METHOD AND APPARATUS FOR THE STATIC DETERMINATION OF THE MINIMUM STRESS REQUIRED TO CAUSE DELAYED CRACKING AND FRACTURE WELDED METALS

摘要

1,267,954. Testing heat affected metal. INSTITUTUL DE CERCETARI TEHNOLOGICE PENTRU CONSTRUCTII DE MASINA. March 20, 1969 [March 20, 1968], No. 14675/69. Heading G1S. A cylindrical test piece 1 has a part b, Fig. 1, which is gripped by a tensioning member 6 in Fig. 3, and its part a is closely surrounded by a truncated cone or collar 2 into which it is pressed by a force F, Fig. 2, and welded as at 4 in a heat controlled welding device 3. As a consequence of a difference in thermal conductivity the test piece increases in length more than the collar 2 so that on later cooling a residual interval axial tensile stress #int appears in part a. The thermal treatment given to the test piece varies of course according to the temperature of pre-heating the collar 2 and the hydrogen content of the welding electrodes. The lower the pre-heat temperature and the higher the hydrogen content the weaker the welded joint at the heat affected zone (HAZ), see Fig. 4. The cooled test piece with its collar 2 welded thereto Fig. 3, is tensioned by being pulled down by the screw-threaded tensioning member 6 against a heavy supported block 5 with an external force #ext greater than the internal tension #int. The residual tensile stress in the test piece may be varied.