Equipment for Testing Sheet Structural Materials under Biaxial Tension. Part 1. Testing under One-Sided Pressure of the Working Medium

We consider specific features of the design of equipment for the investigation of strength and regularities of fracture of sheet structural materials under biaxial tension created by loading specimens by one-sided pressure of the working medium. We propose solutions of several methodical problems connected with testing under high pressures of the working medium which enable one to realize the required modes of cooling of the specimens, decrease the level of fracture energy, and increase the reliability and safety of testing.     

A Biaxial Fatigue Specimen for Uniaxial Loading

Abstract: The aim of this paper is to present a novel un‐notched fatigue test specimen in which a biaxial stress state is achieved using a uniaxial loading condition. This allows the problem of multi‐axial fatigue to be studied using relatively common one‐axis servo‐hydraulic testing machines. In addition the specimen presented here is very compact and can be made using a small volume of material (100 × 40 × 4.5 mm). For this specimen, the degree of biaxiality, defined by the parameter is equal to approximately 0.45. The specimen geometry was optimised using the Dang Van multi‐axial fatigue criterion. In addition to use as a fatigue specimen, it has been demonstrated that the biaxial specimen presented here is also suitable for biaxial tensile tests, to determine the rupture strength of a material in a biaxial stress state. Two different materials have been investigated: The first was wrought aluminium 2024‐O in the form of 5 mm sheets. The second was a cast aluminium‐silicon alloy AlSi7Cu0.5Mg0.3, commonly used in automotive and aeronautical applications. The fatigue strengths were determined at 2 × 10⁶ cycles and at various R‐ratios using a staircase procedure. For the aluminium 2024, it is shown that the biaxial stress state increases the maximum permissible first principal stress when compared to the uniaxial condition. However, in terms of the cast aluminium alloy, it has been demonstrated that this type of fatigue specimen is not suitable for materials containing casting defects, in particular micro‐shrinkage pores, because the volume of material, in which the stress state is biaxial, is not large enough.     

10Ni5CrMoV钢双轴弯曲应力下表面裂纹疲劳扩展特性研究

以10Ni5CrMoV钢为研究对象,在加载条件与构件使用环境相近条件下,在原板厚大尺寸试样表面引入人工缺口模拟实际构件中存在的类表面裂纹缺陷,采用双轴弯曲疲劳试验方法,开展原板厚大尺寸试样双轴弯曲应力下的表面裂纹疲劳扩展特性试验研究。结果表明,裂纹半长c和裂纹深度a都随循环次数N单调递增,且曲线a-N满足一定的线性关系。建立表面裂纹半长c与深度a之间的定量关系式预测模型,从而定量解决裂纹深度尺寸不好直接测量的难题。     

Load-Carrying Capacity of a Cracked Plate under Biaxial Tension

The paper presents the findings of an experimental investigation into the possibility of estimating the load-carrying capacity of sheet materials with a central through crack under biaxial tension at low temperatures from the fracture-toughness parameters determined in uniaxial tests.     

双轴载荷下复合材料十字型试样几何形状对中心测试区系数的影响

基于双轴拉伸载荷下复合材料十字型试样的设计特点,对比分析了不同几何形状的十字型试样在不同厚度比和载荷比条件下中心测试区应力集中系数和承力系数的变化规律,并开展了不同载荷比的双轴拉伸实验进行验证。研究表明:十字型试样中心测试区系数与载荷大小无关,与试样几何形状、厚度比及载荷比有关;等宽加载臂宽度越小、厚度比越大,应力集中系数越小,载荷比不同,应力集中系数也不同;一般而言,中心测试区承力系数随厚度比增加而增大,x向承力系数βx随载荷比增加呈非线性增大,y向承力系数βy随载荷比增加呈线性减小;在双轴拉伸载荷条件下,形状D十字型试样在载荷比f=4/1时中心测试区y向应力分量为负值,表现为压应力状态。     

On modelling cracks in orthotropic plates under biaxial loading: synthesis and summary

The model of a crack with a process zone is considered and generalized to orthotropic materials. It is assumed that a material in the process zone satisfies a strength condition of arbitrary form. Based on the crack model, the fracture of an orthotropic cracked plate under biaxial loading is studied. The crack is directed along one of the anisotropy axes with external loads being applied in parallel and perpendicularly to it. The influence of the biaxiality of external loading on the critical state of the cracked plate is analysed within the framework of the critical crack opening displacement and critical J ‐integral criteria. Numerical solution is obtained using the Mises‐Hill and Gol’denblat‐Kopnov strength criteria. Theoretical results are compared with experimental data obtained by testing specimens made of structural metals.     

聚醚砜中空纤维超滤膜的双向拉伸

提出了中空纤维的“双向拉伸”这一新概念，研究了纵向拉伸、径向张力、凝固浴浓度对膜性能的影响，为设计具有合适性能的聚醚砜中空纤维膜提供参考．     

Stress Distributions around Holes in Composite Laminates Subjected to Biaxial Loading

An approximate solution has been derived for the in-plane stresses near a circular hole, in an orthotropic composite laminate under biaxial loading. The derived stresses were found to be in good agreement with the exact analytical solution, for a series of laminates investigated. However, the degree of accuracy of the approximate stress distribution is strongly influenced by the laminate lay-up and the biaxiality ratio. The resultant stresses could be employed in stress based fracture models to investigate the notch sensitivity and fracture mechanisms of composite plates with an open-hole subjected to biaxial loading.     

Molecular Dynamics Calculation of the Viscosities of Biaxial Nematic Liquid Crystals

We have evaluated the Green–Kubo relations for the viscosities of a biaxial nematic liquid crystal by performing equilibrium molecular dynamics simulations. The viscosity varies by more than two orders of magnitude depending on the orientation of the directors relative to the streamlines. The molecules consist of nine fused Gay–Berne oblates whose axes of revolution are parallel to each other and perpendicular to the line joining their centers of mass. This gives a biaxial body, the length-to-width-to-breadth ratio of which is equal to 5:1:0.4. The numerical evaluation of the Green–Kubo relations for the viscosities is facilitated by the application of a Gaussian director constraint algorithm that makes it possible to fix the directors in space. This does not only generate an inertial director-based frame but also a new equilibrium ensemble. In this ensemble the Green–Kubo relations for the viscosities are simple linear combinations of time correlation function integrals, whereas they are complicated rational functions in the conventional canonical ensemble.     

Failure process and mechanism of sandstone under combined equal biaxial static compression and impact loading

The process and mechanism of impact fractures in sandstone were investigated under equal biaxial static compression. The cracking process was captured by a high‐speed video camera. The results indicate that the main crack propagates along the circumference and finally forms a crater‐shaped failure zone. The size of the crater‐shaped failure zone increases as the static stress and impact velocity increase. In addition, microscopic features of the fracture surface were observed using a scanning electron microscope. It was found that the microcracks expand after combination loading, making the rock more susceptible to damage. Finally, the influence mechanism of static loading on dynamic failure of the rock was revealed by theoretical analysis and numerical simulation.     

轴向加荷疲劳试验机动态力修正方法分析

疲劳试验机的动态力修正量与试验机参振质量、刚度及其分布、试验机的传感器安装位置有关。通过对传感器安装在2种不同位置的疲劳试验机力学模型的动态力分析,给出试验机使用时动态力的近似修正公式。通过动态力与参振系统质量分布的分析,结合频率在1000Hz以下动态法与静态法力值校准的实验数据,认为疲劳试验机检定时采用静态法力值校准较动态法力值校准更为合理。     

Visualization of Shear Motions of Cohesive Powders in the True Biaxial Shear Tester

Steady-state flow of powders is defined as a continuous deformation of the material without volume change while the stresses at the specimen's boundaries remain constant. Recent investigations have shown that this state, especially for cohesive powders, is not always as steady as it should be by definition. In this article a recent extension of the true biaxial shear tester is introduced that allows a view of the shear motion of the brick-shaped powder specimen inside the tester. By applying a dark-colored powder pattern onto a light powder sample, the movement of the powder can be captured using a CCD camera. Development of shear bands and inhomogeneities of the sample can be visualized. Experiments with a cohesive powder with purely strain-controlled, volume-preserving shear cycles, as well as mixed stress-strain controlled experiments, are presented. The recorded images as well as stress-strain data from discrete elements simulations are compared to the experimental results.     

脆性材料在双向应力下的断裂和失效研究

采用热力学方法对脆性薄片试样成功地进行了双向和单向平面拉伸试验,通过观察和记录试片中心的直通裂纹的扩展和断裂过程,测试出玻璃和陶瓷薄片的断裂韧性在双向和单向拉伸载荷时的差别．结果表明双向拉伸使裂纹阻力增强,平行于裂纹的应力对裂纹扩展有影响．该研究表明,对线弹性材料在双向载荷作用下,传统的应力强度因子准则不适用．裂纹张开的应变依赖性被证实在双向应力的断裂评价中．     

试验夹具动态设计

为考核汽车电器的可靠性,需对其进行振动可靠性实验。装夹和固定电器系统元件的夹具,是实验的重要组成部分,其动态性能对振动试验有重要影响。根据试件的外形及安装定位方式建立了夹具的三维模型,用有限元方法计算了夹具的模态频率与振型,依据分析结果对夹具的结构进行了改进,使夹具动态性能满足试验要求。     

Testing of scaleless measuring instruments

Conclusions The article deals with four methods which are intended for continuous automatic testing of scaleless measuring instruments and raise considerably the precision and efficiency of testing. Three of them can, in many instances, be used without developing special equipment. Continuous testing provides an incomparably larger amount of information about the qualitative condition of the tested instruments than normal discrete static testing, thus serving to obtain a technical diagnostic of instruments both under adjustment and quality control conditions. This makes it possible to reduce considerably the number of failures in the course of operation by eliminating in time the instruments' defects which in normal testing remain undiscovered. Continuous automatic testing simplifies prolonged testing of instruments for reliability and evaluation of their reliability parameters. The testing methods under consideration provide in principle the possibility of determining the tested instruments' dynamic errors with respect to the input signal's rate of change.Translated from Izmeritel'naya Tekhnika, No. 5, pp. 70–73, May, 1967.     

挪威海格纳斯潜艇水声试验场测量设施综述

利用水声试验场对潜艇的水下辐射噪声进行测量和分析,是先进国家改善潜艇安静性的重要方法。位于挪威卑尔根附近的海格纳斯潜艇水声试验场,是德国、荷兰、丹麦、挪威等北约国家最重要的潜艇水声检测机构。本文介绍了该潜艇水声试验场的选址特点和主要测量设施,分析峡湾水域建设潜艇水声试验的利弊,分析航行试验场和静态试验场对水声试验场建设的不同作用,为我国水声试验场的建设提供参照。     

双轴载荷下缝合层板的强度预测

基于缝合层板单层单胞细观力学模型,研究了单层板在拉、压、剪下的力学特性。根据经典层板理论建立了缝合层板在双轴载荷下的强度模型,并考虑了缝合造成表面层和内部层刚度和强度的差异。通过有限元软件ABAQUS分析了双轴载荷多种工况下缝合层板的损伤演化过程,揭示了缝合层板的失效机理,获得了缝合层板在双轴载荷下的失效包络线以及对应比率载荷下的应力应变曲线。所预测的失效模式和失效强度与实验取得了较好的吻合。通过分析表明缝合层板单层在剪切载荷下表现出一定的非线性特性。多轴多向层板在双轴载荷下表现出较强的耦合性。     

动态测试中的抗干扰技术

分析了动态测试系统中引起干扰的主要因素，运用硬件技术实现的抗干扰方法。     

Biaxial Yield for Nonlinearly Viscoelastic Materials with a Strain Clock

A constitutive equation with a dilatation dependent reduced time is used to model the mechanical response of solid amorphous polymers such as polycarbonate. Such constitutive equations have the property that stress relaxation occurs faster with increasing dilatation. In previous work, it has been shown that this constitutive equation can account for yield in materials undergoing uniaxial strain or stress control histories. In the present work, yield is discussed when materials described by this constitutive equation undergo homogeneous biaxial and triaxial strain histories. Four sets of conditions are considered: in-plane biaxial constant strain rate histories and in-plane biaxial constant stress rate histories, for both plane stress and plane strain states. Yield is defined in a manner analogous to that in the corresponding strain and stress control conditions in the uniaxial case.     

Biaxial fatigue for proportional and non‐proportional loading paths

In order to study the use of a local approach to predict crack‐initiation life on notches in mechanical components under multiaxial fatigue conditions, the study of the local cyclic elasto‐plastic behaviour and the selection of an appropriate multiaxial fatigue model are essential steps in fatigue‐life prediction. The evolution of stress–strain fields from the initial state to the stabilized state depends on the material type, loading amplitude and loading paths. A series of biaxial tension–compression tests with static or cyclic torsion were carried out on a biaxial servo‐hydraulic testing machine. Specimens were made of an alloy steel 42CrMo4 quenched and tempered. The shear stress relaxations of the cyclic tension–compression with a steady torsion angle were observed for various loading levels. Finite element analyses were used to simulate the cyclic behaviour and good agreement was found. Based on the local stabilized cyclic elastic–plastic stress–strain responses, the strain‐based multiaxial fatigue damage parameters were applied and correlated with the experimentally obtained lives. As a comparison, a stress‐invariant‐based approach with the minimum circumscribed ellipse (MCE) approach for evaluating the effective shear stress amplitude was also applied for fatigue life prediction. The comparison showed that both the equivalent strain range and the stress‐invariant parameter with non‐proportional factors correlated well with the experimental results obtained in this study.