Fatigue Microcrack Behavior under the Influence of Surface Residual Stresses.
Abstract
The boundary integral technique has been used to calculate complete crack opening profiles under conditions of zero and compressive surface residual stress states. The results show that in addition to reducing the overall opening of the crack during loading, a compressive surface residual stress can induce a lenticular crack profile through-the-thickness of the material. The boundary integral calculations also provided excellent correlation with observed SCOD behavior. These results lend a great deal of credibility to the boundary integral stress intensity factor calculations. Direct observation of SCOD behavior and growth rate measurements on microcracks in HY-130 steel in both air and an aqueous solution of 3.5% NaCl indicate that residual stresses reduce SCOD much in the same way as in Ti alloys. In addition to this purely mechanical affect, teh compressive residual stress induced lenticular crack profile apparently disrupts the crack tip chemistry in a brine environment and eliminates the crack growth acceleration due to the so called small crack effect. A possible mechanism for this is discussed. The results of preliminary optical metallography of the microstructural development in three types of welding processes for one inch thick plate of Ti-6A1-2Nb-1Ta-0.8Mo are also presented. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1982
- Accession Number
- ADA121775
Entities
People
- Gerald R. Leverant
- John E. Hack
Organizations
- Southwest Research Institute