On the Influence of the Initial Shear Damage to the Cyclic Deformation and Damage Mechanism

Abstract

The accuracy and precision of lifetime predictions for cyclically loaded technical components are still lacking. One of the main reasons for the discrepancy between the calculated life time and experimental results is that it is not yet possible to create a model capable of describing the microstructural damage process that occurs in the tested material and to subsequently incorporate this model into the calculation. All of the presently available research results recognize that the growth of microcracks is significantly influenced by the microstructure of the material. In order to take into account the influence of the microstructure on the damage process, research on the very early fatigue damage is carried out. The results are obtained from tension and torsion fatigue testing. For this purpose, the surfaces of the tested specimens are carefully observed to discover and analyze microcracks, which are classified according to their orientation. Moreover, the mechanisms of crack initiation and propagation are major points of interest. Through a mix of mechanical and metallurgical points of view, calculations and multi-level FEA modeling are carried out to gain a better understanding of the properties of the phases. The simulation is based on continuum mechanics, which considers the positions and mechanical metallurgy, which account for each constituent character’s failure laws. It is concluded that both the experimental and computational approaches conform, showing that such an approach is indeed a necessity and should become a trend in the near future. Statistically, microcracks under tension modes are highest at 45° (approximately 30%), while under torsion they are highest at 0° (approximately 20%) with respect to the sample orientation. The influence of the microstructure is explained via the finite element analysis.

A methodical approach to determining the damage characteristics of cyclically loaded samples of metal structures

“…The authors of the work [13] established that the change in physical and mechanical properties under cyclic loading causes the inhomogeneity of local deformation, as a result of which different structural elements of the material are at different stages of damage development, which determines the discreteness of the characteristics of periods of fatigue damage. Likewise, when analyzing the degree of fatigue damage of an elastic-plastic polycrystal, it is necessary to take into account the kinetics of changes in properties during cyclic loading.…”

Assessing Toughness of Pressurized Fluid Channel: Experiment using CTOD in Spiral Submerged Arc Welded Pipes

“…These flaws propagate through the wall thickness and longitudinally, exhibiting unstable propagation when their length exceeds a critical value 23) . The CTOD methodology is instrumental in determining this critical value, employing notched and pre-cracked samples subjected to static stress to assess material strength in the presence of a crack.…”