Novel Method for Analyzing Crack Growth in Polymeric Microtensile Specimens by In Situ Atomic Force Microscopy

In this paper a micro tensile test which allows the determination and observation of the crack growth behaviour in thin polymer layers is presented. The setup consists of micromanipulators and piezo actuators for straining the sample while an atomic force microscope (AFM) is used for scanning the crack tip area with high lateral resolution. The stress in the specimen is determined by an optical microscope for observation of the deflection of a force sensing beam. The material under investigation is an amorphous and strongly entangled thermoplastic polyimide which can be patterned photolithographically and is spin cast to form layers of 3 mu m thickness. The results show the potential of the setup to measure crack length, crack tip opening and nominal stress. The stress-crack length-diagram then allows to determine different stages during crack growth.