Tuesday  |  Virtual Track 4  |  09:36 AM–09:48 AM

#11411, Non-destructive Stress and Strain Measurement of PDMS Buffer Layers under Ball Drop Impact

Due to the high flexibility and stretchability, flexible hybrid electronics (FHE) can be used for the wearable devices, smart patches, smart textiles, in-vehicle systems, etc. However, the FHE products are occasionally subject to the impact loads as they are operated in complicated situations and/or used over the long term. The impact loads may cause the electronic components in FHE the damage or destruction so that the reliability of FHE products may be difficult to be estimated and assured. The buffer layer structure of FHE is utilized for cushioning the impact forces to protect the electronic components in FHE. Therefore, the mechanical behavior analysis of the buffer layers under impact loads has been a critical and necessary link in the FHE developing and manufacturing processes.

Photomechanics methods have been widely applied to measure and analyze the mechanical behavior of structures and elements because of their advantages such as full-field, non-destructive, high-accuracy, automated, and real-time measurement. Digital photoelsticity is the major approach to determine the state of stress of the specimen with temporary birefringence. Besides, digital image correlation (DIC) method is the technique to calculate the strain of the specimen by tracing the speckle pattern features before and after deformation. Recently, the authors have been constructed a real-time full-field non-destructive stress and strain measurement system by combining the digital photoelasticity and DIC method. Furthermore, the polydimethylsiloxane (PDMS) substrate with 230μm thickness used as the buffer layer of FHE had been measured. Based on the stress and strain measurement results of the PDMS tensile specimens under uniaxial loadings, the measurement feasibility and repeatability of the constructed measurement system were verified.

In this study, the real-time full-field stress and strain distribution of the PDMS substrates under whole ball drop impact process were measured by the constructed measurement system. By analyzing the time-series measurement results, the relationships between stress and strain values at the impact point and the impact process time can be established. The relationships showed that the stress and strain at impact point reached the maximum value of 27MPa and 25*10^3με, respectively. The residual stress and strain value after impact were 21MPa and 15*10^3με, respectively.

Po-Chi Sung   National Tsing Hua University
Wei-Chung Wang   National Tsing Hua University
Yu-Ming Peng   Industrial Technology Research Institute
Chih-Hao Chang   National Tsing Hua University
Kai-Ming Chang   Industrial Technology Research Institute