Tensile fracture of soft and hard PZT

Power applications generate high stresses which can damage piezoceramic components. In this study tensile fracture of several types of PZT (hard/soft) is investigated. After validation of the specimen geometry by means of numerical simulation, samples are led to failure using a specific device. Weibull law parameters enable the characterisation of the tensile strength distribution and highlight clear differences between soft and hard ceramics. A fractographic approach emphasises the specificities of the fracture mode and the fracture origin for each type of samples.     

Novel three-dimensional cocoon-like hydrogels for soft tissue regeneration

Large three-dimensional hydrogels (> 150 cm³) of bacterial cellulose (BC) were synthesized by using Gluconacetobacter hansenii ATCC 23769 under controlled agitated culture conditions. The macroscopic cocoon-like structures are gelatinous and translucent and may find applications in several areas, particularly in tissue and organ engineering. Internal microstructure was investigated by scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM), which revealed that the cocoons are composed of cellulosic nanofibres randomly and three-dimensionally dispersed. The macroscopic bodies are delimited by a dense semi-permeable membrane with thickness between 0.2 and 2 mm, also composed of cellulosic nanofibres. Endothelial cells were seeded on the hydrogels and incubated for 7 days. HUVECs grew and migrated into the inner part of the structure. The three-dimensional BC hydrogel structures can be directly implanted in tissue deficient regions as scaffolds containing the appropriate cultured cells.     

The influence of FeNi nanoparticles on the microstructures and soft magnetic properties of FeSi soft magnetic composites

In this work, a new type of FeSi/FeNi soft magnetic powder core (SMPC) was successfully fabricated by coating FeNi nanoparticles on the surface of FeSi micrometer powder. The effects of different contents of FeNi nanoparticles on the micromorphology, internal structures, and soft magnetic properties of SMPCs were studied. The results show that FeNi nanoparticles adhere to the surface of FeSi powder, which can effectively fill the air gap between FeSi powder and is beneficial to the compaction of the powder cores during the pressing process. Thus, the density of the SMPCs is increased. Compared to FeSi SMPCs, the comprehensive soft magnetic properties of FeSi/FeNi SMPCs have been greatly improved. When adding 15 wt% FeNi nanoparticles, the SMPCs exhibit excellent magnetic properties with high effective permeability (increased by 43.8 %) and low core loss (decreased by 22.1 %). The high performance FeSi/FeNi SMPCs prepared in this work are expected to be widely used in power choke coils, uninterruptible power supplies, and boosts and inverter inductors.     

Stress tensor and elastic properties for hard and soft spheres

Properties determined from the microscopic stress tensor are discussed for the related systems of a steeply repulsive pair potential and hard spheres. The microscopic stress tensors determined from the local conservation law for momentum are different in these two cases. Consequences are discussed for both fluid and solid phases.     

纳米软、硬磁性晶粒间的交换耦合及其有效各向异性

以软磁性相α-Fe和硬磁性相Nd2Fe14B为例,研究了软、硬磁性晶粒间的交换耦合作用和有效各向异性常数〈Ksh〉随晶粒尺寸的变化关系。由于晶粒间的交换耦合作用,晶粒可分为晶粒内部无界面交换耦合作用影响和晶粒表面有界面交换耦合作用影响两部分,其各向异性常数为两部分的统计平均值。计算结果表明：对固定的软磁性晶粒尺寸Ds,〈Ksh〉随硬磁性晶粒尺寸Dh一致增加;对固定的Db,〈Ksj〉随Ds一致减小。为使软、硬磁性晶粒间的有效各向异性常数墨。保持较高的值,应控制硬磁性晶粒大于35nm,软磁性晶粒在10nm左右。     

Integration of on-chip isotachophoresis and functionalized hydrogels for enhanced-sensitivity nucleic Acid detection

We introduce an on-chip electrokinetic assay to perform high-sensitivity nucleic acid (NA) detection. This assay integrates electrokinetic sample focusing using isotachophoresis (ITP) with a background signal-removal strategy that employs photopatterened, DNA-functionalized hydrogels. In this multistage assay, ITP first enhances hybridization kinetics between target NAs and end-labeled complementary reporters. After enhanced hybridization, migration through a DNA-functionalized hydrogel region removes excess reporters through affinity interactions. We demonstrate our assay on microRNAs, an important class of low-abundance biomarkers. The assay exhibits 4 orders of magnitude dynamic range, near 1 pM detection limits starting from less than 100 fg of microRNA, and high selectivity for mature microRNA sequences, all within a 10 min run time. This new microfluidic framework provides a unique quantitative assay for NA detection.     

Analysis of drilling failure in soft and hard sandwiching of coal seam

The severe abrasion of drill bits will be confronted during drilling in soft and hard sandwiching of coal seam. Not only does this failure result in the increasing consumption of bits, but also it delays the construction period, significantly extending the duration of the delay, even causing borehole instability, resulting in a catastrophic buried well accident. In order to reveal the failure causes, the authors of this paper researched the wear properties of the tooth of bit. As the thermal damage is one of the main threats to drilling failure in soft and hard sandwiching, thermal related effects on the wear performance of polycrystalline diamond compacts (PCD) were studied by an Amsler friction and wear testing machine. Meanwhile, silica sands were added to the interface of wear couples throw a funnel instrument to meet the demand that wear conditions correspond more closely to those in actual coal seam drilling. The friction coefficient and wear rates was measured. The X-ray diffraction analysis was used to investigate the chemical composition and crystal structure of the PCDs soaked at different temperatures. The morphologies of the surface of PCDs were examined by metalloscope and scanning electron microscopy. The results show that the wear rate and wear coefficient all rose with the increase of wear load. So the drilling load over proper operation limits especially when the equipment stuck happened is the primary threat to bit failure. On the other hand, the wear coefficient is not sensitive to the soaking temperature when it is under 700 °C. But it decreases obviously when the temperature was over 800 °C, which seems to be corresponding to the graphitization of diamond and the oxidation of Co. This phenomenon indicates that the high temperature over 700 °C is the main cause of the drilling failure.     

掺磷对硬碳及软碳嵌锂性能的影响研究

为了提高碳材料的嵌锂性能，以沥青和自制的热固性酚醛树脂为原料，制备了掺磷酚醛树脂热解碳和掺磷沥青焦炭，通过充放电实验测量了两种掺磷碳材料的可逆容量，XRD，XPS技术分析了磷的掺杂对碳的组成与结构的影响。结果表明：掺磷使两种碳材料的可逆容量均有明显增加，且磷添加量为20%时增加最显著；磷的掺杂对硬碳的晶格参数无明显影响，而使软碳的石墨化程度下降；酚醛树脂热解碳中的磷主要与碳环相接，少部分同时还与氧相连，而焦炭中的磷则主要与氧成键，且掺磷使焦炭表面氧和氮含量明显增加。     

Mixtures of hard and soft grains: micromechanical behavior at large strains

In this paper, several simulations involving the compaction and the shearing of mixtures of hard and soft grains are performed in 2D plane-strain conditions. The multibody meshfree numerical tool developed for this purpose is first presented, and the focus is then put on the influence of the proportions of rigid and deformable grains in the mixture on the mechanical response at large strains. Dedicated postprocessing techniques reveal a wide range of behaviors, both in terms of macroscopic response and in micromechanical phenomena. Broadly speaking, the strength and the dilatancy of the mixture decrease when the proportion of soft grains is increased. There are, however, interesting exceptions to this trend at very high and very low contents of soft grains, which are analyzed in dedicated sections. This preliminary work paves the way to more comprehensive studies of this class of materials, which is still hardly understood but presents some potential in a wide range of applications.     

交换耦合的纳米软-硬磁性晶粒的有效各向异性常数

以α-Fe、Nd2Fe14B为例,研究了纳米晶粒尺寸对交换耦合的软-硬磁性晶粒各向异性的影响.结果表明,软-硬磁性晶粒的有效各向异性常数〈Ksh〉随软磁性晶粒尺寸Ds的增加而减小,随硬磁性晶粒尺寸Dh的增加而增大.当Ds/Dh为固定值且1/1.1≥Ds/Dh≥1/1.4时,〈Ksh〉在Ds为10～20nm之间取得一极大值.当Dh＞25nm,Ds在10nm左右时,可获得较大的〈Ksh〉.     

交换耦合软/硬磁双层膜体系磁动力学性质的研究

基于Laudau-Lifshitzt方程,在一维原子链模型的框架内研究了交换耦合软/硬磁双层膜体系的磁动力学性质,得到了软磁层在磁反转前处于一致磁结构和交换弹性磁反转过程中处于螺旋磁结构时的本征自旋波模式的频率及其空间分布特点,以及自旋波色散关系曲线。研究表明,软磁层的反磁化机制与自旋波的软模现象有密切关系,一阶自旋波模式的软化诱导了软磁层的磁反转,且磁反转的形式与一阶自旋波模式的空间分布状态相关。由磁动力学方法得到的磁反转临界场与近似的解析解得到的结果一致。     

Multiple diffraction of plane waves by a soft/hard strip

A uniform asymptotic high-frequency solution is developed for the problem of diffraction of plane waves by a strip which is soft at one side and hard on the other. The related three-part boundary value problem is formulated into a modified matrix Wiener-Hopf equation. By using the known factorization of the kernel matrix through the Daniele-Khrapkov method, the modified matrix Wiener-Hopf equation is first reduced to a pair of coupled Fredholm integral equations of the second kind and then solved by iterations. An interesting feature of the present solution is that the classical Wiener-Hopf arguments yield unknown constants which can be determined by means of the edge conditions.Also with Tübitak Marmara Research Center, Department of Mathematics, 41740 Gebze, Kocaeli, Turkey     

Controlled two-photon photodegradation of PEG hydrogels to study and manipulate subcellular interactions on soft materials

Cell adhesion and detachment to and from the extracellular matrix (ECM) are critical regulators of cell function and fate due to the exchange of mechanical signals between the cell and its microenvironment. To study this cell mechanobiology, researchers have developed several innovative methods to investigate cell adhesion in vitro; however, most of these culture platforms are unnaturally stiff or static. To better capture the soft, dynamic nature of the ECM, we present a PEG-based hydrogel in which the context and geometry of the extracellular space can be precisely controlled in situ via two-photon induced erosion. Here, we characterize the two-photon erosion process, demonstrate its efficacy in the presence of cells, and subsequently exploit it to induce subcellular detachment from soft hydrogels. A working space was established for a range of laser powers required to induce complete erosion of the gel, and these data are plotted with model predictions. From this working space, two-photon irradiation parameters were selected for complete erosion in the presence of cells. Micron-scale features were eroded on and within a gel to demonstrate the resolution of patterning with these irradiation conditions. Lastly, two-photon irradiation was used to erode the material at the cell-gel interface to remove cell adhesion sites selectively, and cell retraction was monitored to quantify the mesenchymal stem cell (MSC) response to subcellular detachment from soft materials.     

Glass-ceramics with random and oriented microstructures

The variation of a number of physical properties of a glass-ceramic composition as a function of the crystallization heat-treatment temperature are reported. The properties studied include mechanical strength, modulus of elasticity, electrical properties and linear coefficient of thermal expansion. It is shown that several of the properties are dependent on microstructural effects. This dependence is especially marked for modulus of rupture and is also apparent for electrical properties such as conductivity and loss tangent. For the latter, however, compositional changes in the residual glass phase also exert a significant influence. For other properties, such as indentation hardness, the microstructural dependence is less well defined.     

Glass-ceramics with random and oriented microstructures

The technique of hot extruding a glass-ceramic to produce a material with an aligned crystal microstructure is described. The results of a statistical investigation to analyse the degree of morphological orientation of an extruded glass-ceramic based on the Li₂O-SiO₂ system are reported. Details are also presented of the determination of the crystallographic orientation in the aligned glass-ceramic.     

Effects of soft hemispherical particle on local surface stress of hard matrix

Abstract

Finite element analysis was performed to investigate the stresses within and around a soft hemispherical particle located on the surface of a hard matrix under a remote external tensile load. The purpose was to understand the effects of neodymium rich particles on the fatigue properties of Ti-55 alloy. Three case studies were considered. First both particle and matrix were perfect, second a crack existed within the particle, and third a crack was located in the matrix adjacent to the particle. Numerical results show that soft particles cause stress concentration in regions of the matrix adjacent to the particle, but that such stress concentrations are much weaker than those associated with a cavity. A crack within the particle increases the stress concentration in the matrix only a little when the crack is far from the interface. However, a crack in the matrix significantly increases local stress in the particle.     

叶片受软体和硬体外物撞击的损伤分析

针对发动机叶片常遭受外物的撞击损伤,不同材料的外物的撞击损伤存在着差别。从能量守恒和基本水动力学的角度分析了软体和硬体撞击叶片时的不同的撞击载荷模型。通过在LS-DYNA中就软体（以明胶为例）和硬体（以砂石为例）外物对叶片的撞击损伤过程进行了数值仿真分析。结果表明：在相同的初始撞击能量、相同的撞击速度及相同的撞击入射角度下,砂石撞击叶片时的撞击接触力幅值较大,但持续时间较明胶撞击时的要短,在撞击瞬间砂石和叶片获得最大的应变能。撞击过程中,由于明胶发生了流变,其对叶片产生的局部损伤比砂石要小。