Accession Number : ADA141107

Title :   The Use of Novel Processing Procedures for Improving the Overall Fatigue Resistance of High Strength Aluminum Alloys.

Descriptive Note : Annual scientific rept. 1 Jan-31 Dec 83,


Personal Author(s) : Starke,E A , Jr

PDF Url : ADA141107

Report Date : Feb 1984

Pagination or Media Count : 38

Abstract : Its objective is to develop an understanding of the mechanisms involved in the initiation and propagation of fatigue cracks in metals in order to optimize the microstructure of high strength aluminum alloys for overall fatigue resistance. The research conducted during this year was divided into three tasks. Task I was concerned with the effects of slip character and grain size on the intrinsic material and extrinsic closure contributions to fatigue crack growth resistance of 7475. Special thermal mechanical processing procedures were developed to control the microstructural features of interest. Task II was concerned with the use of the cyclic stress strain curve and a damage model for predicting fatigue crack growth thresholds. Fatigue crack initiation and fatigue crack propagation both involve the concept of cyclic accumulated damage. The details of the damage structure can be related to a material's cyclic stress strain response (CSSR). Task III is concerned with the effect of ion implantation on the low cycle fatigue response of 7475. Since fatigue crack initiation is a surface phenomenon and fatigue crack propagation is a bulk phenomenon, the fatigue properties may be optimized by production processes that develop microstructures resistant to FCI on the surface, and microstructures resistant to FCP throughout the bulk.

Descriptors :   *Aluminum alloys, *Fatigue(Mechanics), *Crack propagation, Microstructure, Grain size, Aging(Materials), Heat treatment, Stress concentration, Vacuum, Stress strain relations, Cyclic rate, Threshold effects, Ion implantation, Iron alloys, Particle size, Surface reactions

Subject Categories : Properties of Metals and Alloys

Distribution Statement : APPROVED FOR PUBLIC RELEASE