冲击作用下含预制裂纹梁柱试件的动态断裂

利用焦散线实验系统,进行了冲击加载下含预制裂纹梁柱试件的断裂实验,研究了梁柱试件的梁柱节点、梁上和柱端裂纹的扩展轨迹、扩展速度和应力强度因子的变化规律。实验结果表明:受冲击后,试件首先在梁柱节点处开裂,并在裂纹扩展过程中发生明显的曲裂运动,证明梁柱节点处最容易受到破坏。预制裂纹条数越多,梁柱节点处开裂越晚,说明裂纹条数少,能量可以在裂纹尖端积聚得更集中、更快。含柱端预制裂纹的试件,2条裂纹的开裂相隔时间要长于含梁上预制裂纹的试件;同时,试件的第2条裂纹优先在梁上裂纹处开裂,说明固端支座比简支梁断裂需要更多的能量。随着预制裂纹的增多,梁上裂纹在扩展过程中的曲裂现象减弱, 由于部分能量在柱端裂纹处积聚,用于推动梁上裂纹扩展的能量相应地减少。并且由于柱端裂纹的存在,梁上裂纹受到的拉应力分量减小,导致裂纹尖端受到弯矩变小,影响了裂纹的曲裂运动。     

含预制裂纹L形梁柱试件动态断裂过程

针对含预制裂纹L形梁柱试件,为研究预制裂纹动态扩展的力学特征及其对梁柱试件破坏模式的影响,采用数字动态焦散线实验系统,对距节点核心区不同距离l处含有预制裂纹的试件进行落锤冲击实验,得到预制裂纹的扩展轨迹、速度、动态应力强度因子的变化规律。结果表明,l值增大,扩展裂纹在梁下边缘的贯通点与预制裂纹的夹角逐渐增大,曲裂程度变大。裂纹扩展速度随着l的增大振荡性增强,裂纹扩展平均速度逐渐降低。l值为2 mm时,裂尖表现为Ⅰ型断裂,l值增大,裂尖受到剪应力作用增强,Ⅰ型动态应力强度因子减小,Ⅱ型动态应力强度因子增大,断裂逐渐转变为Ⅰ-Ⅱ复合型。     

含偏置裂纹三点弯曲梁的动态断裂行为研究

采用动态焦散线方法，对含偏置裂纹三点弯曲梁承受横向冲击的弯曲断裂行为进行了一系列动态断裂力学实验研究，分析了无量纲量ａ／ｌ的改变（ａ——初始裂纹偏离梁中心线的距离；ｌ——梁长度的一半）对于裂纹动态扩展行为（裂纹起始状态、裂纹尖端的复合应力强度因子、裂纹扩展速度、裂纹扩展轨迹）的影响，并借助动态光弹性应力分析，对应力波与扩展裂纹的相互作用以及应力波传播规律进行探讨．给出了裂纹尖端复合应力强度因子、裂纹扩展速度的变化、裂纹曲裂轨迹以及方向与梁中应力波传播的相互关系     

EXPERIMENTAL STUDIES ON DYNAMIC PROPAGATION OF CRACKS UNDER BIAXIAL COMPRESSION

This paper deals with the initiation and non-coplaner propagation ofcracks under biaxial compression.The running process of the propagating cracks issuccessfully recorded with the method of dynamic photoclasticity.A series of importantfracture parameters such as cracks' propagating velocity,critical opening loading andinitial angle of cracks' growth under hiaxial compression is calculated.Results showthat the stress field in front of the non-closed crack tip under biaxial compression is amixed-mode singular field,the dynamic propagation of the new tensile cracks is juststable and shows distinct stages,but the unstable crack appears under high loads andresults in the rupture of the matrix.     

双轴压缩载荷下裂纹动态传播的实验研究

本文研究了双轴压缩载荷下裂纹的起裂和非共面传播问题，用动态光弹性方法成功地记录下裂纹的动态扩展过程。获得了双轴压缩载荷下扩展裂纹的传播速度，临界开裂载荷以及开裂角第一系重要断裂参数。研究表明，在双轴压缩载荷下不闭合裂纹前缘应力场是一个混合型的奇异场，裂纹的扩展过程为稳态过程并且表现出显著的阶段性特点。     

Analysis of crack moving and curving in anisotropic solids

The general equations for a dynamically curved crack in an anisotropic solid are derived, and the asymptotic fields of a moving crack under arbitrary distributed loading on the crack surface are calculated from them. For a moving crack under mixed-mode loading conditions a general Muskhelishvili type approach is proposed to calculate intensity factors due to crack surface loading in anisotropic materials. The kinking and curving caused by dynamic loading in anisotropic materials are calculated using the maximum normal stress ratio criterion. The results show that cracks in anisotropic solids may deviate from the straight path and approach a direction parallel to the stiff axis even under symmetric loading and that a crack will tend to deviate more from the crack path to the direction of the stiff axis as the crack speed becomes higher.     

Stress wave fields in plates weakened by curvilinear holes with edge cracks

The dynamic fracture of plates weakened by holes with edge cracks and subjected to impulsive loading is studied using the dynamic photoelastic method. The time dependences of the stress intensity factors and the crack growth rate are examined for three models of plates with circular holes and edge cracks __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 2, pp. 79–84, February 2006.     

压应力场中爆生裂纹分布与扩展特征实验分析

采用动静组合加载实验装置和数字激光焦散线实验系统,进行了0、3、6、9 MPa等4种压应力场中PMMA试件的爆破致裂实验,分析了沿静态主应力方向扩展的裂纹运动学和力学行为。实验结果表明:首先,静态竖向载荷在预制炮孔周围产生应力集中,在炮孔壁上下端部处出现最大拉应力;随后,在动态爆炸载荷的叠加作用下,裂纹优先在炮孔壁上最大拉应力位置处起裂,并沿最大主应力方向扩展;裂纹扩展过程中,静态竖向载荷越大,裂纹扩展速度越大,且裂纹尖端应力强度因子值越大。     

缺陷介质切槽爆破断裂行为的动焦散线实验

利用数字激光动态焦散线实验系统,对含缺陷介质在切槽爆破和普通炮孔爆破中爆生裂纹的断裂行为进行对比研究。结果表明,切槽爆破中沿切槽方向起裂的主裂纹比非切槽方向早10 μs,有利于能量优先沿切槽方向释放;切槽方向主裂纹的起裂韧度为0.58 MN/m3/2,其裂纹扩展的平均速度为277 m/s,分别是普通爆破时主裂纹相应值的54%和86%;当切槽方向主裂纹与缺陷介质贯通后,为爆生气体提供了足够的膨胀空间,诱导爆生气体向预制裂纹两端释放,翼裂纹起裂以Ⅰ型拉伸破坏为主,并在裂纹扩展的60~250 μs内,Ⅰ型动态应力强度因子保持在0.6~0.8 MN/m3/2,形成了明显的平台,延缓了翼裂纹扩展速度的衰减,最终较普通炮孔翼裂纹扩展时间和扩展长度分别增加了22.7%和17.8%。     

The scattering of harmonic elastic anti-plane shear waves by two collinear cracks in the piezoelectric plate by using the non-local theory

In this paper, the dynamic interaction between two collinear cracks in a piezoelectric material plate under anti-plane shear waves is investigated by using the non-local theory for impermeable crack surface conditions. By using the Fourier transform, the problem can be solved with the help of two pairs of triple integral equations. These equations are solved using the Schmidt method. This method is more reasonable and more appropriate. Unlike the classical elasticity solution, it is found that no stress and electric displacement singularity is present at the crack tip. The non-local dynamic elastic solutions yield a finite hoop stress at the crack tip, thus allowing for a fracture criterion based on the maximum dynamic stress hypothesis. The project supported by the Natural Science Foundation of Heilongjiang Province and the National Natural Science Foundation of China(10172030, 50232030)     

Dynamic curving cracks in functionally graded materials under thermo-mechanical loading

Mixed-mode dynamic crack growth along an arbitrarily smoothly varying path in functionally graded materials (FGMs) under thermo-mechanical loading is studied. The property gradation in FGMs is considered by varying shear-modulus, mass density, thermal conductivity and coefficient of thermal expansion exponentially along the gradation direction. Asymptotic analysis in conjunction with displacement potentials is used to develop the stress fields around propagating cracks in FGMs. Asymptotic temperature fields are developed first for the exponential variation of thermal conductivity and later these temperature fields are used to derive thermo-mechanical stress fields for a curving crack in FGMs. Using these thermo-mechanical stress fields, various components of the stresses are developed and the effect of curvature parameters, temperature and gradation on these stresses are discussed. Finally, using the minimum strain energy density criterion, the effect of curvature parameters, crack-tip speeds, non-homogeneity values and temperature gradients on crack growth directions are determined and discussed.     

应力波载荷作用下线弹性断裂过程的动态分析方法研究

利用Hopkinson单压杆实验装置 ,对材料的线弹性动态断裂特性进行了研究 ,建立了应力波载荷作用下动态裂纹起裂及扩展过程的动态分析方法 ,采用该方法可同时测得材料的动态裂纹起裂时间、断裂韧性和裂纹扩展速度。40Cr钢三点弯曲试样的实验结果表明 :该钢的动态裂纹扩展过程主要是减速过程 ,在2 2 5TPam /s的加载速率下 ,起裂时间为 2 8 0 0 s,最大裂纹扩展速度为 478 91m/s ,动态断裂韧性为6 3 12MPam。     

平面应变下紧凑拉伸试样的动态断裂韧性的实验研究

材料的动态断裂韧性是衡量材料在动载荷作用下抵杭裂纹扩展能力的重要指标,以往的材料动态断裂韧性测试多采用三点弯曲试样,而针对紧凑拉伸试样的动态断裂韧性研究很少.本文将紧凑拉伸试样(即CT试样)简化成等效弹簧质量模型,得到了CT试样动态应力强度因子的近似表达式.对Hopkinson压杆装置进行了改进,利用改进后的实验装置进...     

拱形试件动态断裂的动光弹分析

本文采用动光弹方法,分析了对带边裂纹的拱形三点弯曲试件在抢击加载条件下的瞬态反应。从多火花动光弹仪记录下来的16幅断裂过程的照片和微机输出的电火花光信号图上,得到了各时刻的等差线图形和裂纹长度。使用运动裂纹尖端附近的应力场解,去计算动应力强度因子。对环氧树脂材料,测定了动态应力强度因子与裂纹扩展速度之间的关系,并给出了当裂纹扩展速度达到410m/s时,为裂纹产生分叉的条件。     

切槽孔爆破动态力学特征的动焦散线实验

应用爆炸加载的透射式动焦散线测试系统,分析了有机玻璃切槽孔爆破模型的裂纹动态特征变化规律。比较了不同切槽角度、切槽深度的定向断裂裂纹尖端的扩展长度、扩展速度和动态应力强度因子。初步探讨了切槽爆破的动态效应,研究表明切槽孔爆破早期裂纹破坏模式为爆炸拉应力波作用下的I型快速扩展裂纹,裂纹尖端拉应力集中积聚的较大应变能维持了爆炸裂纹进一步扩展,裂纹尖端扩展后期表现为P波、S波共同作用下的复合型扩展特征。切槽角为60时获得的定向断裂效果最好,合理切槽深度为炮孔半径的1/4～1/2。     

EXPERIMENTAL AND THEORETICAL INVESTIGATIONS ON THE VELOCITY OSCILLATIONS OF DYNAMIC CRACK PROPAGATING IN BRITTLE MATERIAL TENSION

设计了一种精确测量裂纹在预拉伸带板中的传播速度的实验装置, 系统研究了裂纹在受不同预加载荷作用的不同尺寸的有机玻璃 板中的传播行为.实验结果表明:在一个细长、上下表面固定的带板中, 裂纹速度分为加速和稳定2个阶段.在稳定速度阶段, 裂纹平均速度v₀ 是预加载荷在板中储存的弹性能Wh的增函数.由于此时裂纹处于自相似传播阶段, 可以认为材料的动态断裂能G_c是裂纹传播速度v₀的增函数, 即材料存在"速度增韧性".当裂纹传播速度达到一定阈值, 裂纹的传播速度出现明显的振荡现象, 裂纹的振荡周期与断裂面出现的周期性沟槽的尺度一致.在更高的预加能量下, 裂纹传播路径出现弯曲、微分岔以及宏观分岔现象.建立了一个描述裂纹在带板中的直线传播行为的动力学模型, 并用这个模型模拟裂纹在传播过程中的速度振荡现象.     

定向断裂控制爆破的空孔效应实验分析

采用新型数字激光动态焦散线实验系统, 对爆炸荷载作用下空孔周围的动应力场分布及空孔对爆生主裂纹扩展行为的影响进行了研究。研究结果表明, 在空孔周围强应力场的影响下, 2条相向扩展的爆生主裂纹逐渐向空孔处偏转, 并在空孔处贯通; 空孔附近的主应力方向与炮孔连心线夹角基本稳定在约12°, 增大空孔尺寸对空孔附近的主应力方向影响不明显; 爆炸应力波与空孔相互作用, 产生反射拉伸波, 改变了主裂纹尖端的应力场, 降低了主裂纹的扩展速度, 且空孔直径越大, 主裂纹的扩展速度越低; 当爆生主裂纹扩展到空孔附近时, 主裂纹尖端动态应力强度因子再次出现上升的趋势。     

孔边裂纹对SH波的散射及其动应力强度因子

采用Ｇｒｅｅｎ函数法研究任意有限长度的孔边裂纹对ＳＨ波的散射和裂纹尖端场动应力强度因子的求解．取含有半圆形缺口的弹性半空间水平表面上任意一点承受时间谐和的出平面线源荷载作用时位移函数的基本解作为Ｇｒｅｅｎ函数,采用裂纹“切割”方法并根据连接条件建立起问题的定解积分方程,得到动应力强度因子的封闭解答．最后给出了孔边裂纹动应力强度因子的算例和结果,并讨论了圆孔的存在对动应力强度因子的影响     

Crack kinking in sandwich structures under three-point bending

Sandwich beams under three-point bending containing cracks in the core material very close to the upper skin interface are investigated. The cracks considered parallel or with an imperceptible inclination to the longitudinal beam axis and at different distances from the upper skin interface, are analyzed with static non-linear elastic two and three dimensional finite element analyses. From the proposed analyses stress intensity factors are calculated using linear elastic fracture mechanics. It is demonstrated that the crack propagation on the compression side of the core is mainly subjected in shear. The strain energy density criterion is used in order to determine the angle of kinking of the crack into the core.     

不同倾角预制裂纹缺陷与运动裂纹的相互作用

为了研究运动裂纹与不同倾角预制裂纹缺陷之间的作用机制,采用数字激光动态焦散线方法对含不同倾角预制裂纹缺陷的三点弯曲梁进行冲击实验。研究结果表明,在冲击载荷作用下,预制裂纹缺陷尖端均产生了次生裂纹;当运动主裂纹与预制裂纹缺陷贯通时,次生裂纹不会立即起裂,而是经过0~10 μs的能量积蓄后,次生裂纹才起裂;运动主裂纹应力强度因子峰值与次裂纹起裂时的应力强度因子值均随预制裂纹倾角的增大而增大。