Measurement of tearing toughness on BS4360:50D structural steel

Abstract

Toughness was measured and crack growth resistance curves determined on BS4360:50D steel, over a range of orientations and temperatures from + 20 to − 50° C in terms of both J-integral and crack opening displacement (COD) values, for a number of configurations in static bending. All fractures occurred in a ductile micro-mode. The results are discussed here only in terms of J, but several different methods of estimation are used. These fall into two main groups: for measurement of work done, the results are some 10% higher than those determined from load and clip gauge. Values of JIC found according to the standard ASTM method were some 30% higher than a value for no growth. Maximum load toughness was about twice the JIC value. Over the range studied (0.3 < a/W < 0.5; W/2 < B < W; 20 mm < B < 50 mm; Δa/b < 0.1 where a is crack length, W and B specimen width and thickness, and b=W−a) both J and COD values depended strongly on orientation, but J by either type of analysis was invariant with respect to temperature and sensitive to geometry only in respect of thickness in one case. Conditions of testing do not therefore seem at all critical in this regime, although the values found depend on the methods of analysis used.