Environmentally-Controlled Fracture of an Overstrained A723 Steel Thick- Walled Cylinder
Abstract
A through-wall, 1.7-m long crack grew suddenly from a notch in a 285- mm outer diameter (OD) of an A723 steel overstrained tube that was undergoing plating operations with no externally applied loads. The fracture mechanics tests and analyses and the fractography performed to characterize the cracking are described in this report. The tube had a yield strength of 1200 MPa, fracture toughness of 150 MPavm, and a tensile residual stress at the OD of about 600 MPa. The composition was typical of an air-melt A723 steel, and the electropolishing bath, consisting of sulfuric and phosphoric acids, was held at 54 deg C. The bolt-loaded test for the threshold stress intensity factor for environmentally-controlled cracking described by Wei and Novak was used here with two significant modifications. Some tests included only a notch with the radius matching that of the tube, and a new expression for K in terms of crack- mouth displacement was developed and used. Scanning electron microscope fractography and energy dispersive x-ray spectra were used to identify crack mechanisms. Results of the investigation include: (a) a measured threshold of hydrogen stress cracking for the material/environment below 20 MPavm; (b) da/dt versus K behavior typical of classic environmental control; and (c) an improved K/v expression for the bolt-loaded specimen and associated criteria for determining plane-strain test conditions in relation to the Irwin plastic zone. Environmental Cracking, Test Methods, Hydrogen Stress Cracking, Thick-Walled Cylinder, K Analysis, Scanning Electron Microscopy, Residual Stress.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1992
- Accession Number
- ADA257303
Entities
People
- A. A. Kapusta
- G. A. Young
- J. C. Askew
- John H. Underwood
- V. J. Olmstead
Organizations
- United States Army Armament Research, Development and Engineering Center