Experimental evaluation of hinge phenomenon in notched three point bend bars using laser speckle metrology

Abstract

In elastic-plastic fracture, material behavior is often characterized by the J-integral or crack tip opening displacement (CTOD) parameters. In order to evaluate these parameters accurately, the location of the plastic hinge point, and subsequently the value of the plastic rotational factor, r p , must be determined. Traditionally, hinge point location and r p have been inferred through crack opening displacement (COD) measurements. However, this work indicates that laser speckle metrology can be used to analyse directly the hinging phenomenon. Using notched three point bend bars fabricated from a high stretch low alloy steel, a full-field map of in-plane displacements was generated over the course of each test. The results indicate the existance of a hinge region, rather than an explicit hinge point. The hinge region appears to contain the computed hinge point location using the range of cited r p values. This indicates that it may be appropriate to use the centroid of the hinge region in subsequent CTOD and J-integral calculations.