Changes in the Longitudinal Modulus of Elasticity and Logarithmic Decrement After 50 Years of Cast Iron Storage

Abstract The paper highlights the natural relaxation of internal stresses in cast iron by analyzing the changes in the longitudinal modulus of elasticity and the logarithmic decrement that occurred over 50 years, under conditions in which the samples were not subjected to mechanical stress during this period. The evaluation of elastic properties was carried out by analyzing the resonance curves of the samples subjected to forced bending oscillations. It is found that, over time, discrete changes in the dynamic response of cast iron occur, which can be identified by resonance-based measurements. In all samples, an average increase in the longitudinal modulus of elasticity, ΔE med = +3.55% within the limits of 2-5.94% was found. The logarithmic decrement, respectively, the internal friction, decreased, on average, by Δδ med = −7.15% within the limits of 1.98−11.43%. These findings lead to the conclusion that, over time, in cast irons that have not undergone a stress-relief heat treatment, processes occur that are part of the dissipation of internal energy in the material. The spontaneous relaxation of internal stresses is associated with slow time-dependent processes that modify the elastic and damping behavior of the material and can be detected through changes in its dynamic properties.