Authors: Omar Suliman Zaroog, Aidy Ali, Sahari B. Barkawi, Rizal Zahari
Abstract: The residual stress relaxation can be divided into two stages: The first cycle relaxation and the following cycles. In both stages, residual stress relaxed considerably from the initial state. The aim of this study is to investigate the residual stress relaxation and microhardness reduction after first and second cyclic load. A 2024 T351 aluminum alloy specimens were shot peened into three shot peening intensities. The fatigue test for first and second cyclic loads of two loads 15.5 kN and 30 kN was performed. The initial residual stress and residual stress after the first and second cycle stress was measured for the three shot peening intensities using X-ray diffraction. Microhardness test was performed for each specimen. The results showed that the residual stress relaxation for first cycle was reached more than 40% of the initial residual stress and it depends on the load amplitude, and microhardness decreased for the first cycle reached 22% and also it depended on load amplitude.
343
Authors: Omar Suliman Zaroog, Aidy Ali, Sahari B. Barkawi
Abstract: Specimens of 2024-T351 aluminium alloy under different three shot peening intensities were studied. The modifications of the surface layers of the shot peened specimens were investigated through microhardness, surface microstructure and residual stress relaxation after the first and second load cycles under two cyclic loads. No significant changes in microstructure after the three shot peeing intensities were observed with respect to untreated specimens. Rapid residual stress relaxation was observed in specimens after the first cycle. Relaxation of residual stresses occurred within first loading cycles were increased with increasing loading stress amplitude and due to quasi-static relaxation effects.
912
Authors: Omar Suliman Zaroog, Aidy Ali, Sahari B. Barkawi
Abstract: The initial compressive residual stresses induced or inherent in a component will not remain stable during the life of the component, it relax and redistributed. In design of the component, it is important to consider the relaxation of residual stress phenomenon. In this study, equations to predict residual stress relaxation of 2024 T351 aluminium alloy specimens were proposed. The equations developed from the experimental data of 2024 T351 aluminium alloy specimens that were shot peened under three different shot peening intensities and undergoing cyclic tests for two load magnitudes for 1, 2, 10, 1000 and 10000 cycles. The residual stress, cold work and microhardness results were recorded after each cyclic load as well as the initial state. The presented model incorporates parameters including the degree of cold work, initial induced residual stress and the number of applied loading cycles.
1349
Authors: Renaud Frappier, Yvan Bordiec, Benoit Grimault, Paul Lefèvre, Frédéric Chateau
Abstract: Ultrasonic needle peening (UNP) is a post-weld high frequency mechanical impact (HFMI) treatment process. This study describes a practical method for measuring residual stress (RS) distribution after UNP and its application to a simple case. Laboratory sin²ψ XRD RS analysis is performed on an UNP single-track on a flat structural steel specimen. This situation is studied as a reference case to characterize RS creation during UNP. It is demonstrated that successive mechanical and electrochemical polishing stages combined with relatively high resolution sin²ψ XRD measurement permits to get an effective surface and in-depth characterization of longitudinal and transverse RS around the UNP groove. High magnitude longitudinal compressive RS are found in the middle of the groove whereas transverse RS compression peaks are located on both sides of the groove. Discussion is conducted about sources of error associated with the experimental method and outlook for UNP process fundamental characterization.
91
Authors: J.L. Ocaña, J.L. González-Carrasco, M. Lieblich, S. Barriuso, J.A. Porro, L. Ruiz de Lara, M. Díaz, J.A. Santiago
Abstract: Laser shock processing (LSP) is increasingly applied as an effective technology for the improvement of metallic materials’ mechanical and surface properties in different types of components, mostly as a means of enhancement of their fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists in the generation of relatively deep compression residual stresses fields into metallic components allowing an improved mechanical behaviour. In this paper, the special case of Ti6Al4V alloy is considered from a more fundamental point of view, with specific consideration of the microstructural changes and residual stresses fields justifying those macroscopic effects. From a concrete point of view, the effect of the application of different typical LSP intensities on the microstructure and residual stresses fields introduced in this material and their possible correlation to the associated surface effects are analyzed.
1408
