The Method to Obtain JR- Curve by Continuous Ball Indentation Method

JR-curve is one of an important index to characterize the fracture properties of metal materials. It is usually determined by multi-sample unloading method and single-sample unloading compliance method recommended by standard methods; In consideration of the similarity between the continuous ball indentation method and the single-sample unloading compliance method, The JR-curve is obtained by using the empirical correlation between effective elastic modulus ED of the continuous ball indentation and the unloading compliance C for single simple in this article. The calculation conducted by the correlation formula of the extension length of crack with unloading compliance C. However, results indicate that the fracture toughness J0.05 obtained by empirical correlation of load-depth curve of continuous spherical indentation is still quite different from those given by the standard test.

Determination of J-R Curve for X60 Pipeline Steel Using SENT Specimens and Normalization Method

The normalization method is adopted in this paper to determine J-R curves for X60 pipeline steel using single-edge notched tension (SENT) specimens. A resistance curve procedure associated with the normalization method is developed to estimate crack extension, calculate crack growth corrected J-integral and generate a J-R curve directly using load-displacement data from a single test on SENT specimens. Based on experimental data for a typical pin-loaded SENT specimen, J-R curve for X60 pipeline steel is obtained by the normalization method and the conventional elastic unloading compliance method. The results show that the normalization method is simple and cost-effective, and can obtain J-R curves equivalent to the unloading compliance method in use of SENT specimens.

Further Extension of the Unloading Compliance Method to Measure J-R Curves Based on CMOD Data

Laboratory testing of fracture specimens to measure resistance curves (J-Δa) have focused primarily on the unloading compliance method using a single specimen. Current estimation procedures (which form the basis of ASTM 1820 standard) employ load line displacement (LLD) records to measure fracture toughness resistance data incorporating a crack growth correction for J. An alternative method which potentially simplifies the test procedure involves the use of crack mouth opening displacement (CMOD) to determine both crack growth and J. This study provides further developments of the evaluation procedure for J in cracked bodies that experience ductile crack growth based upon the eta-method and CMOD data. The methodology broadens the applicability of current standards adopting the unloading compliance technique in laboratory measurements of fracture toughness resistance data (J resistance curves). The developed J evaluation formulation for growing cracks based on CMOD data provides a viable and yet simpler test technique to measure crack growth resistance data for ductile materials.