Single strain gage based determination of mode I stress intensity factor in orthotropic laminates

Abstract

In applying the concepts of linear elastic fracture mechanics (LEFM) to orthotropic composites, it is important to accurately determine the stress intensity factors (SIF). In strain gage based determination of SIF, Dally and Sanford (DS) [1] first showed that a single strain gage could be effectively used to determine the mode I SIF (KI) in isotropic materials. Only very recently, extension of DS technique to orthotropic materials was reported. The objective of the present work is to demonstrate the possible extension of DS technique for experimental determination of KI of edge cracked carbon/epoxy laminates with a crack length to width ratio of 0.71 in order to establish that the technique could be used even for larger crack length and to demonstrate the importance of pasting the strain gage within optimal radial location. A finite element (FE) based method using extended DS technique has been presented for numerically estimating the optimal gage location for accurate determination of KI of edge cracked [902/0]10S carbon/epoxy laminates. Experiments have been conducted using a single strain gage to determine KI. Results show that it is possible to accurately determine KI in such components following the proposed technique. Results also show that while highly accurate values of KI could be obtained if the strain gage is pasted within the optimal location, highly erroneous values of KI result by pasting the strain gage outside the optimal locations thereby substantiating the importance of knowing apriori the optimal radial location proposed by the authors.