Papers by Keyword: Crack Initiation Life

Abstract: In the geomagnetic field, stress can induce spontaneous magnetic signals in ferromagnetic materials, the method, named metal magnetic memory testing, can be potentially applied in estimating the fatigue life. In this paper, the normal component of magnetic field, Hp (y), was measured during dynamic tension test on the surfaces of ferromagnetic specimens with stress concentration factor of 5. The results indicated that the gradient of magnetic field intensity, K, was the key parameter to characterize crack initiation life. Then the numerical fitting of K and fatigue cycles were done under three level loads, 568.7MPa, 698.8MPa and 864.4MPa, meanwhile, a simple model was derived.

Abstract: Based on the continuum damage mechanics theory, according to the development of the fatigue damage evolution equation, and combining the interaction coefficient of stiffener and plate, with plastic strain as the control quantity of damage evolution, the stiffened plate low cycle fatigue damage mechanics model is established, and the calculation method of the fatigue crack initiation life is obtained. This method for the initiation life of fatigue crack is divided into the life before the damage and the life of the damage evolution. The model results are compared with those of the finite element results. Conclusions show that the model can reflect the regularity of axial plastic strain evolution of stiffened plate, and can be directly used for fatigue loads analysis under the mechanism of initiation life.

Abstract: The life excess of shaft part of the traditional design is a major source of industrial waste. This paper presents a vision for excess life of the shaft parts, which is expected to use the crack initiation life instead of the traditional fatigue endurance limit, achieve the purpose of reducing the excess life, try to give the method of calculation of the crack initiation life, and provide technical support for the shaft parts life design.

Abstract: This document describe accelerated corrosion test and fatigue test for the LD2 aluminum alloy test specimen, the research object is a LD2 aluminum alloy test-piece which has crack in the corrosion pit, the crack initiation life in the area of Corrosion pit has been defined, the influence of the Corrosion on the crack initiation life in corrosion pit area has been researched. Finally, the simulation of crack propagation for the LD2 aluminum alloy test-piece has been made. By comparing, the result of simulation is more conservative than the actual test value.

Abstract: Applied damage mechanics and coupled finite element method, to study the fatigue crack initiation life problem. Application of coupling finite element method, the damage coupling effect can be modified through the global stiffness matrix to achieve. The step length of the damage evolution is divided by the damage variable of the critical element, and then the damage evolution is analysised. The corresponding stiffness matrix and loading matrix can be obtained continually under the condition of increasing the damage evolution step of the critical element,then the equivalent stress can be calculated. The corresponding fatigue crack initiation life can be calculated by using the damage evolution equation, the progress will not stop until the damage degree of the critical element reaches to one. The fatigue crack initiation life is obtained by adding the fatigue crack initiation lives with different damage variable.

Abstract: A numerical model is presented to analyze effect of wheel/rail friction on rolling contact fatigue. A three-dimension finite element model of rail is built up to investigate the rail stresses and strain around wheel/rail patch. Then, based on the critical plane concept, a new model was proposed to predict the rolling contact fatigue (RCF) crack initiation life under different wheel/rail frictions by using stress and strain on the critical plane as fatigue parameter. The numerical results obtained show that the wheel/rail friction coefficient has a great impact on the fatigue crack initiation life.and the curve of fatigue crack initiation life under different wheel/rail friction coefficient is roughly "S" type. The results are very useful in the wheel/rail friction management and determining grinding interval and grinding removal.

Abstract: In this study, the simulation of contact fatigue based on stress analysis is conducted under Elastohydrodynamic Lubrication (EHL) state. To predict a crack initiation life accurately, it is necessary to calculate contact stress and subsurface stresses accurately. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions and the subsurface stress is obtained using rectangular patch solutions. The numerical algorithm using newton-rapson method was constructed to calculate the EHL pressure. Based on these stress values, three multiaxial high-cycle fatigue criteria are used. As a result, the effects of EHL on contact fatigue life are calculated.