Microstress Distribution Research Articles

LOCAL BIREFRINGENCE ANALYSIS IN GLASS HARDENED VIA ION EXCHANGE METHOD

For the first time, a local Abrio method for estimating birefringence was applied to hardened glasses, and the distribution of microstresses in float glass subjected to ion exchange hardening was studied. The possibility of precision determination of the thickness of the stressed layer is shown, the correlation between the depth of the stressed layer and the penetration depth of potassium cations during ion exchange is established.

Modifying the microstructure and stress distribution of crossover Al-Mg-Zn alloy for regulating stress corrosion cracking via retrogression and re-aging treatment

For next-generation high-performance Al alloys, stress corrosion cracking (SCC) under the combined action of anodic dissolution and hydrogen embrittlement has been a long-standing problem. Herein, a novel SCC-resistant Al alloy design strategy that maintains high strength by optimizing the microstructure and microstress distribution is proposed and developed. Results demonstrated that stress corrosion cracks sprouted and expanded along stress concentration regions. In a T-phase strengthened crossover Al–5.0Mg–4.0Zn alloy, minimal stress concentrations at the grain and phase boundary improved the SCC resistance by high-temperature retrogression and re-aging treatments. Compared with the T6 alloy, the high-temperature retrogression RRA435 °C alloy reduced stress concentration by 36.7% and decreased the diffusion rate of H atoms by 81 folds. The improved SCC resistance was primarily attributed to the reduced diffusion coefficient of hydrogen because of the minimal stress concentrations.

Characteristics of microstructure evolution of surface treated IN718 superalloy by warm laser shock peening during long-term aging at high temperatures

The microstructure evolution behavior and its mechanism of the surface treated IN718 superalloy by laser shocking peening (LSP) and warm laser shocking peening (WLSP) followed by long-term aging at high temperature ranging from 600 °C to 680 °C were investigated in the present study. It was found that the substructure evolution behavior, compressive residual stress reduction and γ″ phase coarsening of the hardened surface layer of WLSP sample could be effectively inhibited at high temperature, in comparison with those of LSP counterpart. Owing to the formation of complex structure of γ″ phase and high-density dislocation with stacking faults (SFs) and micro-twins in γ″ phase in the hardened layer of WLSP alloy, more stable and higher density geometrically necessary dislocations (GNDs) were developed around γ″ phase, which changed the micro-stress distribution of the hardened layer and produced more stable hetero-deformation induced strengthening effects. The findings of the present study provide a new cognition for further deepening the micro-mechanism of strengthening and toughening of hardened surface layer in WLSP treated IN718 superalloy at high temperature, promoting the more practical application of WLSP technology in the manufacturing field of key components of superalloys. • High temperature aging was performed on WLSP strengthened IN 718 alloy. • Strengthening effect of WLSP showed excellent high temperature stability. • Complex Structure of γ″ phase/high-density dislocation were formed in WLSP alloy. • Stacking faults and micro-twins were included in γ″ of this complex structure. • This particular structure and GNDs density were characterized by HRTEM and EBSD.

Effect of crystal orientation on micro-stress distribution in a damage-tolerant titanium alloy TC21

Micro-stress distribution interior of TC21 alloy under abrasive processing was systematically investigated by combining EBSD data and crystal plasticity finite element model (CPFEM). The ductility enhanced of ground specimens after aging treatment, which can be attributed to the randomness of crystal orientation increased result in the decrease of micro-stress in polycrystal. For prismatic slip {101¯0}〈12¯10〉, the α-colonies with SF value of 0.16 suggest that further slip activation becomes difficult, leading to a higher local stress concentrated on grain boundaries of α-lamellae. The higher micro-stress almost distributed at the interface of α-lamellae with a preferred orientation, while in randomly oriented grains, higher micro-stress distributed interior of some grains or local interface of α-lamellae. Moreover, the maximum micro-stress in randomly oriented grains is smaller than that of preferred orientation grains.

Study on stress distribution of SiC/Al composites based on microstructure models with microns and nanoparticles

Abstract The simulation model represents the microstructure that can accurately analyze and predict composites’ micro-stresses and mechanical properties. The conventional representative volume element (RVE) model can only contain one single-particle form. It makes that all the particles in the simulation model have the same shape, which is significantly different from actual particles. In the present study, four typical particle-modeling methods were adopted to establish geometric models to analyze the particle morphology and RVE size selection rules. Particles with the same granularity and similar volume were selected to generate RVE models with randomly distributed particles to predict the mechanical properties and analyze the micro-stress. The micro-stress distribution of the matrix and particles conformed to the rule of normal distribution, while the stress of the interphase does not conform to this law. The particle morphology has a negligible effect on the stress distribution of the matrix; however, it has a significant influence on the stress distribution of particles and interphases, especially during plastic deformation. Furthermore, the micro-stress of composites containing nanoparticles also conforms to the above law, but the stress of the interphase is more minor, and the stress of particles is more dispersed than composites with micron particles.

Analysis method of micro stress sensitivity of aviation bearing based on Voronoi model

The micro-stress distribution of the bearing in actual work directly affects its service performance. This paper attempts to unify the bearing multi-field coupling service conditions with the micro-inhomogeneity of the internal material of the bearing steel, establish a micro-stress sensitivity analysis method for aviation bearings. The bearing motion parameters are solved based on the pseudo-dynamics method. The bearing fluid lubrication model was then established to calculate the lubricant state based on the CFD method. A bearing heat-fluid–solid multi-field coupling model is established based on the grid mapping method. According to EBSD, SEM and nanoindentation experiment, the microstructure model of bearing was established, and the micro stress of bearing was solved based on sub model method. A response surface model is established by the BOX-Behnen Design method. A multivariate random parameter evaluation method is proposed based on the SPEA coefficient. And the influence of inclusions on the bearing microscopic stress is quantitatively evaluated. The calculation results show that the inclusions' size and the inclusions' position significantly influence the degree of stress concentration. The degree of influence is divided into 0.478 and 0.650. The difference in stress components is mainly affected by the location of inclusions. The degree of influence exceeds 0.9. The overall effect of inclusion morphology is the smallest.

Friction coefficient of solid lubricating coating as a function of contact pressure: experimental results and microscale modeling

The paper presents experimental analysis of relation between friction coefficient and contact pressure of hbox {MoS}_2 film deposited on hbox {Ti}_6hbox {Al}_4hbox {V} substrate in contact with sapphire ball during reciprocating sliding motion. It is shown that the value of friction coefficient decreases with increasing contact pressure. A microscale modeling approach is next developed to mimic the experimental observations. Representative volume element is defined based on the actual topography of outer surface of hbox {MoS}_2 film. Assuming thermo-elastic material properties, the calculations on the asperity level are performed in two steps. Firstly, the mechanical contact between two surfaces is calculated. As a result, the relation between the global load and micro-stress distribution is obtained. Secondly, for a given stress load, thermal analysis is performed providing temperature fluctuation within simplified conical asperity. By assuming relation between friction coefficient and temperature on the microscale, it is possible to obtain macroscopic friction coefficient as a function of contact pressure. In the end, model results are compared with experimental data. The novel aspects of presented approach lie in the selection of three main factors on a micro-level defining macroscopic friction. They are actual surface topography, microscopic temperature and microscopic friction-temperature relation.

Generalized magneto-thermo-microstretch elastic solid with finite element method under the effect of gravity via different theories

The present paper is aimed at studying the effect of gravity on the general model of the equations of generalized magneto-thermo-micro-stretch for a homogeneous isotropic elastic half-space solid. The problem is in the context of the Green-Lindsay (G-L) theories, as well as the coupled theory (CT). Finite element method is used to obtain the expressions for the displacement components, the force stresses, the temperature, the couple stresses, and the micro-stress distribution. Comparisons are made with the results in the presence and absence of gravity and magnetic field of a particular case for the generalized micropolar thermo-elasticity elastic medium (without micro-stretch constants) between the three theories.

On Plane Waves for Mode-I Crack Problem in Generalized Thermoelasticity

A general model of the equations of generalized thermoelasticity for an infinite space weakened by a finite linear opening Mode-I crack is solving. The material is homogeneous and has isotropic properties of elastic half space. The crack is subjected to prescribed temperature and stress distribution. The formulation is applied to generalized thermoelasticity theories, the Lord-Shulman and Green-Lindsay theories, as well as the classical dynamical coupled theory. The normal mode analysis is used to obtain the exact expressions for the displacement components, force stresses, temperature, couple stresses and micro-stress distribution. The variations of the considered variables through the horizontal distance are illustrated graphically. Comparisons are made with the results between the three theories.

Poling and depoling influence on the micro-stress states and phase coexistence in KNN-based piezoelectric ceramics

In this work a microstructural qualitative and quantitative study of spatial stress distributions in modified KNN ceramics (K0.44Na0.52Li0.04)1-xCox/2 (Nb0.86Ta0.10Sb0.04)O3, according to the polarization state is shown. X-ray diffraction reflects a perovskite crystalline structure with coexistence of Tetragonal and Orthorhombic phases (T/O). Confocal Raman microscopy shows that these crystalline phases are distributed in randomly micrometric regions through the ceramic volume. Tetragonal regions show higher piezoelectric coefficient and exhibit a higher micro-stress that hardens the ferroelectric response. By the contrary, the occurrence of orthorhombic micro-regions softened the ferroelectric behavior and reduced their piezoelectric coefficients. The ferroelectric response of ceramics is studied, where poling is also shown as a factor that affects the spatial micro-stress distributions. Finally, a model that relates the results obtained by Raman characterization with the ferroelectric properties and stress states is proposed.

Elastodynamic interactions of laser pulse in microstretch thermoelastic mass diffusion medium with dual phase lag

The aim of the present investigation is to study the effects of laser heat source and phase lags on a microstretch thermoelastic mass diffusion medium including dual phase lag model. The normal mode analysis technique has been adopted to obtain the components of displacement, microrotation, microstress, mass concentration and temperature distribution due to the presence of ultra-laser heat source. The numerical computation has been performed (using Matlab software) on the resulting quantities. The computed numerical results are shown graphically to depict the effect of laser heat source and diffusion phase-lags. Some particular cases of interest are also deduced from the present investigation.

A damage model of mechanical behavior of porous materials: Application to sandstone

In this work, a multiscale model based on the Fast Fourier Transform (FFT) technique is applied to describe the mechanical behavior of porous materials. The effects of the microstructures (such as pore shape, number, size, distribution and orientation) on the overall strength of the porous medium and its microstress distribution are fully studied. The elastoplastic model is further extended by including a damage process. The influences of microstructure on the damage evolution of the porous medium are discussed and illustrated numerically. Then the proposed multiscale damage model is applied to study the macroscopic behavior of porous sandstone. According to the microstructure of the studied material, a representative elementary volume with randomly distributed spherical pores is considered. The solid phase of the sandstone is assumed to obey the Drucker–Prager criterion. Taking advantage of the FFT-based method, the evolution of generated damage is clearly illustrated during the loading process at the microscopic level. Comparisons between numerical results and experimental data show the efficiency of the proposed numerical model.

Residual micro-stress distributions in heat-pressed ceramic on zirconia and porcelain-fused to metal systems: Analysis by FIB–DIC ring-core method and correlation with fracture toughness

ObjectivesThe production of fixed partial dentures (FPDs) induces complex residual stress profiles, due to both the thermal expansion coefficient mismatch between the veneering ceramic and the framework and to the thermal gradients occurring during the final cooling. Detailed knowledge of residual stress distributions in the veneering ceramics is important to understand the interface phenomena with the framework and the consequences of the different firing systems. The first objective of this study was to analyse the residual stress distribution in heat-pressed ceramic on zirconia core with micrometer spatial resolution, with also a focus on the stress at the interface versus porcelain-fused-to-metal samples. The second purpose was to correlate the residual stress with the fracture toughness. MethodsThe micron-scale focused ion beam (FIB) ring-core method was used to map the residual stress over the cross-sections of the veneering ceramics. The methodology is based on FIB micro-milling of annular trenches, combined with high-resolution in situ scanning electron microscope (SEM) imaging, a full field strain analysis by digital image correlation (DIC) and numerical models for residual stress calculation. Fracture toughness was evaluated by using high load Vickers indentation and hardness/modulus were measured by nanoindentation testing also across the interfaces. ResultsBoth prosthetic systems showed a compressive stress at the ceramic surface on a micron-scale. The stress profile for porcelain fused to metal (PFM) showed a transition to tensile stress at the half of the layer, whilst the stress in proximity of the interface was more compressive in both the cases. Residual stress on a micron scale are higher in magnitude than the corresponding macro-scale values reported in the literature, due to the stress relaxation given, at larger scales, by micro-voids and cracks. The stress field was directly correlated with the indentation fracture toughness, which was higher in those areas where the compressive stress is greater. Stress analysis in correspondence of interfacial porosity for the zirconia sample also showed that micro-defects could induce local modifications of the residual stress field, which may even locally generate a tensile stress state. SignificanceThe interfacial stress in dental systems was analysed on a micron scale and can give further insights into the process/property/performance correlation for this class of materials. In particular, interfacial and/or local modifications of the residual stress are expected to have a significant influence on crack nucleation mechanism in correspondence of micro-defects. A direct correlation between residual stress distribution and fracture toughness was proposed. It is noteworthy that the method can be used to study real crowns and bridges. In fact, complex geometries can be easily analysed by this procedure.

Progressive failure analysis of composite structure based on micro- and macro-mechanics models

Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stress distribution of the composite structure is calculated by commercial finite element software. According to the macro-stress, the damaged point is found and the micro-stress distribution of representative volume element is calculated by finite-volume direct averaging micromechanics (FVDAM). Compared with the results calculated by failure criterion based on macro-stress field (the maximum stress criteria and Hashin criteria) and micro-stress field (Huang model), it is proven that the failure analysis based on macro- and micro-mechanics model is feasible and efficient.

The Effect of Gravity on Plane Waves in a Rotating Thermo-Microstretch Elastic Solid for a Mode-I Crack with Energy Dissipation

The present article is aimed at studying the effect of gravity on the general model of the equations of generalized thermo-microstretch for a homogeneous isotropic elastic half-space solid rotating about the fixed axis of rotation and whose surface is subjected to a Mode-I crack problem considered. The problem is in the context of the Green and Naghdi theory (GN). The normal mode analysis is used to obtain the exact expressions for the displacement components, force stresses, temperature, couple stresses, and microstress distribution. The variations of the considered variables perpendicular to the axis of rotation are illustrated graphically. Comparisons are made with the results in the presence and absence of gravity and rotational frequency of a particular case for the generalized micropolar thermoelasticity elastic medium (without microstretch constants) between the two types (II, III).

Effect of rotation on plane waves in generalized thermomicrostretch elastic solid: comparison of different theories using finite element method

The present investigation is aimed at studying the effect of rotation on the thermomicrostretch elastic solid. The formulation is applied in the context of the generalized thermoelasticity Lord–Şhulman theory with one relaxation time and Green–Lindsay’s theory with two relaxation times, as well as the classical dynamical coupled theory. The problem has been solved numerically using a finite element method. Numerical results for the temperature distribution, the displacement components, the force stresses, the couple stresses, and the microstress distribution are represented graphically. The results indicate that the effects of rotation are very pronounced. Comparisons are made with the results in the presence and absence of rotation and in the presence and absence of microstretch constants between the two theories.

Thermodynamic behaviour of microstretch viscoelastic solids with internal heat source

The dynamical interactions caused by a line heat source moving inside a homogeneous isotropic thermo-microstretch viscoelastic half space, whose surface is subjected to a thermal load, are investigated. The formulation is in the context of generalized thermoelasticity theories proposed by Lord and Shulman (J. Mech. Phys. Solid, 15, 299 (1967)) and Green and Lindsay (Thermoelasticity, J. Elasticity, 2, 1 (1972)). The surface is assumed to be traction free. The solutions in terms of displacement components, mechanical stresses, temperature, couple stress, and microstress distribution are procured by employing the normal mode analysis. The numerical estimates of the considered variables are obtained for an aluminium–epoxy material. The results obtained are demonstrated graphically to show the effect of moving heat source and viscosity on the displacement, stresses, and temperature distribution.

Gravitational effect and initial stress on generalized magneto-thermo-microstretch elastic solid for different theories

The present paper is aimed at studying the effect of gravity and initial stress on the general model of the equations of generalized magneto-thermo-microstretch for a homogeneous isotropic elastic half-space solid. The problem is in the context of the Lord–Şhulman and Green–Lindsay theories, as well as the coupled theory. The normal mode analysis is used to obtain the exact expressions for the displacement components, force stresses, temperature, couple stresses and microstress distribution. The variations of the considered variables perpendicular to the axis of rotation are illustrated graphically. Comparisons are made with the results in the presence and absence of gravity and magnetic field of a particular case for the generalized micropolar thermoelastic medium (without microstretch constants) between the three theories.

Effect of Magnetic Field and Rotation on Generalized Thermo-Microstretch. Elastic Solid with Mode-I Crack Under the Green Naghdi Theory

This paper scrutinizes the effect of magnetic field on the general model of equations of rotating generalized thermo-microstretch for a homogeneous isotropic elastic half-space solid whose surface is subjected to a Mode-I Crack in the context of the Green and Naghdi theory. The normal mode analysis is used to obtain the exact expressions for the displacement components, force stresses, temperature, couple stresses, and microstress distribution. The variations of the considered variables through the horizontal distance are illustrated graphically. Comparisons are made with the results in the presence and absence of rotation for two cases: case (1) for the generalized micropolar thermoelasticity elastic medium (without microstretch constants) between the two types (II, III); case (2) for the generalized microstretch thermo-elasticity elastic medium (without micropolar constants) between the two types (II, III).

Fatigue design of a mechanically biocompatible lattice for a proof-of-concept femoral stem

A methodology is proposed to design a spatially periodic microarchitectured material for a two-dimensional femoral implant under walking gait conditions. The material is composed of a graded lattice with controlled property distribution that minimizes concurrently bone resorption and interface failure. The periodic microstructure of the material is designed for fatigue fracture caused by cyclic loadings on the hip joint as a result of walking. The bulk material of the lattice is Ti6AL4V and its microstructure is assumed free of defects. The Soderberg diagram is used for the fatigue design under multiaxial loadings. Two cell topologies, square and Kagome, are chosen to obtain optimized property gradients for a two-dimensional implant. Asymptotic homogenization (AH) theory is used to address the multiscale mechanics of the implant as well as to capture the stress and strain distribution at both the macro and the microscale. The microstress distribution found with AH is also compared with that obtained from a detailed finite element analysis. For the maximum value of the von Mises stress, we observe a deviation of 18.6% in unit cells close to the implant boundary, where the AH assumption of spatial periodicity of the fluctuating fields ceases to hold.In the second part of the paper, the metrics of bone resorption and interface shear stress are used to benchmark the graded cellular implant with existing prostheses made of fully dense titanium implant. The results show that the amount of initial postoperative bone loss for square and Kagome lattice implants decreases, respectively, by 53.8% and 58%. In addition, the maximum shear interface failure at the distal end is significantly reduced by about 79%.A set of proof-of-concepts of planar implants have been fabricated via Electron Beam Melting (EBM) to demonstrate the manufacturability of Ti6AL4V into graded lattices with alternative cell size. Optical microscopy has been used to measure the morphological parameters of the cellular microstructure, including cell wall thickness and pore size, and compared them with the nominal values. No sign of fracture or incomplete cell walls was observed, an assessment that shows the satisfactory metallurgical bond of cell walls and the structural integrity of the implants.