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弱正交异性材料残余应力测量的声弹性方法 总被引:7,自引:0,他引:7
为了适应工程材料的残余应力无损测量的要求,本文将横波和纵波声弹性相结合,建立适用於弱正交异性材料的平面声弹性残余应力测量方法,并应用该方法及自行研制的横波换能器对焊接试件的二维残余应力进行了测试。 相似文献
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1 引言
在层裂的实验研究中,目前尚无法直接测量发生在材料内部的动态断裂过程。通常采用测量自由面速度剖面,推演出材料层裂特性的方法。在计算材料发生断裂时的拉伸应力即层裂强度时,需要知道拉伸应力即负压下的声速。测量负压下的声速比测量冲击压缩下的声速要困难得多。仅仅从自由面速度剖面并不能计算出负压声速,因为通常无法确定材料中应力由压应力转变为拉伸应力的“位置”、发生层裂的位置以及时间。能否通过特别的实验设计,确定发生这些过程的时一空位置,进而获得负压声速,一直是实验研究者企求解决的问题。下面介绍两种测量负压声速的实验装置设计和计算负压声速、层裂强度和断裂密度的方法,是这方面研究工作的尝试。 相似文献
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用实验和数值模拟方法,研究在爆炸载荷下岩体内部一对平行裂纹对扩展主裂纹的影响规律。实验中,采用带有中心装药孔及预制裂纹的砂岩圆盘试件,利用由示波器、超动态应变仪及裂纹扩展计所组成的测试系统,监测主裂纹扩展速度和扩展距离;数值模拟中,采用了AUTODYN软件进行,模拟了主裂纹及两平行裂纹的扩展规律,对岩石材料,采用线性状态方程及最大拉应力失效准则,并在两平行裂纹间设置相应的观测点记录应力曲线。通过实验与数值模拟分析,得到:爆炸载荷下,紧随冲击波后的稀疏波经过两平行裂纹面反射后变成压缩波,并在两平行裂纹间产生垂直于主裂纹扩展方向的压应力,对裂纹的扩展有压制、止裂作用;而且,这种压应力的大小与两平行裂纹的间距有关,进而导致了不同的止裂效果,影响裂纹的扩展速度及最终扩展长度。 相似文献
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超声反射纵波法检测钢轨应力的实验研究 总被引:1,自引:0,他引:1
钢轨的应力状况直接影响列车运行的安全,因此对钢轨应力的研究特别重要.用超声波测量应力的方法由于其对被测材料无损的特性而受到广泛关注.文章重点叙述了利用反射纵波法(the reflected longitudinal waves)来检测钢轨应力的实验方法.该方法如果用于实际测量,可以提高钢轨检测的工作效率,大大节约在铁路维护上的开支,提高铁路运输的安全系数,加速实现人民铁路的高效运营.文中详细介绍了整套实验测量系统、所用的探头、探头放置的位置、信号耦合与放大电路图以及实验测量结果,并根据实验测量结果进行分析.结果显示应力变化引起的钢材料特性变化导致了声传播速率的变化,且应力变化与声传播速率的变化呈线性关系.该结果证明了超声波测量钢轨应力的可行性. 相似文献
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渗透率各向异性是沉积岩层理结构中一个非常典型的现象,一方面它由原生沉积结构决定,即原生各向异性,另一方面它受到总应力和孔隙压力影响,即诱发各向异性.为研究真三向应力条件下储层砂岩渗透率原生与诱发各向异性,以中国东北部S6储气库储层砂岩为研究对象,采用东北大学自主研制的硬岩真三轴应力-渗流耦合装置对储层砂岩进行渗流实验,通过稳态法完成同一砂岩3个相互垂直方向的渗透率测试.实验结果表明:储层砂岩在施加的应力和孔隙压力范围内,平行层理方向的渗透率k x为100.94~113.98 m D,k y为98.34~111.41 mD,垂直层理方向的渗透率k z为54.98~63.29 mD;储层砂岩3个正交方向渗透率均随主应力增加而减少,随孔隙压力加载而递增;与气体渗流方向垂直的应力对渗透率的影响大于与气体渗流方向平行的应力对渗透率的影响;当外部应力方向都垂直于气体渗流方向时,与层理垂直的应力对渗透率的影响大于与层理平行的应力对渗透率的影响;孔隙压力对储层砂岩渗透率的线弹性响应并不是各向同性的,孔隙压力对水平层理方向所产生的渗透率增量超过了垂直层理方向.研究结论为地下储气库储层砂岩渗透率准确预测提... 相似文献
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声弹性方法测量金属材料的塑性损伤 总被引:3,自引:0,他引:3
本文提出一个利用非线性参数研究材料损伤的声弹性方法.在该方法中定义了一个由二阶和三阶弹性常数所组合的损伤变量.以20#钢为例,采用横波声弹性方法测量金属材料的塑性损伤.同时用声速法作了损伤测量.对比两种方法的实验结果表明,新方法是对金属材料塑性损伤测量的有效技术. 相似文献
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平面声弹性技术的研究 总被引:3,自引:0,他引:3
本文从弹性波理论出发。导出了微正交各向异性材料平面应力问题的应力—声关系。借助于一个新引进的参数S,给出了一个独立的新方程,使这类问题的解决大为简化。在实验技术方面,研制了垂直入射平面偏振横波的可旋转换能器,建立了平面声弹性实验系统,改进了耦合和测速技术。 相似文献
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为研究闪长岩在单轴加载过程中的声发射和各向波速变化规律,在单轴阶段加载和循环阶段加载条件下,对闪长岩岩样破裂过程中的声发射累计数、不同应力水平不同方向的波速、切线模量、轴向应变速率进行了研究。实验结果表明:(1)随着应力水平的增高,声发射事件数不断增加,在高应力水平(约80%峰值强度)时,声发射累计数急剧增多,随后切线模量出现震荡变化。(2)在加载过程中,压密程度及裂纹扩展方向对波速产生了巨大的影响,导致不同方向波速在不同的应力水平呈现出不同的变化规律,由此可以推测破裂面位置和破裂模式。在较高应力水平下(约60%峰值强度),平行于加载方向的波速趋于稳定,而垂直于加载方向的波速则持续下降,故用垂直于加载方向传播的波速预测岩石的破坏更具可靠性。(3)随着应力的增加,应变速率有逐渐减小的趋势,但临近岩石破裂时无异常变化出现,说明利用变形观测难以预测此类岩石的破坏。以上研究表明,根据纵波波速、声发射累计数和切线模量的变化可以有效预测岩石的破坏。 相似文献
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This paper proposes a method to evaluate surface stresses in orthotropic materials by the use of vertically polarized shear waves (SV waves). It is assumed that the normal to the surface coincides with one of the axes of anisotropy, and that the material anisotropy is not necessarily small. The speeds of the waves are expressed in terms of the material properties, the stress, the rigid body rotation and the propagation direction. From the expressions, and for the following two cases: (1) the rigid body rotation is known, (2) the anisotropy is weak, it is possible to determine the components of the surface stress by measuring the speeds of SV waves propagating in several directions. When the anisotropy is weak, the acoustoelastic birefringence for SV waves is also derived, to separate the material anisotropy and the difference of the principal stresses. The theory can be applied to stress evaluation by using ultrasonic Lamb waves whose speeds are nearly equal to those of SV waves. 相似文献
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Nelson N. Hsu 《Experimental Mechanics》1974,14(5):169-176
Stress-induced optical birefringence in transparent materials has long been a common technique of stress analysis. Although
stress-induced acoustic birefringence was discovered more than 20 years ago, its development and actual applications are still
limited. This paper will look at the similarities and differences between the propagation of light waves in photoelastic materials
and the propagation of ultrasonic waves in deformed solids. Critical comparisons of the experimental methods employed in photoelasticity
with those available in modern ultrasonic measuring technique show why previous studies on ultrasonic measurement of stresses
were not very successful.
A new experimental technique is devised for using ultrasonic waves for stress analysis. The technique employs a single rotatable
10-MHz shear transducer as the transmitter and receiver of ultrasonic pulses. The enlarged display of the 10-MHz modulated-pulse
pattern of reflected echoes provides a convenient way to determine the directions of principal axis of the stress within ±3
deg. The pulse-echo-overlap method is used to measure the absolute velocities of the two principal shear waves. The difference
in principal stresses is then calculated from the velocity measurements. Test results of common structural-aluminum and steel
specimens under uniaxial compression show a linear relation between the velocity changes and the applied stress. Ultrasonic
measurements of stress distribution in a 6.35-cm diameter, 1.9-cm-thick aluminum disk under diametric compression are also
reported.
Paper was presented at Third SESA International Congress on Experimental Mechanics held in Los Angeles, CA on May 13–18, 1973. 相似文献
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An acoustoelastic method for residual stress measurement in slightly orthotropic materials by using ultrasonic longitudinal and shear waves is presented. A shear transducer with small vibrator 2 × 2mm2 is developed and described, and the measurement of 2-D residual stresses in a seam welded plate was carried out by this method with the shear transducer developed.This project was supported by National Natural Science Fundation of China 相似文献
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The acoustoelastic stress analysis is based on the fact that an initially isotropic material becomes anisotropic under stress. The birefringent effect for polarized ultrasonic shear waves in the stressed material will then be similar to the photoelastic effect in which a light wave and a transparent model specimen are used. In this paper, the velocity differences of acoustical, perpendicularly polarized waves are measured directly by a ‘sing-around’ method using a 5-MHz shear-type transducer. The residual-stress distribution in a mild-steel circular plate with a concentrically patch-welded joint is measured by this method. The acoustoelastic coefficient is obtained separately by uniaxial testing of the base material. The results show that the acoustical stress measurement, carried out nondestructively, agrees well with those obtained by conventional destructive methods as well as with theoretical predictions. 相似文献
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A device for measuring the velocity of ultrasonic waves: An application to stress analysis 总被引:3,自引:0,他引:3
In this paper we present a device for the practical application of an ultrasonic critical-angle refractometry (UCRfr) technique.
UCRfr is a technique for measuring the velocity of longitudinal, shear and Rayleight waves, developed to improve the traditional
ultrasonic methods for measuring the stress level in materials by means of acousto-elasticity. The technique consists of relating
the variations in wave propagation velocity to variations in the angle of refraction at the interface with a second medium.
Variations in the angle of refraction are determined on the basis of delay in receiving of the same wave at two different
points.
The study deals with the measurements of velocity changes of longitudinal wave due to uniaxial stress. In the present work
the effects of stress on aluminum and steel specimens have been studied.
Experimentation has show the potential of the technique for stress measurement; on the other hand, when the applied stress
is known, it allows the measurement of the acoustoelastic constants of longitudinal waves.
As regards measuring variations in velocity induced by stress, using this method it is possible, with a suitable choice of
the material the device is made of, to isolate the effects of stress on velocity from the possible effects of temperature. 相似文献
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The shear orientation of hexagonal and lamellar liquid crystalline phases of polymeric surfactants was investigated by rheo-optical
techniques (flow birefringence (Δn), small-angle light scattering) as well as by nuclear magnetic resonance and optical microscopy. The evolution of birefringence
in the hexagonal phase is discussed for simple and oscillatory shear, and an alignment of rodlike micelles along the flow
direction was found. A shear induced formation of vesicles (“onions”) is observed with the lamellar phase. They displayed
a characteristic four-lobe pattern in depolarized light scattering. Above a critical shear stress vesicles were degraded and
perpendicularly aligned lamellae (i.e. with their normal along the vorticity direction) were obtained. A comparison of experiments
performed at constant stress and constant rate revealed that the vesicle to planar lamellae transition occurred above a critical
shear stress. The behavior of the polysoap lyotropic mesophases under shear, i.e. the strain dependent alignment in the hexagonal
phase, the shear induced formation of vesicles, and a transition to planar lamellae in the lamellar phase, is very similar
to the behavior of lyotropic mesophases formed by low molar mass surfactants or amphiphilic block copolymers. The geometrical
constraints that are introduced when amphiphilic side groups are fixed to a polymer backbone do not significantly alter the
response of the mesophase to a shear deformation.
Received: 4 May 1999 /Accepted: 19 July 1999 相似文献
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三向应力Mohr圆的真实构成及剪应力作用方向的确定 总被引:2,自引:1,他引:1
三向应力Mohr圆的构成在传统上是借助公式推证而得,并以平面图形来表示,缺乏三维的真实感和直观性。在应力应变分析中,对于平面应力问题,可以通过平面应力摩尔圆确定过一点不同斜面上的应力分量及其作用方向。对于三维问题,利用摩尔圆图解法可以确定某一斜面上的正应力和剪应力的数值,但不能表示剪应力的作用方向。剪应力的作用方向需要通过另外的图解方法来确定。本文分别从坐标系旋转和数值计算的角度解释了三向应力Mohr圆的构成过程,形象地说明了Mohr圆的物理本质。针对三向应力Mohr圆不能表示剪应力作用方向的问题,通过矢量运算,给出了剪应力作用方向的确定公式。 相似文献
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为了研究建筑织物膜材的剪切力学性能,提出一种新的剪切测试方法。采用中心区域宽度和四臂长度均为16cm的十字形试件,试件纱线的经纬向与加载方向呈45°角。根据膜材变形和应力关系,推导了剪应力和剪应变的计算方法。定义了使试件中心区域产生三个循环剪应力场的加载谱,循环产生正负交替的剪切应力。试验采用表面抛光的(Polyvinylidene Fluoride,聚偏氟乙烯)涂层膜材,测量x、y两个方向的应力和应变,通过计算得到剪切应力应变曲线,并对试验结果进行分析。结果表明,新的剪切测试方法能够反映建筑织物膜材剪切力学性能。最后通过有限元方法模拟材料受剪状态下的应力和应变,与试验得到的应力值和应变值相近。 相似文献
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针对结构中微裂纹检测难题,本文对结构中微裂纹与超声波的混频非线性作用进行了数值仿真研究。基于经典非线性理论,得到了两列超声纵波相互作用产生混频效应的理论条件。通过有限元仿真,研究了两列纵波与微裂纹相互作用产生混频的条件,并分析了界面处静应力、摩擦系数和裂纹方向对混频效应的影响。研究发现,超声波与微裂纹相互作用产生混频非线性效应的发生条件仍符合经典非线性理论下的混频产生条件。裂纹界面处施加的静应力对差频横波幅值有明显影响;当施加静应力与无裂纹模型得到的最大应力值接近时,混频非线性效应最强;裂纹界面的摩擦系数对超声波的混频非线性效应影响较小;透射差频横波传播方向与经典非线性理论预测的理论差频分量方向基本一致,且几乎不受裂纹方向变化的影响,而反射差频横波的传播方向随裂纹方向的改变而有所不同。本文研究工作为微裂纹检出及方向识别做了有益探索。 相似文献