Vol.2, No1&2, 2002, pp. 23-27
UDC 620.178.7

The paper presents results of evaluating static and dynamic J-R curves using two methods of single specimen, applying pre-cracked Charpy specimens, produced of 700 MPa yield strength HSLA steel class. The first method uses potential drop applied to continuously cracked single specimen for crack length measurement (SSPD). The value of J integral was calculated for corresponding crack length by dividing the diagram into sections, using suitable calibration. The second method is based on the condition of nonvariable bend angle of single edge notch SE(B) specimen and constant ligament net stress state during ductile crack growth.

Static and dynamic resistance curves are designed based on the same basic diagrams, obtained in standard stress intensity factor test (ASTM E1737) and on instrumented Charpy pendulum. SSPD method and new proposed R-curve design procedure, based on constant relation between ligament length and load (PLLL method) have been applied. Static J-R curves, obtained by SSPD and PLLL method are in agreement mutually and with master curve, obtained by ASTM E1737 multispecimen method. Dynamic J-R curve, obtained by SSPD method is clearly above static curves, and only slightly above them in the case of PLLL method up to 1.3 mm of crack extension.

The advantage of new proposed method for evaluating dynamic J-R curve is in use of single continuously cracked specimen, but without additional requirement for crack growth measurement. This opens the possibility for application to materials with microstructural heterogeneity, e.g. welded joints.

Keywords: instrumented Charpy test, pre-cracked Charpy specimen, crack resistance curve, crack length measurement, potential drop, load vs. load line displacement curve, static load, impact load