Transition and fracture shift behavior in LCF test of dissimilar welded joint at elevated temperature

Investigation on LCF Behavior of Welded Joint at Different Temperatures for Bainite Steel

“…LCF tests of 9Cr-1Mo steel with different strain rates (10 −3 /s and 10 −2 /s) under LCF loading were performed by some researchers [22][23][24] at three temperatures (RT, 300 °C and 600 °C), finding that the fatigue life and the plastic strain amplitude increased at higher strain rates for each temperature, which can be attributed to higher fatigue crack growth rate induced by the dynamic strain aging (DSA). In our previous study [25] on the LCF behavior of martensite-bainite dissimilar welded joint at 500 °C, the fatigue failure shifted from bainite BM to OTZ with the increasing strain amplitude, reflecting the load distribution on each zone varied greatly for the inhomogeneous structure with different strain amplitudes.…”

A comparative study on the cyclic plasticity and fatigue failure behavior of different subzones in CrNiMoV steel welded joint

“…To simulate the stress and strain field in the WM specimen at the half-life cycle, the BM and WM was treated as the elastic-plastic materials and described with the cyclic stress-strain relations. The constitutive model employed for the BM and WM is the Ramberg-Osgood model [13], which can be expressed as: is the stress amplitude and plastic strain amplitude at the half life cycle, respectively, K is the cyclic strength coefficient and n is the cyclic hardening exponent, the value of which will be exhibit in Section 3.2.3. Meanwhile, the HAZ was considered as elastic material due to the extremely higher hardness and yield stress observed in the nanoindentation and micro-tensile tests, which will be shown in Section 3.1.…”

“…The strain-controlled low cycle fatigue (LCF) and the stress-controlled ratcheting are the major cyclic deformation phenomena under cyclic loadings [5]. In the last several decades, extensively research works on the strain-controlled LCF behavior of welded joints have been published [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Taking the joints as bulk material, the cyclic hardening/softening features and the fatigue strength of several homogenous welded joints (with base metal of Ti6Al4V [6], 9-12% Cr steel [7][8], 7075Al alloy [9], Ni based alloy 617 [4], etc.)…”

“…Taking the joints as bulk material, the cyclic hardening/softening features and the fatigue strength of several homogenous welded joints (with base metal of Ti6Al4V [6], 9-12% Cr steel [7][8], 7075Al alloy [9], Ni based alloy 617 [4], etc.) and dissimilar welded joints (such as the dissimilar titanium alloy [10][11][12], the 9Cr/CrMoV steel [13], and the 2024/7075 aluminium alloy joints [14]) have been studied by many researchers. It is shown in most works that the welded joints exhibit lower fatigue strength than that of the base metal due to the heterogeneity and welding defects [15,16].…”

“…Nevertheless, limited research works were reported in the past on the ratchetting test and its contribution to the fatigue life for the welded joints, the comparative study on the cyclic deformation and fatigue behavior of welded joints under the stress and strain control modes has not been examined in literature. In addition, due to the significant heterogeneity in microstructure and local properties, the LCF failure location of welded joints may be influenced or shift with the changing of the loading levels or environment temperature [8,13]. Under the cyclic stress-controlled loadings, the local deformation distributions in the welded joints were studied by Luo et al [21] and Corigliano et al [27] by the digital image correlation method.…”