The stress distributions in a thick welded specimen with a partial repair weld were measured with the three-cut contour method. The longitudinal stress maps in the original weld and the repair weld were obtained and the transverse stress map at the weld centerline in the original weld was acquired. The difference between the longitudinal stress in the partial repair weld and that in the original weld was investigated. Results show that the longitudinal stress increases significantly within the entire repair region with a peak tensile longitudinal stress close to the yield strength of weld material; and the longitudinal stress in the region above the repair weld decreases distinctly after repair; the introduction of the partial repair weld does not affect the stress distribution trend in the original weld (whether it is beyond or above the repair weld), and it has a slight effect on the tensile stress distribution width in the repair region.
A multipass thick welded specimen restrained by three saddle-shape plates welded to the bottom surface was prepared and treated using the post-weld ultrasonic impact treatment (UIT). The stresses in the specimen were measured and analysed. Results show that the as-welded stresses on the top surface of the restrained specimen do not drop quickly beyond the weld zone as compared with the typical welding stress distributions in thick unrestrained specimens. The UIT induces compressive stresses with a depth up to 2-4 mm and it has little effect on the as-welded stresses outside of the UIT-treated region. The welding of restraining plates causes a significant increase of the longitudinal stress within the local welding region.
Fatigue crack growth behavior under single-peak overloads is investigated for structural steel JIS SM52OB. Fatigue test is carried out on seven center prenotched specimens.Three parameters, i. e. overload ratio, overload application stage and stress ratio are introduced to investigate the retardation effect. It is verified that fatigue crack growth rate is retarded after overloading and then gradually recovers to the normal.It is also observed that the retardation effect is intensified when the overload ratio and the stress range between overload stress and the following minimum stress increase. From the test results the crack length increment in which retardation occurs is compared with Irwin's and Dugdale's plastic zone sizes.
In order to evaluate accurately fatigue life of weldments under variable amplitude loading, load interaction effect due to load sequence has to be clarified. A simple case is the fatigue crack growth retardation effect resulting from single or periodic overloads. In the present study, fatigue crack growth rates were measured under single and periodic overload conditions on center-cracked tension specimens of structural steel SS400, SM520B and HT780. Effects of several parameters including overload ratio, stress ratio, yield strength of material and interval between overloads on fatigue crack growth retardation were investigated.
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