A coupled interface-multilayer approach for mixed mode delamination and contact analysis in laminated composites

An accurate laminate model developed by using multilayer shear deformable plate modeling and interface elements, based on fracture mechanics and contact mechanics, is proposed to analyze mixed mode delamination in composite laminates. Perfect adhesion along the undelaminated portion of the delamination plane is simulated by treating interface stiffnesses as penalty parameters, whereas to enforce interface displacement continuity between plate elements constituting each sub-laminate above or below the delamination plane, the Lagrange multiplier method is used. The governing differential equations are derived through a variational procedure by using a modified total potential energy functional. Results are obtained by numerical integration of the non-linear three-point boundary value problem modeling mixed-mode delamination of the laminate plate subjected to end loading, which accounts also for the frictionless contact condition.The coupling of a penalty procedure with the Lagrange multiplier method, results in an accurate and direct energy release rate evaluation. Comparisons with results available from the literature obtained with a local continuum approach, show that mode partition may be performed to the desired accuracy by refining multilayer plate models for each sub-laminate. In addition, original analytical formulas for mode partition are obtained by coupling the interface approach and fracture mechanics concepts, evidencing the effectiveness of the proposed approach and gaining a better insight into the influence of shear effects on mode decomposition. Numerical computations for practical problems, evidence both the relative simplicity and the efficiency of the proposed model to represent mixed mode interlaminar fracturing as well as crack–face interaction.     

A continuum damage model for delaminations in laminated composites

Delamination, a typical mode of interfacial damage in laminated composites, has been considered in the context of continuum damage mechanics in this paper. Interfaces where delaminations could occur are introduced between the constituent layers. A simple but appropriate continuum damage representation is proposed. A single scalar damage parameter is employed and the degradation of the interface stiffness is established. Use has been made of the concept of a damage surface to derive the damage evolution law. The damage surface is constructed so that it combines the conventional stress-based and fracture-mechanics-based failure criteria which take account of mode interaction in mixed-mode delamination problems. The damage surface shrinks as damage develops and leads to a softening interfacial constitutive law. By adjusting the shrinkage rate of the damage surface, various interfacial constitutive laws found in the literature can be reproduced. An incremental interfacial constitutive law is also derived for use in damage analysis of laminated composites, which is a non-linear problem in nature. Numerical predictions for problems involving a DCB specimen under pure mode I delamination and mixed-mode delamination in a split beam are in good agreement with available experimental data or analytical solutions. The model has also been applied to the prediction of the failure strength of overlap ply-blocking specimens. The results have been compared with available experimental and alternative theoretical ones and discussed fully.     

Asymptotic fields in the finite element analysis of electrically permeable interface cracks in piezoelectric bimaterials

Summary The interface crack problem for a piezoelectric bimaterial based on permeable conditions is studied numerically. To find the singular electromechanical field at the crack tip, an asymptotic solution is derived in connection with the conventional finite element method. For mechanical and electrical loads, the complex stress intensity factor for an interface crack is obtained. The influence of the applied loads on the electromechanical fields near the crack tip is also studied. For a particular case of a short crack with respect to the bimaterial size, the numerical results are compared with the exact analytical solutions, obtained for a piezoelectric bimaterial plane with an interface crack.One author (V.G.) gratefully acknowledges the support provided by the Alexander von Humboldt Foundation of Germany.accepted for publication 7 June 2004     

电催化剂设计中表面和界面工程的最新进展

电催化已发展为一种涉及电化学、表面科学、材料科学和催化科学等众多科学分支的交叉学科和综合技术,在工农业生产、经济和国防建设、能源开发和环境保护等方面发挥了不可或缺的作用。金属纳米催化剂的可控合成和创新构建,极大地推动了电催化的广泛应用和巨大进展。过渡金属尤其是贵金属Pt、Pd等电催化剂,在电催化中表现出良好的选择性、活性和稳定性,很难完全被其他材料所取代。制约电催化可持续发展的瓶颈问题是,如何设计、合成和构建高性能低成本的金属纳米催化剂。为实现这一目标,人们付出了大量的努力并取得了一些可喜的进展。电催化是发生在电解质与电极材料表面和界面的异相催化反应,金属纳米电催化剂的性能与其形貌、结构、尺寸和组成相关。本文着力总结和探讨如何从表面工程和界面工程角度设计、合成和构筑金属纳米结构及其复合结构,以实现金属电催化剂性能和成本的双优化。本文提出了在金属纳米结构及其复合结构的设计、合成和构筑过程中需要考虑的几个重要的表面和界面因素,即表面面积、表面晶面、活性位点和界面结构等。首先,有效表面面积越大,越有利于电催化反应。我们总结了增大催化剂有效活性面积的四种有效方法,包括减小颗粒尺寸、制成薄层二维纳米结构、增大粗糙度、形成中空、多孔或介孔及框架结构等。其次,表面晶面也可决定电催化的性能。我们简单总结了低指数晶面和高指数晶面在表面能、晶面形成和催化活性上的“挑战与机遇”矛盾关系,并简要阐述了晶面选择性即晶面效应以及晶面与尺寸的依赖关系。再次,活性位点一般指的是低配位表面原子位点,是电催化反应的决定因素之一。我们描述了活性位点与表面和界面结构特征、纳米晶表面晶面、表面缺陷和空穴、表面面积和粒子尺寸等的依赖关系。最后,界面结构工程是调控电催化性能的最丰稔因素。我们简述了界面结构的形成、分类及其对优化界面活性位点的成分和几何结构、表面悬键和原子配位数、电子结构与电子传递、质子传输和物种交换等方面调控作用,并在界面工程的基础上推介了贵金属基复合结构的合成、组装的几种典型方式。本文以具体示例的形式,分别从表面工程和界面工程的角度,扼要介绍了本课题组最近在甲酸氧化、氧还原、析氢等电催化反应体系中贵金属基纳米结构及其复合纳米结构电催化剂的设计、合成与构筑的具体做法。我们分别介绍了低指数晶面和高指数晶面的表面设计对于提高催化剂性能的关键作用。对于低指数晶面,我们重点介绍了如何获得相似尺寸的不同表面晶面以研究其晶面效应,如何维持相同晶面调节尺寸以研究其尺寸效应,如何建造与电极有良好电学接触的低指数晶面纳米结构,以利于提升其电催化性能。对于高指数晶面,介绍了几种形成高指数晶面的途径,并阐明了其晶面对电催化性能的影响。另一方面,我们从金属纳米结构及其复合结构的成分和结构调控策略介绍了界面构建对于提升电催化性能的奇妙作用,包括建造多金属纳米结构、与二维材料负载组装和利用界面极化。由此,本文总结了表面和界面工程对于电催化剂设计、合成和构筑目前面临的三个关键挑战。     

Green’s functions for anti-plane deformations of a circular arc-crack at the interface of piezoelectric materials

Summary The anti-plane deformation problem of an interfacial debounding crack between a circular piezoelectric inclusion and a piezoelectric matrix is investigated by means of the complex variables method. For a line load applied within the matrix or inside the inclusion, Greens functions are presented for the complex potentials, intensity factors and electric fields on the crack faces, respectively, in closed and explicit form. The solutions are valid for both permeable and impermeable crack models. It is shown that, in the general case of permeable cracks, the electric field singularity is always proportional to the stress singularity.The first author (C.F.Gao) would like to express his gratitude for the support of the Alexander von Humboldt Foundation (Germany).     

Slip pulse along an interface between two anisotropic elastic half-spaces in sliding contact with separation

The Stroh sextic formalism, together with Fourier analysis and the singular integral equation technique, is used to study the propagation of a possible slip pulse in the presence of local separation at the interface between two contact anisotropic solids. The existence of such a pulse is discussed in detail. It is found that the pulse may exist if at least one medium admits Rayleigh wave below the minimum limiting speed of the two media. The pulse-propagating speed is not fixed; it can be of any value in some regions between the lower Rayleigh wave speed and minimum limiting speed. These speed regions depend on the existence of the first and second slip-wave solutions without interfacial separation studied by Barnett, Gavazza and Lothe (Proc. R. Soc. Lond. 1988, A415, 389–419). The pulse has no free amplitude directly but involves the arbitrary size of the separation zone that depends on the intensity of the motion. The interface normal traction and the particle velocities involve a square-root singularity at both ends of the separation zones that act as energy source and sink.     

Effect of interface stress on the fracture behavior of a nanoscale linear inclusion along the interface of bimaterials

This paper investigates the influence of residual interface tension on the fracture behavior of a nanoscale linear interface inclusion in a bimaterial matrix. Solutions to the inclusion opening displacement and the energy release rate are obtained. The results show that the interface effect on the inclusion deformation and inclusion tip field are prominent at nanoscale. Especially, the residual interface stress has a dramatic influence on the energy release rate. It is also found that the importance of the interface effect depends on the size of the inclusion, the shear modulus ratios of the bimaterial. The inclusion opening displacement and the energy release rate can be reduced considerably by decreasing the inclusion length at nanoscale.     

CORRELATION AMONG MORPHOLOGY,INTERFACE, AND MECHANICAL PROPERTIES: EXPERIMENTAL STUDY

The effect of the disperse phase and the diffuse interface between phases on the tensile and impact strengths of polypropylene (PP)/poly(ethylene terephthalate) (PET) (75/20 by weight) blends compatibilized with maleic anhydride–grafted PP derivatives and on the tensile modulus of poly(vinyl chloride)/polystyrene (PVC/PS) nanoparticle blends compatibilized with polystyrene/poly(vinyl acetate) (PS/PVAc) block copolymers were investigated experimentally. The weight fraction of the diffuse interface between the PP and PET phases in the PP/PET blends was determined by modulated differential scanning calorimetry (MDSC). A correlation between the diffuse interface content and mechanical properties was found. With increasing diffuse interface weight fraction, the impact and tensile strengths of the PP/PET blends increased. There is a brittle-tough type transition in these PP/PET blends. With increasing diffuse interface content in the PVC/PS nanoparticle blends in which the particle size was fixed at about 100 nm, the tensile modulus also clearly increased.     

A Fully Amorphous,Dynamic Cross-Linked Polymer Electrolyte for Lithium-Sulfur Batteries Operating at Subzero-Temperatures

Solid-state lithium-sulfur batteries have shown prospects as safe, high-energy electrochemical storage technology for powering regional electrified transportation. Owing to limited ion mobility in crystalline polymer electrolytes, the battery is incapable of operating at subzero temperature. Addition of liquid plasticizer into the polymer electrolyte improves the Li-ion conductivity yet sacrifices the mechanical strength and interfacial stability with both electrodes. In this work, we showed that by introducing a spherical hyperbranched solid polymer plasticizer into a Li⁺-conductive linear polymer matrix, an integrated dynamic cross-linked polymer network was built to maintain fully amorphous in a wide temperature range down to subzero. A quasi-solid polymer electrolyte with a solid mass content >90 % was prepared from the cross-linked polymer network, and demonstrated fast Li⁺ conduction at a low temperature, high mechanical strength, and stable interfacial chemistry. As a result, solid-state lithium-sulfur batteries employing the new electrolyte delivered high reversible capacity and long cycle life at 25 °C, 0 °C and −10 °C to serve energy storage at complex environmental conditions.     

Steric-hindrance Effect Tuned Ion Solvation Enabling High Performance Aqueous Zinc Ion Batteries

Despite many additives have been reported for aqueous zinc ion batteries, steric-hindrance effect of additives and its correlation with Zn²⁺ solvation structure have been rarely reported. Herein, large-sized sucrose biomolecule is selected as a paradigm additive, and steric-hindrance electrolytes (STEs) are developed to investigate the steric-hindrance effect for solvation structure regulation. Sucrose molecules do not participate in Zn²⁺ solvation shell, but significantly homogenize the distribution of solvated Zn²⁺ and enlarge Zn²⁺ solvation shell with weakened Zn²⁺−H₂O interaction due to the steric-hindrance effect. More importantly, STEs afford the water-shielding electric double layer and in situ construct the organic and inorganic hybrid solid electrolyte interface, which effectively boost Zn anode reversibility. Remarkably, Zn//NVO battery presents high capacity of 3.9 mAh ⋅ cm⁻² with long cycling stability for over 650 cycles at lean electrolyte of 4.5 μL ⋅ mg⁻¹ and low N/P ratio of 1.5, and the stable operation at wide temperature (−20 °C~+40 °C).