Experimental and Theoretical Investigations on Mode I Crack Propagation in Notches under Cyclic Loading

Research works regarding crack opening stresses covering various types of Mode I cracks initiated and growing in notches under cyclic loading are shown. A large number of parameters influence the crack opening behavior, i.e. material, crack length, notch geometry, and load amplitude. The experimental results indicate uniform relationships cracks in notches and build the basis for developing improved formulae and algorithms to describe Mode I crack opening behavior. Theoretical calculations of crack opening stresses based on Newman’s equations have been found out to be in good agreement with corresponding experimental data determined from thin, notched specimens subjected to fatigue loading with constant amplitudes

An Analytical Procedure for the Prediction of the Stress-Strain State in Notches under Multiaxial Fatigue

This work presents an analytical procedure for estimating elastic-plastic stresses and strains in notched shafts subjected to synchronous non-proportional torsional and tensile cyclic loading. The specification of the equivalent stress concentration factor is firstly accomplished. Neuber’s rule in conjunction with the assumed material law provides the relation between the applied loading and the equivalent stress and strain. Principal stresses and strains yield from the corresponding equivalent values incorporating Hencky’s equations. The transformation of the principal stresses and strains to the appropriate coordinate system yields the final result. For the assessment of the analytical procedure, notch stress-strain results from several finite element analyses of an axisymmetric cylindrical shaft with a circumferential groove subjected to multiaxial synchronous fatigue loading are presented. A satisfactory agreement between the analytical and numerical results is observed

Experimental Investigation of Fatigue of Thin-Walled Welded Structures of Commercial Vehicle Frames

The fatigue behavior of bus frame components consisting of thin-walled tube beams joined together by fillet welding has been investigated. Numerical analysis by means of finite elements and experimental stress analysis by means of strain gages explored the failure-critical locations at the weld toe. In addition, a proposal for finite element modeling in particular of the welded area, and evaluation of hot spot stresses to be used for fatigue life calculations of such thin-walled structures has been developed. The calculation results have been verified based on experimentally determined fatigue lives of the components under constant amplitude loading. A satisfactory agreement between experimental and theoretical results has been observed

Investigation of the Shot Size Effect on Residual Stresses through a 2D FEM Model of the Shot Peening Process

Shot peening is a surface treatment process commonly used to enhance the fatigue properties of metallic engineering components. In industry, various types of shots are used, and a common strategy is to regenerate a portion (approximately up to 35% of the total shot mix weight) of used and worn shots with new ones of the same type. Shots of the same type do not have a constant diameter, as it is concluded by experience that the diameter variation is beneficial for fatigue life. The process of stochasticity raises the difficulty for the application of computational methods, such as finite elements analysis, for the calculation of pivotal parameters, for instance, the development of the residual stress field. In the present work, a recently developed plane strain 2D FEM model is used, which has the capability to consider various shot size distributions. With the aid of this model, it became feasible to study the effect of the shot-size distribution, its sensitivity, and to draw conclusions considering the industrial practice of using a mixture with new and worn shots. The diameter of these shot types differs significantly, and a used shot may have a diameter three times smaller than a new one. As concluded from the finite element results, which are verified from experimental measurements, a shot type with a larger diameter causes a wider valley in the stress profile, and the peak stress depth increases. Alongside the peak stress depth movement, with smaller shots, larger residual stresses are observed closer to the surface. Thus, the superimposition of many shots with variable diameters causes the development of a residual stress field with enhanced characteristics. Furthermore, this residual stress field may be further enhanced by adjusting or increasing the percentage weight of the used shots, up to ~50%

Mode I fatigue crack growth at notches considering crack closure

Fn analytical elastic–plastic model is presented describing the fatigue life of arbitrary engineering components with elliptical notches under constant amplitude loading. A DJeff-based crack growth law is integrated from a starting crack size of micro-structural dimension up to the total fracture of the component. Plasticity-induced crack opening and closure effects are explicitly taken into account. Calculated opening load levels for cracks growing in notch affected areas have been found to be in good agreement with corresponding experimental values determined from notched specimens made of two different metallic materials. Comparison of experimentally determined and calculated crack growth curves for specimens with central notches confirm the satisfactory accuracy of model. The experimental verification of the model’s calculation accuracy covers various ductile materials, notch geometries, load amplitudes and mean load effects

Investigation of the Shot Size Effect on Residual Stresses through a 2D FEM Model of the Shot Peening Process

Shot peening is a surface treatment process commonly used to enhance the fatigue properties of metallic engineering components. In industry, various types of shots are used, and a common strategy is to regenerate a portion (approximately up to 35% of the total shot mix weight) of used and worn shots with new ones of the same type. Shots of the same type do not have a constant diameter, as it is concluded by experience that the diameter variation is beneficial for fatigue life. The process of stochasticity raises the difficulty for the application of computational methods, such as finite elements analysis, for the calculation of pivotal parameters, for instance, the development of the residual stress field. In the present work, a recently developed plane strain 2D FEM model is used, which has the capability to consider various shot size distributions. With the aid of this model, it became feasible to study the effect of the shot-size distribution, its sensitivity, and to draw conclusions considering the industrial practice of using a mixture with new and worn shots. The diameter of these shot types differs significantly, and a used shot may have a diameter three times smaller than a new one. As concluded from the finite element results, which are verified from experimental measurements, a shot type with a larger diameter causes a wider valley in the stress profile, and the peak stress depth increases. Alongside the peak stress depth movement, with smaller shots, larger residual stresses are observed closer to the surface. Thus, the superimposition of many shots with variable diameters causes the development of a residual stress field with enhanced characteristics. Furthermore, this residual stress field may be further enhanced by adjusting or increasing the percentage weight of the used shots, up to ~50%