CURRENTLY SEVERAL FRACTURE MECHANICS CONCEPTS ARE BEING DISCUSSED WITH RELATION TO GUARANTEEING THE FRACTURE SAFETY OF STRUCTURAL STEEL ELEMENTS, ALTHOUGH THE CONCEPTS ARE NOT FULLY DEVELOPED AND THEIR APPLICATION, IN PARTICULAR IN WELDED JOINTS, GIVES RISE TO NUMEROUS PROBLEMS.
THIS PROJECT WILL CONCENTRATE ON THE J-R-CURVE CONCEPT. AN EXAMINATION WILL ALSO BE MADE OF THE CONDITIONS UNDER WHICH SIMPLER CONCEPTS WHICH DO NOT TAKE STABLE CRACK FORMATION INTO ACCOUNT SUFFICE; PARTICULAR ATTENTION WILL BE PAID TO THE PLASTIC LIMIT LOAD METHOD AND THE BURDEKIN-DAWES CURVE.
THE APPLICABILITY AND TEMPERATURE RANGE OF THESE CONCEPTS WILL BE EXAMINED BY MEANS OF TESTS ON MEDIUM-SIZED 15 AND 30 MM THICK TENSILE SPECIMENS WITH VARIOUS TYPES OF NOTCH AND DIFFERENT WIDTHS IN THE RANGE UP TO 200 MM; THE TESTS WILL BE CARRIED OUT ON A 4 MN MACHINE.
THESE TESTS ARE CHEAPER THAN THE NORMAL LARGE PLATE TESTS AND CAN THEREFORE BE USED MORE EXTENSIVELY FOR PARAMETER STUDIES. COMPACT AND BEND SPECIMENS WILL BE USED FOR THE FRACTURE MECHANICS MATERIALS TESTS NECESSARY FOR THE ABOVE CONCEPTS AND FOR COMPARISON WITH THE JR CURVES USING THE ABOVE CONCEPTS AND FOR COMPARISON WITH THE JR CURVES USING THE ABOVE TENSILE SPECIMENS. THE TRANSITION TEMPERATURES TGY, TI AND TA WHICH DEFINE FRACTURE BEHAVIOUR WILL BE USED TO ESTABLISH THE VALIDITY RANGE OF THE CONCEPT.
THE MATERIALS USED WILL BE THERMOMECHANICALLY-ROLLED STEEL (E.G. STE 460 TM) AND ALSO ST 52; THEY WILL BE SUBJECTED TO MULTI-LAYER SUBMERGED-ARC WELDING AND SPECIMENS FROM THE BASIC MATERIAL, THE HEAT-AFFECTED ZONE AND THE WELD STEEL WILL BE TESTED AT VARIOUS TEMPERATURES.