Lee Tae-Ik, Jo Woosung, Kim Wansun, Kim Ji-Hye, Paik Kyung-Wook, Kim Taek-Soo
ACS Appl Mater Interfaces. 2019 Apr 10;11(14):13416-13422. doi: 10.1021/acsami.9b01480. Epub 2019 Apr 1.
For flexible devices that inevitably undergo repetitive deformations, it is important to evaluate and control the mechanical strain imposed on the flexible systems for enhancing the reliability. In this paper, a novel experimental method to directly visualize cross-sectional strain distribution in the thin flexible devices is proposed. Digital image correlation (DIC) is effectively adapted by using microscopic images of the cross section for accurate analysis of the microscale deformations. To conduct the DIC strain analysis, speckle patterning is accomplished by using microparticles from diamond-abrasive suspensions with optimized fabrication conditions. First, the cross-sectional micro-DIC analysis is performed successfully for 100 μm-thick substrates. Full-field strain quantification and easy inspection of a neutral plane are demonstrated and compared with results of finite element analysis simulation. Using the presented method, generation of multiple neutral planes is clearly visualized for a trilayer structure with a very soft adhesive midlayer, where strain decoupling occurs by severe shear deformation of the soft adhesive layer. Furthermore, bending strain distribution in a flexible fabric-reinforced polymer (FRP) substrate is also investigated to analyze and predict fatigue fracture in the complex inner structure under repetitive bending loading.
对于不可避免地经历重复变形的柔性器件，评估和控制施加在柔性系统上的机械应变对于提高可靠性至关重要。本文提出了一种直接可视化薄柔性器件横截面应变分布的新型实验方法。通过使用横截面的微观图像有效地采用数字图像相关（DIC）技术，以精确分析微观尺度的变形。为了进行DIC应变分析，通过使用具有优化制造条件的金刚石研磨悬浮液中的微粒来完成散斑图案化。首先，成功地对100μm厚的基板进行了横截面微观DIC分析。展示了全场应变量化和中性面的轻松检测，并与有限元分析模拟结果进行了比较。使用所提出的方法，可以清晰地观察到具有非常柔软粘合剂中间层的三层结构中多个中性面的产生，其中由于柔软粘合剂层的严重剪切变形而发生应变解耦。此外，还研究了柔性织物增强聚合物（FRP）基板中的弯曲应变分布，以分析和预测重复弯曲载荷下复杂内部结构中的疲劳断裂。
