Stability of Arrays of Multiple-Edge Cracks

• Main Author: Parker, Anthony P.
• Other Authors: ROYAL MILITARY COLL OF SCIENCE SWINDON (UNITED KINGDOM)
• Format: Text
• Language: English
• Published: 1998
• Subjects: Mechanics; *FRACTURE(MECHANICS); *CRACK PROPAGATION; *RESIDUAL STRESS; STRESS ANALYSIS; GUN BARRELS; CRACKING(FRACTURING); CERAMIC COATINGS; CONCRETE; ENERGY TRANSFER; PRESSURE VESSELS; THERMAL STRESSES; PERMAFROST; STRESS CONCENTRATION; UNITED KINGDOM; STRESS INTENSITY FACTOR; FOREIGN REPORTS; CRACK SHEDDING; permafrost
• Online Access: http://www.dtic.mil/docs/citations/ADA348587; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA348587

The creation and subsequent shedding of arrays of edge cracks is a natural phenomenon which occurs in heat-checked gun tubes, rapidly cooled pressure vessels, and rock, dried-out mud flats, paint, and concrete and in ceramic coatings and permafrost. The phenomenon covers five orders of magnitude in crack spacing. A simple model is developed which indicates that the shedding behavior is governed by energy release from individual cracks rather than global energy changes. The model predicts that all cracks will deepen until a crack-spacing/crack-depth ratio (2h/a) of 3.0 is achieved, at which stage crack-shedding will commence. Two out of every three cracks will be shed, leading to a new (higher) crack-spacing/crack-depth ratio at which stage growth of all currently active cracks will be dominant. An approach based upon rapid, approximate methods for determining stress intensity provides good indications of behavior provided near-surface stress gradients are not excessive. in cases where stress gradients are high, it is shown that it is necessary to employ numerical techniques in calculating stress intensity. Two specific examples are presented, the first at very small scale (heat-check cracking, typical crack spacing 1 mm) and the second very large scale (permafrost cracking, typical crack spacing 20m). The predicted ratios for the proportion of cracks shed and for crack-spacing/crack-depth are in agreement with experimental evidence for gun tubes, concrete, and permafrost. The ratios also appear to match experimental observations of 'island delamination' in ceramic coatings and paint films.