The impact objects can be hard small particles, a bunch of needles, a simple hammer, or a laser beam and the process would be known as shot peening, needle peening, hammer peening, or laser peening, respectively. Peening is the process of impacting a metal surface causing plastic deformation in the surface.
There are more calculations published than peening residual stress intensity factors calculations, where the concept of cohesive zone model is used with the finite element method to estimate compressive stress relaxation in shot peened specimens. The weight function method has been used in many cases with welding residual stress distributions such as those proposed by Structural Integrity Assessment Procedures for European Industry and stress intensity factors associated with welding residual stresses are determined. The most common analytical approaches to calculate values are the weight function method and the finite element method. The experimental residual stress distribution is implemented in an analytical method and can be determined. Experimental measurements of residual stresses by neutron diffraction and X-ray diffraction can be done.
ĭespite the uncertainty in estimating a weldment residual stress distribution, it is possible to estimate values for a given crack location and geometry. Recommended upper-bound welding residual stress profiles for use in analyses are given in Structural Integrity Assessment Procedures for European Industry.
The International Institute of Welding recommends fatigue tests for the verification of a procedure such as peening in the endurance range of interest.
For the case of a shot peened weldment, residual stresses are the result of adding residual stresses by welding plus compressive residual stresses by shot peening. This research is focused on the estimation of the peening effect on stress intensity factors, since is a key input in fracture mechanics calculations for fatigue life predictions.Īnalytical estimation of in weldments considering residual stresses is a complex task, since a distribution of residual stresses through the plate thickness during crack growth is required. It is expected that compressive stresses improve the fatigue crack performance, since cracks grow due to the opening effect induced by tensile stresses. This paper describes the addition of compressive residual stresses by shot peening to the ground notch surface to improve the fatigue performance of the repaired weldment.
Research on improvements to fatigue crack repair for offshore structures incorporated metal filling of the ground notch by dry or wet welding to improve the fatigue performance of the repaired weldment surface. The repair profile has a predesigned geometry to reinstate a fatigue life that can be even larger than the as welded fatigue life.
In the offshore industry, repair in situ is the most feasible option, since offshore structures have to operate continuously.Īlternative to joint clamping, a fatigue crack repair procedure based on the removal of cracked material by grinding has been proposed for offshore structures.
Inspection of components subjected to fatigue loading can reveal fatigue cracks presence thus, depending on the particular component, the option of component replacement or repair in situ is an issue. Experimental stress intensity factors determined from a set of fatigue tested T-butt specimens allowed estimating preliminarily that peening has a limited effect on fatigue crack propagation inhibition for edge repaired T-butt weldments subjected to bending loading. Experimental estimation of the peening effect on stress intensity factors in fatigue crack repaired weldments was validated by comparison against an analytical weight function solution. The experiments were designed to estimate the residual compressive stress depth layer and its effect on crack propagation inhibition. A set of T-butt specimens were experimentally fatigue tested and crack propagation data was gathered for the calculation of stress intensity factors.
This paper is in relation to the peening effect estimation on stress intensity factors in fatigue crack repaired weldments, since the stress intensity factor is a key parameter in fracture mechanics calculations. To improve the fatigue performance of the crack repair, residual compressive stresses induced by peening can be considered. The periodic inspection-assessment cycle can lead to the implementation of a fatigue crack repair by crack removal. Fracture mechanics calculations are required to validate the safety level defined in design codes to prevent a fatigue failure.