Anisotropic Mechanical Response Research Articles

Equivariant graph convolutional neural networks for the representation of homogenized anisotropic microstructural mechanical response

Composite materials with different microstructural material symmetries are common in engineering applications where grain structure, alloying and particle/fiber packing are optimized via controlled manufacturing. In fact these microstructural tunings can be done throughout a part to achieve functional gradation and optimization at a structural level. To predict the performance of particular microstructural configuration and thereby overall performance, constitutive models of materials with microstructure are needed.In this work we provide neural network architectures that provide effective homogenization models of materials with anisotropic components. These models satisfy equivariance and material symmetry principles inherently through a combination of equivariant and tensor basis operations. We demonstrate them on datasets of stochastic volume elements with different textures and phases where the material undergoes elastic and plastic deformation, and show that the these network architectures provide significant performance improvements.

Structural origin of the anisotropic local mechanical response of amorphous silicon

Structural origin of the anisotropic local mechanical response of amorphous silicon

The anisotropic and region-dependent mechanical response of wrap-around tendons under tensile, compressive and combined multiaxial loads

The present work reports on the multiaxial region and orientation-dependent mechanical properties of two porcine wrap-around tendons under tensile, compressive and combined loads based on an extensive study with n=175 samples. The results provide a detailed dataset of the anisotropic tensile and compressive longitudinal properties and document a pronounced tension-compression asymmetry. Motivated by the physiological loading conditions of these tendons, which include transversal compression at bony abutments in addition to longitudinal tension, we systematically investigated the change in axial tension when the tendon is compressed transversally along one or both perpendicular directions. The results reveal that the transversal compression can increase axial tension (proximal-distal direction) in both cases to orders of 30%, yet by a larger amount in the first case (transversal compression in anterior-posterior direction), which seems to be more relevant for wrap-around tendons in-vivo. These quantitative measurements are in line with earlier findings on auxetic properties of tendon tissue, but show for the first time the influence of this property on the stress response of the tendon, and may thus reveal an important functional principle within these essential elements of force transmission in the body. Statement of significanceThe work reports for the first time on multiaxial region and orientation-dependent mechanical properties of wrap-around tendons under various loads. The results indicate that differences in the mechanical properties exist between zones that are predominantly in a uniaxial tensile state and those that experience complex load states. The observed counterintuitive increase of the axial tension upon lateral compression points at auxetic properties of the tendon tissue which may be pivotal for the function of the tendon as an element of the musculoskeletal system. It suggests that the tendon’s performance in transmitting forces is not diminished but enhanced when the action line is deflected by a bony pulley around which the tendon wraps, representing an important functional principle of tendon tissue.

Mechanical characterization and constitutive modeling of additively-manufactured polymeric materials and lattice structures

Additively manufactured polymeric lattice structures are being extensively studied, primarily because their mechanical properties can be tailored by controlling the unit cell geometry, giving them higher designability than stochastic materials. However, the inherent layer-wise additive manufacturing process affects the base material properties related to the printing direction, which in turn affects the macroscopic responses of the entire lattice materials. A robust understanding and modeling of lattice structures' elastic and plastic yield behavior in a homogenized approach are essential to enhance their design and analysis efficiency in engineering applications. In pursuit of this goal, a unified printing angle-dependent constitutive model of base materials is proposed in line with the tensile experimental data. The elastic material properties (elastic modulus, shear modulus, and Poisson's ratio), obtained through numerical simulations of one unit-cell with periodic boundary conditions, exhibit anisotropic properties, with the degree of anisotropy determined by the angle of the constituent members and base materials. Furthermore, both experimental and numerical results of lattices demonstrate anisotropic mechanical response under horizontal and vertical compression. Virtual multiaxial experiments are conducted through multi-cell numerical simulations, enabling the determination of initial yielding points of two different lattice structures (Kelvin and Simple cubic and body-centered cubic hybrid structures) under various loading conditions using a dissipation energy-based criterion. Overall, the multiaxial yield surface of the investigated lattices under various stress states, except for the isotropic principal stress plane, can be properly depicted by the Extended-Hill anisotropic yield criterion.

Anisotropic Mechanical Response of Nacre to Heat Treatment Under Indentation: Effect of Structural Orientation

Anisotropic Mechanical Response of Nacre to Heat Treatment Under Indentation: Effect of Structural Orientation

Constitutive model of an additively manufactured combustor material at high-temperature load conditions

ABSTRACT In this paper, the high-temperature constitutive behaviour of an additively manufactured ductile nickel-based superalloy is investigated and modelled, with application to thermomechanical fatigue, low-cycle fatigue and creep conditions at temperatures up to 800 ∘ C. Thermomechanical fatigue tests have been performed on smooth specimens in both in-phase and out-of-phase conditions at a temperature range of 100 − 800 ∘ C, and creep tests at 625 ∘ C, 700 ∘ C, 750 ∘ C and 800 ∘ C. Additionally, low-cycle fatigue tests at different strain ranges and load ratios have been performed at 700 ∘ C, and tensile tests have been performed at 600 ∘ C, 700 ∘ C and 800 ∘ C. A clear anisotropic mechanical response is obtained in the experiments, where the anisotropic effects are larger at high stress levels in creep loadings. To capture this behaviour, a rate-dependent strain based on a double-Norton model has been adopted in the model, by which the creep and mid-life response of the thermomechanical fatigue tests can be simulated with good accuracy.

Microstructure and texture control of Ni-Mn-Ga magnetic shape memory alloys manufactured by laser powder bed fusion

The Laser Powder Bed Fusion (LPBF) process was used to manufacture Ni-Mn-Ga polycrystalline samples. The initial powders with a fine particle size of about 20 µm were firstly prepared by a ball milling from melt-spun ribbons. The microstructure and texture evolution of Ni-Mn-Ga alloy manufactured by LPBF were investigated employing SEM, TEM, and synchrotron radiation diffraction. Using two different scanning strategies, optimization of laser parameters and post-processing heat treatment, a homogeneous microstructure with a strong crystallographic texture was obtained. The localized heating/cooling conditions allow obtaining a layered structure with preferred <100> fiber orientations along the growth direction. The crystal structure and crystallographic texture drastically change when the laser oscillation mode is chosen. The strong crystalline anisotropy and layered-type microstructure have a significant impact on twining flow behavior giving rise to an anisotropic mechanical response. The variant reorientation during mechanical training is realized by the so-called orthogonal shearing. It is also shown that the resulting crystal structure and characteristic transformation temperatures are strongly dependent on chemical composition related to Mn losses and internal stresses along with chemical order creating metastable phases due to the extremely high cooling rate upon the 3D printing. Therefore, all the above parameters are thoroughly monitored during the three-stage fabrication process.

Insights into microstructure evolution and fracture mechanisms of welded joints of high strength steel patchwork components

The hot roll bending patchwork components of B1500HS uncoated ultra-high strength steel processed at industrial scale were welded with filler wire. The microstructure, grain orientation, mechanical properties and fracture behavior of the joint were investigated. The results showed that the weld metal (WM) was mainly composed of lath martensite and lower bainite (LB). Various microstructure appeared in different positions of the HAZ, among which martensite-austenite (M-A) constituents in the incompletely quenched zone and tempered martensite (TM) in the tempered zone were the key factors determining the performance of the joint. The welded joint exhibited complex structure and anisotropic mechanical response due to the decarburization and rolling texture of the original base material (BM). In the tempered zone, lath merge and boundaries disappear lead to the annihilation of dislocations, carbide precipitation leads to reduction of mobile dislocations, and recrystallization and recovery eliminate work hardening. The reduction of the effect of dislocation strengthening results in the formation of a softening belt at 6 mm from the center of the weld, with a minimum hardness of 266 HV. The tensile strength of the joint in the rolling direction (RD) was 983 MPa, and the fracture occurred in the softening belt. Both brittle and ductile fracture features were observed. The reason why the fracture occurs in the high temperature tempered zone instead of the incompletely quenched zone was the difference in the effect of “constraint strengthening”. Fracture occurred through delamination cracking along the “weak interface” owing to precipitated high-hardness cementite particles and the unfavorably oriented ferrite cleavage planes.

Structural parameters defining distribution of collagen fiber directions in human carotid arteries

Collagen fiber arrangement is decisive for constitutive description of anisotropic mechanical response of arterial wall. In this study, their orientation in human common carotid artery was investigated using polarized light microscopy and an automated algorithm giving more than 4·106 fiber angles per slice. In total 113 slices acquired from 18 arteries taken from 14 cadavers were used for fiber orientation in the circumferential-axial plane. All histograms were approximated with unimodal von Mises distribution to evaluate dominant direction of fibers and their concentration parameter. 10 specimens were analyzed also in circumferential-radial and axial-radial planes (2-4 slices per specimen in each plane); the portion of radially oriented fibers was found insignificant. In the circumferential-axial plane, most specimens showed a pronounced unimodal distribution with angle to circumferential direction μ = 0.7° ± 9.4° and concentration parameter b = 3.4 ± 1.9. Suitability of the unimodal fit was confirmed by high values of coefficient of determination (mean R2 = 0.97, median R2 = 0.99). Differences between media and adventitia layers were not found statistically significant. The results are directly applicable as structural parameters in the GOH constitutive model of arterial wall if the postulated two fiber families are unified into one with circumferential orientation.

A numerical multi-scale method for analyzing the rate-dependent and inelastic response of short fiber reinforced polymers: Modeling framework and experimental validation

This research presents a numerical multi-scale approach that efficiently addresses the inelastic and time-dependent mechanical response of short fiber reinforced polymers (SFRPs) under monotonic loading conditions by linking the mechanical analysis from microscale analysis to a continuum model. To do so, first, the mechanical performance of a recently suggested unit cell, considering the intrinsic mechanical characteristics of both fiber and matrix, is studied to address the inelastic and rate-dependent mechanical behavior of completely aligned SFRPs. Then, the evaluated mechanical response is linked to the Hill's plasticity and two-layer viscoplastic (TLVP) models to represent the anisotropic mechanical response of SFRPs. Furthermore, an easy-to-use multi-step homogenization process is considered to numerically incorporate the influence of fiber misalignments. Finally, the suggested multi-scale technique is thoroughly validated at different strain rates, by using experimental observations of short fiber composites with high volume fraction and direct FE simulations of RVEs with complex microstructures.

Investigation of the anisotropic mechanical response of layered shales

AbstractLayered shales exist widely and are often encountered during shale gas development. However, the mechanical response of layered shales is significantly affected by the existence of beddings, resulting in the obvious anisotropy characteristics regarding deformation, strength and failure mode. To clarify the underlying mechanisms of shale anisotropy that control the safety of engineering projects, the numerical simulation and theoretical analysis were conducted. The results show that with the growth of confining pressure, the compressive resistance of shales gradually increases, the shear fractures govern the instability and the anisotropy index decreases. Furthermore, several strength criteria for layered rock masses were summarized, and the modified Jaeger strength criterion was proposed by introducing the anisotropic parameter . It can effectively reflect the failure modes and strength features of layered shales under triaxial conditions with a higher accuracy. Besides, the variation of cohesion and internal friction angle of layered shale samples was comprehensively analysed under the triaxial conditions. Clearly, as the inclination angle of bedding planes increases, the cohesion of layered shales first decreases, but then increases under triaxial compression, showing the ‘U’‐shaped changing trend. Additionally, the internal friction angle of layered shales gradually increases with the increase in the inclination of bedding planes.

Effects of the injection molding processing settings on the phase morphology and mechanical anisotropy of thermoplastic vulcanizates

AbstractThermoplastic vulcanizates show significant anisotropic mechanical properties when processed to components via injection molding. This effect is related to a process‐dependent distortion of the incorporated elastomer particles in high‐shear regions during the injection phase. In a plate geometry, the elastomer particles in the shear regions are oriented and deformed in the flow direction. However, the ongoing distortion processes and the influencing factors of the process parameters on the resulting phase morphology and mechanical response are not entirely understood. Therefore, in this study, the effect of the injection molding machine settings for the production of a plate component on the local phase morphology and mechanical anisotropy is investigated. The investigations are conducted on two commercial material grades with different Shore‐A hardness 30 and 90. A significant inverse effect of the injection volume flow rate on the particle distortion and anisotropy is found. Increasing the volume flow rate results in a reduction of the anisotropy. This is counterintuitive from the experience of other materials with process‐dependent anisotropy. Also, a significant influence of the process on the overall stiffness of the compounds is observed.Highlights Sturcture–property relation for phase morphology in thermoplastic vulcanizates Quantitative microstructure analysis in injection molded plates Macroscopic analysis of anisotropic mechanical response under uniaxial loading Effect analysis of injection molding parameters on the mechanical anisotropy Additional effects of process settings on overall stiffness of the material

Multi-disciplinary characterization of shrinkage effects in Opalinus clay

Multi-disciplinary characterization of shrinkage effects in Opalinus clay

A functional M-BN monolayer for application of photocatalytic water splitting via first-principles calculations

A BN monolayer (M-BN) was designed by introducing the Stone-Wales defects to h-BN. Using first principles calculations, we verified the energetic, dynamical, thermal and mechanical stability of M-BN. M-BN has a high Young's modulus and an anisotropic mechanical response. Moreover, the calculations results of electronic properties show that M−N- is an indirect band gap semiconductor. The band edge positions of the M−N- monolayer span the redox potential of water, which suggest its great potential in the application of photocatalytic water splitting. Remarkably, the high optical absorption capability of M−N- in the ultraviolet range make it to be a potential candidate in optoelectronic device applications. The current results provide insights for further exploring the new 2D materials for nanoelectronic and optoelectronic applications.

Anisotropic mechanical response of AA7475-T7351 alloy at different loading rates and temperatures

The mechanical behaviour of aluminium alloy 7475-T7351 along the three principal directions (i.e rolling, transverse and normal) are compared here at different rates and temperatures under tensile and compressive loading. The aluminium alloy is examined in quasi-static circumstances using the Zwick/Roell Z-50 UTM, while the SHPB (for compression and tension) technique is utilised to investigate the high strain rate behaviour of the material under tensile (up to 2950 s−1) and compressive (up to -4438 s−1) loading. Both the quasi-static and dynamic experiments are performed at five different temperatures (25 °C, 100 °C, 150 °C, 200 °C, 250 °C). JC, KHL and m-KL constitutive models are calibrated along different directions. Quadratic and non-quadratic anisotropy model was further modified to incorporate tension–compression asymmetry and constants were also evaluated to predict the yield surface of AA7475-T7351 for temperatures and strain rates. The loading direction (tension/compression), strain rate and temperature are observed to affect the ductility and strength of AA7475-T7351 immensely. The KL phenomenological model is modified to incorporate the tension–compression asymmetry, strain hardening, strain rate hardening and thermal softening of AA7475-T7351. The efficiency of the modified KL model is compared with Johnson–Cook and KHL constitutive models along the principal material directions.

Plastic anisotropy and composite slip: Application to uranium dioxide

The mechanical behaviour of UO2 single crystal is under debate due to the unexpected multi-slip observations in the experiments that involve dislocations in 12〈110〉{100} slip systems but also in 12〈110〉{110} and 12〈110〉{111}. We propose a multi-scale model based on a composite slip in which, under the effect of cross-slip, part of the dislocation density in primary slip systems can be transferred in secondary systems with a lower propensity to glide but a more favourable orientation regarding the shear stress. This approach allows to describe the anisotropic mechanical response of UO2 single crystal with an accuracy never reached up to now. After identifying the relevant slip systems depending on the orientation using a Schmid approach, dislocation dynamics simulations are used to assert if the cross-slip induces a composite slip and to quantify its effect on the flow stress which appears constrained by the activity of 12<110>{111} systems. In agreement with this result, the composite slip is adapted to couple the activity of slip systems with common Burger vectors in a crystal plasticity framework for a closer comparison to the experiment. This multi-scale approach significantly improves our current knowledge on the links between dislocation microstructures and mechanical properties in UO2. Composite slip mechanism appears as a candidate to explain unexpected plastic behaviours as often observed in complex materials with multiple slip modes underling that slip activation may be more complex than in usual constitutive laws.

Formula omitted]-CP: Open source dislocation density based crystal plasticity framework for simulating temperature- and strain rate-dependent deformation

This work presents an open source, dislocation density based crystal plasticity modeling framework, ρ-CP. A Kocks-type thermally activated flow is used for accounting for the temperature and strain rate effects on the crystallographic shearing rate. Slip system-level mobile and immobile dislocation densities, as well slip system-level backstress, are used as internal state variables for representing the substructure evolution during plastic deformation. A fully implicit numerical integration scheme is presented for the time integration of the finite deformation plasticity model. The framework is implemented and integrated with the open source finite element solver, Multiphysics Object-Oriented Simulation Environment (MOOSE). Example applications of the model are demonstrated for predicting the anisotropic mechanical response of single and polycrystalline hcp magnesium, strain rate effects and cyclic deformation of polycrystalline fcc OFHC copper, and temperature and strain rate effects on the deformation of polycrystalline bcc tantalum. Simulations of realistic Voronoi-tessellated microstructures as well as Electron Back Scatter Diffraction (EBSD) microstructures are demonstrated to highlight the model’s ability to predict large deformation and misorientation development during plastic deformation.

In vivo estimation of anisotropic mechanical properties of the gastrocnemius during functional loading with MR elastography

Objective. In vivo imaging assessments of skeletal muscle structure and function allow for longitudinal quantification of tissue health. Magnetic resonance elastography (MRE) non-invasively quantifies tissue mechanical properties, allowing for evaluation of skeletal muscle biomechanics in response to loading, creating a better understanding of muscle functional health. Approach. In this study, we analyze the anisotropic mechanical response of calf muscles using MRE with a transversely isotropic, nonlinear inversion algorithm (TI-NLI) to investigate the role of muscle fiber stiffening under load. We estimate anisotropic material parameters including fiber shear stiffness (), substrate shear stiffness (), shear anisotropy (), and tensile anisotropy () of the gastrocnemius muscle in response to both passive and active tension. Main results. In passive tension, we found a significant increase in and with increasing muscle length. While in active tension, we observed increasing and decreasing and during active dorsiflexion and plantarflexion—indicating less anisotropy—with greater effects when the muscles act as agonist. Significance. The study demonstrates the ability of this anisotropic MRE method to capture the multifaceted mechanical response of skeletal muscle to tissue loading from muscle lengthening and contraction.

Anisotropic mechanical response of a 2D covalently bound fullerene lattice

Contrary to the monotype intercell connection in a hexagonal structure material, newly synthesized stable monolayer C60 fullerene (mC60) lattice possesses two kinds of intercell connection, and anisotropic properties are thus expected. Herein, we have investigated the anisotropy mechanical properties of the mC60 using first-principles calculations within the framework of density functional theory (DFT) and theoretical analysis. Uniaxial tensile properties of mC60 are orientation-dependent, and the ultimate tensile strength and the work-to-fracture of mC60 reach their maxima at 15° and minima at 75°, respectively. A theoretical expression, based on strain-governed bond failure criterion, has been developed for the strength-loading direction relationship of mC60. The theory captures well with the orientation-dependent strength from DFT calculations. We further illustrate that mC60's band gap may be largely tuned through strain engineering. Our atomistic insights and the theoretical on the structure – mechanical property relationship might be helpful in the exploring of the functioning and application of mC60, which may be further generalized to the mechanical analysis of other monolayer lattices.

Exploiting Partial Solubility in Partially Fluorinated Thermoplastic Blends to Improve Adhesion during Fused Deposition Modeling.

This work studies the effect of interlayer adhesion on mechanical performance of fluorinated thermoplastics produced by fused deposition modeling (FDM). Here, we study the anisotropic mechanical response of 3D-printed binary blends of poly (vinylidene fluoride) (PVDF) and poly (methyl methacrylate) (PMMA) with the isotropic mechanical response of these blends fabricated via injection molding. Various PVDF/PMMA filament compositions were produced by twin-screw extrusion and, subsequently, injection-molded or 3D printed into dog-bone shapes. Specimen mechanical and thermal properties were evaluated by mode I tensile testing and differential scanning calorimetry, respectively. Results show that higher PMMA concentration not only improved the tensile strength and decreased ductility but reduced PVDF crystallization. As expected, injection-molded samples revealed better mechanical properties compared to 3D printed specimens. Interestingly, 3D printed blends with lower PMMA content demonstrated better diffusion (adhesion) across interfaces than those with a higher amount of PMMA. The present study provides new findings that may be used to tune mechanical response in 3D printed fluorinated thermoplastics, particularly for energy applications.