NEW TOUGHNESS TESTS FOR WELDMENTS AND CONCRETE

Two new inexpensive quality tests have been developed to determine the notch toughness of weld joints and fracture toughness of concrete in direct tension. Both tests sample materials before construction to measure their load capacity and tolerance for cracking. The first test, the welded notch toughness test, measures the actual impact toughness of weld joints. Two 30 deg beveled plates of 5/8 in. (16 mm) thickness with 4-6 mm land areas are butted together, using specified or preferred electrodes and welding parameters. As an alternate, a 45 deg bevel joined to a square-cut plate may also be used. After welding, an as-welded notch develops, typically sharper than a standard V-notch. The plates are then cut into ASTM E23 Charpy style bars. When the bars are struck at different temperatures by an ASTM E23 impact hammer, the as-welded notch initiates a crack, which then selects a fracture path of least toughness, including the weld metal, fusion or heat-affected zones. This test can evaluate how toughness is affected by joining different base metals, use of various electrodes, or other welding parameters. The second test measures the plane-strain fracture toughness of concrete in direct tension. A standard 6 x 12 in. (15 x 30 cm) concrete cylinder is used, except that a sharp-edged 2.5 in. (6 cm) diameter plexiglass disk is mounted between two separate threaded bars before the concrete is poured into the cylinder. After curing, the bars are pulled apart, directly measuring both the tensile strength and fracture toughness of the concrete. Fracture planes are flat; numerous tests and finite element analysis have indicated that a uniform stress field develops beyond a 1 in. (2.5 cm) internal radius. This test promises to be a practical, quantitative evaluation tool for measuring toughness of various concrete mixes, aggregates and cements, curing cycles, experimental materials, and for field quality evaluations of concrete.