小试件材料弹性常数超声测量线聚焦PVDF探头的研制

本文针对小试件材料力学性能测试的特殊需求,利用PVDF压电薄膜设计制作了无透镜柱面线聚焦超声探头。文中介绍了探头材料的选择和结构参数的确定,对探头性能进行了数值模拟。该探头具有孔径角大、频带宽、中心频率高等特点。采用线聚焦PVDF探头的弹性常数超声测量系统对多种小试件材料进行了弹性常数测量,测量结果表明,本系统具有波形清晰,信噪比大。分辨率高,测量误差小,结果准确等特点,能够满足工程实验和科学研究的需要。由于线聚焦探头可以发射与聚焦线垂直的表面波,因此,基于线聚焦PVDF探头的小试件材料弹性常数超声精密测量系统,不仅适用于各向同性材料,而且适用于各向异性材料。     

小尺寸材料弹性常数超声测量系统的研制及其应用

提出一种小尺寸材料弹性常数测量的新方法——利用线聚焦超声传感器和超声浸水技术同时测定纵波和漏表面波的波速，求得材料的弹性常数。基于PXI-8186嵌入式控制器构建了小尺寸材料弹性常数测控系统，利用LabVIEW软件平台开发了小尺寸材料弹性常数自动测量软件。实验结果表明，该方法可以实现小尺寸材料弹性常数的测量，测量结果具有很好的重复性。     

基于双模式超声换能器的选择性激光熔化316L制件弹性常数无损表征研究

选择性激光熔化技术(SLM)可以快速成型任意结构的金属零件,但其制件的内部组织和材料性能与传统制件有着显著区别。基于双模式超声换能器对SLM 316L不锈钢制件的不同方向弹性常数及其分布进行表征研究。首先通过设计并制备高性能双模式超声换能器,搭建超声弹性常数分布测量系统。对SLM制备的316L不锈钢试样依次进行纵波和两个正交横波声速测量,获得同位置处不同方向弹性模量和泊松比。通过不同成型方向的声速测量,发现SLM制件在堆积z方向熔化层内呈现显著区别,表现出明显的各向异性。而y-z平面内弹性常数分布表征表明,杨氏模量E_(13)大于E_(12),泊松比σ_(13)小于σ_(12),且制件各熔化层弹性常数分布规律相似。此外,还讨论了加工过程中扫描速度和扫描间距等工艺参数对弹性参数的影响。选择性激光熔化制件弹性常数的有效无损表征将为增材制件内部质量控制和工艺改善提供技术基础。     

ODS铁素体钢弹性性能的超声检测方法

采用超声显微镜技术,针对核能领域新型基础工业材料ODS铁素体钢的声学传播特性和质量评价方法展开研究.运用时域分析和频域分析2种方法,通过对比实验测定了不同铬(Cr)含量ODS铁素体钢试样的弹性力学常数.实验结果表明,2种超声检测方法不仅可测定该类材料的弹性性能,而且通过波速对比可检测成型材料的致密性,这为ODS铁素体钢材料的力学性能表征和质量检测技术研究提供了一种可行方法.     

薄板涂层结构镍镀层声学特性检测与弹性常数反演表征方法研究

针对表面涂层技术应用中薄板涂层结构材料弹性常数声学表征无损检测方法开展理论和试验研究。基于声学显微镜技术,利用自主研制的宽频线聚焦探头和非常规小尺寸材料超声无损检测系统,进行小步距(20μm)精确散焦测量和大数据量回波信号(601组)数据采集;采用V(f,z)分析方法获取薄板涂层结构材料的试验频散曲线;结合涂层结构材料声波传播特性分析及理论建模结果,改变纵波波速和横波波速获得不同的理论频散曲线,通过理论频散曲线与试验测量结果的曲线拟合,获取涂层材料声波波速,进而反演材料的弹性常数(如泊松比和弹性模量)。多厚度镍镀层试验测量结果与理论值相吻合,表明测量分析方法可行、结果可靠。该研究成果为涂层材料力学性能无损检测和质量评价奠定了基础。     

前保蒙皮塑料表征及在行人保护中的仿真应用

对保险杠塑料材料进行一系列的准静态和动态加载试验,获得不同应力下的力学性能曲线。基于LS-DYNA显示分析的方法,开发模拟塑料性能的187号材料模型,该模型屈服面是将拉伸、剪切、压缩和双向拉伸4个屈服试验点采用最小二乘法拟合得出,更适用于表征塑料材料的力学性能。将所开发的187号材料模型模拟动态拉伸、剪切、压缩和穿孔4项基本工况,并将仿真和试验结果进行了对标。最后将该材料模型应用于系统级的行人保护腿部碰撞中,验证了所开发材料模型的可靠性。     

基于相位-频率测量的材料残余应力超声表征方法

针对材料中残余应力无损检测的问题,提出一种基于相位-频率关系测量超声信号传播时间的方法,并以声弹性理论为基础,采用纵波和横波相结合的测量模式,建立残余应力的超声测量方法。该超声测量方法应用于焊接接头的残余应力测量,不仅能够表征两轴方向上的残余应力,而且还适用于短距离声时的精确测量,测量精度达到9 mm试样距离上0.3 ns的分辨率(加载应力为20 MPa)。制作16Mn钢材料的焊接接头,并采用所提出的超声测量方法对焊接接头的残余应力分布进行测量。同时,采用理论计算、X射线衍射技术等分别对16Mn钢材料的声弹性参数及焊接接头残余应力分布进行验证测量。研究结果表明基于相位-频率精确测量声时的残余应力超声测量方法具有较高的应力分辨率和较好的测量稳定性,可适用于焊接接头两轴方向上的残余应力表征。     

多层回转体预紧结构层间转动试验

为研究含黏弹性材料多层回转体结构在轴向振动作用下的层间转动特性,设计了多层回转体试验件,进行了黏弹性材料压缩力学性能研究,建立了考虑黏弹性材料非线性力学特性的结构动力学模型。基于模态试验考察了不同预紧力条件下结构的模态变化规律,在此基础上开展了随机振动环境下试验件层间转动特性试验,获得了确定的层间转动现象,并研究了不同振动量级及预紧力对层间转动的影响。基于随机振动试验获得了含黏弹性材料回转体预紧结构层间转动与否的预紧力、振动量级分界线。相关试验结果可为工程设计提供支持。     

管线钢断裂韧度测试实验研究进展

随着管道钢强度和韧度的增加,表征材料断裂韧度的参数也在变化,同时断裂韧度测试技术也得到了不断的发展。本文介绍了几种测试材料断裂韧度的小试件实验以及存在的问题。重点介绍了一种准静态测试CTOA的小试件,以及测量CTOA的实验方法,为天然气管道止裂研究提供帮助。     

材料局部力学性能测试方法

采用穿孔剪切试验和有限元模拟相结合的方法对材料的局部性能进行研究,通过将修正模拟阻力曲线与试验数据相匹配,在模拟分析中利用迭代修正的方法反向推导出材料的本构关系.由此提出利用穿孔剪切试验间接获得材料拉伸力学性能的基本方法.研究中以典型的车用铝合金材料(5052H34和6063T5)及紫铜作为测试对象,对该材料表征方法的精确性进行验证.分析表明,穿孔剪切试验结合有限元反求迭代技术获得材料拉伸应力-应变曲线关系与拉伸试验数据对比最大误差不超过5%,结果较为准确.该方法适用于微区或局部材料的力学性能表征,可为后续接头梯度力学性能研究提供参考.     

Measurement of elastic constants of limited-size piezoelectric ceramic sample by ultrasonic method

Measurement of material elastic constants for limited-size samples by ultrasonic method is described and validated. Based on acoustic microscope technology, the material elastic constants are determined by longitudinal wave and leak surface wave velocities simultaneously measured by developed ultrasonic system with a line-focus PVDF transducer. In this paper, the elastic constants of limited-size Cr₂O₃ doping on 0.2 PZN–0.8 PZT piezoelectric ceramic wafer sample are determined and the measurement errors are analyzed. The experimental results show this ultrasonic system can be used for measurement of material elastic constants for limited-size samples with high measurement precision, and the relative errors for Poisson’s ratio and Young’s module measurements are, respectively, less than 1% and 3%. It can satisfy the requirement of engineering and science research. Furthermore, it is suitable to measure elastic constants of both isotropic and anisotropic materials by ultrasonic method with help of developed ultrasonic system.     

Physical basics of evaluating elastic characteristics of anisotropic composites by ultrasonic method

As a result of analyzing the generalized Hooke law and wave equations for an anisotropic medium, computational expressions have been derived for evaluating the elastic constants of orthotropic, transversely isotropic, and isotropic media using the propagation velocities of longitudinal and shear elastic waves measured with the pulsed ultrasonic method in the corresponding directions.     

Means for Increasing the Sensitivity of Acoustic Probing when Studying the Structure of Metals

As exemplified by the use of different approaches to processing the results of probing metals with elastic waves, means have been studied for increasing the sensitivity of the ultrasonic method. Representing processes that determine the effect that a medium has on the parameters of an elastic wave by a statistical model in the form of a Dirichlet distribution makes it possible to numerically characterize changes in the structure of a probing pulse and to improve the understanding of phenomena that occur when an elastic wave interacts with a medium, with the degree of material damage taken into account.     

一种磁致伸缩式超声波激发/接收传感器的研究

以研制磁致伸缩式超声波传感器为目标，分析了磁致伸缩式超声波传感器的工作原理——磁致伸缩效应及逆效应，重点讨论传感器结构设计及线圈参数选择计算，制作了磁致伸缩式超声波传感器。本文研制的传感器在脉冲激励电流的作用下，可在细丝中激发超声波，同时还可以接收细丝中传播的超声波；该传感器既可以激发扭转波，又可以激发纵波。可用于测量液位、温度、液体密度和材料的声速、弹性模量等物理量。     

A broadband spectroscopy method for ultrasonic wave velocity measurement under high pressure

A broadband spectroscopy method is proposed to measure the ultrasonic wave phase velocity of Z-cut quartz under high pressure up to 4.7 GPa. The sample is in a hydrostatic circumstance under high pressure, and we can get longitudinal wave and shear wave signals simultaneously in our work. By fast Fourier transform of received signals, the spectrum and phase of the received signals could be obtained. After unwrapping the phase of the received signals, the travel time of ultrasonic wave in the sample could be obtained, and the ultrasonic wave phase velocity could also be resolved after data processing. The elastic constant of measurement under high pressure is also compared with previous studies. This broadband spectroscopy method is a valid method to get ultrasonic wave travel parameters, and it could be applied for elasticity study of materials under high pressure.     

基于单片机的高精度超声波测距系统

研制了一种收发一体式超声波测距系统,介绍了发射驱动及接收转换电路、随时间变化的自动增益控制(AGC)电路及环境温度补偿电路的电路结构,详细阐述了发射驱动及接收转换电路的工作机理及实现方式,提出了解决收发一体式超声波测距电路难题的新方法,设计的自动增益控制(AGC)电路,有效地解决了回波信号过于微弱而导致系统测量误差加大的难题。在此基础上,设计了相应的超声波测距系统的软件。在实验室对系统进行了实地测试,给出了实测结果并分析了产生误差的原因。实验表明,该测距系统具有较高的测量精度。     

An ultrasonic technique for the measurement of elastic properties of soft surface coatings

The properties of thin layers of materials can be different from those in the bulk form. The response of a coating to any given load and its ability to remain bonded to the substrate will depend on its elastic modulus and Poisson's ratio. In this study a measurement method based on ultrasonic bulk wave reflection was evaluated. As a model system, a thin layer of polyethylene was pressed between two solid steel bodies. The reflection spectra of longitudinal and shear ultrasonic waves were recorded from the coating. The frequencies at which the layer resonates were measured and from this the wave speeds deduced. The Poisson's ratio can be determined from these two wave speeds and if the layer thickness is known the modulus is also available. The tests yielded reasonable values for both. This approach is only suitable if the layer can be made to resonate by the available ultrasonic frequencies; typically this will be the case for thicker coatings (tens of microns). Further, good coupling between the layer material and the steel bodies is necessary so that the interfaces do not themselves act to reflect ultrasound. This is better achieved with a smooth soft coating.     

微机化的多通道超声螺栓应力仪

本文介绍了一种新型的由微机控制及显示的超声应力仪的工作原理,该仪器可同时测定２４根螺栓应力,文章提出了声时差法测预紧应力,并推导了声时差同轴向应力以及三阶弹性常数的关系。采用声时差法多探头同时测量同一法兰上的各螺栓的预紧应力,可以克服偶合误差,可免测三阶弹性常数及温度等,使测量过程简便且严谨高。程序在Ｗｉｎｄｏｗｓ下设计,操作简便,应力能以多种图形方式显示。实验结果表明应力你于２５０ＭＰａ,夹紧距