Experimental Verification of the Averaged Strain Energy Density Criterion for Brittle Fracture in Blunt V-Notches under Pure Compression

Strength of Materials - The goal of the present study is to verify experimentally the Averaged Strain Energy Density (ASED) criterion for brittle fracture in blunt V-notches under pure compression....     

Energy Consumption for Deformation to Fracture of a Circular-Clamped Thin Plate under Impact Loading

An experimental procedure for evaluating energy spent for fracture of a circular-clamped sheet structural element upon transverse flexure, induced by impact loading of a spherical head-face body, is briefly outlined. Flexure test results for two sheet metals (a 20 mild steel and a D16T aluminum alloy 1.0 and 0.75 mm thick, respectively) and a 2.0-mm PA6 shock-resistant composite are cited. Experimental data analyses and stress-strain state calculations for a plate material within the circular boundary upon flexure made it possible to establish the relation between the work of deformation and the dynamic strength and plasticity. Sheet structural element materials are comparatively evaluated by their specific energy spent for deformation under transverse static and impact loading.     

Crack Healing under Antiplane Deformation of Anisotropic Bodies

Strength of Materials - A mathematical model of longitudinal shear crack healing in an anisotropic body was constructed. The problem was reduced to the solution of the singular integro-differential...     

Fracture of Polymethylmethacrylate under Pulse Loading Conditions

Crack propagation in polymethylmethacrylate has been investigated experimentally under shock loading conditions generated by a pulse magnetic field. Using microstructural investigations, dynamic fracture surfaces of polymethylmethacrylate were analyzed and compared depending on the distance from the notch tip. A diagram of various fracture types depending on the pulse loading duration has been constructed.     

Fictitious Notch Rounding Concept Applied to V-Notches with End Holes Under Mode I Loading

Taking advantage of some recent closed form expressions for the stress distributions due to V-notches with end holes, the micro-structural support factor, s, to apply the Fictitious Notch Rounding (NFR) approach, is evaluated by adopting a normal stress criterion. The closed form expressions for the micro-structural support factor (s) as well as for the fictitiously enlarged end radius (ρ _f), provided here for the first time, highlight the crucial role played by the notch opening angle for this notch configuration.     

On Suitability of the Averaged Strain Energy Density Criterion in Predicting Mixed Mode I/Ii Brittle Fracture of Blunt V-Notches with Negative Mode I Contributions

Strength of Materials - The main goal of the present research is to check the suitability of the well-known brittle fracture criterion, namely the averaged strain energy density (ASED), in...     

Mixed Mode Fracture of Concrete under Proportional and Nonproportional Loading

A novel testing procedure for mixed mode crack propagation in concrete is presented: four point bend of notched beams under the action of two independent force actuators. In contrast to classical procedures, this method allows nonproportional loading and crack trajectory modifications by changing the action of one actuator. Different experimental crack trajectories, under mixed mode and nonproportional loading, are presented together with the corresponding curves of load-CMOD and load-displacement. The tests were performed for three homotetic specimen sizes and two mixed mode loading conditions. The results are useful for checking the accuracy of mixed mode fracture analytical and numerical models. The models should predict the crack trajectory and a complete group of experimental records of load and displacements on several control points in the specimen. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of Fracture of Spheroplastics under Static and Dynamic Loading

An experimental study of static and dynamic fracture properties of a spheroplastic that has a matrix of polyester resin containing a filler of glass microspheres was conducted. Crack propagation was investigated under loading conditions generated by a pulse magnetic field. Microstructure features of dynamic fracture were analyzed.     

弹塑性随动强化结构在动载荷下的一个安定准则

本文考虑动载荷和温度影响下，借助于分段线性加载面对弹塑性随动强化结构进行了安定分析，提出一个动力安定准则。文中提出的屈服面是由分片凸曲面构成，各屈服面的强化规律由强化系数Ｃｋｌ所确定，通过调整Ｃｋｌ可以得到几种不同的强化模型。文末又以一个交变载荷作用下的线性强化材料的商支梁为例对动力安定准则的应用进行了说明。     

Dynamic Tensile Fracture Behaviours of Selected Aluminum Alloys under Various Loading Conditions

Experiments investigating dynamic tensile fracture were performed on the extruded rods of 2024‐T4 and 7075‐T6 aluminum alloys under varying loading conditions. The initial yield stress and fracture strain of 7075‐T6 alloy obtained in spilt Hopkinson tension bar tests are higher than that of 2024‐T4 alloy. But the initiation fracture toughness and spall strength of 2024‐T4 alloy are higher than those of 7075‐T6 alloy in three‐point bending and plate impact experiments, which indicates that 2024‐T4 alloy has better crack initiation tolerance and stronger spall failure resistance. Based on metallurgical investigations by using optical and scanning electron microscopes, it is revealed that the microstructure has a profound effect on the dynamic tensile fracture mechanism of each aluminum alloy. The 2024‐T4 alloy is relatively brittle due to voids or cracks nucleated at many coherent CuMgAl₂ precipitate phases in the grain interiors, and the fracture mode is predominantly transgranular. The 7075‐T6 alloy exhibits relatively ductile fracture because voids or cracks growth is partly intergranular along the grain boundaries and partly transgranular by void formation around coarse intermetallic particles. The obvious differences of damage distribution and void coalescence mechanisms for 2024‐T4 and 7075‐T6 alloys under plate impact are also discussed.     

Fracture Parameters for Natural Rubber Under Dynamic Loading

Abstract: An experimental study was conducted to evaluate the tear energy of unfilled and 25 phr carbon black‐filled natural rubber with varying loading rates. The variation of the tear energy with far‐field sample strain rate between 0.01 to 10 s^?1 was found to be different from tensile strip and pure shear specimens. Above a sample strain rate of 10 s^?1, the tear energy calculated from either specimen was comparable. The differences in the tear energy derived from the tensile strip and pure shear specimens were attributed to differences in the local crack tip stress state and strengthening of the material due to strain‐induced crystallisation. Both of these factors resulted in crack speeds 3–4 times higher in the pure shear specimen as compared to the tensile strip specimen. Finite element analysis (FEA) indicated that fracture would initiate at the crack tip either when the strain energy density approached the material toughness or when the maximum principal stress and strain approached the material tensile strength and fracture strain, respectively. It was concluded that these parameters would be better than the tear energy in predicting fracture of natural rubber under dynamic loading.     

近似二维应力状态下I_1断裂准则假设有效性的试验验证

I_1断裂准则假设是基于原子间相互作用模型和断裂物理过程分析提出的一个新的断裂准则,该准则认为,对于完整材料和含缺陷材料,当局部区域的应力第一不变量I_1达到临界值Ib时,材料发生断裂,临界值Ib定义为断裂强度。利用该准则与Mises屈服准则,可给出材料的四种基本力学行为判据,包括弹性变形、塑性变形、脆性断裂与塑性断裂。为验证近似二维应力状态下I_1断裂准则假设的有效性,设计了液压-轴向拉伸联合作用下的薄壁圆管双向应力试验并针对304不锈钢、10Ni5CrMoV钢和EH50钢三种材料开展了试验研究,试验结果表明,对于同一种材料,在不同应力组合下断裂时的第一主应力和第二主应力满足线性关系,应力第一不变量I_1保持恒定,材料存在特定的断裂强度Ib值,从而验证了近似二维应力状态下I_1断裂准则假设的有效性。     

Computer Simulation of Plastic Deformation in GrainBoundary Region under High Rate Loading

The computer simulation of Al three-dimensional crystallite containing grain boundary of special type was carried out and its behaviour under high rate loading was investigated. The molecular dynamics method was used and interaction betwen atoms was described based on pseudopotential method. Vortical character of the atom movements in the grain boundary region is realized under shear loading in certain directions. Back and forth movements of atoms in the direction which is perpendicular to the shear also arise. Amplitude of such movements is approximately equal to an interplanar distance in this direction.     

Interlaminar Fracture Testing Method for CFRP Using Tensile Loading with Acoustic Emission Analysis

A method is described to characterize the uniformity of interlaminar fracture toughness of laminated carbon-fiber-reinforced polymer (CFRP) composites fabricated by the modified vacuum assisted resin transfer molding process. To prepare specimens for Mode I fracture toughness tests, pieces were sectioned from the inlet and vent regions of a CFRP plate ([+30/-30]₆), with a starter crack inserted. The specimens were packed between two rectangular epoxy plates to apply a load using a universal testing machine. Acoustic energy signals were monitored using two sensors attached to the epoxy plates during tensile loading. The difference between the material properties of specimens from the inlet and vent regions of the CFRP plate were statistically compared using one-way analysis of variance (ANOVA); we show that the specimens showed no statistically significant differences in the interlaminar fracture characteristics depending on the part of the mold from which they were taken.     

冲击加载下厚靶后表面早期几何变形特征分析

通过数值模拟研究了厚靶后表面在冲击加载下早期的几何变形特征,计算结果表明：厚靶变形存在一个由前凸型翻转为内凹型的时间窗口期,与传统研究薄靶的前凸型几何变形存在差异。结合电探针阵列测试方法获得的实验结果,从一个方面解释了工程实验中重复性不强的原因,因为这个窗口期非常敏感,与电探针阵列与后表面的距离密切相关。     

Deformation and Life of Titanium Alloy VT9 under Conditions of Nonproportional Low-Cycle Loading

Results of experimental investigation of low-cycle fatigue of titanium alloy VT9 under nonproportional loading are presented. Tensile-torsional low-cycle fatigue tests were carried out on thin-walled tubular specimens under proportional and nonproportional cyclic deformation at room temperature. It has been found that cyclic hardening in a steady state at the same value of the equivalent von Mises strain range is the same in circular cycles and in torsion (or tension–compression) cycles. In the case of nonproportional loading of specimens, the life of titanium alloy VT9 shortens in comparison with proportional loading, but not as much as for stainless steels.