Determination of the dynamic stress intensity factorsK I d andK II d,for a mixed-mode propagating crack

In this paper, the dynamic propagation problem of a mixed-mode crack was studied by means of the experimental method of caustics. The initial curve and caustic equations were derived under the mixed-mode dynamic condition. A multi-point measurement method for determining the dynamic stress intensity factors,K _I ^d , andK _II ^d , and the position of the crack tip was developed. Several other methods were adopted to check this method, and showed that it has a good precision. Finally, the dynamic propagating process of a mixed-mode crack in the three-point bending beam specimen was investigated with our method.     

Dual-parameter elastic-plastic fracture criterion of metals and alloys in the plane strain case

In recent years, some investigators discussed the applicability of the HRR theory for engineering materials based on the results of numerical analyses and experimental studies. In the present paper, the finite element method is employed to analyze the crack tip fields of the engineering elastic-plastic material with a variety of geometry configurations of cracked specimens from elastic state to intensely general yielded state in the plane strain case. The results indicate that the HRR theory loses its validity of application for engineering elastic-plastic materials in the plane strain case. The reasons for this are analyzed. A dual-parameter fracture criterion is suggested for this case.     

飞机起落架活塞杆断裂原因分析

针对飞机起落架活塞杆在外场使用过程中裂纹失效问题,利用扫描电子显微镜对其断裂面微观形貌进行观察,研究其断裂机理.结果表明:该活塞杆断裂性质为服役过程中循环应力作用下的疲劳断裂.应力使活塞杆件表面出现微裂纹,在其内部形成微孔.随着应力循环次数增加,微孔的数量和大小都不断增加,最终导致了钢的疲劳断裂.通过优化其热处理工艺,使活塞杆获得良好的强韧配比,提高了抗疲劳性能.     

Observation of mechanical fracture and corresponding domain structure changes of polycrystalline PbTiO3 nanotubes

PbTiO₃ (PTO) nanotubes (NTs) were synthesized at various temperatures by gas phase reaction between PbO gas and anatase TiO₂ NTs and characterized by piezoresponse force microscopy (PFM). PTO ferroelectric phase was synthesized at as low as 400 °C as evidenced by PFM domain images and piezoresponse hysteresis loop measurement. Furthermore, the PTO NTs fabricated at above 500 °C underwent mechanical fracture through development of nanocracks due to grain growth, leading to ferroelectric domains with larger size and lower aspect ratio. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Digital image correlation approach to cracking and decohesion in a brittle coating/ductile substrate system

By using a digital image correlation technique, the full/local field strain in a brittle coating/ductile substrate system during tension has been successfully monitored. One of the most important experimental results indicates that the distribution of interfacial shear stress in the segmented coating is antisymmetric about the center, which clarifies several controversial assumptions introduced in theoretical models. Two key mechanical properties of thermal barrier coatings, fracture strength in coating and interfacial adhesion strength, were determined as 35.0 ± 4.6 and 14.1 ± 3.2 MPa, respectively, which are consistent with available experimental data.     

一种钨合金含损伤本构的唯象模型

利用多压阻传感器拉氏实验分析方法对受冲击90w钨合金材料中形成的应力波场进行了测试，并利用拉格朗日分析方法获得的结果建立了合金的不含损伤的本构关系．然后以动态层裂试验获得的层裂参数曲线和数据为依据．提出了一种考虑材料内部损伤成核，成长及汇合效应的唯象本构模型，并通过对层裂实验曲线进行数值模拟，确定了该合金的含损伤本构的参数．     

钽的层裂实验数值模拟

 采用连续介质力学基唯象模型模拟分析了钽的平板撞击层裂行为。该模型包括了材料的非线性弹性（状态方程）、率相关塑性和孔洞的形核及生长等多种效应,并且采用一种对角隐式Runge-Kutta方法来求解本构率方程组,提高了热粘塑性本构关系计算的稳定性及精度。将数值模拟结果和相关实验数据进行了对比分析,结果表明,对于样品中的拉应力峰值明显高于材料层裂强度的实验（中、高速平板撞击实验）,理论模型具有较好的预估能力,但对于临界层裂问题（低速平板撞击实验）,该模型对材料损伤与失效过程的描述可能不够准确,需要进一步改进。     

焦散线法及其与应力“解冻”相结合的应用

详细地阐述了焦散线法原理，对焦散线的形成作了说明，简述了焦散线法在平面问题中的应用，结合笔者研究工作介绍了将焦散线法拓广应用于三维问题的关键技术和实例。     

The effect of time step,thermostat, and strain rate on ReaxFF simulations of mechanical failure in diamond,graphene, and carbon nanotube

As the sophistication of reactive force fields for molecular modeling continues to increase, their use and applicability has also expanded, sometimes beyond the scope of their original development. Reax Force Field (ReaxFF), for example, was originally developed to model chemical reactions, but is a promising candidate for modeling fracture because of its ability to treat covalent bond cleavage. Performing reliable simulations of a complex process like fracture, however, requires an understanding of the effects that various modeling parameters have on the behavior of the system. This work assesses the effects of time step size, thermostat algorithm and coupling coefficient, and strain rate on the fracture behavior of three carbon‐based materials: graphene, diamond, and a carbon nanotube. It is determined that the simulated stress‐strain behavior is relatively independent of the thermostat algorithm, so long as coupling coefficients are kept above a certain threshold. Likewise, the stress‐strain response of the materials was also independent of the strain rate, if it is kept below a maximum strain rate. Finally, the mechanical properties of the materials predicted by the Chenoweth C/H/O parameterization for ReaxFF are compared with literature values. Some deficiencies in the Chenoweth C/H/O parameterization for predicting mechanical properties of carbon materials are observed. © 2015 Wiley Periodicals, Inc.     

水力劈裂问题的态型近场动力学建模

将态型近场动力学理论引入水力劈裂问题的模拟。构建了能反映岩土类材料准脆性断裂特征的态型近场动力学本构模型,并在物质点间相互作用力模型中加入等效水压力项,以实现在新生裂纹面上跟踪施加水压力。同时,考虑裂纹面间的接触,引入物质点间的短程排斥力作用,并设计了相应的接触算法。通过自编程序将模型和算法应用于含初始裂纹、不含初始裂纹以及含坝基软弱结构面的混凝土重力坝在高水头作用下的水力劈裂过程模拟,并与扩展有限元等模拟结果对比,验证了本文模型和算法的可行性和准确性。