【作者】 邝文川；

【导师】 轩福贞；

【作者基本信息】 华东理工大学 ， 安全技术及工程， 2011， 硕士

【摘要】 高温结构长时间受载会产生蠕变损伤,影响结构的服役安全性,因此实现对高温结构蠕变损伤进行快速有效检测以及剩余寿命定量预测具有重要意义。本文研究高温结构／材料蠕变过程中超声波传播非线性特性变化规律,为利用非线性超声技术无损评价高温蠕变损伤及预测蠕变剩余寿命提供依据。本文首先以钛合金Ti60材料为对象,通过设计实施经历不同高温蠕变试验时间的试验,模拟获得代表不同蠕变寿命阶段的损伤试样。利用金相显微镜、扫描电子显微镜分析了Ti60材料蠕变过程的显微结构变化情况。利用SNAP 5000高能超声检测系统搭建了超声检测平台,对处于不同蠕变寿命阶段的Ti60材料进行超声检测。得到如下结果：(1)随着蠕变损伤的演化和发展,超声纵波声速变化并不明显；(2)衰减系数在蠕变前期变化并不明显,而在蠕变寿命后期,衰减系数显著增加；(3)二次谐波参量β在整个蠕变过程中变化量达到80%以上,其变化总体上呈逐渐增大趋势,表现为振荡上升规律。最后,以实验研究结果为基础,提出一种利用超声非线性参量p来预测材料蠕变剩余寿命的无损评价方法。更多还原

【Abstract】 Components and structures being operated at high temperature for long periods usually face the threat of creep damage. Therefore, it is of increasing importance to perform quick and effective testing and quantitative life prediction for structure health monitor (SHM) during creep damage. In this paper, we have performed a research on the characteristics of the nonlinear ultrasonic wave propagating in the creep damaged components or materials after different thermal loadings. The results from this paper may lay a foundation for nondestructive evaluation and life prediction of creep damage by using nonlinear ultrasonic technique.In this research, the creep damaged samples were acquired by high-temperature creep tests based on titanium alloy Ti60 for different holding times, which can represent the simulation of various creep damage levels. Then, the microstructure changes of the creep degraded samples were observed based on metallographic studies, such as scanning electron microscope (SEM) and optical microscope (OM). The ultrasonic parameters such as velocity, attenuation coefficient, second harmonic based nonlinear parameter and third harmonic based nonlinear parameter of these samples are measured using the SNAP 5000 high power ultrasonic testing system. The results show that:(1) The longitudinal velocity does not change significantly during the creep process. (2) The attenuation coefficient does not change significantly during the early creep period, but it increases obviously in the latter period. (3) The second harmonic based nonlinear parameterβis sensitive to the creep damage, whose variation reaches to 80% compared with that of the initial state. Moreover, the change ofβdoes not exhibit a monotonic increase with increasing creep life, but an oscillatory increase.Finally, we proposed a nondestructive evaluation method based on the nonlinear parameterβfor life prediction of metallic material under creep loading.更多还原