Biaxial Cyclic Loading Test for Bauschinger Effect Characterization of Q890 High-Strength Steel

Area of Science:

• Materials Science
• Mechanical Engineering
• Manufacturing Processes

Background:

• High-strength steel components are vital for deep-sea pressure hulls and heavy machinery.
• The Bauschinger effect in these steels complicates springback prediction during forming, leading to errors and increased costs.
• Current testing methods are limited to uniaxial stress states, failing to represent complex biaxial loading conditions.

Purpose of the Study:

• To develop and validate a cyclic four-point bending method for characterizing the Bauschinger effect in Q890 steel under in-plane biaxial cyclic loading.
• To investigate the influence of varying width-to-thickness ratios on the material's mechanical response and Bauschinger parameters.
• To establish the relationship between biaxial stress states and springback behavior for improved forming accuracy.

Main Methods:

• Proposed a cyclic four-point bending technique using specimens with tailored width-to-thickness ratios to achieve diverse plane stress states.
• Employed digital image correlation (DIC) for real-time, full-field strain measurement during cyclic loading.
• Acquired equivalent stress-strain curves over multiple cycles to quantify Bauschinger effect parameters under various biaxial stress ratios.

Main Results:

• The Bauschinger effect, including yield strength and flow stress, significantly degrades with increasing width-to-thickness ratio (indicating increased biaxial stress influence).
• Key Bauschinger parameters (B, BHP, BEP) decreased from 0.479, 0.789, 4.747 to 0.363, 0.655, 2.900, respectively, demonstrating strong stress-ratio dependence.
• Springback ratio was found to be dependent on biaxial stress ratio, loading direction, and cyclic history.

Conclusions:

• The proposed cyclic four-point bending method effectively characterizes the Bauschinger effect under biaxial loading conditions.
• In-plane biaxial stress states significantly influence the Bauschinger effect and springback behavior of Q890 high-strength steel.
• Accurate springback prediction for large-scale, thick, curved components requires consideration of biaxial stress-state effects during material characterization.