【作者】 宋国荣；

【导师】 何存富；

【作者基本信息】 北京工业大学 ， 机械设计及理论， 2009， 博士

【摘要】 随着性能优异的新型材料不断出现,迫切需要对材料的力学及其他物理性能进行测定。但由于制备工艺的原因,一方面,制备满足常规力学性能测试用的大尺寸试件十分困难,如块体纳米材料、金属玻璃等;另一方面,材料的力学性能(如弹性常数等)时常会呈现各向异性。因此,研究这类材料/结构的力学性能(弹性性质)的表征方法与测量技术,对于评价材料的制备工艺和表征材料的力学性能,具有重要的学术意义和广阔的应用背景。本文针对小尺寸块体材料弹性常数的测定问题,主要完成了以下工作:(1)提出了一种基于声学显微镜技术的材料弹性常数超声测量方法。基于材料力学性能声学表征,利用纵波与漏表面波波速表征材料的弹性常数,建立了完备的小尺寸材料弹性常数超声表征与测量方法。(2)开发了一套完整的小尺寸材料弹性常数超声测量系统,包括:设计制作了高频无透镜大孔径柱面线聚焦PVDF超声探头;构建了以PXI总线嵌入式控制器为核心,以四轴精密运动机构为测量平台,利用超声波激励/接收装置,通过PVDF柱面线聚焦探头发射超声波和接收回波信号,经高速数字化分析仪等,可实现超声信号自动采集和分析处理的系统。开发了一套在空间域同时测定纵波与漏表面波速度的方法及波形处理算法程序,实现了小尺寸材料弹性常数自动测量。实验结果表明,回波信号清晰可辨,信噪比高,可满足信号分析与处理的需要,为小尺寸材料弹性常数的准确测量提供了可靠保证。(3)利用小尺寸材料弹性常数超声测量系统对常规材料,如:铝、铜、碳钢、钛合金等小尺寸试件材料弹性常数进行超声实验测量和误差分析。结果表明,测量结果准确度高,完全满足工程及科学研究的要求。(4)针对非晶材料、纳米材料和非金属小尺寸等非常规材料弹性常数进行了试验研究,并与其它方法所得结果进行了对比,结果吻合较好。说明超声无损测量法,克服了压痕法不能测试材料的泊松比,且为有损检测等不足。(5)利用超声测量系统对冷轧钢板、电子束焊焊缝等特殊材料或区域进行了实验研究。结果表明该方法可以用于测量像冷轧钢板这类由于加工工艺所致的各向异性材料。同时可用于测量微区的力学性能,以便研究材料的力学性能变化梯度。(6)在对表面波波速较低的材料(如钆)进行超声法力学性能测试时,针对耦合液中波速对漏表面波波速测量范围的影响与限制,采取了低波速耦合液。由此,解决了水浸法被测材料的表面波速过低引起测量结果奇异的问题,拓宽了现有系统可测试材料的范围。更多还原

【Abstract】 Along with the emergence of new materials unceasingly, it is an urgent demand of the measurement for material mechanical and other physical properties. However, due to prepared technology, some new materials, such as bulk nano-materials and metal glasses, are hard to process large size samples to satisfy the requirement of common static tension experiment, furthermore, many materials exhibits anisotropic characteristics in their mechanical behaviors. Therefore, it has very important scientific values and wide application foreground for the investigation of characterization method and measurement technique to evaluate prepared technology and mechanical properties including elastic behaviors of these types of materials or structures.In this dissertation, aimed at the existing problem of elastic constant measurement of limited size bulk materials, the main technical contributions of the research work are shown as following.(1) Ultrasonic measurement method for material elastic constants based on low frequency acoustic microscopy technology. Based on acoustic characterization method of material mechanical properties, elastic constants characterization method and measurement technique of limited size bulk materials is fully developed by the relation between the velocities of longitudinal and leak surface waves and material elastic constants.(2) Ultrasonic system for elastic constant measurement of limited size materials is wholly established. In this developed system, high frequency non-lens large aperture line focus cylindrical PVDF ultrasonic transducer is designed and manufactured. In this system, NI PXI bus embedded controller is the core and a four-axis moving precisely framework is used as measurement platform. Ultrasonic wave signals are excited and received by line focus cylindrical PVDF ultrasonic transducers driven by ultrasonic pulser/receiver. With the help of high velocity digital analyzer, automatic collection and analysis of ultrasonic signals can be achieved. The software program including measurement of the velocities of longitudinal and leaky surface waves simultaneously in spatial domain and waveform processing algorithm is developed. With the help of the combination of the method and software, automatic measurement of limited size materials can be achieved. Experimental results show that the system provides reliable guarantee of accurate measurement of limited size materials and the echoes with high signal-noise ratio can be obtained to satisfy the need of signal analysis and processing.(3) Common metal materials, such as aluminum, copper, carbon steel, titanium alloy, are measured by using this developed ultrasonic system for limited size material elastic constant measurement. In these experiments, elastic constants of these materials are obtained and measurement error factor is analyzed. Primary experimental results show that this measurement method with high precision and low error can satisfy the need of the engineering and scientific research.(4) Elastic constants of uncommon materials such as amorphous materials, nano-materials and non-metal materials are experimentally measured. Furthermore, the measurement value of Young’s module of amorphous materials by using ultrasonic method is agreement well with that by using other methods. Non-destructive Ultrasonic testing can overcome the shortcoming of limitation of indentation method which fails to measure Poisson’s ratio of materials and its intrinsic destructive nature.(5) Special property materials or areas such as cold rolled steel sheet and electronic beam welding are measured by using ultrasonic measurement system experimentally. Experimental results show that the method can be used for the measurement of cold rolled steel sheets which exhibit anisotropic characteristics induced by machining process. Furthermore, material mechanical properties of micro areas can be measured to evaluate their gradient.(6) When mechanical properties of gadolinium with relatively low surface wave velocity are measured by ultrasonic method, a coupling liquid with a low wave velocity is employed for conquering the effect of the velocity of coupling liquid and its restriction to measurement range of leaky surface wave velocity. Therefore, the singularity problem induced by excessively low surface wave of measured samples when water immersion method is adopted can be solved and extend the range of material applications.更多还原