A Theoretical and Experimental Investigation into the Development of Coverage in Shot Peening

Author:  Karuppanan, Romero, de los Rios, Rodopoulos, Lever
Source:  Conf Proc: ICSP-8 Sept. 16-20, 2002 Garmisch-Partenkirchen, Germany
Doc ID:  2002015
Year of Publication:  2002
Abstract:  
Authors Saravannan Karuppanan*, Jose Solis Romero+, Eduardo R. de los Rios+, Chris Rodopoulos+ and Andrew Levers# *Universiti Teknologi Petronas, Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia +SIRIUS, Department of Mechanical Engineering, University of Sheffield, S1 3JD Sheffield, UK #Airbus UK Chester Road, Broughton, Chester CH4 0DR, UK Introduction Shot peening is a mechanical pre-stressing surface treatment that substantially improves the strength of metals if the process is carefully controlled. The earliest record of mechanical pre-stressing probably predates 2700 BC, when hammered gold helmets were found during the Crusades, as reported in reference [1]. Peening was a well-accepted technology in the early 1920's when hand-peening with specific hammers was used in the race-car industry [2]. However, shot peening as a process of the cold working of metal surfaces, was only realised in the middle of 1920's, as a consequence of the accidental observation that the parts which were sand-blasted for cleaning purposes showed an increased fatigue life. Since the 1960's, the understanding of the shot peening process has increased significantly, especially in the area of fatigue life improvement. The use of shot peening to improve component fatigue life has also been standardised [3]. However, shot peening process parameters are still selected by means of empirical considerations or by experience. Determining the peening schedules required for optimum shot peening is still a grey area. In most shot peening applications, uniform residual compressive stress in the surface zone is the sole desired effect, as the stresses will resist the formation of fatigue cracks within the component during service, thereby improving significantly the life of the peened component. A few examples of the type of part which have shown a good response to shot peening, include crankshafts (900% life increase), gears (1500% life increase) and connecting rods (1000% life increase) [4]. Although the mechanism of shot peening is a simple concept, the process is complex. The effectiveness of the shot peening process is dependent upon the uniformity of the induced compressive residual stresses and the energy transfer that occurs during the impact of the shots with the target surface. In practice, the process efficiency is established by means of coverage, intensity and saturation. The scope of this study is to investigate the development of coverage and its relationship to intensity and saturation peening. Within this scope, the objectives of this research are: (i) to compare coverage results obtained experimentally with theoretical models of coverage development, (ii) to establish a relationship between coverage and intensity and (iii) to obtain an empirecal relationship to predict coverage.