Magnetic Technique Estimation of Weld Residual Stress Failure Due to Tensile Loading

In Nigeria, most welding activities are carried out by road side welders, majority of this welders are ignorant of weld residual stress and its adverse effect on weldment. Residual stress (RS) measuring device is vital in the measurement of inherent stresses in material. The aim of this research was to employ proof of principle in analyzing the weld residual stresses in a material. This was achieved by measuring samples with magnetic residual stress device and then subjecting the weld samples to mechanical tensile test with hope that materials with more residual stresses fail first. Finally the result from both procedures was compared to establish a relationship. Four (4) pieces of mild steel coupons measuring 100 × 40 × 3 mm were welded, producing two specimens, A11 and B11 of 200 × 40 × 3 mm, respectively. The specimens were measured using the Magnetic device developed and 37 signals were obtained per specimen, thereafter, the welded specimens were subjected to tensile testing and results analyzed. From the results obtained, Specimen A11 was observed to have the highest signal peak at the weld zone with RS signal of 20.3983 mV compared to B11 with 19.358 mV. While under tensile loading, it took 1.63 kN to cause failure to specimen A11 and 8.65 kN for specimen B11. From this simple experiment, it implies that the Magnetic RS device was able to mimic the behavior of residual stress and also predicted that A11 would fail first.