Fatigue Life Of Welds Research Articles

Fatigue Life of Welded and Bolted Repair Parts

Fatigue crack propagation and residual stress measurement tests were conducted by using deep‐notched wide plate specimens with repaired parts. The main purpose of this study was to evaluate numerically the effects of some weld repair methods and a mechanically patching method with high strength grip bolts on residual fatigue life. The test results proved that the conventional welded repair method with no special treatment reduced fatigue life due to high tensile residual stress induced by welding repairs. However, through application of adequate treatment to cracks, compressive residual stress was induced in repair welds to increase the fatigue life. The remaining fatigue life of welded repair parts was further investigated using Fracture Mechanics. The patching method with high strength bolts and welded splice plates, on the other hand, had a remarkable effect on retarding the fatigue crack growth rate by decreasing it after bolted repairs to about 1/100‐1/1,000.

Predicting the Fatigue Resistance of Welds

Because the fatigue resistance of welds is generally less than that of the members they join, it has been extensively studied through tests on full-size weldmentsan expensive and time-consuming procedure. Munse (I), Gurney (2), and Sanders (3) have reviewed the results of the fatigue testing of weldments and have identified the main variables influencing their fatigue resistance. Extensive bibliographies of the literature relating to the fatigue of weldments have been compiled (4-6). Munse and Sanders have each created computerized weldment fatigue data banks (7, 8). Others, such as the British Welding Institute, may also have similar resources. The fatigue data obtained by testing often exhibit significant scatter­ ing, two major sources of which are uncertainty as to the actual state of stress in the weldment and seemingly small variations in weld geometry. To reveal the causes of this scatter, to interrelate the parameters that influence the fatigue life of welds, and to accurately predict weldment fatigue resistance, an analytical model for estimating the total fatigue life of welds has been developed (9). It assumes that the total fatigue life of a weldment (NT) is composed of a fatigue crack initiation period (NJ) and a fatigue crack propagation period (Np) such that

Effect of Residual Stresses on the Low Cycle Fatigue Life of Large Scale Weldments in High Strength Steel

A determination was made of the influence of various mechanical finishing procedures on residual stresses and the resulting effect on the low cycle fatigue life of tee-fillet welds in 1-1/2 in. thick rolled steel plate with a yield strength of 80,000 psi. Included in this work were tee-fillet welds in the as-welded, ground, shot-peened, ground and shot-peened, and mechanically peened condition. Residual stresses were measured by a hole drilling technique developed at the Naval Applied Science Laboratory for application to linearly varying biaxial stress fields. This method has been found suitable for determining residual stresses at any point over a limited area at the toe of the weld. Fatigue tests were conducted on plate type specimens, 32 in. by 29 in. by 1-1/2 in. which were simply supported at two edges, free at the other two edges, and uniformly loaded with compressed air to develop a zero to maximum tension range of stress at the toe of the fillet weld. It was found that tensile residual stresses do not have a significant effect on fatigue life for the type of pulsating load used. Compressive residual stresses have been found to have a beneficial effect on fatigue life. Welds with relatively high residual stresses which were ground smooth to eliminate “stress raisers” showed very good fatigue resistance.