The extraordinary mechanical properties of high strength aluminum alloys such as AA7075-T6 are caused by coherent nanoprecipitations. These nanoprecipitations generate local stress fields and interact with moving dislocations and propagating microcracks. In this paper, image correlation techniques are used to determine the local strain and stress field in the vicinity of fatigue crack tips during the loading of compact tension (CT) specimen. The fatigue crack tip was sharpened with decreasing fatigue loading after fatigue cracks initial appearance. Images of the crack tip were taken using atomic force microscopy/ultrasonic force microscopy (AFM/UFM) and white light interference microscopy (WLIM) before and after mechanical loading of the specimen. Both techniques are applicable for measuring the out-of-plane displacement during the loading process. In addition, image correlation techniques can be used to determine the in-plane displacement resulting from mechanical loading. This information is used to calculate the local stress intensity factor in the vicinity of the crack tips.
Interactive forces between particles play an important role in diverse fields of science and technology. With the advent of Atomic Force Microscopy, investigation of interactive forces has been extended to micro and nano-scale particles with new applications. These forces are known to vary with the dimension of the particles and with the different levels of humidity. In the present paper we have investigated the interactive forces between a spherical particle probes of eutectic BaF2-CaF2 and a single crystal surface of CaF2 using an Atomic Force Microscope. The effect of humidity on the interactive forces has been examined by analyzing the force-displacement curves at controlled levels of humidity. Force distance curves obtained with two different probes, 5 μm and 17 μm in diameter, and have been examined to investigate the effect of probe dimensions. The results are discussed in view of the application of eutectic BaF2-CaF2 particles in self-lubricating coatings for aerospace applications.