Simpler J sub IC Test and Data Analysis Procedures for High Strength Steels

摘要

Tests of five medium and high strength steels were used to investigate someprospective simplification in J sub Ic test and data analysis procedures. Three-point bend specimens with materials strength of 500 to 1500 MPa and nominal thickness of 10 mm were tested at room temperature. The investigation (1) J sub Ic test using measured crack-mouth displacement to calculate load-line displacement based on an expression that relates the two displacements; (2) a simple zero-point adjustment for J versus Delta a curves, whereby certain intermediate Delta a values are shifted to the blunting line to correct for errors at low values of Delta a and (3) a comparison of Delta a and J sub Ic results from the load-drop method, which gives a simple measure of crack growth after maximum load, with results from the usual unloading compliance method. The various results and comparisons are discussed in relation to their usefulness as general J sub Ic test procedure for a variety of materials, or a limited use test for certain materials. Two specific test and data procedures are proposed for general use in J sub Ic testing, as follows: (1) A new expression is described that calculates load-line displacement for the bend specimen from measured crack-mouth displacement, for a range of a/W values and strain-hardening exponents. The expression makes possible a single-displacement unloading compliance J sub Ic test for the bend specimen, using a single, standard, crack-mouth clip gage. (2) A simple zero-shift procedure is proposed for general use with J sub Ic test for addition to ASTM Method E-813.