and the fracture properties was proposed, resulting in accurate estimates of the fatigue life regardless of the aging conditions. Satisfactory agreement was observed between the model predictions and the data for nine aging conditions encompassing four different temperatures. The CDM approach also allows assessing the evolution of mechanical damage within the material influenced by TOA. The novelty of this approach lies in establishing a direct relationship between fatigue and fracture properties. Moreover, this is the first time to the best of our knowledge that TOA has been explicitly incorporated into a fatigue life prediction model via the evolution of the EAC density.