Low-cycle fatigue test and life assessment of carbon structural steel GB Q235B butt joints and cruciform joints

Abstract

Axial low-cycle fatigue tests are conducted on transverse butt joint specimens and cruciform joint specimens made of carbon structural steel GB Q235B. The effect of slip between the specimens and the grips of the test machine is considered by the proposal of a linear slip model. The cyclic softening properties are studied by observing the variation of stress amplitude with cycles. The cyclic stress-strain curve and the strain-life curve for both kinds of specimens are obtained based on the fatigue test data, and the corresponding coefficients are fitted. In order to verify the fatigue test results, finite element models of specimens are established and the corresponding fatigue life assessment is conducted using the local stress-strain approach and the equivalent structural stress approach, respectively. The results show that the effect of slip is unneglectable and the established linear slip model is reasonable. The two kinds of specimens both show a strain softening property, but cruciform joint specimens experience sudden falls of stress amplitude during the test due to the damage of welded lines; cruciform joint specimens show an either one-side failure mode or two-side failure mode while butt joint specimens only show a one-side failure mode; the two-side failure mode tends to lead to shorter fatigue life, so in the design of cruciform joint, such failure mode should be avoided.

Three-dimensional surface fatigue crack growth life assessment model of steel welded joints and structures

“…The ground flush specimen of a butt joint made of carbon structural steel (GB Q235 in the PRC, approximate to S235JR in BS code or E235B in ISO 630 code) as illustrated in Figure 2(a) is taken as an example. Two plates with a thickness of 5 mm were connected by Gas Metal Arc Welding (GMAW) process with a welding consumable of H08Mn2SiA, which is similar with the butt-welded joint specimen discussed by the authors (Fang et al, 2019). The steel and the welding consumable were mainly composed of carbon (C), silicon (Si), manganese (Mn), sulphur (S), phosphorus (P), and copper (Cu).…”

Low-cycle fatigue life evaluation of buckling-restrained braces based on cumulative plastic deformation curves

“…Note that the CPD is calculated as the ratio of the cumulative plastic strain to the yielding strain of the BRB. By summarizing the results of many studies, CPD can be used to reflect the low-cycle fatigue life of BRBs and is closely linked to the loading history (Black et al, 2004; Carden et al, 2006; Fahnestock et al, 2007; Fang et al, 2019; Karunananda et al, 2012). A method for estimating the cumulated deformation capacity is suggested by decomposing the hysteretic loop into the part of the skeleton and the part of Bauschinger, proposed by Takeuchi et al (2008).…”