Elastic Limit Research Articles

An improved dynamic constitutive model for ceramics

An accurate constitutive model for ceramic is essential for guiding its application in armor systems. Inspired by previous work, an improved dynamic constitutive model for ceramics is developed. In the constitutive model, a new equation of state is proposed by modifying the polynomial equation of state; the strength surface takes into account pressure dependency, strain rate effect, Lode effect, strain hardening and softening. To validate the present model comparisons are made between the model predictions and the material test data for alumina ceramics in terms of strength surface, strain rate effect, and pressure-volumetric strain relationship, and good agreement is obtained. Furthermore, numerical simulations using the present model are conducted, which cover a wide range of impact scenarios and impact velocities (namely, spalling of a long round bar, planar impact, pure ceramic target perforation, dynamic indentation, and projectile impact on ceramic composite armor). Comparisons are made between the numerical results and the experimental data for two similar alumina ceramics (i.e., AD995 and C98 ceramic) in terms of spalling position, particle velocity-time history, longitudinal wave velocity, Hugoniot elastic limit (HEL), residual velocity, cratering size, cracking pattern, and target deflection, and good agreement is also obtained, which lend further support to the accuracy and usefulness of the improved dynamic constitutive model for ceramics.

Single-phase equiatomic Co-Cr-Fe-Ni high-entropy alloy with excellent strain gauge sensitivity

Single-phase Co-Cr-Fe-Ni high-entropy alloys boast exceptional mechanical and electrical properties. These alloys are suitable for various functional applications, particularly as strain gauges and high ohmic resistors, due to this fact. The resistance-tension tests of the equiatomic CoCrFeNi high-entropy alloy demonstrate higher strain gauge factor (GF) and elastic limit values than commercial strain gauges. In the elongation range of ε = 0–0.2%, the resistivity of the studied alloys follows a strictly linear pattern with respect to the applied load, up to 435 MPa. Heat treatment enhances the GF value of the as-cast alloy from 3.07 to 3.45. The annealing process changes the sample structure, resulting in an increase in the GF.

Enhancing thermal stability of Nb nanowires in a NiTiFe matrix via texture engineering

Metallic nanowires, renowned for their high strength and large elastic strain limits, have shown significant potential in rendering extraordinary structural and functional properties in composites. However, their integrity at high temperatures is often compromised due to fragmentation and spheroidization, processes driven by excess interfacial energy. Here, we demonstrate in a NiTiFe/Nb nanocomposite that the fragmentation and spheroidization of Nb nanowires can be significantly suppressed by tailoring the interfacial crystallographic orientation relationship between the nanowires and the matrix. By doping Fe into NiTi, we inhibit the typical deformation-induced amorphization of the NiTi-based matrix during severe deformation processing. The common (111)NiTi//(110)Nb texture is inherently suppressed and (110)NiTiFe//(110)Nb texture is formed instead. Such a change in texture allows Nb nanowires to retain their integrity up to 700 °C in the NiTiFe matrix, in contrast to the 550 °C in the counterparts. Simulation results indicate that the enhanced thermal stability of Nb nanowires is attributed to the reduced interfacial energy between (110)NiTiFe and (110)Nb. Additionally, Fe doping elevates the migration energy barrier for Nb diffusion, imposing further resistance to fragmentation and spheroidization.

On Thermoelastic Impact Modelling of Frozen Composite Target During Pre – Heated Projectile Penetration Starts of Motion

This study investigates a composite double-layer structure for improved thermal shock resistance. A modified Hugoniot elastic limit model is presented for the composite, followed by a 2D thermo-elastic impact simulation using commercial software. The simulation focuses on a composite material under initial extreme low temperature conditions with alternating metallic (Steel, Aluminum) and non-metallic layers (Kevlar 49, Graphite). The frozen target is subjected to pre- heated projectile. The objective is to optimize the composite's durability by strategically placing reinforcement particles within specific layers. The analysis explores the effect of different particle types (oil, water, Aluminum, Steel) and sizes (0.3mm, 0.5mm, 1mm) on the composite's stress response. It was found that aluminum and steel particles significantly reduce stress compared to fluid/gas particles, confirmed qualitatively by literature. Kevlar particles within the SiCp layer enhance its resistance, while Aluminum particles within the Kevlar layer offer weight reduction benefits. Moreover, for Kevlar, larger particles improve resistance, and vice versa for the SiCp case. Considering weight, a particle size of 0.5mm is chosen for both layers. Moreover, a finite element analysis of the optimized composite model subjected to thermoelastic impact loading demonstrates its superior performance compared to the non-reinforced composite. Specific layer combinations (SiCp with Kevlar particles, Graphite or Kevlar with Aluminum particles) show the most significant stress reduction. Finally, separate 3D ballistic analysis was performed for Tungsten having 600m/sec projectile into 5 layered target with thickness of 2.8mm each layer and appropriate interaction friction (SiCp - Steel 304 - Al 7075-T651 - Kevlar 49 - Graphite Crystalline) during penetration time of 0.006sec at 300K. The dynamic explicit transient analysis was confirmed with the predecessors' analytic calculations.

The influence of plasticizer on the mechanical, structural, thermal and strain recovery properties following stress-relaxation process of silk fibroin/sodium alginate biocomposites for biomedical applications

The influence of plasticizer glycerol (GLY) on the mechanical, structural, and thermal properties of silk fibroin (SF)/sodium alginate (SA) biocomposite films was investigated in detail. As the SF/SA ratio increased up to 65%, the SF content significantly improved the Tensile strength (σT), Young's modulus (Ey) but reduced the elongation at break (εb). To modify and enhance the elasticity and flexibility of the biocomposite films, the GLY as a plasticizer was used at different ratio from 20 to 50% for each SF/SA biocomposite films. Although the extensibility of the films was improved greatly with increasing GLY ratio, σT and Ey reduced significantly. The effect was observed more apparently for the GLY ratio starting from 35%. It was also shown that crystallinity index in the Amide I region increased as the SF/SA ratio increased to 65%. Increasing SF content improved the thermal stability of the SF/SA biocomposites. The XRD results showed that crystallinity was increased as SF/SA ratio increased. Stress-relaxation of SF/SA (30%) biocomposite films plasticized with GLY revealed that each kind of plasticized films showed a viscoelastic behavior and a fast relaxation in the first stage (1–2 min) of the processes and then continued slowly. The GLY increased the extensibility and elasticity limit of the SF/SA (30%) composite films. During the strain recovery processes, the plasticized composite films recovered completely in a quite shorter time than that of unplasticized films. It was observed higher the GLY content, the recovery times became shorter.

Machine learning prediction of mechanical properties of bamboo by hemicelluloses removal

The use of bamboo as a sustainable material is becoming increasingly prevalent; however, the optimisation of its mechanical properties remains a significant challenge. In this study, different concentrations of sodium hydroxide (NaOH) were used to remove the hemicellulose of bamboo and the effect of mechanical properties such as modulus of elasticity, flexural strength and elastic limit were evaluated. A total of 90 samples of data were collected and five machine learning algorithms including Principal Component Regression (PCR), Partial Least Squares Regression (PLSR), Ridge Regression (RR), Lasso Regression (LR) and Elastic Network Regression (ENR) were employed to build predictive models based on these properties. The models were trained and tested using 5-fold cross validation. The results showed that the mechanical properties of elastic modulus and elastic limit of bamboo medium were enhanced to 9.63 GPa and 66.44 MPa treated by 10 % NaOH, while the flexural strength of bamboo medium was up to 147.29 GPa with 5 % NaOH. The Ridge Regression algorithm was the best compared to other four algorithms. This methodological approach is not only offers an efficient way to optimize the mechanical properties of bamboo, but also enhances sustainable practices in the environmental sector.

Comprehensive analysis of wave interactions and resulting spall damage in layered heterogeneous medium under impact

The effect of dynamic spall damage on the response of layered medium subjected to one-dimensional impact involving an impactor and a multi-layered target is investigated. The study examines the damage caused by elastic waves below the Hugoniot Elastic Limit (HEL) during impact events. Analytical expressions of stress and particle velocity derived from mass and momentum conservation principles are utilized to solve the wave interactions within the impactor-target system, considering reflections, transmissions, and wave interactions between layers. These analytical expressions, integrated into a computational framework, facilitate the monitoring of material responses following each wave interaction, thereby analysing the impact response of the layered medium. Wave interactions, resulting in tensile stresses, that can cause damage to the target have been identified. A strain-based damage initiation and evolution law is incorporated into the developed computer program to predict damage in each layer of a medium. Damage alters the medium’s impact behaviour by decreasing stress magnitude and inducing temporal delays in the response due to attenuated wave propagation speed. The occurrences of tensile stress are explored, analysing spatial and temporal variations of multiple damage incidents within the layered medium. The tension at the interface between two layers can induce damage in one or both adjacent layers, leading to debonding between layers. The effect of damage on the impact response of the medium is analysed by comparing the results for the damaged and undamaged target scenarios. The impact behaviour of a single-layer and a multi-layer target obtained from the present model, in terms of stress and particle velocity, is verified through Finite Element simulations of the identical impact problems, where the damage evolution criterion is incorporated using a VUMAT subroutine. The outcomes derived from this study align closely with Finite Element (FE) results.

The effect of autoclave cycles on the mechanical properties and surface roughness of NiTi archwires: ex-vivo study

ObjectivesTo evaluate the effect of the universal and rapid autoclave cycles on the mechanical properties and surface roughness of nickel-titanium archwires following clinical use.Material and methodsThirty-six NiTi archwires (0.016 × 0.022 inch) were equally divided into a control group (Group A) and 2 experimental groups (Group B & C). Wires in group A were tested in the “as-received” form. Wires in the two other groups were installed in patients mouth for 4 weeks, and then autoclaved using the rapid-cycle (Group B) or the universal-cycle (Group C). All wires were subjected to 3-point bending test to calculate the elastic limit, modulus of elasticity, spring-back, yield strength, resilience and toughness. Atomic force microscopy (AFM) was used for surface roughness qualitative and quantitative analysis.ResultsGroup B showed significantly higher values of elastic limit, modulus of elasticity, resilience, yield strength and toughness than the other two groups. No significant differences were detected between groups A and C (P > 0.05). Group B showed significantly lower average surface roughness than the other two groups, but no significant differences were detected between groups A and C (P > 0.05).ConclusionsThe mechanical properties and surface roughness of clinically used NiTi wires were less affected by the universal-cycle than the rapid-cycle autoclaving. However, the difference between the effect of both autoclave cycles was diminutive.Clinical relevanceThe mechanical properties and surface roughness of the tested NiTi wires were not notably altered by clinical use and autoclaving.

Parameter-normalized probabilistic seismic demand model considering the structural design strength for structural response assessment

The Probabilistic Seismic Demand Model (PSDM) is a crucial component of the performance-based seismic design framework when establishing the relationship between the ground motion intensity measure (IM) and the engineering demand parameter (EDP). The definitions of IMs and EDPs introduce varying degrees of uncertainty into the PSDM and notes different fragility or hazard analysis results. In accordance with the elastic limit state of the structural seismic response, this study normalizes two key parameters, the IM and EDP, within the PSDM. Normalized EDP (EDPN) is the ratio of the structural response to the elastic limit state of the structure, as defined by the onset of the strength yielding of the main structural element. Similarly, the IM (IMN) is normalized based on corresponding ground motions (scaled) that cause the structure to offer an elastic limit state response. This means that structural design strength is considered in IMN following the construction of a parameter-normalized PSDM. The study examined two typical isolated bridges presented their hazard curves with IMN. The results show that IMN can unify the efficiency and sufficiency of different IMs and reduce uncertainty in the PSDM. The assessment error of the structural elastic limit state for its design strength had little effect on the parameter-normalized PSDM, so the model is robust. Additionally, the IMN outperformed traditional IMs for efficiency and sufficiency in most instances.

Experimental model of crushing coriander seeds

Seed crushing is one of the main technological operations [1] in the process of obtaining essential and fatty oils, on which their yield and quality depend [2]. Improving the process of preparation for the extraction of coriander seeds by selective cryodesintegration and creating technological lines of various productivity is of significant importance and relevance. However, modern methods and means of cryodesintegration of coriander seeds require research and improvement. The process of seed grinding is divided into three phases [3]: elastic deformation, which occurs from the beginning of the action of the applied force on the material being ground until the elastic limit is reached and is accompanied by compaction and compression of the structural aggregates of the seeds; plastic deformation, which occurs from the moment of the beginning of the shift of individual elements of the material relative to each other and is characterized by the relative displacement of the structural aggregates of the seed kernel, as a result of which the material is compacted and flattened; destruction of the material with the formation of a free surface of particles. The main parameter of the process of cryodesintegration of coriander seeds is subject to theoretical justification - normal pressure, leading to deformation, where the pressure on the seeds exceeds their tensile strength, but there is no appearance of oil on the surface of the opened seeds. This prevents oil loss and contamination of the working parts, especially with essential oils. Monitoring theoretical studies of the grinding process allows us to talk about the need to develop a mathematical description of this process.

Rock failure mechanisms based on rheological dynamics

This paper investigates the mechanisms of rock failure related to axial splitting and shear failure due to hoop stresses in cylindrical specimens. The hoop stresses are caused by normal viscous stress. The rheological dynamics theory (RDT) is used, with the mechanical parameters being determined by P- and S-wave velocities. The angle of internal friction is determined by the ratio of Young's modulus and the dynamic modulus, while dynamic viscosity defines cohesion and normal viscous stress. The effect of frequency on cohesion is considered. The initial stress state is defined by the minimum cohesion at the elastic limit when axial splitting can occur. However, as radial cracks grow, the stress state becomes oblique and moves towards the shear plane. The maximum and nonlinear cohesions are defined by the rock parameters under compressive strength when the radial crack depth reaches a critical value. The efficacy and precision of RDT are validated through the presentation of ultrasonic measurements on sandstone and rock specimens sourced from the literature. The results presented in dimensionless diagrams can be utilized in microcrack zones in the absence of lateral pressure in rock masses that have undergone disintegration due to excavation.

Exploring the mechanisms of enhanced piezoelectric properties in (K,Na)NbO3 single crystals

(K,Na)NbO3 (KNN)-based piezoelectric materials are candidates for replacing Pb-based materials. However, the piezoelectric properties of existing KNN-based single crystals are still inferior to those of Pb-based relaxor ferroelectric single crystals. Moreover, the piezoelectric response mechanism of KNN-based single crystals remains unclear. In this study, (Li,K,Na)(Nb,Sb,Ta)O3:Mn (KNNLST:Mn) single crystals with an excellent piezoelectric coefficient d33 of approximately 778 pC/N were prepared. Systematically studies of intrinsic and extrinsic piezoelectric responses have revealed that the high d33 of KNNLST:Mn single crystals is related to the shear piezoelectric response of a single-domain state and irreversible domain wall motion of the engineering domains. Furthermore, the effect of the orthorhombic (O)-tetragonal (T) phase boundary on intrinsic and extrinsic piezoelectric response is systematically studied, and the impact mechanism is elucidated. The results indicate that a lower dielectric response and elastic constant limit the intrinsic shear piezoelectric response of KNNLST:Mn single crystals, and approaching the O–T phase boundary can enhance both intrinsic and extrinsic piezoelectric responses. This study improves our understanding of the structure-performance relationship in KNN-based single crystals and offers insights for optimizing piezoelectric properties in KNN-based materials.

Probing the Linear-to-Plastic Transition in Polymer Nanocomposites via Atomistic Simulations: The Role of Interphases.

Polymer nanocomposites have found ubiquitous use across diverse industries, attributable to their distinctive properties and enhanced mechanical performance compared to conventional materials. Elucidating the elastic-to-plastic transition in polymer nanocomposites under diverse mechanical loads is paramount for the bespoke design of materials with desired mechanical attributes. In the current work, the elastic-to-plastic transition is probed in model systems of polyethylene oxide (PEO) and silica, SiO2, nanoparticles, through detailed atomistic molecular dynamics simulations. This comprehensive, multi-scale analysis unveils pivotal markers of the elastic-to-plastic transition, highlighting the quintessential role of microstructural and regional heterogeneities in density, strain, and stress fields, featuring the polymer-nanoparticle interphase region. At the atomic level, the behavior of polymer chains interacting with nanoparticle surfaces is traced, differentiating between free and adsorbed chains, and identifying the microscopic origins of the linear-to-plastic transition. The mechanical behavior of subregions are characterized within the PEO/SiO2 nanocomposites, focusing on the interphase and bulk-like polymer areas, probing stress heterogeneities and their decomposition into various force contributions. At the inception of plasticity, a disruption is discerned in isotropy of the polymeric density field, the emergence of low-density regions, and microscopic voids/cavities within the polymer matrix concomitant with a transition of adsorbed chains to free. The yield strain also emerges as an inflection point in the local versus global strain diagram, demarcating the elastic limit, and the plastic regime shows pronounced strain heterogeneities. The decomposition of the atomic Virial stress into bonded and non-bonded interactions indicates that the rigidity of the material is primarily governed by non-bonded interactions, significantly influenced by the volume fraction of the nanoparticle. These findings emphasize the importance of the microstructural and micromechanical environment at the polymer-nanoparticle interface on the linear-to-plastic transition, which is of great importance in the design of nanocomposite materials with advanced mechanical properties.

Predicting maximum deflection of N-Edged thin-shelled hyperbolic-Paraboloid umbrella using machine learning techniques

Many thin-shelled hyperbolic paraboloid (hypar) umbrella forms have been built in the last 60 years as roof coverings. While the stresses in these forms remain relatively low, the deflections are a critical design parameter, and one that must be considered by architects and engineers in the conceptual design phase, meaning the design stage when the scale and form is given to the structure. To-date, there is no closed-form solution that can predict the maximum deflection of umbrellas due to their highly varying and complex geometry. The best option for predicting deflection is via finite element analysis, which is time-consuming for conceptual (preliminary) design purposes. In response, this paper uses machine learning via genetic programming (GP) and gene expression programming (GEP) to develop closed-form equations that predict the maximum corner deflection of N-edged hypar umbrellas – where N = 3, 4, 5, 6, 7, and 8. For a given a boundary condition and material, geometry is the most significant parameter influencing a shell's stiffness; thus, elastic finite element (FE) models use geometric properties as input variables (N, projected area, normalized rise, and shell thickness). The maximum corner deflection is recorded as an output and the FE analyses generate a large dataset of 53,754 results. It is observed that both GP and GEP can effectively parameterize the maximum deflection of N-edged hypar umbrellas, with GEP producing more concise, but relatively less accurate, equations than GP. While the formulations are trained using concrete material, a material factor multiplier transforms the results to other material properties within the assumption of elastic limits. The results of the study can be used to assist with conceptual design of hypar umbrellas and to validate complex FE models of hypar umbrellas. This research also illustrates the use of machine learning techniques as applied to the conceptual design of structures with highly varying geometries.

Failure analysis and structural optimization of unequal-parameter metal bellows in resistance to bending and torsional composite deformation

In practical engineering applications, metal bellows are subjected to complex environmental conditions, and they usually deform under the combined effects of tension, bending and torsion. In this paper, the bending and torsion composite deformation of unequal parameter metal bellows arranged alternately by large wave and wavelet is studied. Firstly, the finite element model of metal bellows is constructed, and the finite element simulation analysis of its mechanical properties is carried out. Taking the simulation results as samples, the multi-objective structural optimization of unequal parameter metal bellows under the condition of bending and torsion composite deformation is carried out. Combined with the bending-torsion composite deformation test and fracture microscopic characterization, the bending-torsion composite deformation characteristics and fracture failure mechanism of equal-parameter metal bellows (EPMB) and unequal-parameter metal bellows (Un-EPMB) were compared and analyzed. The results show that under the same deformation conditions, compared with the EPMB, the elastic limit bending line displacement and elastic limit torsion angle displacement of Un-EPMB are increased by 52.94 %, and the bending and torsional stiffness are greatly improved, moreover, the alternating waveform arrangement led to relatively gradual stress transfer through the Un-EPMB during the bending-torsion composite deformation process, thereby reducing stress concentration. Thus, the Un-EPMB exhibited more favorable mechanical properties. Unlike in the EPMB, which underwent fracture along the grain boundary, the cracks in the Un-EPMB appeared in the middle layer and propagated to both sides in a wavelike pattern. The dimples were distributed in the middle layer of the fracture, which indicates ductile behavior.

Plasticity and strength of an equiatomic and a non-equiatomic HfNbTaTiZr high entropy alloy during uniaxial loading : a molecular dynamics simulation study

Abstract Understanding plasticity and strength of high entropy alloys of HfNbTaTiZr is extremely significant in building nuclear reactors, gas turbines, aerospace devices etc. Here we study an equiatomic (Hf0.20-Nb0.20-Ta0.20-Ti0.2-Zr0.20) and a non-equiatomic (Hf0.35-Nb0.20-Ta0.15-Ti0.15-Zr0.15) mixture of two alloys under uniaxial tensile loading from molecular dynamics simulations. Modified Embedded atom potential is used to model both these bcc alloys and all simulations are performed at 300 K with three different tensile strain rates–0.0002, 0.0005 and 0.001 ps−1. Radial distribution functions, bond-orientational parameters and OVITO are used to analyse the MD trajectories. At 0.001 ps−1 strain, both these alloys deform similarly, but differences are observed at 0.0005 and 0.0002 ps−1 strains. At these rates, both alloys deform elastically till 3%, thereafter they deform plastically till 15%–20% strain. Yield strengths are comparable in the elastic limit but in the plastic limit non-equiatomic alloy have higher strength. In equiatomic alloy, bcc phase transforms to fcc whereas in non-equiatomic alloy bcc phase transforms to both fcc and hcp. Formation of hcp atoms (50%) decrease the plasticity of the non-equiatomic alloy but increases its strength. We also observe that in both these alloys and at all strain rates, bcc atoms transform to fcc/hcp atoms through an intermediate amorphous like state. Local coordination and orientation of all atoms change similarly in equiatomic mixture. But in non-equiatomic mixture local orientation in Hf, Ti and Zr changes differently compared to Nb and Ta.

Spall response and microstructure evolution of additively manufactured AlSi10Mg alloy with different states

The spall response and microstructure evolution of additively manufactured AlSi10Mg alloy with different states were investigated systematically through plate impact experiments, microstructure and texture characterization and quasi-static tensile tests. The results show that the microstructure, texture and spall response are related to the impact velocity and material state. Before deformation and fracture failure occur, the as-built and annealed specimens possess the same <001> texture along the building direction; the former consists of numerous networks, columnar grains and fine equiaxed grains, and the latter is comprised of coarser grain structure and coarse particles. For both the as-built and annealed specimens, as the impact velocity increases, the Hugoniot elastic limit (HEL) stress and spall strength are slightly affected by the impact velocity; however, the peak shock stress tends to increase. Under the same impact velocity conditions, compared with the as-built specimen, the annealed specimen corresponds to a similar peak shock stress but a lower Hugoniot elastic limit stress and spall strength. Independent of the material state, as the impact velocity increases, the damage gradually increases, namely, from incipient spall to complete spall; the grain structure, including size and shape changes; and the texture remains almost unchanged. Under the same impact velocity conditions, compared with the as-built specimen, the annealed specimen has a coarser grain structure and a similar texture. Voids tend to nucleate at grain boundaries (at the bottom of the melt pool) and large particles. Compared with the as-built specimen, the annealed specimen has greater strain rate sensitivity. The effect of the material state on the tensile strength is dependent on the strain rate, and the annealing treatment may significantly decrease the tensile strength under low strain rate conditions; and weakly decrease it under high strain rate conditions. Finally, the spall strength dependence on the material state and the effect of the strain rate on the spall behavior were discussed.

Investigation of time-dependent mechanical loading on the start-stop process of functionally graded rotating disks under thermal conditions

Rotating disks are used in industries, such as aerospace, automotive, and power plants. These disks are under time-dependent mechanical loading when the machine starts or stops working conditions. Thermal stresses caused by temperature changes with this time-dependent mechanical load create dangerous conditions. Therefore, the estimation of the elastic limit angular velocity and acceleration as a criterion for the initiation of plastic deformations has special importance in the start-stop process. An analytical Homotopy perturbation method is used to solve the heat transfer equation and the governing Navier equations in both radial and tangential directions of functionally graded rotating disks with non-uniform thickness. The Tamura-Tomoto-Ozawa model is implemented to calculate the yield stress at a different radius of the disk. The obtained results will be verified with the higher-order finite difference method. The effect of thickness parameter, type of thermal and boundary conditions on the angular velocity and acceleration, and also the starting radius of the plastic deformations are investigated by numerical examples. It is shown that by defining the appropriate temperature gradient on the outer surface of the disk and the parameters in the time-dependent angular velocity function, the level of stresses can be controlled and optimized in all working processes.

Transitioning of deformation mode in bicrystalline Al-Mg alloy with Σ3 [1 1 1] 60° {11 8 5} faceted grain boundary

In this letter, the authors have elucidated the effect of alloying biocompatible and lighter magnesium (Mg) solute atoms in a bicrystalline aluminium (Al) solvent incorporated with a faceted coherent-incoherent grain boundary (GB) to analyze the tensile deformation mechanisms. Cryogenic temperature and high strain rate conditions were imposed through molecular dynamics simulations to report the detrimental effect of Mg addition on the tensile strength of Al-Mg alloys. Evidence of transitioning in deformation modes for pure Al and Al-Mg alloys was seen. On elaborating, for pure Al, GBs acted as the dislocation nucleation site; whereas for Al-Mg alloy, it was both the GBs and grains. It was observed that stacking faults (SFs) originated from GBs and propagated toward grains in Al. In contrast, in Al-Mg alloys, SFs were generated simultaneously from both GBs and grains. This simultaneous nucleation of dislocations and SFs from both GBs and grains renders bicrystalline alloys lower the elastic limit than pure metal. Conversely, beyond this elastic limit, the alloys exhibit higher flow stress than the pure metal due to the Mg-dislocation interactions. These findings offer valuable insights for tailoring the mechanical properties of Al-Mg alloys to meet aerospace, automotive and marine engineering-related application requirements.

Numerical design and experimental validation of shockless plate impact configurations for the Lagrangian analysis of armor ceramics

Ceramic materials are widely used in armor or protective structures, providing weight saving at equivalent performance in comparison to their steel counterparts. Plate-impact experiments are commonly used to investigate the dynamic behavior of ceramics under compressive loading. Using the particle velocity measured at the back of the target, some mechanical properties such as the Hugoniot elastic limit (HEL) as well as the Hugoniot curve of the material can be deduced. Nevertheless, these tests do not provide a direct measurement of the plastic hardening (post-HEL) behavior of the target. In the present work, an experimental shockless plate-impact configuration was developed and implemented to conduct a Lagrangian analysis. This configuration relies on the use of a wavy-machined flyer plate impacting a target made of a buffer, two ceramic plates of different thicknesses, and two window plates as backing. First, the use of wavy flyer plates to generate a loading ramp was validated by considering the impact of the wavy-machined flyer plate against a target, both made of 316L steel. A numerical analysis of this test was developed to confirm the pulse-shaping effect observed experimentally. Next, a ceramic, F99.7 alumina was subjected to the shockless plate impact test in Lagrangian configuration considering the same steel as a buffer and flyer plate material. These tests coupled with Lagrangian analysis enable the curve of axial-stress vs axial-strain beyond the isentropic elastic limit (IEL) to be deduced. The experimental data allow identifying the parameters of an elastoplastic with strain-hardening model to describe the behavior of the tested alumina.