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The overall objective of this work is to provide a fundamental understanding of changes in bone structure–function relationship and failure mechanism with the presence of a certain degree of degradation in bone micro–architecture. Since it is of scientific interest to illustrate the mechanism by which aging, disease, and environmental factors, such as ionizing radiation, affect bone morphology and consequently alter the bone mechanical behaviors. More importantly, such insights would also potentially enhance the assessment of bone fracture risk in a clinical setting.Combing a small animal model, where the mouse vertebral body morphological changes were introduced by the whole–body ionizing radiation, with high–resolution micro–computed tomography (micro–CT) based finite element (FE) analysis, we demonstrated how ionizing radiation altered the mouse vertebral body micro–architecture, structure-function relationship, as well as the failure mechanism. Our key results showed a reduction in trabecular mass fraction (by 12.8% on average, p = 0.0014) and a reduction in trabecular load fraction as the trabecular mass fraction was controlled (by an 8% decrease in the linear correlation slope, p = 0.0264). Related to this, nonlinear FE results showed that there were a reduction in the mouse vertebral stiffness (by 7.4%, p = 0.0054), a reduction in the vertebral strength (by 8.8%, p = 0.0002), and an significant offset for the linear correlation between them (p = 0.011) due to changes in the volume of failure tissue (p = 0.036). Our results suggested that, following ionizing radiation, the loss of trabecular load sharing could be more substantial than the loss of mass sharing since the trabecular structure–function relationship was altered. Moreover, the loss of vertebral strength could be more significant than the loss of vertebral stiffness, as the failure mechanism was altered. Such insights may apply to changes in vertebral micro–architecture induced by aging and diseases.Using eight human vertebral body specimens with high–resolution micro–CT based nonlinear FE analysis, we established the damage law for the human vertebrae. The key results were that the human vertebral body damaged tissue accumulated exponentially as the axial compressive load applied (max p = 0.04, min R2 = 0.98), and the damaged tissue growth rate was nonlinearly correlated with the whole–bone strength (p < 0.001). With the aid of two simplified analytical models, our results implied that a weak human vertebra accumulated fracture tissue at a higher rate than a strong one due to a low number of vertical load paths.In closure, this work presents the fundamental mechanisms by which changes in vertebrae morphology translate into alterations in the vertebrae structure–function relationship and failure mechanism, then ultimately into alterations in vertebrae strength and fracture risk.

A novel computational approach to predicting fatigue crack initiation life in additively manufactured microlattice structures is proposed based on a recently developed microplasticity-based constitutive theory. The key idea is to use the concept of (micro)plastic dissipation as the driving factor to model fatigue degradation in additively manufactured metallic microlattice. An ad-hoc curve-fitting procedure is proposed to calibrate the introduced material constitutive parameters efficiently. The well-calibrated model is employed to obtain fatigue life predictions for microlattices through a diverse set of RVE-based finite element fatigue simulations. The model’s predictive capabilities are verified by comparing the simulation results with experimental fatigue data reported in the literature. The overall approach constitutes a unified setting for fatigue life prediction of additively manufactured microlattice structures ranging from low- to high-cycle regimes. It is also shown that the model can be applied to technologically relevant microlattices with mathematically-created complex microstructure topologies.

Silicon carbide / silicon carbide (SiC/SiC) composites have emerged as a leading candidate for accident tolerant fuel cladding in light water reactors (LWR)s. Their high temperature strength and oxidation kinetics offer marked improvement for enduring severe loss of coolant accidents, thereby providing additional coping time for proper response. A key factor for qualification and implementation of these composites is the ability to model and predict their behavior over ranges of temperature, irradiation, and cyclic fatigue. To do so requires a fundamental understanding of the constituent property evolution and interplay at the fiber/matrix interphase. This dissertation asserts that small-scale mechanical testing provides the resolution and versatility required to capture structure-property relationships of the interphase, at its engineered length scale. This was explored by developing four novel experiments to probe the interphase properties that control composite toughness. First, high-resolution SEM DIC quantified the microscale elasticity across the pyrolytic carbon (PyC) bond layer, finding a gradient in Young’s Modulus and Poisson’s ratio that is directly linked to the PyC graphitic texture. Second, application of a self-aligning microtensile test enabled reliable extraction of the tensile strength and weakest link characteristics of the SiC/PyC/SiC interphase. Third, micropillar compression was used to evaluate 11 composite interphase conditions, defining a phenomenological equation for ultimate shear strength as a function of fiber roughness, PyC thickness, and residual compressive stress normal to the fiber surface. The effects of irradiation and fabrication-induced defects were also quantified. And fourth, a novel fiber fretting technique was developed for direct extraction of the cyclic degradation at the fiber/matrix interphase. Testing across four conditions revealed friction dependence on adhesive and abrasive mechanisms up to 1000 cycles. Post hoc characterization of the tribo-surface revealed a crystalline to amorphous transition of the PyC structure.The relatively accessible lab equipment and straightforward test configurations lend themselves to application in high temperature and oxidative environments, offering a robust toolkit for composite characterization and integrated design feedback on irradiated and next generation composite concepts. It is hoped that this research will open new doors to advanced optimization and modelling opportunities in the field of ceramic composites.

This research discusses the micromechanical modelling for thermoplastic composite material. Elastoplastic and damage model for PEEK matrix composite with the dependency of properties to stress state is presented. Plasticity initiation conditions and failure criterion are analyzed. The influence of manufacturing residual stresses is considered. All typical engineering experiments for neat PEEK under different stress state are good predicted by the model. Numerical experiment for macro-properties estimation based on micromechanical model is conducted and the results are compared with the test data.

Elements of the periodic homogenization framework and deep neural network were seamlessly connected for the first time to construct a new micromechanics theory for thermoconductive composites called physically informed Deep Homogenization Network (DHN). This method utilizes a two-scale expansion of the temperature field of spatially uniform composites in terms of macroscopic and fluctuating contributions. The latter is estimated using deep neural network layers. The DHN is trained on a set of collocation points to obtain the fluctuating temperature field over the unit cell domain by minimizing a cost function given in terms of residuals of strong form steady-state heat conduction governing differential equations. Novel use of a periodic layer with several independent periodic functions with adjustable training parameters ensures that periodic boundary conditions of temperature and temperature gradients at the unit cell edges are exactly satisfied. Automatic differentiation is utilized to correctly compute the fluctuating temperature gradients. Homogenized properties and local temperature and gradient distributions of unit cells reinforced by unidirectional fiber or weakened by a hole are compared with finite-element reference results, demonstrating remarkable correlation but without discontinuities associated with temperature gradient distributions in the finite-element simulations. We also illustrate that the DHN enhanced with transfer learning provides a substantially more efficient and accurate simulation of multiple random fiber distributions relative to training the network from scratch.

Abstract Zirconia-based shape memory ceramics (SMCs) exhibit anisotropic mechanical response when undergoing elastic deformations as well as during austenite–martensite phase transformation. This behavior results in different types of strain incompatibility at grain boundaries, which we study here using a micromechanical model. A single-crystal model is implemented to provide a full mechanistic three-dimensional description of the anisotropic elastic as well as martensitic transformation stress–strain response, including non-Schmid behavior caused by the significant volume change during martensitic transformation. This model was calibrated to and validated against compression tests of single-crystal zirconia micro-pillars conducted previously, and then used to model bi-crystals. Upon the introduction of a grain boundary, the simulation provides detailed information on the nucleation and evolution of martensite variants and stress distribution at grain boundaries. We identify bi-crystal configurations which result in very large stress concentrations at very low deformations due to elastic incompatibility, as well as others where the elastic incompatibility is relatively low and stress concentrations only occur at large transformation strains. We also show how this approach can be used to explore the misorientation space for quantifying the level of elastic and transformation incompatibility at SMCs grain boundaries. Graphical abstract Micromechanics models provide insights on grain boundary elastic and phase transformation strain incompatibility in shape memory zirconia

Micromechanical constitutive parameters are important for many engineering materials, typically in microelectronic applications and material design. Their accurate identification poses a three-fold experimental challenge: (i) deformation of the microstructure is observable only at small scales, requiring SEM or other microscopy techniques; (ii) external loadings are applied at a (larger) engineering or device scale; and (iii) material parameters typically depend on the applied manufacturing process, necessitating measurements on material produced with the same process. In this paper, micromechanical parameter identification in heterogeneous solids is addressed through multiscale experiments combined with Integrated Digital Image Correlation (IDIC) in conjunction with various possible computational homogenization schemes. To this end, some basic concepts underlying multiscale approaches available in the literature are first reviewed, discussing their respective advantages and disadvantages from the computational as well as experimental point of view. A link is made with recently introduced uncoupled methods, which allow for identification of material parameter ratios at the microscale, still lacking a proper normalization. Two multiscale methods are analysed, allowing to bridge the gap between microstructural kinematics and macroscopically measured forces, providing the required normalization. It is shown that an integrated experimental--computational scheme provides relaxed requirements on scale separation. The accuracy and performance of the discussed techniques are analysed by means of virtual experimentation under plane strain and large strain assumptions for unidirectional fibre-reinforced composites. The robustness against image noise is also assessed., Comment: 44 pages, 16 figures, 4 tables, 7 procedures, abstract shortened to fulfil 1920 character limit

Currently, the advancement of nanotechnology provides new insights into the structures with the characteristic length in the nanometer scale. Due to their large specific area, the nano-structures may possess desirable features. Therefore, scientists attempt to employ the nano-structures as the reinforcements in the composite materials; i.e., nanocomposites, to achieve improved properties. It is well known that the local atomic environment at the matrix-reinforcement interface is different from its setting associated with the interior due to the accommodation of two different materials. As a consequence, the free energy associated with the interface is different from that associated with the interior. Since the nanocomposites have much larger interface area than the traditional composites, the interface energy effect becomes one of the main factors that determine the mechanical properties. The objective of the present study is to research on the effective (overall) elastic, elastoplastic and elastoplastic damage behavior of nanocomposites by considering the interface energy effect. Firstly, a nanomechanical framework is proposed in Chapter 3 to investigate the effective elastic behavior of nanocomposites containing randomly distributed spherical particles. The interface energy effect is simulated by the zero-thickness membrane interphase between the matrix and the reinforcement together with the interface stress. In addition, classical micromechanical homogenization procedures are incorporated to determine the volume averaged effective properties. Secondly, the elastic nanomechanical framework in Chapter 3 is extended to consider the more sophisticated spheroidal particle reinforced nanocomposites in Chapter 4. The spheroidal particles are assumed to be aligned and randomly distributed in the matrix. Thirdly, the effective elastoplastic behavior of the spherical particle reinforcednanocomposite is studied in Chapter 5. The effective secant moduli are obtained for the nanocomposite with the elastoplastic matrix and the elastic reinforcements. In Chapter 6, the elastoplastic damage performance of the continuous fiber reinforced nanocomposites isinvestigated. Interface debonding is considered as the damage type that occurs in the nanocomposites. The progressive debonding of the interface and the volume fraction evolution of debonded fibers are presented. The results show that the effective mechanical properties of nanocomposites are dependent upon the total interface area. The interface energy effect increases with the rising total interface area in the composite and becomes negligible when the dimensions of the reinforcements are in micrometer scale. Further, classical micromechanical solutions can be obtained when the interface energy effect is neglected.

The considerable uncertainty in mechanical properties of composite bolted joints not only prevents advanced composite materials from efficient applications, but also threatens the safety and reliability of the aircraft structures. In this paper, the uncertainty in bearing fatigue properties of a CFRP double-lap, single-bolt joint was evaluated by combing a Progressive Fatigue Damage Model (PFDM) with the interval analysis method. In the PFDM, a residual-strain-based gradual material degradation model and a strain-based fatigue failure criterion were combined with a micromechanics-based sudden material degradation model to predict fatigue properties of the joint. Based on the interval analysis, the key uncertain parameters, which were firstly picked out from eighteen structural parameters of the joint, were described by estimated intervals, and the envelope cases were determined to estimate the lower and upper bounds of fatigue properties of the joint. The predicted results have the same tendency with the experimental results in literatures, which indicates that the PFDM combined with the interval analysis shows potential in efficiently evaluating the fatigue reliability of the complex bolted joints with an adequate accuracy.

Sc solute clusters with a high number density were produced in an Al-0.3 wt.%Sc alloy when aged at 250 °C, while fine Al3Sc precipitates were predominantly formed in the same alloy aged at 300 °C. The alloy strengthened by Sc solute clusters displayed higher yield strength and simultaneously greater ductility than its counterpart strengthened by Al3Sc precipitates. This clearly demonstrates a superior strength-ductility synergy promoted by the Sc solute clusters in Al-Sc alloys. The effects of Al3Sc precipitates and Sc solute clusters on ductility were discussed in comparison by using a micromechanics fracture model. Since the Sc clusters were stabilized at 250 °C, the Al-Sc alloys strengthened by Sc solute clusters should find extensive application fields within a wide temperature range, due to their high temperature resistance.

Micromechanics simulations of fiber-reinforced polymer-matrix composites with waviness defects are conducted to investigate the effect of constitutive model selection on the nucleation, evolution, ...

The advent of additive manufacturing (AM) offers the possibility of creating high-performance metallic materials with unique microstructure. Ultrafine dislocation cell structure in AM metals is believed to play a critical role in strengthening and hardening. However, its behavior is typically considered to be associated with alloying elements. Here we report that dislocations in AM metallic materials are self-stabilized even without the alloying effect. The heating–cooling cycles that are inherent to laser power-bed-fusion processes can stabilize dislocation network in situ by forming Lomer locks and a complex dislocation network. This unique dislocation assembly blocks and accumulates dislocations for strengthening and steady strain hardening, thereby rendering better material strength but several folds improvements in uniform tensile elongation compared to those made by traditional methods. The principles of dislocation manipulation and self-assembly are applicable to metals/alloys obtained by conventional routes in turn, through a simple post-cyclic deformation processing that mimics the micromechanics of AM. This work demonstrates the capability of AM to locally tune dislocation structures and achieve high-performance metallic materials.

In this study, the dynamic stability and energy absorption of a novel type of sandwich panels with an extensive application in light vehicles are investigated. The curved panels are laminated multi...

Analytic modeling of 3 D printed natural fiber-reinforced composites is still in its infancy. The existing analytic works on the mechanical properties of these materials seem to be relatively few i...

Asphalt mixture is composed of coarse aggregate, fine aggregate, mineral powder, asphalt, etc., with heterogeneous, discontinuous characteristics. The mechanical behavior of asphalt mixture particl...

Effects of texture on micromechanics, texture evolution and macromechanics of AZ31 magnesium alloy sheets with tailored textures during plastic deformation are thoroughly investigated by visco-plastic self-consistent (VPSC) analysis. These simulated results confirm that as for in-plane tension (IPT), activities of basal slip and $$\{ 10\overline{1}2\}$$ extension twin (ET) are mainly responsible for the observed texture characteristics of all deformed samples. In addition, activities of prismatic slip and $$\{ 10\overline{1}2\}$$ ET in samples with bimodal texture are highly related to the loading direction. With regard to in-plane shear (IPS), sample with weak basal texture possesses the largest activity of prismatic slip. Moreover, basal slip and prismatic slip collectively contribute to the rotation of tilted basal poles in (0002) pole figure, whereas pyramidal slip and $$\{ 10\overline{1}2\}$$ ET are advantageous to the rotation of tilted basal poles away from normal direction (ND) with increasing plastic strain. In terms of plane strain compression (PSC), $$\{ 10\overline{1}2\}$$ ET and prismatic slip largely participate in plastic deformation of samples with four-peak texture and annular (ring-shaped) texture, namely, $$\{ 10\overline{1}2\}$$ ET leads to the rotation of tilted basal poles toward ND during PSC and prismatic slip causes the formation of a small annular texture component after a relatively large plastic strain.

This work analyzes the free vibration of a spinning functionally graded graphene platelet-reinforced metal foam (FG-GPLRMF) beam. The differential transformation method is extended to analyze flap-wise bending vibration and chordwise bending vibration with Coriolis force effect for the first time. The beam is modeled using the Euler–Bernoulli beam theory. The Halpin–Tsai micromechanics model is utilized to predict effective material properties. Various types of graphene platelet (GPL) and porosity distributions are considered. The governing equations and corresponding boundary conditions of the FG-GPLRMF beam are obtained via Hamilton’s principle. Results show that the vibration characteristics of the FG-GPLRMF beam are affected by the GPL geometry size, types of porosity, and GPL distributions. Among different types of porosity, the Porosity-A causes the highest fundamental natural frequency, while the Porosity-B corresponds to the lowest one of the spinning FG-GPLRMF beam in most cases. Moreover, the GPL pattern and porosity distribution have a coupled effect on the bending vibration of the spinning FG-GPLRMF beam.

Nowadays, there are several methods to obtain simulation models for foams which consider important microstructural features. This research study presents a method to obtain low density foam models directly from computed tomography (CT) data. Finite element meshes are created from CT measurement results of a polypropylene extrusion foam with two different densities. Sensitivity studies with regard to the tension behaviour are performed with the microstructural models. The study shows that the tension behaviour highly depends on the examined area of the foam because the microstructure and density vary through the foam. Furthermore, the simulation results are validated with experimental results. The validation shows that the tension behaviour of the investigated foams characterised by the simulation approach is in good agreement with the experimentally observed behaviour and that specific microstructural characteristics (e.g. anisotropic cell shapes) are captured in the model.

A micromechanics-based model is developed to capture the grain-size dependent superelasticity of nanocrystalline shape memory alloys (SMAs). Grain-size effects are incorporated in the proposed model through definition of dissipative length scale and energetic length scale parameters. In this paper, nanocrystalline SMAs are considered as two-phase composites consisting of the grain-core phase and the grain-boundary phase. Based on the Gibbs free energy including the spatial gradient of the martensite volume fraction, a new transformation function determining the evolution law for transformation strain is derived. Using micromechanical averaging techniques, the grain-size-dependent superelastic behavior of nanocrystalline SMAs can be described. The internal length scales are calibrated using experimental results from published literature. In addition, model validation is performed by comparing the model predictions with the corresponding experimental data on nanostructured NiTi polycrystalline SMA. Finally, effects of the internal length scales on the critical stresses for forward and reverse transformations, the hysteresis loop area (transformation dissipation energy), and the strain hardening are investigated.

Transverse cracking and delamination are two of the most common failure modes in cross-ply composite laminates. The initiation and combination of these two failure mechanisms lead to catastrophic f...

A new progressive damage model for the three-dimensional (3 D) woven carbon/carbon (C/C) composites is developed at fiber-matrix level using the micromechanics method. A woven architecture based Representative Volume Element (RVE) model composed of yarns, matrix and yarn/matrix interface is constructed, in which the manufacturing void defects are accounted for. The fiber-matrix concentric cylinder model is employed as a repeating unit cell to represent the yarn, and the matrix micro strain field is computed analytically by the micromechanics method. The maximum stain criteria is utilized for fiber longitudinal breakage, and the Von-Mises criterion is applied for the damage initiation of matrix in both intra-yarns and inter-yarns. The damaged fiber and matrix are modeled by the stiffness degradation method combined with exponential damage evolution equations. The zero thickness cohesive elements governed by bilinear traction-separation constitutive are adopted for yarn/matrix interfacial debonding behavior. The micro progressive damage and failure behavior of the 3 D woven C/C composites subjected to tension is implemented through a developed user-defined material subroutine in commercial software ABAQUS. The predicted stress-strain response is in a good agreement with experimental results. In addition, the effect of manufacturing void defects is also examined by the developed model.

The elastic properties of cementitious composites reinforced by nano-tailored hybrid fibers are analyzed using a micromechanical method. The microstructural feature of the hybrid fiber is that unif...

In this paper, the heat conductivity of two-dimensional (2D) media made of an arbitrarily thermal anisotropic material and containing pores with arbitrary shape and superconductive boundary is considered. In addition to the bulk behavior, the line conduction model is used for the boundary behavior. Such idealized mathematical model can be seen as the limit case of very thin material layer with very high conductivity. The fundamental heterogeneity problem in the micromechanics of a single void embedded in an infinite matrix with both boundary and bulk behavior is then investigated and solved with the complex variable and the Conformal Mapping (CM) techniques. The heterogeneity problem results are then used to obtain the effective heat conductivity of the porous material with different homogenization schemes.

The mechanical interactions of C-(N-)A-S-H (Calcium-sodium-aluminum-silicate-hydrate) gel with slag and fly ash inclusions in alkali-activated materials (AAM) are quantified through image-supported...

Microcrack propagation in asphalt mixtures leads to macroscopic cracks in pavement. It is necessary to study crack evolution from the perspective of micromechanics to precisely predict structural damage. This paper developed a micromechanical model of three-point bending under a bending fatigue load for a bitumen specimen that was a three-phase asphalt mixture composed of coarse aggregate, asphalt mortar and air voids. A three-point bending test was carried out to verify the correctness of the micromechanical model. The microscopic parameters of bitumen were calibrated by fitting the stress–strain curve of the laboratory test data. Microdynamic simulations demonstrated that the growth of microcracks included an initial transition period, a rapid growth period and a stable period. The microcrack propagated from the bottom edge to the center of the specimen under the bending load, mainly within the asphalt mortar or asphalt–aggregate interface. Compared with a static load, the longitudinal stress at the microcracks was much larger, and the number of microcracks increased more rapidly, under the dynamic load. The width of the microcrack increased instantaneously when the internal stress state of the specimen reached its material strength, then changed almost periodically with sinusoidal loading and finally stabilized. The micromechanical modeling method can potentially be used to predict the position and width of macroscopic cracks in asphalt pavement.

A CNT-modified phononic crystal (PC) is investigated numerically to study the real and complex dispersion curves (DCs) and overall stiffness. The Bloch theorem is applied to the PC, and the resulting eigenvalue problem is solved by the finite element method. The ω(k) and k(ω) procedures are exploited for the real and complex DCs extraction, respectively. The CNTs are added to the host PC to enhance the stiffness without a significant increase in the density. So, the density mismatch is preserved, while the matrix impedance is increased. The CNT nanocomposite effective stiffness obtained by the GMC micromechanics procedure and the PC real and complex DCs are validated by experimental and numerical results, respectively. A parametric study is performed to examine the effects of the nanocomposite features, including the CNT volume fraction (CNTVF), aspect ratio (AR), aggregation state, and the CNT/host interface properties. Results of the multi-scale analysis show that the CNTVF and AR have the most influential effects on the properties of a nanocomposite PC, whereas an addition of 3 vol% CNT leads to 45% increase in the BG width. Also, the CNT/epoxy interfacial features possess less influences than the CNTVF and AR. The CNT aggregation state is detrimental to the stiffness and wave attenuation properties, too.

The paper deals with the experimental and theoretical results of elastic constants of polymer modified high strength concrete with high fibre volume fraction. To evaluate elastic properties of this composite system, compressive and flexural strengths were obtained experimentally. Elastic properties such as modulus of elasticity and Poisson’s ratio are first obtained based on experimental results. Simplified equations based on micromechanics, and solid mechanics theories are utilized for the evaluation of elastic properties of polymer modified randomly oriented short steel fibre reinforced high strength concrete. The micromechanics equations for the modulus of elasticity and the Poisson’s ratio are based on the fibre volume fraction and the elastic moduli of the fibre and polymer modified concrete matrix. The existing empirical equations are also used to obtain elastic constants. These equations are applied in the full range of fiber volume fraction (1% to 10%). The comparison of experimental results with theoretical values shows the good agreement with each other. The novelty of the present paper is that the modulus of elasticity of this composite system is obtained experimentally using four point bending test and the Poisson’s ratio is obtained as a function of flexural and compressive strengths with excellent accuracy for the first time.

The common approach to crystal-plasticity finite element modeling for load-bearing prediction of metallic structures involves the simulation of simplified grain morphology and substructure detail. This paper details a methodology for predicting the structure–property effect of as-manufactured microstructure, including true grain morphology and orientation, on cyclic plasticity, and fatigue crack initiation in biomedical-grade CoCr alloy. The methodology generates high-fidelity crystal-plasticity finite element models, by directly converting measured electron backscatter diffraction metal microstructure grain maps into finite element microstructural models, and thus captures essential grain definition for improved microstructure–property analyses. This electron backscatter diffraction-based method for crystal-plasticity finite element model generation is shown to give approximately 10% improved agreement for fatigue life prediction, compared with the more commonly used Voronoi tessellation method. However, the added microstructural detail available in electron backscatter diffraction–crystal-plasticity finite element did not significantly alter the bulk stress–strain response prediction, compared to Voronoi tessellation–crystal-plasticity finite element. The new electron backscatter diffraction-based method within a strain-gradient crystal-plasticity finite element model is also applied to predict measured grain size effects for cyclic plasticity and fatigue crack initiation, and shows the concentration of geometrically necessary dislocations around true grain boundaries, with smaller grain samples exhibiting higher overall geometrically necessary dislocations concentrations. In addition, minimum model sizes for Voronoi tessellation–crystal-plasticity finite element and electron backscatter diffraction–crystal-plasticity finite element models are proposed for cyclic hysteresis and fatigue crack initiation prediction. This publication has emanated from research conducted with the financial support of Science Foundation Ireland under Grant number 16/RC/3872. For the purpose of Open Access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission. The authors wish to acknowledge the Irish Centre for High-End Computing (ICHEC) for the provision of computational facilities and support. The microstructure 668 characterization work is supported by the University of Limerick, which is highly appreciated. The 669 authors would also like to acknowledge Dr P. J. Ashton for the helpful discussion. peer-reviewed

In this research, the Stewart-Cazacu micromechanics coupled damage model is extended and validated adding nucleation and coalescence models as new damage mechanisms. The Ti–6Al–4V titanium alloy is chosen as a suitable hcp ductile material to be modeled using this extended damage law. The characterization of the damage evolution in this alloy is addressed throughout a quasi-static experimental campaign. Damage characterization relies on in situ X-ray tomography data and scanning electron microscopy imaging technique. The validation procedure consists in the implementation into the finite element research software Lagamine of ULiège and in the comparison of numerical predictions and experimental results. Load–displacement curves and damage-related state variables at fracture configuration from smooth and notched bar specimens submitted to tensile tests are analyzed. The nucleation and coalescence model extensions as well as an accurate elastoplastic and damage material parameter identification for Ti–6Al–4V samples are essential features to reach a validated model. The prediction capabilities exhibited for large strains are in good agreement with experimental results, while the near-fracture strains can still be improved.

In this study, we developed a micromechanics scheme to predict the upper and lower bounds on the creep strain and stress relaxation induced by interface diffusion in metal-matrix particulate composites. The normal stress acting on the matrix-inclusion interface, which is the driving force for interface diffusion, is estimated by using the Hashin-Shtrikman bounds and mean-field micromechanics theory. Analytical solutions of upper and lower bounds on the creep strain under constant stress and the relaxed stress at fixed strain are obtained. Results of this work show that the ultimate creep strain and relaxed stress are only related to the material properties and the percentage of each component, such as volume fraction of inclusion and elastic modulus ratio of inclusion to matrix. The parameters of interface diffusion only influence the rate of creep strain. It is found that the creep deformation and stress relaxation of composites are more sensitive to the volume fraction of inclusion than the elastic modulus ratio. The methodology of this study also applies to analysis of creep deformation of composites where both the matrix creep and interface diffusional creep need to be considered. The present study offers new perspectives for in-depth understanding of creep behavior of composites driven by mass diffusion along inclusion-matrix interface.

A numerical model of unidirectional carbon fiber-reinforced polymer composite material at the micro-level has been introduced to complement the experiment and analytical model in estimating the elastic properties of composite material. Idealization was performed in the model by using a periodically distributed fiber following square and hexagonal packing arrangement. The determination of the unit cell configuration was made by considering the periodic boundary condition associated with the selected configuration. The idealization using periodic fiber arrangement was proved to adequately estimate the elastic properties of composite material. The hexagonal model was proved to solve the drawbacks of the square model in estimating the shear properties with error reduction up to 50 % in comparison to the square model.

Micromechanics, which can be used to relate the properties of a composite to the properties of individual constituents, is considered a good approach to understanding the fundamental mechanisms behind the behavior of asphalt materials. Compared with the semi-empirical and numerical micromechanical models, analytical micromechanical models do not need calibration factors. In addition, they can provide analytical solutions on the basis of a series of assumptions. Using these models, researchers have separated the effects of different stiffening mechanisms (i.e., the volume-filling reinforcement, the physicochemical reinforcement, and the particle-contact reinforcement) for mastic. However, similar research work has not been conducted for asphalt mixtures and, moreover, the characteristics of the particle-contact reinforcement have not been deeply analyzed by researchers. Therefore, this paper aims to understand the stiffness of asphalt mixture through micromechanics. The focus of this study was on porous asphalt mixture where particle-contact reinforcement plays an important role in its behavior. The stiffening effects of different mechanisms were separated using analytical micromechanical models. The effects of temperature/frequency and the properties of the matrix phase on the stiffening effect of the particle-contact reinforcement were analyzed.

In this paper, a new format is proposed for rate-dependent cyclic behavior of unidirectional metal matrix composites, which combines the cyclic elasto-viscoplastic constitutive model with the param...