Measurement Method of Internal Residual Stress in Plastic Parts Using Terahertz Spectroscopy

Since internal residual stress in polymers causes dimension errors over time, a measurement method for residual stress in polymers, especially in opaque engineering plastics, is strongly required. In this study, we propose to utilize terahertz (THz) spectroscopy to non-destructively measure internal residual stress in polymers. To verify the validity of the proposed method, we manufactured polytetrafluoroethylene ring samples with and without residual stress, and studied them with THz time domain spectroscopy system. THz spectra of samples without residual stress showed almost no polarization difference, whereas spectra of samples with residual stress showed clear polarization difference. Dimension changes between the samples with and without residual stress were also estimated and it was found that the change had a correlation with THz polarization difference. These experimental analyses confirm the validity for the proposed non-destructive measurement of residual stress in polymer. © 2021, International Society for Nanomanufacturing and Tianjin University and Springer Nature Singapore Pte Ltd.