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Yue Shao Hong-Ping Zhao Xi-Qiao Feng Huajian Gao 《Journal of the mechanics and physics of solids》2012,60(8):1400-1419
Studying the structure–property relation of biological materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of advanced biomimetic materials. In this paper, we present a microstructure-based fracture mechanics model to investigate the toughening effect due to the crack-bridging mechanism of platelets. Our theoretical analysis demonstrates the crucial contribution of this mechanism to the high toughness of nacre. It is found that the fracture toughness of nacre exhibits distinct dependence on the sizes of platelets, and the optimized ranges for the thickness and length of platelets required to achieve higher fracture toughness are given. In addition, the effects of such factors as the mechanical properties of the organic phase (or interfaces), the effective elastic modulus of nacre, and the stacking pattern of platelets are also examined. Finally, some guidelines for the biomimetic design of novel materials are proposed based on our theoretical analysis. 相似文献
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以乙醇胺为辅助溶剂,采用水热合成法,制备了花状、梭状和剑状的ZnO微纳米结构。采用扫描电镜(SEM)、X射线衍射(XRD)、光致发光光谱(PL)和拉曼光谱等测试手段对样品的形貌、结构、晶相等进行了表征。结果表明所有样品均为六方纤锌矿结构ZnO;其形貌和结晶度可通过改变物质的量的配比nZn2+/nOH-来调控。探讨了反应物配比对产物形貌结构的影响,乙醇胺对不同形貌ZnO的制备起到至关重要作用。以亚甲基蓝为目标降解物,采用紫外-可见吸收光谱(UV-Vis)并结合低温氮吸附-脱附比表面测试(BET),研究了花状、梭状和剑状ZnO的光催化活性。结果表明,与商用ZnO相比,制备的ZnO具有更好的光催化活性;样品催化活性与其比表面积不成正比,具有最小比表面积的花状ZnO拥有最好的光催化活性,这可能是由于其低的结晶度和特殊的花状形貌所致。 相似文献
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Phase transformational shakedown of a structure refers to a status that plastic strains cease developing after a finite number of loading cycles, and subsequently the structure undergoes only elastic deformation and alternating phase transformations with limited magnitudes. Due to the intrinsic complexity in the constitutive relations of shape memory alloys (SMA), there is as yet a lack of effective methods for modeling the mechanical responses of SMA structures, especially when they develop both phase transformation and plastic deformation. This paper is devoted to present an algorithm for analyzing shakedown of SMA structures subjected to cyclic or varying loads within specified domains. Based on the phase transformation and plastic yield criteria of von Mises-type and their associated flow rules, a simplified three-dimensional phenomenological constitutive model is first formulated accounting for different regimes of elastic–plastic deformation and phase transformation. Different responses possible for SMA bodies exposed to varying loads are discussed. The classical Melan shakedown theorem is extended to determine a lower bound of loads for transformational shakedown of SMA bodies without necessity of a step-by-step analysis along the loading history. Finally, a simple example is given to illustrate the application of the present theory as well as some basic features of shakedown of SMA structures. It is interesting to find that phase transformation may either increase or decrease the load-bearing capacity of a structure, depending upon its constitutive relations, geometries and the loading mode. 相似文献
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The present article considers the shakedown problem of structures made of either kinematic or mixed strain-hardening materials. Some basic and useful shakedown properties of elastoplastic strain-hardening structures are proved mathematically. It is impossible for a kinematic strain-hardening structure to be involved in incremental plastic collapse, and so its only possible failure mode is that of alternating plasticity. A time-independent self-equilibrium stress field has no influence on the shakedown of a kinematic strain-hardening structure although it contributes to the magnitude of plastic deformation. The sufficient shakedown conditions for either kinematic or mixed strain-hardening structures are deduced, from which the lower bound of shakedown load domain can be obtained via a mathematical programming problem. It should be pointed out that, to guarantee the safety of an elastoplastic strain-hardening structure, the damage analysis is also necessary to determine the maximum load factor the structure can bear. The shakedown analysis of strain-hardening structures can be simplified by the conclusions obtained in this article, as is illustrated by two simple examples. 相似文献
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Elastocapillary phenomena involving elastic deformation of solid structures coupled with capillary effects of liquid droplets/films can be observed in a diversity of fields,e.g.,biology and microelectromechanical systems(MEMS).Understanding the physical mechanisms underlying these phenomena is of great interest for the design of new materials and devices by utilizing the effects of surface tension at micro and nano scales.In this paper,some recent developments in the investigations on elastocapillary phenomena are briefly reviewed.Especially,we consider the deformation,adhesion,self-assembly,buckling and wrinkling of materials and devices induced by surface tensions or capillary forces.The main attention is paid to the experimental results of these phenomena and the theoretical analysis methods based on continuum mechanics.Additionally,the applications of these studies in the fields of MEMS,micro/nanometrology,and biomimetic design of advanced materials and devices are discussed. 相似文献
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Twisting chirality is widely observed in artificial and natural materials and structures at different length scales. In this paper, we theoretically investigate the effect of twisting chiral morphology on the mechanical properties of elas- tic beams by using the Timoshenko beam model. Particular attention is paid to the transverse bending and axial buckling of a pre-twisted rectangular beam. The analytical solution is first derived for the deflection of a clamped-free beam under a uniformly or periodically distributed transverse force. The critical buckling condition of the beam subjected to its self- weight and an axial compressive force is further solved. The results show that the twisting morphology can significantly improve the resistance of beams to both transverse bending and axial buckling. This study helps understand some phenomena associated with twisting chirality in nature and provides inspirations for the design of novel devices and structures. 相似文献
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Helical nanomaterials with superelasticity have a wide range of promising applications in micro-/nanoelectromechanical systems. Based on the theory of surface elasticity, we present a nonlinear rod model to investigate the superelasticity of nanohelices. Our results demonstrate that the superelasticity of nanohelices exhibits a distinct size dependence due to the increased ratio of surface area to volume. The superelasticity can effectively enhance the efficiency of energy storage and retrieval of nanohelices. This study is helpful for the characterization of the mechanical properties of nanosized helical materials and the optimal design of nanohelix-based devices. 相似文献
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