Elastic and Inelastic Energy Density in Cyclic Deformation of Iron-Based Layered Materials Over an Extended Range of Load Amplitudes

Abstract

Three layered materials from technically pure iron sheets with varying degrees of interlayer bonding were produced by hot and cold pseudovacuum rolling methods. The elastic, damping, and high-cycle fatigue characteristics of the materials were determined through resonant vibration testing of flat samples under bending conditions. Known fatigue damage dependences based on the cyclic strength energy density model for structural materials under low-cycle fatigue were considered. Using the studied materials as an example, the feasibility of extending this energy-based approach to the high-cycle fatigue and nondestructive loading regions was demonstrated. The elastic and inelastic components of the strain energy density were calculated from experimental fatigue curves for rolled layered materials over a range of 105 to 107 load cycles and from dependences of the vibration decrement on the cyclic loading amplitude varying from low to destructive strains. Thus, the strain energy density model was extended to the nondestructive cyclic (operational) loading region. In this case, the density of the elastic component of cyclic strain energy was found to be 1.92 times more sensitive to load amplitude than the destructive fatigue curve stresses, while the reliability coefficient for the total cyclic strain energy density was significantly higher than that for the inelastic strain energy density. The decrement of vibrations as a function of cyclic load amplitude and, accordingly, the inelastic component of the strain energy density were shown to be sensitive to the interlayer bonding strength, while the fatigue resistance (endurance limit) was sensitive to the degree of cold rolling applied to the layered materials.