Mechanical Response Of Material Research Articles

A nanoindentation approach for unveiling the photoplastic effects by a “light switch”: A case study on ZnO

AbstractThe nanoindentation method is a widely utilized approach for characterizing the mechanical properties of materials at the nanoscale. In typical nanoindentation tests, the mechanical responses of materials are monitored while maintaining constant environmental factors, such as lighting and temperature, in order to ensure the reliability of the results. Here, we propose a testing method that switches the light conditions during a single nanoindentation creep test to detect slight changes in the mechanical response due to weak light illumination. To achieve this, a reference sample of fused silica was employed, which is insensitive to light, in order to compensate for the thermal expansion/contraction of approximately 1 nm due to the light environment. The calibrated results revealed the instantaneous suppressive influence of light illumination on the indentation creep behavior of ZnO. It was found that upon initiating illumination, the indentation creep rate decreased by 45%, whereas terminating illumination led to a dramatic 19.4‐fold increase in the creep rate. The effective testing pattern involving a “light switch” enables quantitatively visualizing the light illumination effects through the instant “jump” in the creep strain rate within a single test, facilitating the detection of minor and instantaneous effects of light environments on indentation creep behavior.

Coupled field modelling of thermomechanical response in materials using peridynamic heat transport model and non-ordinary state-based peridynamics

Predicting the mechanical response of materials subjected to transient heat processes is crucial in various engineering applications. This paper introduces a novel peridynamic (PD) coupled field model formulated within the framework of Non-Ordinary State-Based Peridynamics (NOSBPD). This model offers the capability to simulate the coupled thermo-mechanical behavior of materials by incorporating both thermal transport and mechanical deformation analyses. To verify the model’s accuracy, a benchmark problem involving a steel plate undergoing transient thermal expansion is investigated. This model presents a valuable tool for various engineering applications involving coupled thermo-mechanical processes.

The effects of the angle between the indenter edge and the scratch direction on the scratch characteristics of Ti–6Al–4V alloy

Ti–6Al–4V alloy has become a crucial raw material in aerospace and other industries owing to its exceptional mechanical properties. However, it is also a typical difficult-to-machine material, and its removal process and mechanism have been widely investigated by scratch testing. Nevertheless, the inherent non-rotational symmetry of the Vickers indenter introduces a crucial parameter, i.e., the angle λ between the indenter edge and the scratch direction, which affects not only the mechanical response of materials but also its surface formation mechanism during scratch. This study systematically characterized the micro/nano scratch characteristics of Ti–6Al–4V alloy under three typical angles λ (0°, 22.5°, 45°) as well as various normal forces and scratch speeds. The coefficient of friction (COF), scratch depth, scratch width, residual scratch morphology, and specific scratch energy were comparatively analyzed. Finite element simulations confirmed that the direction of material flow changed with the change in angle λ. The corresponding deformation mechanisms during scratch were discussed accordingly. The results revealed a significant influence of the angle λ on the scratch behaviors and surface quality of Ti–6Al–4V alloy.

Ultimate resistance and fatigue performance predictions of woven-based fiber reinforced polymers using a computational homogenization method

PurposeIn order to achieve the desired macroscopic mechanical properties of woven fiber reinforced polymer (FRP) materials, it is necessary to conduct a detailed analysis of their microscopic load-bearing capacity.Design/methodology/approachUtilizing the representative volume element (RVE) model, this study delves into how the material composition influences mechanical parameters and failure processes.FindingsTo study the ultimate strength of the materials, this study considers the damage situation in various parts and analyzes the stress-strain curves under uniaxial and multiaxial loading conditions. Furthermore, the study investigates the degradation of macroscopic mechanical properties of fiber and resin layers due to fatigue induced performance degradation. Additionally, the research explores the impact of fatigue damage on key material properties such as the elastic modulus, shear modulus and Poisson's ratio.Originality/valueBy studying the load-bearing mechanisms at different scales, a direct correlation is established between the macroscopic mechanical behavior of the material and the microstructure of woven FRP materials. This comprehensive analysis ultimately elucidates the material's mechanical response under conditions of fatigue damage.

Numerical modeling of systems based on SMA wires and pulleys: A finite element formulation within the Arbitrary Lagrangian–Eulerian framework

Thanks to their properties of superelasticity and shape memory effects, SMA wires are often considered for the design of damping devices or actuators coupled to pulleys. In order to dimension such devices for commercialization, it is necessary to develop reliable, robust and fast numerical tools. To this end, simplifying the management of the wire/pulley contact using an Arbitrary Lagrangian–Eulerian (ALE) formulation is an original and effective solution. In this work, the wires are modeled by three-dimensional truss thermo-mechanical finite elements associated with a superelastic law. For each node, the curvilinear abscissa is used as an additional degree of freedom in order to deal with material flow from one element to another. After presenting the ALE formalism and the necessary precautions (advection of variables), as well as the material behavior and thermo-mechanical contact laws at the pulleys, elementary validation tests are studied. Finally, two devices taken from the literature are modeled using the ALE formalism. The results obtained demonstrate the relevance and effectiveness of the approach adopted, as well as the importance of not neglecting friction at the pulleys and thermal effects on the material mechanical response.

A general hyperelastic model for rubber-like materials incorporating strain-rate and temperature

A comprehensive hyperelastic model that precisely forecasts the mechanical characteristics of materials with rubber-like qualities is presented. This model relies on the well-established five-parameter Mooney-Rivlin model, which is then extended to incorporate strain rate dependent and temperature dependent term. To validate its accuracy, experimental data from ethylene propylene diene monomer (EPDM) rubber materials was utilized to compare with the model prediction. Hyperelastic stress-strain curves were collected from a variety of materials that were subjected to varying temperatures and strain rates to improve the model’s applicability. Its prediction results are compared against the collected experimental data, resulting in consistent and reliable outcomes. The simplified form of the model not only establishes an effective framework for characterizing and predicting the mechanical response of materials that resemble rubber under different working conditions but makes the coding and implementation of finite element analysis easier.

Investigate on material removal of 3C-SiC crystals in nano-polishing via molecular dynamics

While 3C-SiC crystals are widely employed in engineering applications such as aerospace, energy, chemistry, and electronics, the challenge of enhancing surface friction and wear mechanisms in 3C-SiC materials persists. This work focuses on the nano-polishing velocity effect on the material removal mechanism of 3C-SiC crystals in the course of nano-polishing, which is related to material removal, mechanical response, phase transformation, and stress distribution. By employing molecular dynamics (MD) simulations, nano-polishing velocity is modified within a specified range, and its influence on the atomic motion and structural transformation of the workpiece is examined. The simulation results reveal that higher nano-polishing velocities diminish the subsurface damage and the extent of phase transformation induced by nano-polishing. However, the higher velocities also result in reduced machined surface quality and increased residual stress in 3C-SiC crystals. Therefore, it is challenging to address both the surface quality and subsurface quality of the material solely based on nano-polishing velocity. A recommended range of nano-polishing velocity, ranging from 200 m/s to 400 m/s, is deemed appropriate. This work offers a comprehensive understanding of the material removal mechanism of 3C-SiC at the atomic level and holds significant guiding value for achieving ultra-precision machining of surfaces and subsurfaces.

From anti-Arrhenius to Arrhenius behavior in a dislocation-obstacle bypass: Atomistic simulations and theoretical investigation

Dislocations are the primary carriers of plasticity in metallic materials. Understanding the basic mechanisms for dislocation movement is paramount to predicting the material mechanical response. Relying on atomistic simulations, we observe a transition from non-Arrhenius to Arrhenius behavior in the rate of an edge dislocation overcoming the long-range elastic interaction with a prismatic loop in tungsten. Close to the critical resolved shear stress, the process shows a non-Arrhenius behavior at low temperatures. However, as the temperature increases, the activation entropy starts to dominate, leading to a traditional Arrhenius-like behavior. We have computed the activation entropy analytically along the minimum energy path following Schoeck’s method [1], which captures the cross-over between anti-Arrhenius and Arrhenius domains. Also, the Projected Average Force Integrator (PAFI) [2], another simulation method to compute free energies along an initial transition path, exhibits considerable concurrence with Schoeck’s formalism. We conclude that entropic effects need to be considered to understand processes involving dislocations bypassing elastic barriers close to the critical resolved shear stress. More work needs to be performed to fully understand the discrepancies between Schoeck’s and PAFI compared to molecular dynamics.

Regulating loading strain rates under shockless quasi-isentropic compression using a resin-based areal density gradient flyer

Areal density gradient flyers (ADGFs) have important applications in quasi-isentropic compression and high strain rate loading. The wave impedance gradient distribution of the reported ADGFs is single, and the effects of different wave impedance gradient distributions and spikes number density on the loading results are unknown. In this study, the resin-based ADGFs with different spike areal density distribution and spikes number density were designed and prepared using projection micro stereolithography technology (PμSL). The printing accuracy of ADGFs was evaluated using three-dimensional optical profiler, optical microscope, Scanning Electron Microscopy (SEM) and ultra depth of field microscope. The loading process of the ADGF on the target was studied by experiment and simulation. The simulation result was consistent with the experimental result. Augmenting the wave impedance distribution index (P) of spikes and spikes number density increases the loading strain rate. Due to the high printing accuracy of PμSL, the fine ADGF structures with large spikes number density can be prepared, thereby promoting the formation of quasi-isentropic compression plane waves. This work realizes the regulation of loading strain rate under shockless quasi-isentropic compression, which is significant for understanding the mechanical response of materials under high strain rate loads.

Synergistic effects of temperature and strain rate on tensile properties of simulated Ni-6Cu alloy with Σ3 non-Arrhenius grain boundary

ABSTRACT Comprehending the mechanical response of materials on an atomic level is pivotal in the optimisation of advanced materials with superior mechanical properties. This research article utilises the atomistic-scale based molecular dynamics simulations to report the uniaxial tensile behaviour of bicrystalline Ni-6Cu (Nickel – 94% and Copper – 6%) alloy incorporated with pre-existing faceted Σ3 [111] 60° {11 8 5} grain boundaries. The primary aim of this investigation is to comprehend the performance of bicrystalline Ni-6Cu alloy under varying thermodynamic conditions and to assess the influence of pre-existing faceted grain boundaries on its tensile behaviour. This work encompasses a range of strain rates (108 to 1010 1/s) and temperatures (spanning from 100 to 900 K) for the uniaxial tensile deformation simulations. The outcomes unveil that the Young’s modulus of Ni-6Cu alloy (with pre-existing faceted grain boundaries embedded in its domain) was inversely proportional to temperature and constant with respect to strain rate. For the same configuration, yield stress was inversely and directly proportional to temperature and strain rate, respectively. Interestingly, incipient plasticity in the tensile stress–strain response was observed at lower temperature and lower strain rate. From the microstructural point of view, at lower temperatures, the incoherent twin boundary served as a source for the nucleation of stacking faults; however, as the temperature increased, both the incoherent twin boundary and the tips of coherent twin boundary function as the source for stacking faults formation. Our simulations also verified the GB’s anti-thermal (or non-Arrhenius) migration behaviour even under tensile load.

Modified Steinberg–Guinan elasticity model to describe softening–hardening dual anomaly in vanadium

Constitutive models are essential for describing the mechanical behavior of materials under high temperatures and pressures, among which the Steinberg–Guinan (SG) model is widely adopted. Recent work has discovered a peculiar dual anomaly of compression-induced softening and heating-induced hardening in the elasticity of compressed vanadium [Phys. Rev. B 104, 134102 (2021)], which is beyond the capability of the SG model to describe. In this work, a modified SG elasticity constitutive model is proposed to embody such an anomalous behavior. Elemental vanadium is considered as an example to demonstrate the effectiveness of this improved model in describing the dual anomalies of elasticity. This new SG elasticity model can also be applied to other materials that present an irregular variation in the mechanical elasticity and are important to faithfully model and simulate the mechanical response of materials under extreme conditions.

Achieving synchronous compression-shear loading on SHPB by utilizing mechanical metamaterial

Materials in service often experience complex stress states, such as a combination of shear and compression or tension. Therefore, it is crucial to experimentally measure the mechanical responses of materials under complex stress states before designing structures, as these responses differ from those under uniaxial loading. However, conducting combined loading experiments, especially under dynamic impact, is challenging and usually requires complex and costly equipment. In the present work, by employing compression-torsion coupling metamaterials, an easy method is proposed for the first time to achieve synchronous dynamic compression-shear loading on 1D Split Hopkinson Pression Bar (SHPB), which is also feasible for quasi-static experiments on universal material testing machine. The compression-torsion coupling metamaterial can convert a compression wave into combined waves of compression and torsion, and ensures the two waves naturally synchronously act on the thin-walled cylinder specimen. Since the compression-shear dynamic loading experiment can be performed on a traditional 1-D SHPB, it is a cost-effective, convenient, and easily implementable method. Both the dynamic and quasi-static mechanical properties of 1060 Al were measured under various shear-compression ratios, and a well von-Mises yield surface was obtained with strain rate insensitivity, confirming the validity of the proposed experimental methods.

Fabrication, Evaluation, and Multiscale Simulation of Piezoelectric Composites Reinforced Using Unidirectional Carbon Fibers for Flexible Motion Sensors.

Piezoelectric composite materials can convert mechanical energy into electrical energy, thus promoting battery-free motion-sensing systems. However, their substandard mechanical performance limits the capability of sensors developed using flexible piezoelectric materials. This study introduces a novel design strategy for preparing high-strength flexible piezoelectric composite materials comprising unidirectional carbon fiber-reinforced potassium sodium niobate (K0.5Na0.5NbO3) nanoparticle-filled epoxy resin (UDCF/KNN-EP). The fibers significantly improve the Young's modulus of UDCF/KNN-EP along the fiber direction, which reaches 282.5MPa. Moreover, the composite exhibits excellent stretchability and piezoelectric response ( ) in the cross-fiber direction under cyclic tensile loading. Multiscale finite element analysis is performed via simulation, which allows theoretical examination of the experimental results and the material's mechanical response mechanism. Finally, UDCF/KNN-EP is seamlessly incorporated into athletic gear and used to measure the impact caused by baseball catching and track footfall patterns. This study harnesses the superior strength of carbon fibers to enhance the durability and dependability of self-powered sensors without compromising flexibility in specific directions.

Mechanical and Optical Characterization of Lithium-Ion Battery Cell Components/Cross-Ply Lamination Effect

Excessive mechanical loading of lithium-ion batteries can impair performance and safety. Their ability to resist loads depends upon the properties of the materials they are made from and how they are constructed and loaded. Here, prismatic lithium-ion battery cell components were mechanically and optically characterized to examine details of material morphology, construction, and mechanical loading response. Tensile tests were conducted on the cell case enclosure, anodes, cathodes, and separators. Compression tests on stacks of anodes, cathodes, separators, and jellyrolls were made from them. Substantially differing behaviors were observed amongst all components tested. An optical examination of the anodes, cathodes, and separators revealed homogeneities, anisotropies, and defects. Substantial texturing was present parallel to the winding direction. When highly compressed, jellyrolls develop well-defined V-shaped cracks aligned parallel to the texturing. Like many laminates, altering the lay-up construction affects jellyroll mechanical performance. To demonstrate, a cross-ply jellyroll was fabricated by rotating every other complete component set (cathode/separator/anode/separator), reassembling, and compressing. A distinctly different fracture pattern and increased compressive strength were observed.

A data-driven approach for predicting the ballistic resistance of elastoplastic materials

Data-driven methods and machine learning methods provide efficient and accurate approaches for solving impact problems. In this paper, a data-driven approach is proposed for numerical simulations of ballistic impact behavior for elastoplastic materials. An enhanced rate-dependent scheme is employed for improving the predictability of the data-driven constitutive model. A new method that introduces a stress triaxiality indicator to three separate constitutive models is proposed to consider the discrepancy between the mechanical responses of materials under tension, compression, and shear. Additionally, a modified Bai-Wierzbicki fracture criterion considering the strain rate effect and the stress-state effect is used to evaluate the fracture behavior of the materials during impact simulations. Subsequently, a compatible numerical implementation algorithm that considers loading, unloading, and reverse loading is established to enable the application of the data-driven approach in finite element simulations. Numerical validation of the proposed data-driven approach is conducted through several simple loading examples, such as cyclic loading, torsional loading, and tension–torsion combined loading. The data-driven approach is then employed to simulate the ballistic impact behavior of Ti-6Al-4V targets of different thicknesses that are struck by blunt projectiles. Impact properties—including the relationship between residual velocity and impact velocity, ballistic limit velocities, and fracture paths—are comprehensively studied. The results demonstrate the reasonable predictability and accuracy of the data-driven approach when applied to ballistic impact simulations.

Stress–strain relationships and yielding of metal-organic framework monoliths

Metal-organic frameworks (MOFs) have emerged as a versatile material platform for a wide range of applications. However, the development of practical devices is constrained by their inherently low mechanical stability. The synthesis of MOFs in a monolithic morphology represents a viable way for the transition of these materials from laboratory research to real-world applications. For the design of MOF-based devices, the mechanical characterization of such materials cannot be overlooked. In this regard, stress-strain relationships represent the most valuable tool for assessing the mechanical response of materials. Here, we use flat punch nanoindentation, micropillar compression and Raman microspectroscopy to investigate the stress-strain behaviour of MOF monoliths. A pseudo-plastic flow is observed under indentation, where the confining pressure prevents unstable crack propagation. Material flow is accommodated by grain boundary sliding, with occasional stepwise cracking to accommodate excessive stress building up. Micropillar compression reveals a brittle failure of ZIF-8, while plastic flow is observed for MIL-68.

A static stiffness reference object for instrumented indentation with integrated fiber Fabry–Perot displacement measuring interferometer

Instrumented indentation is a technique used for measuring the mechanical response of materials to deformation. The accuracy of these measurements relies on force and displacement values recorded during the indentation process. This paper presents a miniature fused silica parallelogram flexure to serve as a reference object for calibrating the applied indentation force based on Hooke’s law, F = kz, where k is the stiffness of the reference object and z is the displacement of the flexure under force F. This study discusses two independent experimental approaches to determine the stiffness of the flexure. In both cases, the stiffness was calculated from the measured flexure displacement while known forces are applied. In the first method, the displacement is measured using a built-in fiber-based interferometer while reference masses of 100 mg and 200 mg are placed on the flexure. A stiffness of is determined with this method. The second method uses a commercial indenter to apply a cyclic force of 100 mN magnitude on the flexure while recording the displacement of the indenter probe. Experiments using a 5 μm and a 50 μm conospherical tip estimate the stiffness to be , and respectively.Disclaimer: Certain commercial equipment, instruments are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

A semi-analytical approach for elastoplastic impact-contact involving coated medium

Plastic deformation resulting from high stress exceeding material yield limit widely exists in many mechanical components, especially for those subjected to impact load, which further compromises the accuracy and reliability of the affected parts. Coating technology is an effective way to provides protection for the substrate against the heavy impact load. A novel solution method for simulating the elastoplastic impact-contact of coated medium is presented in the current investigation. The second-order Newmark algorithm is introduced for impact dynamics iteration. The plastic yielding and plastic strain accumulation during impact process are determined by the von Mises yield criteria. The effectiveness of the proposed solution method is demonstrated numerically by the finite element method (FEM) via commercial software and experimentally by a nano-impact test. Impact-contact problems for a rigid spherical punch against a coated medium with either a rough or smooth surface are further studied to illustrate the elastoplastic mechanical response of materials under impact contact load.

Inertial effect on dynamic hardness and apparent strain-rate sensitivity of ductile materials

Indentation is a simple and one of the oldest small-scale test methods for characterizing the mechanical response of materials. Recently, there has been a growing interest in dynamic indentation due to its potential to characterize the mechanical response of small volume of materials at high strain-rates. Herein, we focus on understanding the synergistic effects of materials’ inherent strain-rate sensitivity and inertia on the scaling of dynamic hardness with indentation strain-rate. Specifically, we analyze the dynamic indentation response of ductile materials over a wide range of indentation velocities, utilizing both finite element calculations and an analytical cavity expansion model. The materials are assumed to follow isotropic elastic–viscoplastic constitutive relations, with the viscoplastic part described by either an overstress or a simple power-law model. Our results show that below a critical indentation strain-rate, the scaling of dynamic hardness with indentation strain-rate is the same as the viscoplastic constitutive description. Therefore, at these strain-rates, dynamic hardness can effectively characterize a material’s strain-rate sensitivity, provided its viscoplastic constitutive description is known beforehand. However, above the critical indentation strain-rate, the dynamic hardness increases rapidly with indentation strain-rate. This phenomenon indicates an apparent strain-rate sensitivity that exceeds the expected response of the viscoplastic constitutive description. Moreover, above the critical indentation strain-rate, the indentation depth acts as a natural length-scale, with higher hardness observed at greater depths due to increased inertial effects. In other words, above the critical indentation strain-rate, dynamic hardness cannot be taken as an intrinsic material property.

A multi-material-oriented modeling framework to characterize and predict mechanical self-healing

In the family of smart materials termed as “self-healing materials”, there is a prominent number of them sharing many similarities in the way that healing is affecting their post-damaged mechanical response. In this work, a generic and multi-material phenomenological-based healing formulation is proposed to investigate and characterize the self-healing effect in the mechanical response of materials exhibiting strong nonlinearities like rate-dependent plasticity, visco-damage initiation and evolution. The proposed healing formulation uses objective experimental measures such as resting time, loading rate and damage level. This formulation is integrated in a combined computational–experimental procedure, the so-called Generic Healing-Oriented Multi-Material Modeling Framework (GHOM3) that facilitates (i) the understanding of a strongly nonlinear response, (ii) a robust material characterization and (iii) the predictive simulation via the finite element analysis. As study case, the intrinsic self-healable mechanical response of a highly nonlinear asphalt-based composite matrix is characterized at room temperature using the proposed framework. As additional novelty in the framework, an ultra-fast optimization-based material parameter identification process is developed using a master–slave parallelization paradigm that leads to save up to 90% of data processing time. The framework is put into practice to virtually predict the mechanical response influenced by the healing process of the validated material in a dog-bone specimen under Load–Unload–Resting–Reload at multiple loading rates and damage levels. The implemented approach gives direct access to the entire damage and healing histories, which are experimentally inaccessible, as well as providing an alternative definition of the healing indices commonly used in experimentation.