J-integral Jc and Crack Tip Opening Displacement CTODc as a Material Property Evaluating the Fracture Toughness of Paper

Abstract

Determination of the onset of stable crack growth is very significant for evaluating the fracture toughness of paper such as J-integral and crack tip opening displacement (CTOD). For the specimen with small width, an unstable crack growth starts at the maximum load point without a stable crack growth and further no stress concentation is observed at the crack tip. Therefore, the concept of J-integral and CTOD are not applicable to the specimen with small width. J-integral at the onset of stable crack growth (Jc) was examined on the double edge notched specimens of machine-glazed paper, comparing with J-integral at the onset of unstable crack growth i.e. at the maximum load point (Jmax). Jmax depends on the specimen width and is considerably larger than Jc. On the other hand, Jc is nearly constant independent of the specimen width and thus is regarded as a material property for evaluating fracture toughness of paper as long as a stable crack grows before the maximum load point. The specimen geometry used in this study fulfills the condition required for the RPM (single specimen) method of J-integral determination. CTOD at the onset of stable crack growth (CTODc) is also essentially constant independent of the specimen width and thus is regarded as a material property for evaluating fracture toughness of paper unless the width is small.