Study of the Generalized Curves of the Static and Cyclic Deformation, Damage, and Fracture

Abstract

It is shown that materials on the metal, nonmetal, or composite base under the static and cyclic loading have individual deformation diagrams, which relate stresses and strains. These diagrams are obtained during the standard tensile, compression, torsion, or bending testing of laboratory samples with the detection of forces and deformations of their working parts under loading. In this case, the diagram for a single static deformation in the stress–strain coordinates covers both the elastic deformation region and the elastoplastic deformation region, when deformations are localized in the neck of a loaded sample until its destruction at a critical stress level. It is shown that obtained deformation diagrams are often described by a linear, fractional-linear, and power approximation of the obtained deformation curve. The direct experiments, theory of dislocations, and statistical theory of strength confirm the priority of the power approximation of the investigated diagrams. At the same time, for all construction materials, the generalized deformation diagram in relative coordinates is described by a single power equation with the individual hardening parameter, which is determined experimentally or theoretically from the dependences relating data on the elastic modulus, yield stress, strength, and ultimate plasticity of a material. The cyclic elastoplastic deformation diagrams in the form of plastic hysteresis loops are recorded by analogy with the static tension diagrams with the stress–strain axes in conditional and true relative values. The generalized deformation diagrams for a single static and cyclic loading form a scientific basis for plotting a generalized fatigue curve using the deformation fracture criterion for a wide range of cycles to failure. An effective solution to the strength and service life problems for the most complex engineering objects, such as nuclear reactors, aircraft, and rocket and space systems, can be achieved by considering the generalized deformation and fracture diagrams and relevant calculations. Their importance will especially increase in the design and implementation of new unique high-tech facilities.