【作者】 辛春锁；

【导师】 戴景民；

【作者基本信息】 哈尔滨工业大学 ， 仪器科学与技术， 2009， 博士

【摘要】 热膨胀系数、电阻率和热扩散率是表征材料热物理性能的三个重要参数,对航天航空飞行器和武器装备某些关键部件的结构设计具有重要意义。由于热膨胀系数和电阻率测量理论都是针对均匀温度试样建立的,而实际的高温热物性测量装置很难保证大尺寸试样在高温下的均匀温度分布状态,因此如何测定其高温热膨胀系数和电阻率是一个具有重要意义的研究课题。对于热扩散率参数,现在闪光法理论模型普遍采用背温信号计算,而现有的温度信号测量技术已经很难进一步提高温度测量的分辨率,限制了热扩散率的测量精度。本课题的目的是研制一套大尺寸试样的高温热物性测量装置,满足热膨胀系数和电阻率测量不确定度优于6%、热扩散率测量不确定度优于5%的要求。利用该装置对各种材料在高温条件下的热物性参数进行测量,进而为相关产品的结构设计和性能优化提供可靠的高温热物性数据。论文围绕大尺寸试样热物性测量方法的建立,提出了测量不等温体热膨胀系数和电阻率的新方法、建立了测量热扩散率的多光谱闪光法数学模型,研制出了高温热物性参数测量装置并给出了相应的数据分析方法。主要完成了以下几方面的研究工作:为了消除稳态法测量热膨胀系数和电阻率时试样温度分布不均匀对测量结果的影响,本文根据热物性参数与温度间的函数关系建立了测量不等温体热膨胀系数和电阻率的数学模型,分析了不等温体试样部分与整体间的内在关系,推导了通过试样表面温度分布计算热膨胀系数和电阻率的数学解析式,给出了相应的数据分析方法。为了减小将温度与辐射能量做线性化处理给闪光法热扩散率测量结果带来的误差,本文通过对多光谱闪光法实验过程的理论分析,建立了利用多个光谱辐射能量测量热扩散率的多光谱闪光法数学模型,研究了基于最小二乘法的数据处理方法,实现了对热扩散率的高精度测量。最后对多光谱闪光法和闪光法做了有限元仿真实验,通过对热扩散率测量结果的比较证明了多光谱闪光法理论的正确性和可行性。基于上述理论,本文研制了一套集光学、机械、电气于一体的高温多热物性参数测量装置,实现了各项热物性参数的同步测量。在本装置的研制中完成了如下工作:(1)考虑了不同热物性测量实验的要求,设计了可将棒状和圆片状试样均匀加热到高温热平衡状态的高温环境实验箱;(2)设计了可对试样热扩散率和真实温度进行同步测量的多光谱高速高温计;(3)研制了可对棒状试样轴向温度分布快速测量的轴向温度分布扫描测量系统;(4)设计了满足不同材料热扩散率测量实验要求的均匀脉冲加热系统;(5)设计了可对多路数据信号进行高速同步采集和对不同设备进行实时控制的高速数据采集处理系统。(6)通过对不同面积下热扩散率测量结果的比较和分析,确定了本文所建装置的最佳测试面积。利用上述测量装置对不同材料的高温热物性参数进行了实验研究。在不同温度范围内研究了某种碳/碳材料热膨胀系数、电阻率和热扩散率随温度变化的规律,在800℃~ 3000℃温度范围内研究了SRM 8424标准试样热扩散率随温度变化的规律,在800℃~ 1000℃温度范围内研究了Pyrocream 9606标准试样热扩散率随温度变化的规律,分析了相应的实验现象。将上述实验测量结果与同类设备或国外同行的测量结果进行了比对,热扩散率测量温度范围、测量温度上限和测量精度三方面都已达到国际同类装置的技术水平。总结了影响测量结果的原因,并对两个代表性温度下的热膨胀系数、电阻率和热扩散率的测量结果做了不确定度分析。本论文的研究内容为建立大尺寸试样的高温热膨胀系数、电阻率和热扩散率测量数据库提供了理论依据,构建了技术平台。更多还原

【Abstract】 Thermal expansion coefficient, electrical resistivity and thermal diffusivity are the three important parameters in evaluating the thermophysical performance of materials, and are of great significance in the structural design of some key parts of astronautical and aeronautical vehicles. It is well-known that thermal expansion coefficient and electrical resistivity measurement theory is established for the uniform temperature specimen. However, the temperature distribution in big-size sample is not uniform in practical measuring instrument under high temperature, so it is an important issue to measure the thermal expansion coefficient and electrical resistivity with high accuracy. Thermal diffusivity is usually measured by using flash method that depends on the transient temperature of the rear surface of the specimen. However, the accuracy of this method can hardly be improved because of the limited spatial resolution in temperature measurement. The objective of this project is to develop a measuring apparatus that can measure thermophysical properties of big-size samples under high temperature. For thermal expansion coefficient and electrical resistivity, the measurement uncertainties are less than 6%, and for thermal diffusivity it is less than 5%. The thermophysical parameters of various materials under high temperature can be determined by this apparatus so as to present reliable information for designing configuration and optimizing performance in some practical applications.In order to establish the measuring methods of thermophysical properties of big-size samples under high temperature, the principle and technique for measuring the thermal expansion coefficient, electrical resistivity, and thermal diffusivity were systemically investigated in this dissertation. A new apparatus, which can simultaneously measure the three thermophysical properties, was developed, and the data processing methods in this measurement were also discussed. This work can be categorized as follows:In order to eliminate the effects of nonuniform temperature distribution on the steady state measurement, a mathematical model was established for measuring the thermal expansion coefficient and electrical resistivity of nonuniform temperature body according to the temperature dependence of thermophysical properties. The relationship between the whole and parts of the nonuniform temperature body was discussed. The mathematical formula and corresponding data processing methods for calculating thermal expansion coefficient and electrical resistivity were presented.A multi-spectral flash method mathematical model that can measure thermal diffusivity by multiple spectral radiation energy was established based on the experimental process of multi-spectral method. This model decreases the errors induced by the linearization of the relationship between temperature and radiation energy. The least square method was used in the data processing, and the high-precision measurement of thermal diffusion was realized. The finite element simulation of multi-spectral flash method and flash method was carried out. Compared with the measuring results of thermal diffusivity, the correctness and feasibility of the multi-spectral flash theory was justified.An apparatus combing optical, mechanical, electrical measurement for high temperature thermophysical properties parameters, which can measure simultaneously these three parameters, is developed according to the above principles. The work for designing this apparatus is studied as follows: (1) Considering the different heating requirements for different sized samples, we designed a special experiment chamber that can heats rod- or circle-shaped samples to thermal equilibrium state under high temperature; (2) A high-speed multi-spectral pyrometer that can simultaneously measure the thermal diffusivity and temperature of the specimen was developed; (3) A scanning and measuring system that can rapidly measure the rod-like axial temperature distribution was developed; (4) An even pulse heating system that can meet the needs of different measurement requirements for material thermal diffusivity was designed; (5) A high-speed data acquisition and processing system that realizes multi-channel high-speed acquisition and the real-time control of different instruments was improved. (6) The optimum testing area of the instrument was decided through the analysis and comparison of measuring results of thermal diffusivity in different areas.The high temperature thermal properties were measured for different materials by this apparatus. Temperature dependence on the thermal expansion coefficient, electrical resistivity, and thermal diffusivity of a carbon / carbon materials were investigated. The temperature dependence on thermal diffusivity of the SRM 8424 and Pyrocream 9606 standard samples were studied in the temperature range of 800℃~3000℃and 800℃~ 1000℃, respectively. The scope and upper limit of the measuring temperature as well as the precision of the thermal diffusivity measurement compared fairly well with those obtained from the similar equipments in the world. The reasons that impact the measurement results were summarized, and the uncertainty in measuring the thermal expansion coefficient, electrical resistivity, and thermal diffusivity under two typical temperatures were discussed.This work presented the theoretical foundation and established the measurement techniques for building the database of thermal expansion coefficient, electrical resistivity and thermal diffusivity of big sized samples under high temperature.更多还原