Abstract: For combined HCF/LCF loading, whose stress history is simplified so that it consists of one LCF stress block with a number of cycles equal to the number of start-up in-service operations and one HCF stress block with all HCF cycles summed-up, we derived the closed form expression for estimating both the crack initiation life and the crack propagation life at combined HCF/LCF loading. As an example of use, Smith and Haigh diagrams were obtained for titanium alloy (Ti-6Al-4V) components, which enable to estimate the fatigue strength for the designed fatigue life, known load ratio and certain number of HCF cycles per one combined stress block.Keywords: machine elements, fatigue, service life prediction, crack initiation, crack growth, stress historyPublished in DKUM: 01.06.2012; Views: 2594; Downloads: 54 Link to full text
Abstract: A computational model for determination of the service life of gears with regard to bending fatigue at gear tooth root is presented. In conventional fatigue models of the gear tooth root, it is usual to approximate actual gear load with a pulsating force acting at the highest point of the single tooth contact. However, in actual gear operation, the magnitude as well as the position of the force changes as the gear rotates. A study to determine the effect of moving gear tooth load on the gear service life is performed. The fatigue process leading to tooth breakage is divided into crack-initiation and crack-propagation period. The critical plane damage model has been used to determine the number of stress cycles required for the fatigue crack initiation. The finite-element method and linear elastic fracture mechanics theories are then used for the further simulation of the fatigue crack growth.Keywords: crack closure, crack initiation, crack propagation, gear tooth root, moving loadPublished in DKUM: 31.05.2012; Views: 1708; Downloads: 96 Link to full text
