Experimental and modeling study of cyclic plasticity and ductile fracture of thin structural steel sheets

• Published in: Thin-walled structures 2021-05, Vol.162, p.107658, Article 107658
• Main Authors: Xie, Zhiyang, Chen, Yiyi
• Format: Article
• Language: English
• Subjects: Constitutive model; Cyclic test; Ductile fracture; Random loading; Thin steel sheet
• ISSN: 0263-8231; 1879-3223
• DOI: 10.1016/j.tws.2021.107658

The cyclic material properties of thin steel sheets are critical for accurate prediction of the structural response of the thin-walled steel elements. For the experimental study of the cyclic behaviors of thin steel sheets, we proposed a new anti-buckling device equipped with the disc-springs. This improvement aims to compensate the potential gaps between the fixtures and specimens under large plastic deformation so as to avoid the out-of-plane buckling. Furthermore, the negative influences derived from the transverse pressure and friction can be greatly minimized through the implementation of the disc-springs and the lubricated Teflon sheet, as indicated by the percentage errors of 0.31% and 0.08% for the external load and internal stress respectively. By virtue of this improved device, we perform 8 regular and 1 random cyclic testing with the Q345 steel sheet of the 6 mm thickness. It is noted that the smooth hysteresis loops feature no decrease in force under compression applied. Moreover, the sizes of hysteresis loops are dependent upon the current and maximum strain amplitude. The current strain amplitude controls the re-yielding rate, while the maximum value determines the saturated hardening stress. As for the ductile fracture initiation, the similar nominal stress–strain curves in the final tension stage among all cases and the considerably larger accumulated plastic strain than the one under monotonic loading imply the contribution of negative triaxiality to the decrease in the damage variable. Based on these observations, we develop a new cyclic plasticity and ductile fracture model, which is also programmed into the UMAT subroutine compatible with ABAQUS/Standard. By the comparison with the experimental results, the remarkable agreement of the predicted results demonstrates its validity in terms of the constitutive relationship, deformed shape of necking region and the fracture initiation under regular and particularly random cyclic loading. [Display omitted] •We proposed a new anti-buckling device for cyclic testing equipped with disc-springs.•Cyclic tests with Q345 thin sheets are performed under 8 regular and 1 random loading.•Current and maximum strain amplitude dependency of saturated stress is identified.•Reduction of damage under negative triaxiality is confirmed in all loading cases.•Proposed model is validated by regular and random loading testing results.