Development of a Fracture Mechanics Methodology to Access the Competing Mechanics

Author:  Marsha K. Tufft
Source:  Conf Proc: ICSP-6, (presented only)
Doc ID:  1996125
Year of Publication:  1996
Abstract:  
The results from a shot peen Design of Experiment (DoE) conducted a few years earlier suggest that competing mechanisms of beneficial residual stress and detrimental plastic strain and surface roughness may control the low cycle fatigue behavior of shot peened specimens. In order to better understand the mechanisms at work, several coupons were shot peened to a subset of the conditions studied in the DoE. Residual stress and plastic strain distributions were obtained using x-ray diffraction techniques. Mecrostructural evaluation of the specimens included: Micristructures etched to reveal slip character as a function of depth below the peened surface, energy despresive spectrocopy (EDS) to reveal surface chemistry, Auger spectroscopy on selected coupons to determine surface chemistry with depth profile, surface roughness and hardness measurements, determination of weight loss due to shot peening (erosion) and high resolution SEM observation on one electropolished specimen to look for the presence of microcracks. As a result of this effort and a related investigation studying the single particle impact of production shot [1], a fracture mechanics method was developed to provide an estimate of the lower bound life capability of shot peened material. Although a limited number of test conditions have been evaluated to date, the results are encouraging and merit further investigation.