In-situ DIC investigation on local stress-strain behavior in creep-fatigue test of dissimilar steel welded joint

The digital image correlation technique was employed to investigate the variations of local stress-strain behavior in tensile and creep-fatigue tests for 9Cr/CrMoV welded joint. The strain concentration shifts from fine grain HAZ to over-tempered HAZ of CrMoV in tensile test. For strain-controlled creep-fatigue test, different ratcheting of sub-regions is observed, which is attributed to mismatched yielding and negative mean stress caused by stress relaxation. In addition, crack initiates and propagates at fine grain HAZ with characteristics of fatigue-dominated damage, where the actual strain amplitude and hysteresis energy density are about 4 and 10 times of base steel respectively.

Automated summary

The study revealed variations in local stress-strain behavior in tensile and creep-fatigue tests for 9Cr/CrMoV welded joint, including strain concentration shifts and crack initiation and propagation. These changes are mainly attributed to negative mean stress and different cyclic strains caused by stress relaxation.