Enhancement of Fatigue Life of Shafts

This study aims at guiding against fatigue failure to enhance fatigue life. The question of crack initiation, propagation, and failure in parts undergoing stress reversals or repeated stresses is a problem in machine design. Stiffness is degraded, and strength is reduced. Fatigue-based analytical model has been developed. The design philosophy is set on Design for Finite/Infinite life in which the design stress is below some fatigue strength, the endurance limit. Finite/Infinite fatigue life design tool (and calculations using Marin equations) was utilized to obtain the shaft specimen endurance limit of 235.7 MPa. Below this stress level, fatigue life was prolonged. Attention is also paid to Fail safe design, where cracks initiate and propagate; then a structure (composite material) is designed (against stress concentrations) to impede the crack growth. The materials for the shaft (steel matrix and carbon laminates) are notable for certain properties such as strength, which is due to choice, treatment, or processing, and is an inherent property of the part. Finally, there is Evaluation of stiffnesses and strengths. Stiffness depends on both the modulus of elasticity and the geometry. Primary parameters were calculated (fatigue stress concentration factor of 1.5) to aid other parameters (endurance limit of 235.7). The fiber laminates reinforced the matrix. Elimination of degradation in fatigue life of the elastic property produced enhancement. Strength is present whether there is load on the material. The study shows that by using composite materials and designing below the endurance limit, fatigue life of the shaft subjected to loading can be prolonged.