Combination of scanning electron microscopy and digital image correlation for micrometer-scale analysis of shear-loaded adhesive joints

To understand adhesive bonds and their macroscopic behavior, a new experimental method is presented in this paper that allows to investigate micromechanical effects down to nanometer scale under load. The method combines ion milled cross sections, low-voltage scanning electron microscopy (SEM), digital image correlation, and a miniaturized testing machine in the SEM-chamber. Experimental results from shear-loaded adhesively bonded carbon fiber-reinforced polymer specimens illustrate the method's benefits. Through a plasma etching process, the specimen cross section is textured, creating a stochastically distributed speckle pattern visible in SEM images. A miniaturized testing machine placed in the SEM is used to apply a load to the specimens while capturing images simultaneously. The resulting image series can be analyzed by image correlation algorithms. This method enables precise statements regarding strain distribution on the specimen at micro- and nanometer scales. While conventional coupon tests on bonded specimens can only depict the effects of a composite in a homogenized manner, the new method allows to gain additional insights into the underlying mechanisms.