Kusano Masahiro, Takizawa Shota, Sakai Tetsuya, Arao Yoshihiko, Kubouchi Masatoshi
National Institute for Materials Science, Japan.
Graduate School of Industrial Technology, Nihon University, Japan.
Ultrasonics. 2018 Jan;82:178-187. doi: 10.1016/j.ultras.2017.08.001. Epub 2017 Aug 10.
Since thermosetting resins have excellent resistance to chemicals, fiber reinforced plastics composed of such resins and reinforcement fibers are widely used as construction materials for equipment in chemical plants. Such equipment is usually used for several decades under severe corrosive conditions so that failure due to degradation may result. One of the degradation behaviors in thermosetting resins under chemical solutions is "corrosion-layer-forming" degradation. In this type of degradation, surface resins in contact with a solution corrode, and some of them remain asa corrosion layer on the pristine part. It is difficult to precisely measure the thickness of the pristine part of such degradation type materials by conventional pulse-echo ultrasonic testing, because the sound velocity depends on the degree of corrosion of the polymeric material. In addition, the ultrasonic reflection interface between the pristine part and the corrosion layer is obscure. Thus, we propose a pitch-catch method using a pair of normal and angle probes to measure four parameters: the thicknesses of the pristine part and the corrosion layer, and their respective sound velocities. The validity of the proposed method was confirmed by measuring a two-layer sample and a sample including corroded parts. The results demonstrate that the pitch-catch method can successfully measure the four parameters and evaluate the residual thickness of the pristine part in the corrosion-layer-forming sample.
由于热固性树脂具有优异的耐化学性，由这种树脂和增强纤维组成的纤维增强塑料被广泛用作化工厂设备的建筑材料。这种设备通常在恶劣的腐蚀条件下使用几十年，因此可能会因降解而失效。热固性树脂在化学溶液中的一种降解行为是“腐蚀层形成”降解。在这种降解类型中，与溶液接触的表面树脂会腐蚀，其中一些会作为腐蚀层保留在原始部分上。通过传统的脉冲回波超声检测很难精确测量这种降解类型材料原始部分的厚度，因为声速取决于聚合物材料的腐蚀程度。此外，原始部分和腐蚀层之间的超声反射界面不清晰。因此，我们提出了一种使用一对直探头和斜探头的穿透法来测量四个参数：原始部分和腐蚀层的厚度以及它们各自的声速。通过测量双层样品和包含腐蚀部分的样品，证实了所提出方法的有效性。结果表明，穿透法可以成功测量这四个参数，并评估腐蚀层形成样品中原始部分的剩余厚度。
