动脉壁静态力学性质的实验

生命体材料的力学性质具有其特殊性和复杂性．因而,对其进行力学实验研究也具有从实验设计、实验方法到实验技术的特殊性和复杂性．本文详尽地研究了动脉壁三维静态力学实验的方法和技术：进行了四只白兔颈动脉的静态力学性质实验;得到了性态较好的实验结果     

基于研究性实验的多功能组合式力学实验系统

 主要介绍了一种基于研究性实验开发的多功能组合式力学实验系统的基本原理和功能. 本试验系统可以通过结构形式的自主组合、支座形式的自主选择以及多种加载方式实现多种静定、超静定桁架和刚架结构的力学实验, 操作简单, 功能多样. 并且通过实验验证了本实验系统测试效果的准确性和可靠性. 为学生自主设计综合性、设计性实验提供了一个平台.     

界面不稳定性实验的数值研究

采用多介质流体的三阶精度Piecewise Parabolic Method (PPM) 计算方法对界面不稳定性实验模型进行数值模拟,通过对Lawrence Livermore National Laboratary (LLNL)实验室的果冻环实验模型的数值计算,获得了与其计算和实验图像基本一致的结果, 从而验证和确认了计算方法和计算程序. 在此基础上,对于冲击波物理与爆轰物理实验 室设计的果冻内外界面10模峰对峰、峰对谷振幅为1\,mm扰动的界面不稳定性实验模型,给出 了果冻内外界面位置、速度和加速度历史曲线,详细分析了果冻内外界面不稳定性的发展、 演化过程,并给出了两种实验模型实验结果和对应的数值模拟结果.     

非牛顿流体力学实验的开发

 介绍了在所研制的非牛顿流体力学实验装置上，进行的基础性-提高性-研究性实 验. 基础性实验包括爬杆、射流胀大、无管虹吸演示实验；提高性实验包括流变特性、出口 压力测试实验；在以非牛顿流体润滑脂为例的流变特性实验时，发现存在壁滑移，进行了存 在壁滑移时的流变特性和在管道流动中的壁滑移减阻研究性实验.     

水合物沉积物力学性质的实验装置和研究进展

天然气水合物是一种高效、洁净和储量巨大的新型能源,一般蕴含于砂岩、粘土以及其它土质的沉积物中.对水合物沉积物力学性质的实验研究,是水合物地层中基础稳定性分析和水合物开发评价重要的热点课题之一.本文首先介绍了水合物沉积物合成与分解实验、物性参数测量技术以及力学性质实验装置的主要组成部分和特点,然后介绍了目前国内外在水合物沉积物合成和分解及力学性质实验一体化装置和实验研究两个方面所取得的成果,最后指出在实验装置、测试技术和实验研究方面存在的问题以及今后研究的重点和方向.     

垂直界面裂纹断裂力学问题的实验研究

用实验方法研究了具有垂直界面方向裂纹的界面断裂力学问题．根据实验结果对裂尖区域的奇异性性质、角位移分布、应力强度因子等进行了分析，并将实验结果与理论结果进行了比较和讨论     

45钢的J-C损伤失效参量研究

为了在结构碰撞效应的有限元分析中描述材料行为,通过开展45钢在不同应力状态和温度下的准静态材料力学性能实验及拉伸SHB实验,考察了应力状态三轴度、温度和应变率对材料失效应变的影响。由实验数据得到了Johnson-Cook失效模型参量,并通过出现失效的Taylor撞击实验和数值模拟进行了一定的验证,表明模型描述与实验结果的趋势一致。     

压力容器斜接管区域应力状态的实验研究

压力容器接管区域应力场的获得是压力容器强度分析和结构设计的基础。本文采用实验研究的方法,对压力容器斜接管区域的应力状态进行分析研究。根据实验研究的目的,按照工程设计标准设计、制造了一台大型带有两个斜接管压力容器的实验模型,进行了实验方案设计,采用电测法进行了容器斜接管区域的应力测试,在实验数据科学、合理处理的基础上,获得了容器斜接管区域的应力状态和分布规律。实验研究结果表明,容器斜接管锐角侧、钝角侧和相贯线最低点都存在着较大的局部应力,且锐角侧的局部应力数值最大,但是相贯线上的局部应力影响范围较小。     

结构力学虚拟仿真实验教学研究

基于结构力学实验,应用Flash开发系统建立了结构力学实验的虚拟实验环境和虚拟实验物理的模型.通过将实验对象的数学模型引入到虚拟实验对象状态控制程序的方法,实现了对结构力学虚拟实验对象的实时判断和实际数据库的动态链接,使虚拟实验系统具有完好的交互性和实验现象、规律、实验结果的准确性.为加强实践教学环节提供了另一种实验教学的手段,为力学实验教学网络化提供了可视资源.     

以开放实验搭建基础力学与实践的纽带 ——以薄壁圆筒应力分析为例

以材料力学中典型的薄壁圆筒应力分析为例,设计了趣味开放实验.基于材料力学和弹性力学基础知识,将该例题结合易拉罐和储气罐等类似结构阐述薄壁圆筒的应力分布,通过理论分析、拉压实验和电测法实验探究了薄壁圆筒的内压和强度,实验结果与理论分析吻合较好.开放实验达成度表明,本项实验具有一定的趣味性和专业性,学生态度积极,综合应用能...     

Determination of the microscale stress–strain curve and strain gradient effect from the micro-bend of ultra-thin beams

A simple method is established to determine the microscale uniaxial stress–strain curve from the load and deflection data for a doubly clamped beam. The method is based on the fact that, for beam deflection much larger than the beam thickness, the axial stretching dominates the deformation in the doubly clamped beam and the doubly clamped beam behaves like a simple plastic hinge. The microscale uniaxial stress–strain curve, together with the cantilever beam experiments, is used to determine the strain gradient effect in Au thin beams. The effect of finite rotation is also discussed.     

An analysis of ductile rupture in notched bars

Ductile fracture in axisymmetric and plane strain notched tensile specimens is analyzed numerically, based on a set of elastic-plastic constitutive relations that account for the nucleation and growth of microvoids. Final material failure by void coalescence is incorporated into the constitutive model via the dependence of the yield function on the void volume fraction. In the analyses the material has no voids initially; but as the voids nucleate and grow, the resultant dilatancy and pressure sensitivity of the macroscopic plastic flow influence the solution significantly. Considering both a blunt notch geometry and a sharp notch geometry in the computations permits a study of the relative roles of high strain and high triaxiality on failure. Comparison is made with published experimental results for notched tensile specimens of high-strength steels. All axisymmetric specimens analyzed fail at the center of the notched section, whereas failure initiation at the surface is found in plane strain specimens with sharp notches, in agreement with the experiments. The results for different specimens are used to investigate the circumstances under which fracture initiation can be represented by a single failure locus in a plot of stress triaxiality vs effective plastic strain.     

The dynamic mechanical response of fiber-reinforced beams to large transverse loads

The paper describes the results of experiments on fiber-reinforced metal beams which have been subjected to dynamic transverse loading. The beams were fabricated by embedding sets of parallel steel wires in a matrix of lead-tin alloy, and were clamped at one end. The transverse dynamic loading was applied to the tip of the beam so that the problem was one of the transverse deformation of a composite cantilever. Two separate techniques were employed to load the specimens, one being to hit the end with a fast moving hammer in a “Hyge” Shock Testing Machine; the other was to detonate an explosive charge in contact with a small projectile close to the tip. The deformations were monitored by a number of different experimental techniques and the final plastic transverse deflection of the tip as well as the final position of the plastic wave front were compared with the theoretical predictions of Spencer, Jones and their co-workers. The agreement was found to be very satisfactory. In making these comparisons strain rate effects in the lead-tin matrix metal had to be allowed for and this was done with the help of a separate set of tests.     

含切口悬臂梁的大变形塑性冲击动力响应

本文分析了含切口的悬臂梁受飞射物撞击的刚塑性动力响应的完全解,推导了考虑几何大变形效应的“双铰模式”的动力学方程,给出了计算方法和计算结果,最后讨论了耗散能的分配和切口对梁最终变形的影响。     

Plastic stress-strain history at notch roots in tensile strips under monotonic loading

Various authors have proposed analytic relations for predicting the plastic behavior at the root of a notch. Among these are relations by Neuber and by Hardrath and Ohman, the latter having generalized on earlier work by Stowell. These methods have had limited experimental confirmation and it was the objective of the investigation reported herein to assess the predictive value of each of the two theories by comparison with test data on externally notched tensile specimens, monotonically loaded to large strains. Since maximum notch-root strain and net-section stress are the only parameters which can be directly measured in a test, theoretical predictions of these same parameters were developed. This was done using a piece-wise analytical representation of the stress-strain curve. Computer programs were developed for analyzing the stress-strain data and for computing the theoretical results. A comparison of theory with tests on flat, notched specimens of AISI 4340 steel, heat treated, with initial elastic concentration factors of 1.5 to 2.0 showed a systematic discrepancy which is attributed in part to notch strengthening due to triaxial stress. The discrepancy is of the order of 5 percent for the Neuber theory and larger for the Hardrath-Ohman theory for notch strains less than of 0.015 in./in. and becomes progressively larger for both theories at notch strains in excess of 0.015 in./in. For the mild notches studied here, the Neuber theory has better predictive value.     

16MnR钢缺口试样解理断裂行为研究

研究了低合金热轧钢16MnR缺口试样在$-196\,{^\circ}$C和$-130\,{^\circ}$C的解理断裂机 理. 拉伸试验、单、双缺口四点弯曲实验、断口形貌观察以及有限元分析结果表明, 缺口试 样发生解理断裂时均起裂于夹杂物粒子, 一种位于缺口根部前端(IC型), 另一种位于距缺口 根部较远的条形裂纹前端(SIC型); 且随温度升高, 起裂源的类型从$-196\,{^\circ}$C下的IC 型转变为$-130\,{^\circ}$C下的SIC型. 微裂纹均形核于夹杂物, 最终的断裂由铁素体晶粒尺 寸的微裂纹扩展控制. 缺口试样IC型解理断裂遵循裂纹形核条 件$\varepsilon_{\rm p} \ge \varepsilon_{\rm pc}$和裂纹扩展条件$\sigma_{yy} \ge \sigma_{f}$, 而SIC型解理断裂条件则演化为$\varepsilon_{\rm p}+\varepsilon_{\rm ps} \ge \varepsilon_{\rm pc}$和$\sigma_{yy} +\sigma_{yy{\rm s}} \ge \sigma_{f}$.     

An analysis of the shear failure of rigid-linear hardening beams under impulsive loading

A theoretical rigid-plastic analysis for the dynamic shear failure of beams under impulsive loading is presented when using a travelling plastic shear hinge model which takes into account material strain hardening. The maximum dynamic shear strain and shear strain-rate can be predicted in addition to the permanent transverse deflections and other parameters. The conditions for the three modes of shear failure, i.e., excess deflection failure, excess shear strain failure and adiabatic shear failure are analyzed. The special case of an infinitesimally small plastic zone is discussed and compared with Nonaka's solution for a rigid, perfectly plastic material. The results can also be generalized to examine the dynamic response of fibre-reinforced beams.     

环形含内钝缺口试件在斜加载作用下弹塑性场的分布特征

运用有限元数值计算方法,对含内缺口的环形试件在受到与缺口对称面成不同角度的载荷作用下,缺口前端附近的弹塑性场分布特征进行了研究,得到了缺口前端应力和应变场以及塑性区的变化情况,此外,选取缺口弧度不同的模型,探讨了缺口顶端钝化程度对弹生场的影响,为了对计算结果的可靠性进行评价,运用高精度云纹干涉实验力学方法进行了验证性试验,试验得到的位移,应变分布情况与计算结果基本吻合。文中得到的结果为钝口试件的材     

含缺陷半无限长梁在阶跃载荷作用下的塑性动力特性及失效分析

分析了在任意位置含一缺陷的半无限长梁在自由端受阶跃载荷作用下的刚塑性动力响应,重点讨论了结构响应模式和缺陷处的能量耗散,给出了不同载荷大小和缺陷参数组合下的完全解,所得结果对确定管道结构的动态失效准则有参考价值.     

Elastic-viscoplastic notch correction methods

Neuber’s type methods are dedicated to obtain fast estimation of elastic–plastic state at stress concentrations from elastic results. To deal with complex loadings, empirical rules are necessary and do not always give satisfying results. In this context, we propose a new approach based on homogenization techniques. The plastic zone is viewed as an inclusion in an infinite elastic matrix which results in relationships between the elastic solution of the problem and estimated stress–strain state at the notch tip. Three versions of the notch correction method are successively introduced, a linear one which directly uses Eshelby’s solution to compute stresses and strains at the notch, a non-linear method that takes into account plastic accommodation through a β$\beta$-rule correction and, finally, the extended method that is based on the transformation field analysis methods. All the notch correction methods need calibration of localization tensors. The corresponding procedures are proposed and analyzed. The methods are compared on different simulation cases of notched specimens and the predictive capabilities of the extended method in situations where plasticity is not confined at the notch are demonstrated. Finally, the case of a complex multiperforated specimen is addressed.