Non-Contact Stress Measurement during Tensile Testing Using an Emat for SH₀-Plate Wave and Lamb Wave

The stress on a test specimen during tensile testing is generally measured by a strain gauge. This method has some problems in that it would influence the measurement conditions of the tensile test and can evaluate only the position at which the strain gauge is attached. The acoustoelastic method is proposed as a method replacing the strain gauge method. However, an ultrasonic sensor with a piezoelectric oscillator requires a coupling medium to inject an ultrasonic wave into a solid material. This condition, due to the error factor of the stress measurement, makes it difficult for the ultrasonic sensor to move on the specimen. We then tried to develop a non-contact stress measurement system during tensile testing using an electromagnetic acoustic transducer (EMAT) with an SH0-plate wave and S0-Lamb wave. The EMAT can measure the propagation time in which the ultrasonic wave travels between a receiver and a transmitter without a coupling medium during the tensile testing and can move easily. The interval between the transmitter and the receiver is 10mm and can be moved along the parallel direction or the vertical direction of the tensile load. The transit time was measured by a cross-correlation method and converted into the stress on the test specimen using the acoustoelastic method. We confirmed that the stress measurement using an SH0-plate wave was superior to that with an S0-Lamb wave.

Effect of sensor quantity on measurement accuracy of log inner defects by using stress wave

Wood nondestructive testing （NDT） is one of the high efficient methods in utilizing wood. This paper explained the principle of log defect testing by using stress wave, and analyzed the effects of sensor quantity on defect testing results by using stress wave in terms of image fitting degree and error rate. The results showed that for logs with diameter ranging from 20 to 40 cm, at least 12 sensors were needed to meet the requirement which ensure a high testing accuracy of roughly 90% of fitness with 0.1 of error rate. And 10 sensors were recommended to judge the possible locations of defects and 6 sensors were sufficient to decide whether there were defects or not.

Application of Nonlinear Lamb Wave Mixing Method for Residual Stress Measurement in Metal Plate

Harmonic nonlinear ultrasound can offer high sensitivity for residual stress measurements;however,it cannot be used for local stress measurements at a point in space and exhibits nonlinear distortions in the experimental system.This paper presents a feasibility study on the measurement of residual stress in a metal plate using a nonlinear Lamb wave-mixing technique.The resonant conditions for two Lamb waves to generate a mixing frequency wave are obtained via theoretical analysis.Finite element simulations are performed to investigate the nonlinear interactions between the two Lamb waves.Results show that two incident A0 waves interact in regions of material nonlinearity and generate a rightward S0 wave at the sum frequency.Residual stress measurement experiments are conducted on steel plate specimens using the collinear Lamb wave-mixing technique.By setting different delays for two transmitters,the generated sum-frequency component at different spatial locations is measured.Experimental results show that the spatial distribution of the amplitude of the sum-frequency component agrees well with the spatial distribution of the residual stress measured using X-rays.The proposed collinear Lamb wave-mixing method is effective for measuring the distribution of residual stress in metal plates.

Standing,Periodic and Solitary Waves in (1+1)-Dimensional Caudry-Dodd-Gibbon-Sawada-Kortera System

In the paper, the variable separation approach, homoclinic test technique and bilinear method are successfullyextended to a (1+1)-dimensional Caudry-Dodd-Gibbon-Sawada-Kortera (CDGSK) system, respectively.Basedon the derived exact solutions, some significant types of localized excitations such as standing waves, periodic waves,solitary waves are simultaneously derived from the (1+1)-dimensional Caudry-Dodd-Gibbon-Sawada-Kortera systemby entrancing appropriate parameters.

Non-destructive Evaluation of Absolute Stress in Steel Members Using Shear-Wave Spectroscopy

Non-destructive measurement of absolute stress in steel members can provide useful information to optimize the design of steel structures and allow the safety of existing structures to be evaluated.This paper investigates the non-destructive capability of ultrasonic shear-wave spectroscopy in absolute stress evaluation of steel members.The effect of steel-member stress on the shear-wave amplitude spectrum is investigated,and a method of absolute stress measurement is proposed.Specifically,the process for evaluating absolute stress using shear-wave spectroscopy is summarized.Two steel members are employed to investigate the relationship between the stress and the frequency in shear-wave echo amplitude spectrum.The H-beam loaded by the universal testing machine is evaluated by the proposed method and the traditional strain gauge method for verification.The results show that the proposed method is effective and accurate for determining absolute stress in steel members.

An Experi mental Study on Wave-Induced Dynamic Stresses in Seabed

A series of hydraulic model tests with horizontal movable seabed under regular wave actions have been carried out to investigate the dynamic interactions between water waves and seabed soil. Seabed dynamic stresses from experiments are, tound to differ from theoretical resuhs. The response of p0 in permeable seabed has a small decay and phase shift to the nonlinear wave actions, and the dynamic stresses, σs/p0, σh/p0 and u/p0, contain different phase shift characteristics. Such phenomena will strongly affect the dynamic stress path in seabed. If the phase shifts of σs. and σh are neglected, the stress path will become a straight line; otherwise, it will become an elliptical curve. In phase shift cases, the long axis of the p - q diagram will be shortened when the depth increases, and the short axis will become longer when the phase shift increases. For the p＇ - q＇ diagram, the larger the phase lag of u, the longer the short axis. Relative results offer useful information for the analysis of seabed stability.

Relief of Residual Stresses in 800 MPa Grade High Strength Steel Weldments by Explosion Treatment and its Effect on Mechanical Properties

The explosion treatment technique has been used in the relief of residual stresses in 800 MPa grade high strength steel manual welded joints. The residual stresses on surface and through thickness of the weldment were measured for both as-welded and explosion-treated sample, the mechanical properties of welded joints under different conditions were also tested. The effect of explosion treatment on the fracture toughness of materials with a residual defect was investigated by crack opening displacement （COD） test. The results show that explosion treatment can reduce not only the surface residual stress but also the residual stress through thickness in the welded joints. The effect of explosion treatment on the mechanical properties and a residual defect in welded joint were inconspicuous.

Effect of Wave Headings on the Dynamic Response of the Continuous Mating Operation of Floatover Installation

The topside floatover installation is always a great challenge and is sensitive to environmental conditions.In this study,experimental analysis on the mating operation of the floatover installation in different wave headings is presented.The continuous mating operation using the rapid transfer technique was experimentally simulated with the assistance of the jacking system and the ballast system.In the continuous transfer modeling,the topsides loads were transferred onto the jacket by several consecutive steps,including the first rapid jack-down for the 30%loads,continuous 30%−70%load transfer and the second repaid jack-down for the remaining 30%loads.Motions of the barge and the topsides as well as loads on the Deck Support Unite(DSU)and the Leg Mating Unite(LMU)in different wave headings were measured.Experimental results illustrated the complex motion behavior and load characteristics of the continuous transfer operation.Results indicate that the rapid jack-down operations will lead to impact loads and larger lateral DSU loads.The bow quartering seas are much more dangerous as it gives rise to the larger motions and loads.Comparisons with the traditional steady-state modeling indicate that the continuous transfer modeling has greater advantages over the steady-state modeling on predicting the loads.

Transmission ratio (T_n) in the radian direction normal to joints in 2-D compressional wave propagation in rock masses

The transmission ratio along the radian direction normal to the joints was studied in the Universal Distinct Element Code （UDEC）. The variation of the transmission ratio with the ratio of joint spacing to wavelength was generalized into a general curve, which was determined by two critical points. The relationship between the two critical points and the affecting factors, quantity of joints and the normalized normal stiffness of joints, were obtained. A prediction model of the transmission ratio in the radian direction normal to the joints was proposed. The proposed model was applied to a field explosion test. The estimated values of the peak particle velocity from the prediction model were compared with the field records. The comparisons showed that the prediction model of the transmission ratio in the direction normal to the joints in the process of 2-D compressional wave propagation through multiple parallel joints is reliable.

基于多应力加速退化的机载电子部件可靠性试验方法

可靠性试验是获取基础安全性数据的重要来源之一。考虑机载设备的实际工作环境,多种应力共同作用导致产品失效且存在复杂的相互作用,本文提出一种基于多应力广义耦合加速退化的可靠性试验方法,可以直接获取用于适航符合性验证的基础安全性数据。首先,建立考虑多应力广义耦合的非线性Wiener加速退化模型,结合相关性分析确定应力耦合形式;其次,提出基于多应力加速退化模型的最大似然估计与参数优化方法,解决多参数估计难题;最后,以某机载LED芯片为对象开展三应力加速退化试验,实现寿命评估。结果表明,相比于传统多应力加速模型,本文所提方法更贴近实际工况,误差控制在1%以内,寿命评估精度较高,可以有效解决基础数据缺失和不准确的现实适航问题。

水平孔多参数综合测试仪器研发与应用

为研究引大济岷工程隧洞岩体特征、岩溶发育特征、地应力特征和地下水特征等,在泸定取水中线方案的引水线路中布置水平钻孔8个,共计2300 m。为满足对水平孔综合测试的需求,研制了一套适用于水平钻孔的存储式综合测井仪器。本文分析了水平孔多参数综合测试仪器各参数测量的基本工作原理;详细阐述了各功能单元的电路构成选型,主要采用DSP微处理器和大规模集成电路,结合传感器技术实现多种参数的综合测量,包括:水平钻孔的压力、温度、自然伽马、声波波速、孔内电视图像。综合测试仪器集成了模拟传感器、模拟调理电路、数据采集、数据处理、信息存储、数据通讯、信息交换、测控软硬件、电脑显示等功能,是水平孔综合测试不可缺少的技术。在引大济岷工程的水平定向孔中成功应用,一趟起下钻解决了水平钻孔的井斜、方位角、压力、温度、自然伽马、孔内电视测试的难题,尽最大可能保证了钻孔的安全及降低了劳动强度。

远场爆炸冲击波作用下高层建筑上部结构动态响应试验研究

为研究高层建筑上部结构在远场爆炸冲击波整体加载作用下的动态响应规律,设计并制作1:30缩比的整体高层建筑模型,完成野外化爆试验,获取建筑模型迎爆面冲击波压力曲线和不同高度位置处的位移曲线,结合数值模拟的方法判断试验加载状态,并对建筑模型的破坏形态和实测数据进行分析。研究结果表明:在远场爆炸冲击波作用下,高层建筑框架柱破坏模式以受剪破坏为主,框架梁构件以弯曲破坏为主,同时不同构件间的相互作用对破坏模式也有重要的影响;爆心与建筑物夹角θ≤25°时,迎爆面各处冲击波压力参数相同;当建筑结构整体仍处于弹性变形阶段时,各高度位置前期水平位移变化曲线近似重合,运动周期保持一致,后期由于高度不同,位移峰值有一定差别,与高度近似呈线性增长的关系;建筑模型的变形与破坏主要取决于比冲量的大小,冲击波峰值影响较小。

干砂地基初始应力对爆炸波传播影响的模型试验

为了研究砂土地基初始应力对爆炸波压力峰值、上升时间、传播速度和初始应力动态卸载等传播规律的影响,开展多组干砂地基常重力和超重力爆炸模型试验.试验结果表明,初始自重应力会抑制爆炸波近区压力峰值的增长,而对远区的影响较小.初始应力的增加使得爆炸波上升时间更长,更易由冲击波衰减为弹塑性波,并使得爆炸波波速增大.超重力试验通过还原砂土地基的原型自重应力,能够模拟爆炸荷载诱发砂土地基初始应力动态卸载的过程,形成爆炸压力和土体初始应力动态卸载拉应力的耦合波,动态卸载拉应力持续时间更长.与爆炸波压应力的比冲量相比,初始应力动态卸载拉应力的比冲量随着传播距离的增加逐渐成为爆炸能量的主要部分,其产生的破坏作用不可忽视.

水下爆炸下高拱坝坝面冲击荷载特性研究

确定爆炸荷载是高拱坝抗爆性能评估和抗爆设计的前提。为此,开展了高拱坝水下爆炸模型试验,并结合数值模拟方法,研究了高拱坝水下爆炸冲击荷载特性。以原型拱坝按1∶200缩比设计和制作了拱坝模型,测量了水下爆炸作用下库中以及拱坝表面的冲击荷载;采用Abaqus软件进行了拱坝水下爆炸数值模拟,结合试验数据验证了数值模拟的可靠性。研究结果表明,高拱坝水下爆炸冲击荷载可分为三个部分:首波爆炸冲击荷载、岸坡反射爆炸冲击荷载以及基底反射爆炸冲击荷载;对于库中起爆工况,高拱坝中心区域受到首波冲击的影响较大,而底部和靠近岸坡的区域则受到反射波的冲击较大,反射波在这些区域引起了较大的速度响应,在高拱坝的抗爆设计以及性能评估中,应考虑反射爆炸荷载的影响。研究成果可为高拱坝抗爆设计以及抗爆性能评估提供参考。

深部巷道围岩分区破裂带理论及试验对比研究

深部岩体巷道围岩分区破裂化现象形成机制一直存在较大争议。本文从应力波传播的角度对此问题进行了理论探索。以半圆型巷道围岩为对象,建立了巷道围岩应力波传播物理模型。对围岩区域波动方程进行了求解,得到巷道围岩区域应力波幅值分布呈波动衰减变化特征,创新性地提出了巷道围岩分区破裂带宽度及理论深度。以丁集矿井为对象,对其围岩分区中心半径进行理论计算并与实测结果进行对比研究,大部分分区半径吻合度较好。本文的研究成果对巷道围岩分区破裂化理论有一定的推进作用。

冲击波和破片联合作用下U型夹层板毁伤特性研究

为提升舰船抗爆防护性能,探究船用夹层结构在冲击载荷下的毁伤机理,本文设计并开展船用U型折叠式夹层板近距空爆试验,分析夹层板在冲击波载荷作用下的变形及破坏模式,并进行有限元仿真分析。在此基础上,通过在炸药底部预制破片群,研究冲击波与破片联合作用下夹层板的毁伤特性,从面板破口大小、竖向位移和能量吸收三个方面,讨论面板厚度和爆距对夹层板抗爆性能的影响规律。结果表明:在冲击波与破片联合作用下,夹层板上面板的破坏形式为挠曲大变形、边界撕裂、冲塞破口和分散穿孔;下面板以挠曲大变形和凹坑为主;上面板破口形状随上面板厚度增加由“蝶形”向“类圆形”转变,此时上面板和芯层为主要吸能构件;夹层板中心区域的变形对爆距减小较为敏感,而边缘区域变形量无显著变化。夹层板的总吸能、下面板和芯层的吸能量和占比均随上面板厚度减小而增大,下面板和芯层厚度的改变对夹层板整体吸能及各部分占比影响较小。

基于超声平面波成像的钢轨螺孔裂纹检测方法研究

轨道交通在当今社会生产活动中发挥着重要作用。目前在役钢轨大量采用鱼尾板和螺栓联接的方式铺设。钢轨接头在服役过程中会频繁受到冲击载荷作用,容易诱发螺孔裂纹损伤。尽早发现螺孔裂纹,并对裂纹进行定量测量,是保障铁路运输安全,避免发生严重事故的关键。超声相控阵成像检测方法具有精度高、环境适应性强、实施方便的优点,在钢轨在役无损检测中得到了广泛的应用。然而,传统相控阵斜入射扇扫成像方法受裂纹倾斜角度的影响,在工业实践中依赖工人的主观判断和分析能力,难以实现检测的定量化与标准化。基于以上背景,本文提出了一种基于超声平面波全聚焦成像的钢轨螺孔裂纹检测方法。使用复合平面波成像方法对钢轨内部螺孔及附近区域进行高精度重建,获得裂纹伤损的初步检测图像。基于编码器信息,将多个扫查点上的初步检测图像融合,得到合成检测图像,从而覆盖不同倾斜角度的裂纹。基于主成分分析方法,对裂纹倾斜角度进行定量分析,进而借助方向最大强度投影方法,得到裂纹长度的定量检测结果。所述方法在钢轨螺孔裂纹试件检测试验中实现了对[-45°,45°]范围内裂纹的100%检出率;裂纹定位误差最大值为1.47 mm,接近1个波长;长度检测误差最大值1.17 mm,小于1个波长;裂纹角度检测误差最大5.01°。所述方法需要的设备结构简单,可集成于移动式钢轨巡检设备,具备自动化实施的能力。

用于火箭炮炮口振动测量的机械滤波器设计

为了减小火箭炮炮口振动测量时应力波的干扰,设计了一种机械滤波器。通过对组建的落球试验系统进行试验,验证了应力波会影响加速度传感器的测量结果,解释了机械滤波器的滤波机理。通过扫频试验研究了机械滤波器的频率响应特性,其频率响应特性与理论计算相符合。通过对比分析加速度传感器在安装和未安装机械滤波器两种情况下所采集的振动加速度的时域、频域信号,结果显示机械滤波器在火箭炮炮口振动测量中有着良好的滤波效果。对加速度的积分运算表明机械滤波器在一定程度上提高了振动测试的精度,火箭炮振动测试时安装机械滤波器是有必要的。

束状孔与当量大孔爆破应力波在节理岩体中的衰减规律

束状孔当量球形药包爆破技术是基于大直径深孔采矿法的新型爆破技术,与单孔爆破技术相比,其炸药能量利用率更高。为了探究节理岩体中束状孔与当量大孔爆破应力波衰减规律的不同,开展束状孔与当量大孔爆破模型试验研究。试验采用混凝土制作相似模型并用无缝钢管将炮孔包围以忽略爆生气体的作用,同时考虑不同节理厚度的影响,得到了爆炸应力波峰值速度与节理厚度的关系,并将两种布孔方式在相同节理条件下进行对比分析。结果表明:两种布孔方式的爆炸应力波峰值速度均随着节理厚度的增加而逐渐降低,在相同节理厚度条件下,束状孔爆破的应力波衰减相对更小。

基于压电应力波的装配式混凝土灌浆套筒连接质量检测试验研究

为解决装配式混凝土灌浆套筒连接不密实缺陷的无损检测问题,并有效认识连接缺陷的压电应力波特征,本文以合肥市某项目为研究对象,结合室内物理模拟试验,搭建了装配式混凝土灌浆套筒连接质量缺陷室内模拟试验系统,并分别测试灌浆前、后及不同缺陷工况下的压电应力波形,以观测波形响应特征。结果表明,无论是全灌浆还是半灌浆套筒试件,灌浆前后同一个接收传感器位置接收到的压电应力波波形相近,但灌浆后的压电应力波波幅明显偏小;同一灌浆状态下,近端接收传感器采集到的压电应力波幅值比远端同侧接收传感器、对侧接收传感器的更大,而首波初至时间则更短;远端同侧、对侧接收传感器位置上,不同缺陷工况下测试得到的压电应力波波形相近,且随着缺陷长度增加,压电应力波的振幅也越大;近端接收传感器位置,工况4的压电应力波振幅较工况1~工况3有明显增大,工况8较工况5~工况7有增大。