应力波载荷作用下材料断裂韧性测试技术研究进展

本文对应力波载荷（加载速率ＫＩ≥１０＾６ＭＰａ√ｍ／ｓ）作用下,动态断裂韧性测试技术中的非光学方法进行了较全面和较系统的研究,比较了各自的优缺点,并对不同方法的可靠性和适应范围进行了分析。     

循环冲击作用下岩石应力应变曲线及应力波特性

利用研制的岩石动静组合加载实验装置进行循环冲击实验,研究了在循环冲击过程中岩石典型的动态应力应变曲线及反射波和透射波的变化规律。结果表明:岩石在循环冲击过程中的动态应力应变曲线可分为压密阶段、弹性阶段、内部裂纹扩展的加载阶段、第1卸载阶段和第2卸载阶段等5个阶段。在相同入射波循环作用下,随着循环次数的增加,岩石的反射波峰值越来越大,反射波峰值出现的时间越来越迟,透射波峰值越来越小,透射波峰值出现的时间越来越早,表明在循环冲击过程中岩石内部损伤逐渐累积,从而导致抵抗外部冲击载荷的能力逐渐降低。     

冲击加载下材料应力应变曲线振荡现象的研究综述

在冲击加载下获得的材料应力应变曲线往往具有显著的振荡,长期以来由于很难判断振荡的真伪,即不确定振荡是试样材料的本征特性还是纯粹的机械加载等带来的影响,故曲线的振荡往往没有从真实应力应变曲线中直接消除。但这种振荡的存在掩盖了真实的材料响应,导致很难准确确定材料的动态屈服强度,也影响了材料动态本构关系的建立及本构模型参数的准确性,这对重大装备工程在冲击载荷下的优化设计及安全可靠性带来不利影响。针对这个长期困扰科研和工程技术人员的普遍性问题,本文综述了冲击加载下材料应力应变曲线振荡现象的研究进展,首先从加载系统设计、应力波传播、试样变形分布等方面分析了动态测试曲线中出现振荡的原因;其次依据振荡成因重点论述了抑制或消除振荡现象的方法;最后总结了现阶段研究的突出问题,并对未来发展方向提出一些建议。     

测量土、岩石介质中的动态应力用的压电式应力计

本文介绍一种压电式应力计,它的主要性能是:测量量程为10-1000kgf/cm~2;响应时间小于7μs;线性误差小于士1%;综合应力测量误差小于±10%,该应力计可用于测量土、岩石和混凝土介质中的动态应力,也可用于测量动态力和流体介质中的动态压力。     

冲击荷载下岩石动态断裂韧度测定的实验技术

本文介绍了一种研究岩石动态断裂特性的实验技术。该方法采用自行设计的杆式冲击试验机,在加载率K1106Nmm-3/2s-1条件下对三点弯曲试件进行冲击加载。实验中,通过一套光电转换装置测量试件切口张开位移随时间的变化。由双通道的瞬态波形存贮器记录荷载和切口张开位移,得到了冲击条件下的荷载-切口张开位移曲线,通过张开位移速率的转折点来确定起裂点并计算动态断裂韧性K1d。本中给出了长宽高为1804040mm的大理岩试件的典型荷载-切口张开位移曲线和示波照片。试验结果可由微型机直接进行处理。     

弹性体在表面冲击载荷下所激发的应力波

1 引言近年来,随着对工程中许多冲击破坏现象机理研究的不断深入,冲击载荷所激发的应力波传播问题越来越引起人们的关注.尽管,自Lamb 首先捉出并利用Fouricr 变换方法研究了弹性半空间在脉冲点源作用下激发应力波的传播问题之后,迄今已有许多学者,如     

应力波载作用下材料断裂韧性测试技术研究进展

本文对应力波载荷(加载速率KI≥105MPa m/s)作用下,动态断裂韧性测试技术中的非光学方法进行了较全面和较系统的研究,比较了各自的优缺点,并对不同方法的可靠性和适用范围进行了分析．     

岩石在不同加载波条件下能量耗散的理论探讨

采用脆性体动态断裂准则和富氏分析方法,给出了矩形波、钟形波和指数衰减波加载于岩石的能量耗散差异。在此基础上,就应力脉冲的形状、延续时间等对岩石破碎效果的影响进行了讨论,得到了与不同加载波下岩石耗能实验研究相吻合的结果。     

轴向冲击载荷作用下直杆弹性动态屈曲的研究

本文利用分叉的概念,从应力波理论出发,把轴向冲击载荷作用下直杆的弹性动态屈曲问题化为特征值问题,从而导出直杆动态屈曲的临界分叉准则。同时,本文对一端固支直杆受轴向冲击时的弹性屈曲问题进行了实验研究,测到的临界屈曲时间和理论预计值基本符合,证实了理论模型的合理性.理论和实验两方面的结果都表明,直杆受轴向冲击载荷作用时的屈曲现象发生在波动过程的前期,因此在处理这类问题时考虑波动效应是必要的。     

岩石对冲击波的非线性动态响应

对干燥、饱水、饱泵油大理岩和饱和砂岩进行了SHPB冲击压缩实验,得到了干燥岩石和饱和岩石的应力波衰减规律。在应力波传播过程中,其幅值有较大的衰减,干燥岩石的衰减最大,且孔隙度越大衰减越大,饱和岩石还存在较强的波弥散效应。在小于岩石屈服强度时,多次冲击加载下获得随冲击加载次数的增加,加载模量增大,残余应变减小的压实效应。这一结果可用于大型地震工程和防护工程的设计和建造。     

花岗岩体中应力波传播计算的动态本构关系

在花岗岩体的弹性区域,对实测径向质点速度波形运用Lagrangian分析方法,得到了球面应力波传播的加载速率相关的应力应变关系曲线。由速率相关本构关系所作的计算结果表明,它能较正确地描述岩石中球面应力波传播过程中所体现的主要特征,即应力波峰值衰减指数大于1和波形剖面的展宽。     

A shock tube research facility for high-resolution measurements of compressible turbulence

A new shock tube facility with a 30.5 cm (1 ft) inside diameter is currently in operation that allows for high-spatial-resolution measurements of compressible turbulence. Small scales of turbulence behave very differently from large scales when they interact with shock or expansion waves. Highly resolved measurements can provide new information on the interaction at small scales. Another notable characteristic of the present facility is the ability to control the flow velocity behind the reflected shock through the porosity of the reflecting wall. Tests showed good flow quality with sufficiently long observation times. Measurements of piecewise average skin friction over short segments of the tube indicated strong viscous effects very close to the diaphragm where the shock is developing. The skin friction and the shock propagation speed virtually remained constant inside the working section of the shock tube in all investigated flow cases, even in low Mach number cases where viscous effects are stronger. The experimental results are compared with numerical simulations, including the effects of the reflecting porous wall and viscous effects.     

Scattering of elastic waves by a periodic array of cracks in 3-D space

The problem of scattering of normal incident time harmonic plane elastic waves by a co-planar periodic array of cracks in 3-D space is investigated. The scattered waves consist of a superposition of an infinite number of wave modes [M, N]^T and [M, N]^L,M. N=0, 1, 2, , but only a finite number of them are propagating wave modes. The numerical calculation has been made for rectangular cracks and P wave incidence. The reflection coefficient of [O, O] order,R ₀ ³ , has been studied in detail for various wave numbers and parameters of the geometry for the problem. The reliability of the numerical calculation has been checked by an application of the balance of rates of energies. For an elongated rectangular crack,R ₀ ³ in the corresponding 2-D problem in [2] is recovered. The dynamic stress intensity factors around the crack edge have been obtained. The results as the wave number goes to zero have been compared with those in the correspoding static case. Good agreement is observed.     

含孔软铁磁材料Mindlin板中弹性波散射问题

基于考虑磁弹相互作用的Mindlin板弯曲波动方程,采用波函数展开法,分析研究了含孔软铁磁材料Mindlin板中弹性波散射与动应力集中问题,给出了问题的分析解和数值算例. 通过分析发现：磁感应强度对动弯矩集中系数和动剪力集中系数有增加的作用,特别是在低频的情况下.     

爆炸波与地下结构物相互作用的动光弹性探讨

本文用动态光弹性探讨了地表爆炸产生的应力波与地下结构物相互作用的机理,根据等差条纹分布分析了P波、S波、von Schmidt波及R波与结构物基础的相互作用过程。研究表明R波是对地下结构物危害最大的波。可以采取防护措施来反射和消耗R波的能量。     

炮孔之间爆炸应变场的光力学分析

本文分别运用动态云纹-光弹性和电阻应变量测方法研究了相邻两炮孔之间爆炸应变场。多火花式高速像机和超动态量测系统被用于动态记录。根据动态云纹-光弹条纹分析了应力波的叠加作用,定量地计算了爆炸应力波叠加作用期间内不同时刻地孔连心线上_x(沿连心线方向)和_r(垂直于连心线方向)的分布以及_x在连心线中垂线上的分布。用应变片记录了爆炸应力波叠加作用时连心线上应变-时间示波器轨迹。测量和计算所得炮孔间应力波叠加和衰减的规律与理论分析和动光弹模拟分析结果一致。     

Scattering of elastic waves in an elastic matrix containing an inclusion with interfaces

Based on the theory of elastic dynamics, the scattering of elastic waves and dynamic stress concentration in fiber-reinforced composite with interfaces are studied. Analytical expressions of elastic waves in different medium areas are presented and an analytic method of solving this problem is established. The mode coefficients are determined by means of the continuous conditions of displacement and stress on the boundary of the interfaces. The influence of material properties and structural size on the dynamic stress concentration factors near the interfaces is analyzed. It indicates that they have a great influence on the dynamic properties of fiber-reinforced composite. As examples, numerical results of dynamic stress concentration factors near the interfaces are presented and discussed. This paper provides reliable theoretical evidence for the study of dynamic properties in fiber-reinforced composite. Project supported by the National Natural Science Foundation of China (No. 19972018).     

Elastic wave scattering and dynamic stress in composite with fiber

IntroductionTheproblemofscatteringofelasticwavesinsolidstructureshasnotonlytheoreticalsignificancebutalsowideoutlookinengineering .Thisproblemhasabsorbedmanypeople’sattentionsinmanyfieldssuchasaeronautics,compositemechanics,civilengineeringandearthquakeengineering[1～ 3 ] .Thepropagatingvelocityanddirectionofelasticwaveareinvariableasitpropagatesinaninfiniteuniformmedium .Butscatteringofelasticwavescanoccurifthereexistsincontinuitysuchasinclusion ,crackandcavityinelasticmedium .Fiber_reinfor…     

MULTIPLE SCATTERING AND DYNAMIC STRESS ANALYSIS OF ELASTIC WAVES IN A FIBER—REINFORCED COMPOSITE WITH INTERFACES

Based on the theory of elastic dynamics, multiple scattering of elastic waves and dynamic stress concentrations in fiber-reinforced composite are studied. The analytical expressions of elastic waves in different regions are presented. The mode coefficients of elastic waves are determined in accordance with the continuous conditions of displacement and stress on the boundary of the multi-interfaces. By using the addition theorem of Hankel functions, the formula of scattered wave fields in different local coordinates are transformed into those in one local coordinate to determine the unknown coefficients and dynamic stress concentration factors (DSCFs). The influences of the distance between two inclusions, material properties and structural size on the DSCFs near the interfaces are analyzed. As examples, the numerical results of DSCFs near the interfaces for two kinds of fiber-reinforced composites are presented and discussed. The project supported by the National Natural Science Foundation of China (19972018)     

爆炸应力波对高速扩展裂纹影响的动态光弹性试验研究

本文用动态光弹性模拟试验和分析方法,观察和分析研究了爆炸应力波对高速扩展的运动裂纹扩展方向和扩展速度的影响过程和机理。结果表明:当[裂纹扩展方向与入射膨胀波(P波)波阵面法线的夹角]=0时,P波的作用不会改变裂纹的扩展方向,但使其扩展速度发生变化,入射剪切波(S波)能使裂纹改变扩展方向;当0/2时,P波和S波都能改变裂纹扩展方向,而且,P波使裂纹扩展速度降低,S波使裂纹扩展速度提高。这一试验研究对于理解爆炸、冲击载荷与扩展裂纹相互作用的机理,对于理解控制、光面、预裂爆破中相邻炮孔之间后爆炮孔产生的应力波与先爆炮孔壁上产生的裂纹的相互作用具有理论和实际意义。