The yield point in metals depends of its chemical composition, the microstructure and lattice defects. In the last decades a plasticity size effect was also discovered, first shown with nanoindentation experiments and later in compression tests. An increasing number of research groups have investigated the plasticity size effect and have developed experimental methods and theoretical models, however, the size effect is still not fully understood yet. Plastic deformation in face-centered cubic metals at moderate temperatures and strain rates is governed by the movement of dislocations. It seems obvious that the understanding of the behavior of dislocations in restricted volumes will reveal the mechanisms dictating the plasticity size effect. Different methods are used in literature to investigate plastic deformation and dislocations in constrained volumes. Compression-, tension- and bending-tests have been performed on micro-sized and nano-sized samples in the scanning electron microscope, atomic force microscope and the transmission electron microscope. In this work, an atomic force microscope was developed that can simultaneously function inside a scanning electron microscope and was utilized for in-situ deformation studies to contribute to the understanding of the plasticity size effect. The new combined instrument is, in contrary to already existing solutions, compatible to various mechanical and micro-mechanical testing equipment. Microcompression and microbending tests have been performed to show the abilities in this field. A new method, called the “indent@edge” method was introduced. The new method is adopted for mechanical testing experiments in combination with atomic force microscopy. The sample preparation for the new method is less complex compared to the preparation of microbeams and micropillars. Thin metal films on polyamid were also strained in air to investigate the plastic deformation and reliability of the metal films for flexible electronic applications. The electrical resistance and the crack density were determined in dependency of the applied strain.