TWI Industrial Member Report Summary 136/1980
By O L Towers
A major objective of this report is to provide an up-to-date reference for stress intensity correction factors, Y, and non-dimensional elastic compliances, Z, for the major test geometries used in fracture toughness and fatigue assessments. For the same test geometries expressions for Y and Z have been used to derive the elastic component of the nu factor, nue, which is used to estimate the elastic component of the J-integral from the area under the load-versus-load point displacement trace.
It is apparent from a review of Y and Z approximations, that the limitations on crack length which accompany simple polynomial approximations to Y and Z should be adhered to. More complex approximations which retain accuracy for a wider range of crack lengths demonstrate this point as well as providing more comprehensive estimates of Y and Z.
The estimates of nue were compared with a limited amount of published data. The correspondence was generally good, with the exception of the single edge notched tension (SENT) test geometry. The estimated nue values for the threepoint bend (SENB3) and compact tension (CT) test geometries were compared with the nu values specified in a recent JIc test procedure. For these particular bend test geometries it was demonstrated that the elastic component of JIc, calculated using this test procedure, would tend to be underestimated for crack length to width ratios in excess of 0.45. This underestimate may be as high as 10% for the SENB3 test geometry and 14% for the CT test geometry.