Arrestment of cracks in plane extension by local reinforcements

Abstract

Crack stoppers ahead of an edge crack in panels under tensile load are analyzed. They consist of rectangular and semi-annular patches placed symmetrically on both sides of the panel and at a finite distance ahead of the crack tip. Depending on this distance, the predicted crack path could remain straight or curve. Moreover, the crack could either be arrested or run through the reinforcements. Such a behavior can be determined from the local and global stationary value of the strain energy density function. The degree of instability is reflected by an index parameter that accounts for the effect of load, geometry and material. Edge crack plexiglass specimens were made by reinforcing them with steel and aluminum patches placed at different distance from the crack. For sufficiently low local energy intensity, the crack would run straight and arrest at the patch regardless of the other variables. As the local energy intensity is increased, crack would tend to curve and lead to complete fracture of the patched specimens. This is equivalent to moving the patch closer to the crack tip. The test results agree well with the predictions made from the strain energy density theory.