Liu Menglong, Wang Kai, Lissenden Cliff J, Wang Qiang, Zhang Qingming, Long Renrong, Su Zhongqing, Cui Fangsen
Institute of High Performance Computing, A*STAR, Singapore 138632, Singapore.
Department of Mechanical Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong.
Materials (Basel). 2017 May 18;10(5):547. doi: 10.3390/ma10050547.
Hypervelocity impact (HVI), ubiquitous in low Earth orbit with an impacting velocity in excess of 1 km/s, poses an immense threat to the safety of orbiting spacecraft. Upon penetration of the outer shielding layer of a typical two-layer shielding system, the shattered projectile, together with the jetted materials of the outer shielding material, subsequently impinge the inner shielding layer, to which pitting damage is introduced. The pitting damage includes numerous craters and cracks disorderedly scattered over a wide region. Targeting the quantitative evaluation of this sort of damage (multitudinous damage within a singular inspection region), a characterization strategy, associating linear with nonlinear features of guided ultrasonic waves, is developed. Linear-wise, changes in the signal features in the time domain (e.g., time-of-flight and energy dissipation) are extracted, for detecting gross damage whose characteristic dimensions are comparable to the wavelength of the probing wave; nonlinear-wise, changes in the signal features in the frequency domain (e.g., second harmonic generation), which are proven to be more sensitive than their linear counterparts to small-scale damage, are explored to characterize HVI-induced pitting damage scattered in the inner layer. A numerical simulation, supplemented with experimental validation, quantitatively reveals the accumulation of nonlinearity of the guided waves when the waves traverse the pitting damage, based on which linear and nonlinear damage indices are proposed. A path-based rapid imaging algorithm, in conjunction with the use of the developed linear and nonlinear indices, is developed, whereby the HVI-induced pitting damage is characterized in images in terms of the probability of occurrence.
超高速撞击（HVI）在近地轨道中普遍存在，撞击速度超过1千米/秒，对在轨航天器的安全构成巨大威胁。在典型的双层屏蔽系统的外层屏蔽层被穿透后，破碎的弹丸与外层屏蔽材料的喷射物质一起，随后撞击内层屏蔽层，从而在内层屏蔽层上产生点蚀损伤。点蚀损伤包括大量无序散布在广阔区域的坑洼和裂纹。针对这种损伤（单个检测区域内的众多损伤）的定量评估，开发了一种将导波的线性特征与非线性特征相结合的表征策略。在线性方面，提取时域中信号特征的变化（例如飞行时间和能量耗散），以检测特征尺寸与探测波波长相当的宏观损伤；在非线性方面，探索频域中信号特征的变化（例如二次谐波产生），事实证明其对小规模损伤比线性特征更敏感，以表征内层中由超高速撞击引起的点蚀损伤。通过数值模拟并辅以实验验证，定量揭示了导波穿过点蚀损伤时非线性的累积情况，并在此基础上提出了线性和非线性损伤指数。开发了一种基于路径的快速成像算法，并结合所开发的线性和非线性指数，据此以出现概率的形式在图像中表征超高速撞击引起的点蚀损伤。
