A novel method for measuring and characterizing dynamic fracture-initiation toughness of elastic-plastic materials

The characterization and testing methods of the dynamic fracture initiation toughness of elastic-plastic materials under tensile impact are studied. By using the self-designed bar-bar tensile impact apparatus, a novel test method for studying dynamic fracture-initiation has been proposed based on the one-dimensional test principle. The curve of average loadv. s. displacement is smooth until unstable crack propagation, and the kinetic energy which does not contribute to the crack growth can be removed from total work done by external-force to the specimen. The fracture-initiation point is determined by compliance-changing rate method. The results show that these methods are feasible and effective. Through the analysis of the conversion between work and energy of a fracture specimen, the dynamicJ-integral is adopted as a characteristic parameter for elastic-plastic materials under impact loading. TheJ-integral is calculated from and curves by using the formula proposed, by Rice. TheJ-integral at fracture initiation is employed to describe the dynamic fracture-initiation toughness of elastic-plastic materials and the experimental results indicate thatJ _ID can be regarded as a material constant.     

Stress Wave Field Near a Notched Boundary in Anisotropic Plates under Impulsive Loading

The stress distribution near a rectilinear boundary and a boundary with a notch of different depths in an anisotropic plate is analyzed. The plate boundary is under the action of a surface or embedded impulsive source. The results presented have been obtained using the dynamic photoelastic method for optically sensitive orthotropic plates. The results for orthotropic and isotropic plates with different ratios of notch depth to wavelength are analyzed     

高强钢广义屈服和破坏理论

结合经典强度理论和现代损伤力学对金属屈服和断裂解释的力学原理,给出了高强钢在应力三轴空间广义屈服轨迹方程的新诠释.根据三向等拉伸应力状态下高强钢屈服和宏观脆断的重合性,提出了高强钢在应力三轴空间的开裂准则.通过对高强钢刻痕杆断裂试验的数值模拟分析,对比验证了该开裂准则的普适性及精度.最后,给出了高强钢广义强度理论的物理解释及抗断设防.建议的广义强度理论是解高强钢裂纹体和无裂体断裂的一个尝试.     

一种弹塑性材料动态起裂韧度的J表征和测试方法

在数值计算的基础上提出了一个弹塑性材料动态起裂韧度的J表征和测试方法．这一方法利用自行研制的间接杆-杆型冲击拉伸试验装置，对周边切口的短圆柱试件实施基于一维试验原理的弹塑性材料动态断裂试验；利用试件两端的平均载荷—相对位移曲线(P-δ)或平均载荷-裂纹张开位移曲线(P-△)，推广Bice远场公式获得动态J积分；采用柔度变化率法确定裂纹起裂点，从而得到动态起裂韧度JJD．这一方法的优点在于利用P-δ或P-△曲线将外力对试件所做的与裂纹运动无关的质心惯性运动动能近似地从总能量中分离出来，且平均载荷P在起裂前以至失稳扩展前是单调增的，同时试验获得的P-δ和P-△曲线光滑，这使得用J积分作为裂纹尖端的表征参量以及用柔度变化率法确定起裂点和失稳点具有坚实的物理基础．     

凹槽梁试样的动态应力强度因子

对凹槽梁试样动态应力强度因子现有的几种计算方法进行了分析对比。在此基础上,考虑冲击速度、试样的转动惯性和剪切变形对动态应力强度因子的影响,求解得到了一个新的动态应力强度因子的表达式。     

An improvement to the single specimen test method for fracture characterization of elastomer materials using DENT specimen

Fracture behavior of elastomer materials is investigated based upon single specimen and multiple specimen test methods using the practically recommended double edge notched tension (DENT) specimen. Combining analytical, experimental, and numerical analysis, the critical J integral is determined based upon η factor concept. The main challenge with this approach is how to extract the η (or η*) factor. For DENT specimen, previous studies have proposed that η* factor, unlike η, could be considered approximately constant, and even estimated from its homologous LEFM-based formula (η_el). In this paper, it is shown that the values of coefficients η and η* may significantly depend on the material type and the constitutive model and even on the load level. Moreover, η* values deviate significantly from η_el predictions. Consequently, the claim of a constant coefficient η* for DENT specimen is not correct, though numerical estimations of this variable factor by using the appropriate constitutive parameters could still be provided.     

ASA对PVC塑化和冲击性能影响

以聚丙烯酸丁酯（PBA）为核,苯乙烯（St）、丙烯腈（AN）的共聚物为壳,采用种子乳液聚合法制备了一系列丙烯酸丁酯-苯乙烯-丙烯腈（ASA）核壳接枝共聚物。考察了ASA的用量、ASA中核层质量分数和ASA壳层中AN的质量分数对聚氯乙烯（PVC）塑化和冲击性能的影响。结果表明：随着ASA用量的增加,PVC熔融时间缩短,最大扭矩和平衡扭矩增大;断面的扫描电镜图证实了PVC脆-韧转变过程;随着ASA核层质量分数的增加,熔融时间略有缩短,扭矩略有增加,PVC的冲击强度增加幅度不大;随着ASA壳层中丙烯腈的质量分数增加,熔融时间变化不大,但扭矩逐渐增加;当丙烯腈质量分数超过0.40时,PVC的冲击强度开始下降。     

Direct fracture toughness determination of a ductile epoxy polymer from digital image correlation measurements on a single edge notched bending sample

This work presents a combined experimental and numerical study on the fracture toughness behaviour of a ductile epoxy resin system. Quasi-static fracture tests using single edge notched bending (SENB) specimens were conducted under room temperature conditions. In addition, the digital image correlation technique was employed to experimentally map the full-field displacements and strains around the notch and crack tip, allowing direct calculation of the J-integral fracture toughness. The magnitude of fracture toughness was found to be 1.52 ± 0.03 kJ/m², showing good consistency with the results measured according to the standard analytical formulations. A numerical model of the single edge notch bending specimen was built to compute the local strain field around the crack tip, together with the fracture toughness parameter. Good agreement was confirmed for both the experimental J-integral fracture toughness and the local surface strains around the crack-tip from the digital image correlation based optical technique, compared to the results obtained by numerical simulation. The fracture surfaces of the samples were examined using an optical microscope to analyze the failed surface morphology and the corresponding failure mechanisms.     

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.     

拉伸螺杆半椭圆表面裂纹应力强度因子

将拉伸螺杆简化为理论应力集中系数Kt不同的带“V”形缺口圆杆,采用裂纹尖端为20节点奇异单元的三维有限元模型,对螺杆半椭圆表面裂纹的应力强度因子进行了计算.给出了具有普遍性意义的螺杆表面裂纹应力强度因子公式.为验证本文计算结果的有效性,还将本文M22×1.5螺杆的应力强度因子计算结果与试验结果进行了对比.