Anisotropic Elastic Moduli Research Articles

Programmed shape-dependence of shape memory effect of oriented polystyrene: A molecular dynamics study

Oriented polystyrene (PS) has attracted attention due to its capability of sequential self-folding behaviors by infrared (IR) light heating. It has been seen that temporal changes of the shape and properties of PS are affected by its pre-defined molecular structure. In this study, full atomistic molecular dynamics (MD) simulations are carried out to study the effect of initially applied strain on the thermoelastic properties and shape recovery behaviors of the oriented PS. The shape memory creation procedure (SMCP) is described by long-time simulation and initial strains between 15% and 100% are applied by in-plane tensile loadings. As the extent of pre-stretching increases, the anisotropy of elastic modulus and linear coefficient of thermal expansion (CTE) increase primarily due to the molecular alignment. The shape fixity ratio increases by up to 24% and the recovery ratio decreases by up to 32% by increasing the initial strain. In particular, the shape recovery ratio is mainly affected by the orientational order parameter of the oriented PS. The rate of the recoveries of the thermomechanical properties and shape reduce for a more pre-stretched PS. The retardation of conformational transformation comes from a reduction in the sizes of free volume elements. The results demonstrate a microstructure-property relationship which is important in designing the self-folding behaviors of oriented PS.

Micro‐CT based modelling for characterising injection‐moulded porous titanium implants

Design of prosthetic implants to ensure rapid and stable osseointegration remains a significant challenge, and continuous efforts have been directed to new implant materials, structures and morphology. This paper aims to develop and characterise a porous titanium dental implant fabricated by metallic powder injection-moulding. The surface morphology of the specimens was first examined with a scanning electron microscope (SEM), followed by microscopic computerised tomography (μ-CT) scanning to capture its 3D microscopic features non-destructively. The nature of porosity and pore sizes were determined statistically. A homogenisation technique based on the Hills-energy theorem was adopted to evaluate its directional elastic moduli, and the conservation of mass theorem was employed to quantify the oxygen diffusivity for bio-transportation feature. This porous medium was found to have pore sizes varying from 50 to 400 µm and the average porosity of 46.90 ± 1.83%. The anisotropic principal elastic moduli were found fairly close to the upper range of cortical bone, and the directional diffusivities could potentially enable radial osseous tissue ingrowth and vascularisation. This porous titanium successfully reduces the elastic modulus mismatch between implant and bone for dental and orthopaedic applications, and provides improved capacity for transporting oxygen, nutrient and waste for pre-vascular network formation. Copyright © 2016 John Wiley & Sons, Ltd.

Anisotropic Elastic Modulus of Oriented Regioregular Poly(3-hexylthiophene) Films

Specific morphological features of polymer semiconductors are often promoted in devices to optimize optoelectronic behavior. Less studied is the role of morphology on the mechanical properties of the film, such as elastic modulus, which is an important property for the development of flexible and stretchable devices. To gain insight into the morphological origin of elasticity in polymer semiconductors and its relationship to charge transport, we study the anisotropic in-plane elastic modulus of strain-aligned regioregular poly(3-hexylthiophene) (P3HT) films and compare the results to previously measured field effect charge mobility. The film morphology is varied through the amount of applied strain and post strain thermal annealing. Morphological characterization includes UV–vis optical spectroscopy and X-ray diffraction. The elastic modulus is measured using a buckling-based measurement technique. The elastic modulus of the film is found to decrease as the film is plastically strained. Thermally annealin...

Micromechanical analysis on anisotropy of structured magneto-rheological elastomer

This paper investigates the equivalent elastic modulus of structured magneto-rheological elastomer (MRE) in the absence of magnetic field. We assume that both matrix and ferromagnetic particles are linear elastic materials, and ferromagnetic particles are embedded in matrix with layer-like structure. The structured composite could be divided into matrix layer and reinforced layer, in which the reinforced layer is composed of matrix and the homogenously distributed ferromagnetic particles in matrix. The equivalent elastic modulus of reinforced layer is analysed by the Mori-Tanaka method. Finite Element Method (FEM) is also carried out to illustrate the relationship between the elastic modulus and the volume fraction of ferromagnetic particles. The results show that the anisotropy of elastic modulus becomes noticeable, as the volume fraction of particles increases.

First-principle study of structural and mechanical properties of hexagonal polytypes of diamond

The values of unit-cell parameters; C-C bond lengths; elastic constants c ij and s ij ; elastic moduli B, G, and E; and hardnesses and cohesion energies have been calculated for hexagonal diamond polytypes 2H, 4H, 6H, and 8H within the approximation of density functional theory. The anisotropy of elastic moduli and hardness is investigated. It is found that the linear compressibility and hardness of polytypes in the basal plane exceeds that along the hexagonal c axis. It is shown that the difference in the anisotropic properties along and perpendicular to the hexagonal axis may be related to the specific features of polytype structure.

Improved Elasticity of New Ti-Alloys for Biomedical Applications

The low Young's modulus hasa particular importance in metallic bio-implants for preventing or reducing the occurrence of stress shielding. New concerns on different ways to control the effective elasticity of new Ti-alloys for biomedical applications are discussed in this paper. For this, high Zr-containing Ti67Zr20Nb10Ta3 alloy,with α“+β phase structure, was designed and the effect of the addition of small amounts of Fe and O were studied. The elastic modulus of the alloys increased with increasing the β-phase stability in both cold rolled and solution treated conditions. The stress/strain induced phase transformation was observed in the lower β-phase stability alloys. The cold deformation of these alloys resulted in a change in Young's modulus depending on the degree of β-phase stability and the measurement direction. The observed anisotropy of elastic modulus in the alloys is related to the texturing in the β- and α”-phases induced by cold rolling. The non-linear elasticity was observed in both alloys with higher degree in the cold rolled condition. The high elastic admissible strain observed in the present alloys gives a room for developing more mechanically biocompatible alloys as bio-implants.

Determination of Silkworm Silk Fibroin Compressibility Using High Hydrostatic Pressure with in Situ X-ray Microdiffraction

A hydrostatic high pressure cell is used to record pressure resolved wide-angle X-ray microdiffraction data (WAXS) from Bombyx mori silkworm silk fibers with in situ pressurization in the range of 0.01–0.5 GPa (0.1–5 kbar). From the pressure dependent peak positions of (002), (020), (200), and (210) Bragg reflections the (anisotropic) elastic moduli of compression were determined for the different unit cell axes of the crystalline fraction of silk fibroin, comprising of stacked polyalanine β-sheets. The data are compared with X-ray diffraction results previously obtained from silkworm silk at tensile load and spider silk data at high hydrostatic pressure and indicate a different response of the silk fibroin structure to pressure versus tensile load. The response of the unit cell of silkworm silk fibroin to the applied pressure is discussed and modeled taking into account the weak van der Waals bonds between protein β-sheets. Differences are pointed out between the responses of silk’s nanostructure to unid...

Quasi-Static Brittle Damage Evolution in Elastic Materials with Multiple Damaged States

We present energetic and strain-threshold models for the quasi-static evolution of brutal brittle damage for geometrically-linear elastic materials. By allowing for anisotropic elastic moduli and multiple damaged states we present the issues for the first time in a truly elastic setting, and show that the threshold methods developed in (Garroni, A., Larsen, C. J., Threshold-based quasi-static brittle damage evolution, Archive for Rational Mechanics and Analysis 194 (2), 585–609, 2009) extend naturally to elastic materials with non-interacting damage. We show the existence of solutions and that energetic evolutions are also threshold evolutions.

Anisotropic poly(ethylene glycol)/polycaprolactone hydrogel-fiber composites for heart valve tissue engineering.

The recapitulation of the material properties and structure of the native aortic valve leaflet, specifically its anisotropy and laminate structure, is a major design goal for scaffolds for heart valve tissue engineering. Poly(ethylene glycol) (PEG) hydrogels are attractive scaffolds for this purpose as they are biocompatible, can be modified for their mechanical and biofunctional properties, and can be laminated. This study investigated augmenting PEG hydrogels with polycaprolactone (PCL) as an analog to the fibrosa to improve strength and introduce anisotropic mechanical behavior. However, due to its hydrophobicity, PCL must be modified prior to embedding within PEG hydrogels. In this study, PCL was electrospun (ePCL) and modified in three different ways, by protein adsorption (pPCL), alkali digestion (hPCL), and acrylation (aPCL). Modified PCL of all types maintained the anisotropic elastic moduli and yield strain of unmodified anisotropic ePCL. Composites of PEG and PCL (PPCs) maintained anisotropic elastic moduli, but aPCL and pPCL had isotropic yield strains. Overall, PPCs of all modifications had elastic moduli of 3.79±0.90 MPa and 0.46±0.21 MPa in the parallel and perpendicular directions, respectively. Valvular interstitial cells seeded atop anisotropic aPCL displayed an actin distribution aligned in the direction of the underlying fibers. The resulting scaffold combines the biocompatibility and tunable fabrication of PEG with the strength and anisotropy of ePCL to form a foundation for future engineered valve scaffolds.

Superior high tensile elongation of a single-crystal CoCrFeNiAl0.3 high-entropy alloy by Bridgman solidification

The crystallographic orientation, tensile behavior, fracture mechanism, hardness, and elastic modulus of a single-crystal CoCrFeNiAl0.3 high-entropy alloy (HEA) successfully synthesized by Bridgman solidification are investigated in detail. The growth direction of the single-crystal product mainly focuses on the <001> orientation. An ultimate tensile elongation of about 80% is achieved in the single-crystal alloy, accompanied by a large work-hardening exponent and a shear-fracture mode. A quantitative Hall–Petch relationship for the current HEA can be obtained as σy=171.65+0.73/d. The single-crystal sample displays a relatively-lower elastic modulus than the as-cast counterpart, indicating the anisotropy of elastic modulus. The outstanding tensile ductility for the single-crystal product is attributed to (1) low-angle grain boundaries and thus less distance to dislocation motion; and (2) single <001> crystallographic orientation and therefore less plastic-strain incompatibility.

Quantitative Correlation of the Effect of Process Conditions on the Capping Tendencies of Tablet Formulations

Capping is a mechanical defect in tablet formulation and manufacture. Understanding what influences tablet capping in terms of process variables and formulation properties and developing specialized techniques to correlate these variables with mechanical failures are practical interests of the pharmaceutical industry. Tablet compression emulator was used to rank order capping tendencies of a diverse sample set. The compression forces of 5-25 kN were used to compress round, beveled edge, and oval shape tablets. Compression speeds of 25, 40, and 80 rpm were chosen as representative ranges for bench-to-manufacturing-scale processing. Tablets were tested by in-house developed nondestructive ultrasonic method. The measurements revealed that elastic modulus vary with different testing orientations that indicated elastic modulus anisotropy in tablets. It was shown that altering process conditions such as tooling, compression force, and compression speed significantly impact the capping tendencies of formulations. A systematic approach has been applied to develop a predictive tool to assess capping tendencies of formulations. The developed tool is fast, material sparing, and has potential to flag the risk of manufacturability issues and provide insight into the performance of formulations during early development.

G0310102 金属の塑性変形が弾性係数の異方性および微視組織に及ぼす影響の評価(材料力学部門一般セッション:変形・ひずみ(1))

G0310102 金属の塑性変形が弾性係数の異方性および微視組織に及ぼす影響の評価(材料力学部門一般セッション:変形・ひずみ(1))

多結晶塑性解析における弾性異方性の弾塑性挙動に及ぼす挙動

多結晶塑性解析における弾性異方性の弾塑性挙動に及ぼす挙動

Shock compression of aluminum single crystals to 70 GPa: Role of crystalline anisotropy

Crystalline anisotropy effects were examined at high stresses by shock compressing Al single crystals along ⟨100⟩, ⟨110⟩, and ⟨111⟩ orientations to peak stresses ranging from 40 to 70 GPa. Laser-interferometry was used to monitor particle velocity histories, including unloading wave profiles. A single, flat-top shock wave followed by a structured release was observed in all the experiments. Shock velocities and longitudinal sound speeds (onset of release) were also determined from the measured particle velocity histories. Within experimental uncertainty (1%–2%), the Hugoniots for the three orientations were indistinguishable, and a single longitudinal stress-density curve was fit to all peak state data. In contrast, the longitudinal sound speeds (and the resulting longitudinal elastic moduli) in the shocked state showed crystal anisotropy effects over the entire stress range examined (up to ∼50% density compression). The measured longitudinal elastic moduli at the highest stress represent more than a fourfold increase from the ambient value and showed continuing anisotropy with compression. The present findings show that Hugoniots may not be the optimal measure of crystalline anisotropy, and even low-anisotropy single crystals, like Al, can manifest significant anisotropy in elastic moduli at large shock compressions.

Influence of oxygen content on the mechanical properties of hexagonal Ti—First principles calculations

In this work we report results of ab initio modeling of structure stability, mechanical properties, lattice distortion and electronic structures of α-Ti as a function of concentration and positions of oxygen atoms. The heats of formation for all solutions were negative and in excellent agreement with experimental data. The single crystal elastic constants, elastic modulus anisotropy and polycrystalline Voigt bulk B and shear G moduli were calculated. Based on the values of B/G ratio, the effect of oxygen on Ti ductility was estimated with the conclusion that approximately 1at% O addition improves elastic and plastic properties. This can be explained by the effect of O concentration on the Ti–Ti bonds and the value of the c/a lattice parameter.

Thickness scaling of ferroelastic domains in PbTiO3 films on DyScO3

We report on the thickness dependence of the ferroelastic domains of PbTiO3 films grown on (110)-DyScO3 with low thicknesses (up to 240 nm), which fall outside the validity range of the square root law proposed by Roytburd. For slow-grown films, the data reveal the linear thickness dependence predicted by Pertsev and Zembilgotov, using a complete elastic description, while a 2/3 scaling exponent is found for fast-grown films. Extremely long domains running all through the samples have been observed in the latter case, compared to the short domains observed in slow-grown films. These differences are ascribed to the in-plane anisotropy for domain wall nucleation, which is likely caused by the anisotropic elastic modulus of the substrate.

On the Biaxial Distribution of Anisotropic Elastic Modulus of Thin-Plate Polycrystalline Elements and the Identification by Ultrasonic Methods

Abstract A new method for the interpolation of biaxial anisotropy of elastic modulus of thin-plate polycrystalline elements has been developed. The dependence of shear modulus and modulus of longitudinal elasticity as a function of an angular distribution of Poisson's ratio, achieved by the method of ultrasonic critical-angle refractometry (UCR), has been derived.

Crystallographic texture determines mechanical properties of molluscan nacre

"Crystallographic texture determines mechanical properties of molluscan nacre." Computer Methods in Biomechanics and Biomedical Engineering, 16(sup1), pp. 292–293Keywords:: nacrecrystallographic texturehardness and reduced elastic modulusanisotropy AcknowledgementsThis study was supported by Grant No. 334600 from the CGS; project VZ 0002700604 (Section 010) and also by Grant No. TA01010185 of the Technology Agency from the Czech Republic.

Warpage analysis of a micro-molded parts prepared with liquid crystalline polymer based composites

The purpose of this study is to understand the warpage behavior of a micro-injection molded part induced by anisotropy of the material. Microstructural anisotropy was characterized to understand warpage behavior of liquid crystalline polymer based composites. A new definition of the microstructure was introduced along the thickness of a molded part, i.e., “skin–shear–core” layer was proposed depending on the orientation of LCP molecules and fillers. The microstructural anisotropy of LCP composites was verified by using WAXD, CT, and SEM analyses. The anisotropic elastic modulus and coefficient of thermal expansion (CTE) of micro-injection molded parts were investigated by using a new numerical method with the modified Mori–Tanaka (M–T) model. The interaction coefficient, CI, and coefficient of thermal expansion (CTE) were the most important factors determining the warpage of a micro-injection molded part made of an anisotropic material. The control of warpage due to the orientation of glass fibers was investigated by simulation.

Nanoindentation on the doubler plane of KDP single crystal

The nanohardness is from 1.44 to 2.61 GPa, the Vickers hardness is from 127 to 252 Vickers, and elastic modulus is from 52 to 123 GPa by the nanoindentation experiments on the doubler plane of KDP crystal. An indentation size effect is observed on the doubler plane in the test as the nanohardness and elastic modulus decreases with the increase of the maximum load. Slippage is identified as the major mode of plastic deformation, and pop-in events are attributed to the initiation of slippage. And the variation of unloading curve end is the result of stick effects between the indenter and the contact surface. The depth of the elastic deformation, which is between 40 and 75 nm, is responsible for the elastic deformation. The doubler plane of KDP crystal has anisotropy, and the relative anisotropy of nanohardness is 8.2% and the relative anisotropy of elastic modulus is 8.0%.