Papers by Keyword: Fatigue Crack Propagation

Abstract: The Direct Optimized Probabilistic Calculation (DOProC) is originally developed as one way of solving probabilistic problems which don't use any simulation technique. DOProC is based on general terms and procedures used in probabilistic theories. Input random quantities (such as the load, geometry, material properties, or imperfections) are in DOProC method expressed by the parametric or empirical distribution in histograms. DOProC applications are processed in ProbCalc software, in which the calculation model under analysis can be expressed analytically as a sign arithmetic expression or can be expressed using code from the dynamic library. The method requires high-performing information systems for complex tasks. Therefore, efforts have been made to optimize calculations in order to reduce the number of operations, keeping, at the same time, reliable calculation results. The paper will also focus on other special software applications that are able to assess the reliability of bearing structures with respect to fatigue damage or underground works with anchors.

Abstract: A new fatigue life simulation analysis method for spot weld joints is proposed which considers the fatigue crack propagation from the point of fracture mechanics. The traditional fatigue simulation analysis methods for spot weld joints are mainly LBF method based on force and LMS method based on stress, while there exist some issues such as the prediction accuracy is not high, modeling and computational efficiency is low. A modular spot weld model is adopted in this paper, the node forces and moments around the spot weld are extracted through the finite element analysis, then a average stress intensity factor through the crack propagation path is calculated as the evaluation parameter of fatigue life. Shear fatigue test is designed for spot weld joints with two high strength steel materials (HSLA340GI and DP600GI) and four different thicknesses, then double logarithmic regression analysis is implemented between the average stress intensity factor and the fatigue life data of spot weld joints, then a matching curve is obtained as the fatigue life prediction curve for spot welds. Comparative analysis of prediction accuracy is implemented for these three methods, the results show that the prediction accuracy of fatigue simulation method for spot weld joints in this paper is higher than traditional LBF and LMS methods.

Abstract: The effect of Friction Stir Welding joining process on the damage tolerance behaviour of friction stir welded aluminium alloys is experimentally investigated. Fatigue crack propagation tests for different aluminium alloys and welding configurations have been performed. The main conclusion arising from the experimental study is that the damage tolerance behaviour of the welded material is in most cases comparable to the base material. Furthermore, the most critical area of the joint was identified to be the weld interface, i.e. the area between the nugget and the thermo-mechanically affected zone

Abstract: This study investigated the fatigue crack propagation of Al–Mg–Mn–Zr alloys with erbium. The research found that in this alloy the crack propagation path prefers to extend along the grain boundary. If there are too many second phases or impurities in the gain boundary, the crack propagation will be influenced. The dispersed Al₃(Er, Zr) precipitate in the alloy can act as a core of heterogeneous nucleation to attract Mg, Zn and Al element, and reduce the large brittle Al₃Mg₂ second phase appear on the grain boundary, so the fatigue crack propagation rate can be slow down. In addition, these Al₃(Er, Zr) precipitate can pin the dislocation in the alloy to reduce stress concentration at the grain boundary, so it also has some positive effect to the fatigue crack propagation.

Abstract: Material damage state is described by a restraining stress zone. Then, a macro/micro trans- scale fatigue crack growth model is established. The proposed model is used to simulate the whole fatigue process from a micro-defect to the final macroscopic fracture. Numerical calculations are performed. The fatigue test data for the LC4 aluminum alloy plate specimens are accurately re-produced by the present model. Furthermore, when the microscopic effects are taken into account, the scatter feature of the fatigue test data can also be reflected.

Abstract: With times of tensile tests, the tensile behavior of a kind of stainless steel at room temperature was determined. According to the results of tensile tests, some parameters of mechanical properties of the stainless steel can be obtained. Fatigue crack expansion of COD stainless steel specimens at room temperature can be simulated with the finite element software extensions.

Abstract: The Inconel’s alloy IN 718 has been developed by International Nickel Company in early 50-ties of 20^th century. It is high-strength; corrosion-resistant nickel chromium material used at temperature range from-250°C up to 705°C. In this study, the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of IN718 superalloy with given chemical composition were investigated under push-pull high frequency fatigue test at room temperature. A S – N curve was obtained after testing. With the help of scanning electron microscope (SEM), fractography analyses were performed to disclose the fracture features of specimens in different life ranges.

Abstract: The paper deals with an estimation of the residual fatigue lifetime of the railway axles. The railway axles can include some cracks either from manufacturing process or from previous loading operation. Because of cyclic loading of the railway axles there is a risk of fatigue failure of the railway axles with unacceptable consequences. Based on this fact, for conservative establishment of the residual fatigue lifetime of the railway axle is necessary to consider an existing crack in the railway axle during design process. The fatigue lifetime estimation of railway axles is very sensitive to used crack propagation rate description (e.g. v-K curve). Typical bending of this curve (knee) can be found in the vicinity of the threshold value in fatigue crack propagation rate dependence (typically v-K curve expressed in log-log coordinates). For accurate estimation of residual fatigue lifetime of the railway axle is necessary to use approximation of v-K curve that takes into account existence of the knee close to the threshold value of the stress intensity factor. The paper shows important differences between different crack propagation rate descriptions on the residual fatigue lifetime estimation of the railway axles. Results obtained can be used for safer design and operation of the railway axles.

Abstract: Fatigue crack propagation is studied in thin wires of about 1 mm in diameter of an ultrahigh strength steel (σ_max> 2400MPa) in ambient air and in air with controlled residual humidity. A specific equipment is developed based on an electro-dynamic testing machine equipped with an environmental chamber for air humidity control. Threshold tests are run using a load shedding procedure specifically adapted to the specimen size. The relation between load ratio and crack closure is evaluated from constant K_max tests. The results are discussed on the basis of fracture surface observations and of existing modelling for environmentally assisted fatigue crack propagation.

Abstract: This paper deals with fatigue crack propagation under 4 bar hydrogen atmosphere in low alloyed steel (3.5Ni-1.5Cr-0.5Mo-V) used for turbine generator of nuclear plant. The tests are conducted in the same way in ambient air and high vacuum on CT specimens and the fatigue crack growth rate specially investigated in the near threshold range is plotted with respect to the applied stress intensity factor. It is shown that the propagation under hydrogen atmosphere is similar to that obtained in air up to a K_max value of 16,5 MPam^1/2 with increased growth rate compared to that in high vacuum leading to a threshold value lower that in vacuum, this effect being related to residual water vapor. For K_max higher than 16,5 MPam^1/2, much faster growth rates under hydrogen atmosphere becomes are associated to an intergranular propagation mechanism induced by an hydrogen effect. The results are discussed on the basis of available models.