The aim of the work is to develop a technique on the experimental study of inelastic deformation of structural metal materials in various types of stress-strain state. A technique is proposed based on the use of original samples of specialized complicated geometry, in the working zone of which a controlled biaxial stress state is realized, and the use of a contactless 3D digital image correlation measurement system Vic-3D for recording displacement and deformation fields. The authors proposed the use of original samples of variable thickness in the form of plates located inside a rigid circular rim and a rim of reverse curvature. Under uniaxial tension of these samples in the central area of the plate (working part of the sample), the plane stress state is realized with principal stresses of different signs, depending on the shape and rigidity of the rim. In the working part of the plate with a ring-shaped rim, tensile forces in the longitudinal direction and compressive forces in the transverse direction are realized due to the curvature of the circular rim and its narrowing in the transverse direction. In a plate with a rigid rim of reverse curvature, biaxial tension is realized in the working section. High efficiency of the proposed experimental technique has been shown to solve problems in the mechanics of solids, in particular, to study the processes of macroscopic localization of plastic flow in Al-Mg alloys (AlMg6) under the conditions of the Portevin - Le Chatelier effect. Using a video system, experimental data of the realized ratio of the deformation components (longitudinal and transverse deformations) in the working zone of the samples were obtained. The analysis of the kinetics of band formation and discontinuous yield strain occurring under conditions of a plane stress state has been carried out. The use of the Vallen Amsy-6 system made it possible to obtain data on the occurrence of acoustic emission signals accompanying the observed processes of inelastic deformation of the material. The graphs of the dependence of the energy parameter and frequency characteristics of acoustic emission signals on time have been constructed and analyzed.