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Nature consists of various soft tissues with well-ordered hierarchical anisotropic structures, which play essential roles in biological systems to exhibit particular functions. Mimicking bio-tissues, synthetic hydrogels with anisotropic structures have received considerable attention in recent years. However, existing approaches to fabricate anisotropic hydrogels often require complicated procedures, which are time-consuming and labor-demanding. Inspired by the dry-induced crystallization phenomenon, we report a simple yet effective prestretching-drying-swelling method to afford anisotropic crystalline polyvinyl alcohol hydrogels. Owing to the distinct anisotropic microstructure, the hydrogels demonstrate excellent mechanical properties with noticeable directional distinction. It is revealed that both the enhancing of pre-orientation strain and the extending of heating time make the hydrogels with better mechanical properties and more remarkable anisotropicity. Owing to the anisotropically aligned structure, the hydrogels exhibit remarkably differential ionic conductivity: the difference between the parallel and vertical conductivity of the same sample can reach as high as 6.6 times, making the materials possible candidates as nano-conductive materials. We anticipate that this simple yet effective approach may become highly useful for fabricating oriented hydrogels and endow the materials with more promising application prospects in the future.

SiC honeycomb ceramic reinforced Al (SiCH/Al) composite with anisotropic microstructure was fabricated by spontaneous infiltration method, and the effect of SiC honeycomb reinforcement on the tribological performance of SiCH/Al composite in axial and radial directions was investigated. The SiC particle reinforced Al (SiCP/Al) composite with the same SiC content was prepared as a counterpart to reveal the effect of SiC reinforcement architecture on the tribological performance of the Al-matrix composites. Compared with the SiCH/Al composite in radial direction and the SiCP/Al composite, the SiCH/Al composite in axial direction shows the highest thermal conductivity of 140.96 W m−1 K−1 and hardness of 97.14 H V, which hinder the formation of oxidative wear and eroding of counter ball. Additionally, a mechanical mixed layer can be formed on the worn surface of SiCH/Al composite in axial direction during the friction process. As a consequence, the SiCH/Al composite in axial direction exhibits the optimal tribological performance with the lowest averaged friction coefficient (0.53) and wear rate (0.98 mm3 N−1 m−1). The results indicate that the SiC honeycomb reinforcement is a promising candidate to improve the tribological performance of metal-matrix composites, especially in their axial direction.

This study investigated effects of initial deviatoric stress state and the orientation of their major principal stresses on the strain components and shear strength of soft marine clay. Hollow cyli...

This work reports the behavior of annealed commercially pure cold-drawn thin iron wires. Primary recrystallization is complete after holding for 180 s at 1123 K. After recrystallization, grain growth takes place within the central region but not close to the surface. For annealing times up to 14400 s, the grain size distribution broadens and the texture strengthens. The resulting texture is intense along the direction parallel to the wiredrawing direction (WD). For longer times, abnormal grain growth takes place. The center of the wire is the preferred place for abnormal grain growth. By contrast, the grains closer to the surface do not experience any growth, and abnormal grains cannot consume them. Throughout the microstructure, one finds AlN and MnS particles. Close to the wire surface, there is a significantly higher particle density than in the center. We discuss mechanisms for the onset of abnormal grain growth, considering particle pinning and crystallographic texture. We observed two kinds of abnormal grains. Most abnormal grains belonged to the // WD fiber texture component, whereas a minority did not. We propose two mechanisms of abnormal grain growth initiation. The first mechanism explains the initiation of the abnormal grains with the assistance of the texture. The second mechanism associates the formation of a candidate abnormal grain to the topological path of the largest grains during normal grain growth preceding the onset of abnormal grain growth.

Uni-modal, not bi-modal, of abnormal grain growth has been observed in (111) oriented and nano-twinned Cu films. Because of the highly anisotropic microstructure, our kinetic analysis and calculation showed that it is the mobility which dominates the uni-modal growth, in which the lateral growth rate can be two orders of magnitude higher than the vertical growth rate. As a consequence, the abnormal grain growth has been converted from bi-modal to uni-modal.

Human hair keratin (HHK) has been successfully explored as raw materials for three-dimensional scaffolds for soft tissue regeneration due to its excellent biocompatibility and bioactivity. However, none of the reported HHK based scaffolds is able to replicate the strain-stiffening capacity of living tissues when responding to large deformations. In the present study, strain-stiffening property was achieved in scaffolds fabricated from HHK via a synergistic effect of well-defined, aligned microstructure and chemical crosslinking. Directed ice-templating method was used to fabricate HHK-based scaffolds with highly aligned (anisotropic) microstructure while oxidized dopamine (ODA) was used to crosslink covalently to HHKs. The resultant HHK-ODA scaffolds exhibited strain-stiffening behaviour characterized by the increased gradient of the stress-strain curve after the yield point. Both ultimate tensile strength and the elongation at break were enhanced significantly (~700 kPa, ~170 %) in comparison to that of HHK scaffolds lacking of aligned microstructure or ODA crosslinking. In vitro cell culture studies indicated that HHK-ODA scaffolds successfully supported human dermal fibroblasts (HDFs) adhesion, spreading and proliferation. Moreover, anisotropic HHK-ODA scaffolds guided cell growth in alignment with the defined microstructure as shown by the highly organized cytoskeletal networks and nuclei distribution. The findings suggest that HHK-ODA scaffolds, with strain-stiffening properties, biocompatibility and bioactivity, have the potential to be applied as biomimetic matrices for soft tissue regeneration. Agency for Science, Technology and Research (A*STAR) This research is supported by the Agency for Science, Technology and Research (A*STAR) under its Acne and Sebaceous Gland Program & Wound Care Innovation for the Tropics IAF-PP (H17/01/a0/008 & H17/01/a0/0L9).

Ni-rich NiTi alloy was successfully fabricated for the first time using wire arc additive manufacturing (WAAM) technique. The distinct anisotropic microstructure with increased amount of Ni4Ti3 but decreased amount of Ni3Ti from lower to upper region leads to obviously decreasing transformation temperature, increasing hardness and tensile strength but reduced ductility.

Measurement and control of stress in the metal forming layer is the basic problem of selective laser melting (SLM) forming parts. The critical refraction longitudinal (LCR) wave method to test stress in metallic materials has been extensively studied. However, when testing of stress in selective laser melting (SLM) forming parts using this method, some deep-seated regularities of this technology are still not clear. In order to reveal the mechanism of the LCR wave method to measure stress in SLM forming parts, specimens made of 316 L stainless steel were manufactured using meander, stripe, and chessboard scanning strategies. Static load tensile test were applied to SLM forming specimens, with the purpose to demonstrate the scanning strategy has important effect on the LCR wave method to test stress in SLM forming parts. The regularity of the LCR wave velocity on stress is obtained in this study. The anisotropic microstructure of SLM forming parts has an unneglectable effect on the LCR wave stress test. The essential principle of anisotropic microstructure effecting the LCR wave velocity in SLM forming parts were revealed in the experiments. The results of the experiment provide a basis for non-destructive and reliable test of stress in SLM forming parts and other inhomogeneous materials.

Due to the intrinsic nature of a heterogeneous and anisotropic microstructure of cement based materials and the small indentation size, the measured microhardness values are subject to considerable variability. This work presents an in-depth assessment of microhardness of hardened cement pastes (HCPs) from a statistical perspective. Hundreds of microhardness measurements were conducted on an HCP sample using a Vickers Microhardness Tester. The results showed that the microhardness measured from the HCP sample significantly scattered with a large standard deviation, varying from tens to hundreds. The data-set of microhardness values was not normally distributed but fit best with a three-parameter lognormal model. By using a statistical software, the probability density function of the microhardness distribution can be readily obtained. The arithmetic mean and its 95% confidence intervals of the measured microhardness values can be used to best represent the microhardness characteristics of HCPs.

High-speed photography was used to record metal transfer during double-wire pulsed gas metal arc welding (GMAW) in the synchronous, alternating and independent phases, while the voltage and current waveforms were recorded simultaneously. According to the relationships between voltage, current, and metal transfer, the effect of phase on the behavior of metal transfer was analyzed. The experimental results demonstrated that metal transfer was all a “one drop per pulse” (ODPP) spray transfer mode in the three phases. ODPP was easier to achieve and metal transfer was more stable in the alternating phase. The deviation distance of droplets in the synchronous phase was larger than that in the alternating and independent phases, and the deviation distance of droplets in the alternating phase was minimum. The surfaces of weld beads acquired showed a desirable weld bead appearance that resembled fish scales. The weld bead in the alternating phase exhibited more obvious fish scales. Phase had little effect on weld width and reinforcement, though it had a significant effect on penetration. Penetration in the alternating phase was significantly deeper than penetration in the synchronous or independent phases, and penetration was minimum in the synchronous phase. The alternating phase facilitated the growth of columnar grains to be inhibited and the directions of ferrites to be disrupted. The columnar grains were discontinuous and the directions of ferrites were more chaotic in the alternating phase when compared with in the synchronous phase. And the anisotropic microstructure in the independent phase was between the synchronous and alternating phases.

Matsuzaka T., Matsugaki A., Nakano T.. Control of osteoblast arrangement by osteocyte mechanoresponse through prostaglandin E2 signaling under oscillatory fluid flow stimuli. Biomaterials, 279, 121203. https://doi.org/10.1016/j.biomaterials.2021.121203., Anisotropic collagen/apatite microstructure is a prominent determinant of bone tissue functionalization; in particular, bone matrix modulates its anisotropic microstructure depending on the surrounding mechanical condition. Although mechanotransduction in bones is governed by osteocyte function, the precise mechanisms linking mechanical stimuli and anisotropic formation of collagen/apatite microstructure are poorly understood. Here we developed a novel anisotropic mechano-coculture system which enables the understanding of the biological mechanisms regulating the oriented bone matrix formation, which is constructed by aligned osteoblasts. The developed model provides bone-mimetic coculture platform that enables simultaneous control of mechanical condition and osteoblast-osteocyte communication with an anisotropic culture scaffold. The engineered coculture device helps in understanding the relationship between osteocyte mechanoresponses and osteoblast arrangement, which is a significant contributor to anisotropic organization of bone tissue. Our study showed that osteocyte responses to oscillatory flow stimuli regulated osteoblast arrangement through soluble molecular interactions. Importantly, we found that prostaglandin E2 is a novel determinant for oriented collagen/apatite organization of bone matrix, through controlling osteoblast arrangement.

The effect of rolling and annealing on microstructures and mechanical properties of V-Ti-Ni alloy for hydrogen separation has been investigated in this work. The rollability of the heat treated alloy is better than that of the as-cast alloy. The microstructure resulting from different processing conditions has a significant influence on hardness. Rolling formed anisotropic microstructures and preferential orientation and resulted in dislocation and hardness increasing. Annealing at elevated temperature can reduce hardness, and eliminate the anisotropic microstructure and reduce dislocation caused by rolling deformation, is positive for hydrogen permeability. The present work has illustrated that rolling and the subsequent annealing may be effective and useful for the fabricating of the high hydrogen flux and permeability V-Ti-Ni alloy membranes.

International audience

We study a three-dimensional, incompressible, viscous, micropolar fluid with anisotropic microstructure on a periodic domain. Subject to a uniform microtorque, this system admits a unique nontrivial equilibrium. We prove that when the microstructure is inertially oblate (i.e. pancake-like) this equilibrium is nonlinearly asymptotically stable. Our proof employs a nonlinear energy method built from the natural energy dissipation structure of the problem. Numerous difficulties arise due to the dissipative-conservative structure of the problem. Indeed, the dissipation fails to be coercive over the energy, which itself is weakly coupled in the sense that, while it provides estimates for the fluid velocity and microstructure angular velocity, it only provides control of two of the six components of the microinertia tensor. To overcome these problems, our method relies on a delicate combination of two distinct tiers of energy-dissipation estimates, together with transport-like advection-rotation estimates for the microinertia. When combined with a quantitative rigidity result for the microinertia, these allow us to deduce the existence of global-in-time decaying solutions near equilibrium.

Research on Laser Powder Bed Fusion (L-PBF) of Al alloy powders increased exponentially over the last decade, and Al powders have become the third most studied metal alloy composition for L-PBF. This study evaluates the trends of the literature in this field to understand which material properties, process properties, and as-built part properties were decisive and of interest for L-PBF processing within the last decade. Even though the effect of the powder properties is often not discussed in detail within the studied 100 referenced Sci-Index articles, it was found that the use of particulate additives in Al powders overcame the main processing and metallurgic problems, such as anisotropic microstructure, segregations, and crack formation in the as-built parts during L-PBF. By quantifying related statistics and extracting data from the studied articles, it is found that powder size ranges of Al feedstock powders overlap in a narrower size range. AlSi10Mg is the most studied alloy; it is a eutectic Al composition that avoids the problems associated with resolidification in L-PBF. The latest research trends focused on additives for grain refinement to improve the mechanical properties and to avoid crack sensitivity in the as-built Al-Zn-Mg-(Cu) and Al-Cu-Mg parts. Additives are found to be promising to industrialize new Al alloy compositions in L-PBF. A Principle Component Analysis is carried out to determine the correlation between reported material, process, and as-built part properties.

LTCC films with thickness of 130 μm were cast on the alumina substrate and the free and constrained sintering behavior was measured by utilizing an optical dilatometer. It was found that constrained films started to densify at a low temperature of 720 °C. The apparent activation energies for free and constrained films were calculated through densification data obtained in the constant-heating-rate experiment. Of particular notice, with increasing density, the activation energy for constrained films decreased from 690 kJ/mol to 359 kJ/mol, whereas a relatively fixed value of 530±30 kJ/mol was yielded for the freely sintered ones. The final density for constrained films was lower than that of the free ones, which could be attributed to the constraint from the substrate. Moreover, anisotropic microstructure was evolved in the constrained film with the increase of density and elongated pores were more prone to align parallel to the substrate.

Recent years have witnessed a surging growth in developing anisotropic hydrogels. Particularly, a new type of microfiber-based anisotropic hydrogel has emerged by transforming nature's existing anisotropic soft materials into hydrogels. For example, wood-based hydrogels feature crosslinked networks serving as the matrix with stiffer micro-sized cellulose bundles as the reinforcement. These anisotropic hydrogels resemble the anisotropic microstructure of living organisms and hold promise for broad applications. Despite its promising outlook, well-formulated mechanical models remain unavailable for microfiber-reinforced anisotropic hydrogels. The existing constitutive models are limited to simplified fiber configurations, making them only suitable for anisotropic hydrogels with macro-sized fibers but inadequate to capture complex microfiber distribution. Moreover, in sharp contrast to the nonlinear behavior of cellulose microfibers in wood-based hydrogels, fibers in most existing models are usually linear-elastic. Aiming to address this deficiency, we have established a micromechanical constitutive model suitable for microfiber-reinforced anisotropic hydrogels. Fiber distributions are included in the proposed constitutive model, which makes possible the investigation of various fiber reinforcement configurations. We explore several important anisotropic mechanical behaviors of the microfiber-reinforced hydrogel, including the anisotropic swelling, and anisotropic stress-strain relation in uniaxial tensile loading. More importantly, we apply the present model to analyze the performance of a humidity-sensitive actuator based on a bilayer of wood-based hydrogel and polyimide. The proposed constitutive model may promote theoretical understandings on the mechanical properties of anisotropic hydrogels and anisotropic-hydrogels-based soft machines.

Due to their hexagonal closed-packed (HCP) crystal structure, magnesium (Mg) and its alloys typically exhibit strong plastic anisotropy which gives rise to their orientation-dependent mechanical properties. Tribological performance in terms of friction and wear is of critical importance to manufacturing and applications of Mg alloys, particularly for components subjected to sliding motion. However, anisotropic microstructure evolution of Mg alloy and its effects on friction and wear properties have rarely been investigated. In this study, the orientation-dependent microstructure behaviors of an AZ31B Mg alloy during dry sliding were investigated. The coefficient of friction (COF) and wear rate of worn surfaces were analyzed and compared. The results indicated pronounced anisotropic friction and wear behaviors. The mechanism responsible for the anisotropic tribological behaviors was discussed.

Scaffold nanotopography plays the most significant role in the mimicry of the in vivo microenvironment of the hepatocytes. Several attempts have been made to develop methods and substrates suited to growing hepatocytes into aggregates. Functional biomaterials, particularly biodegradable polymers, have been used in several studies aimed to develop improved scaffolds with ordered geometry and nanofibrous architecture for tissue engineering. However, there are still some limitation in their fabrication: it is not cost-efficient, is time-consuming, and exhibits some technological complications. The synthetic scaffolds are usually non-biodegradable and can be non-biocompatible compared to the naturally derived biomaterials. Here, we utilized a simple, cost-effective, and green method with two-step chemical treatment to get more selected hydrophilic butterfly wings from Morpho menelaus, Papilio ulysses telegonus, and Ornithoptera croesus lydius as a chitin-based natural scaffolds to growing hepatocyte aggregates. We established a three-dimensional (3D) in vitro model for culture of HepG2 cells and aggregate formation that maintained the hepatocytes function on these natural anisotropic microstructures. Cells cultured on these substrates show higher viability than those cultured on a two-dimensional (2D) culture plate. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay results revealed excellent viability of HepG2 cells on P. u. telegonus wings (fibrous area). The results also demonstrated appropriate cell activity, cell retention, and stable and functional expression in terms of albumin secretion and urea synthesis activity compared to the 2D monolayer culture of hepatocytes on the culture dish surface. With a slightly different degree, the other substrates also shown similar results. We anticipate that these natural anisotropic, biodegradable, and biocompatible substrates can maintain long-term hepatic culture as an in vitro 3D model for potential therapeutic applications and regenerative tissue applications. The model presented here provides a feasible alternative to the synthetic scaffolds and is expected to be more reliable for 3D organotypic liver culture models based on such scaffolds.

LTCC films constrained by rigid substrate were sintered at different temperatures ranging from 760 °C to 800 °C. An optical dilatometer together with a rocking arm was employed to record sintering strains of the constrained films during the sintering process. The densification behavior of constrained films was systematically studied through the measured sintering strains by comparing with that of freely sintered films. For the constrained films, the final density was smaller and the activation energy for the densification was larger than that of the freely sintered ones. Moreover, anisotropic microstructure was induced by the tensile stress.

International audience; Following the ban of its use in brake linings, asbestos has been replaced by various materials based on industrial feedback and trial and error, but without any real understanding of how it affects contact during braking. As copper too will be prohibited in a few years' time, we set out to study the influence of one of its alloys, namely brass. A simplified brass-containing material was developed for this purpose. This material has an anisotropic microstructure and consequently exhibits anisotropic mechanical behavior and increased thermal diffusivity. It displays good tribological behavior at moderate and high temperatures. A surface analysis shows that the contact area is very effective at trapping third bodies and developing secondary plateaus, which provide good conditions for stabilizing friction to a high degree, even at high temperatures.

B 4 C matrix composites containing 0.5–10 vol% carbon nanotubes (CNTs) were fabricated by hot-pressing using Al additive and the effects of CNT addition on mechanical and thermal properties of the B 4 C/CNT composites were investigated for improvement of control material of fission reactors. Bulk densities of the composites decreased with increasing the amount of CNT. The CNTs in the composites were orientated slightly perpendicular to the hot-pressing direction and the anisotropic microstructure was formed. Vickers hardness and elastic modulus of the composites decreased with an increase in the amount of CNT. Fracture toughness of the composites was slightly improved by CNT addition, and at high CNT contents, bridging by CNT was observed in the cracks. Thermal conductivities of the composites increased slightly as compared with those of B 4 C without CNT. However, clear improvement effect by the CNT addition on the thermal conductivities of the composites was not observed within the evaluated compositions.

Due to the potentially anisotropic microstructure of bread dough, the pre-test deformation produced during the making of the specimens significantly affects the rheological properties of dough, and the resistance to deformation is increased. Some new experimental results for JANZ dough are reported in this paper. Lubricated compression tests have been made up to medium-size (order 1) Hencky strains, and we find that the stress response given by the compression test is consistent with the one given by the spherical bubble test if pre-strain is taken into account. Therefore a damage function model can be successfully used to describe the rheological behaviour of the dough for elongation, compression and biaxial stretching. The Mooney–Rivlin term in the model is very important for the biaxial stretching, but not for elongation and shear. The damage function used in compression is the same as that used in elongation and shear, when computed using the maximum positive Hencky strain in all cases. Thus the deformation mode does not make the damage function change; it depends only on the dough variety. Good agreement between the experimental data and the predictions given by the model is observed.

When self-pressurized containers, or aerosols, are accidentally dropped they are susceptible to puncture. The likelihood of puncture depends on the distance of the fall, the nature of the object that the aerosol might strike, the orientation of the impact, and the aerosol’s materials of construction, including microstructure. Due to the flammable nature of the propellants common to aerosols as well as other flammable contents, the accidental puncture of an aerosol has on occasion resulted in significant personal injury and property damage. While the Department of Transportation regulates several aspects of aerosol containers, there are no government regulations concerning puncture resistance. Likewise, there are no standard tests for the puncture resistance of aerosol containers. This article presents two different test methods that can be used to quantify the puncture resistance of aerosol containers. One mode of puncture is not a pure puncture, but rather an impact-induced circumferential puncture or crack. This is due to the anisotropic microstructure of the body material of most 3-piece steel aerosol containers. Experimental testing has shown that the most common type of aerosol container is highly vulnerable to impact-induced impact circumferential puncture. Free falls from a little as 20.32 cm (8 in.) onto wood pyramids are able to induce this type of puncture. This is a hidden and unexpected vulnerability inherent in most 3-piece steel aerosol containers. Experimental tests show that this susceptibility to impact-induced circumferential puncture as well as pure puncture can be greatly reduced, if not eliminated, by using container bodies with more isotropic microstructures.

Bone possesses many functions because of its well-organized hierarchical structure at various levels. Original intact bone exhibits specific anisotropic biological apatite (BAp) crystallite orientation that is closely related to the arrangement of collagen fibrils. Preferential alignment of anisotropic BAp crystallites/collagen fibrils in typical cortical and spongy bones, for example, changes depending on the bone shape, in vivo stress distribution, and bone turnover. The preferential alignment of the BAp c-axis, in particular, tends to orient along the stress distribution in the original bones, indicating bone mechanical anisotropy.

Additive manufacturing (AM) processes have the ability to build complex geometries from a wide variety of materials. A popular approach for metal-based AM processes involves the deposition of material particles on a substrate followed by fusion of those particles together using a high intensity heat source, e.g.a laser or an electron beam, in order to fabricate a solid part. These methods are of high priority in engineering research, especially in applications for the energy, health, and defense sectors. The primary reasons behind the rapid growth in interest for AM include: (1) the ability to create complex geometries thatare otherwise cost-prohibitive or difficult to manufacture, (2) increased freedom of material composition design through the adjustment of the elemental ratios of the composing powders, (3) a reduction in wasted materials, and (4) fast, low-volume, production of prototypeand functional parts without the additional tooling and die requirements of conventional manufacturing methods. However, the highly localized and intense nature of these processes elicits many experimental and computational challenges. These challenges motivate a strong need for computational investigation, as does the need to more accurately characterize the response of parts built using AM. The present work will discuss these challenges and methods for creating multiscale material models that account forthe complex phenomena observed in additively manufacturedproducts. The linkage between process, structure, and property of AM components, e.g., anisotropic plastic behavior combined with anisotropic microstructural descriptors afforded through enhanced data compression techniques, will also be discussed.

This paper reviews the available literature on computational modelling in two areas of bone biomechanics: fracture and healing. Bone is a complex material, with a multiphasic, heterogeneous and anisotropic microstructure. The processes of fracture and healing can only be understood in terms of the underlying bone structure and its mechanical role. Bone fracture analysis attempts to predict the failure of musculoskeletal structures by several possible mechanisms under different loading conditions. However, as opposed to structurally inert materials, bone is a living tissue that can repair itself. An exciting new field of research is being developed to better comprehend these mechanisms and the mechanical behaviour of bone tissue. One of the main goals of this work is to demonstrate, after a review of computational models, the main similarities and differences between normal engineering materials and bone tissue from a structural point of view. We also underline the importance of computational simulations in biomechanics due to the difficulty of obtaining experimental or clinical results.