# Study on the Damage Mechanisms in the Forming Process of High-Strength Steel Laser Tailor Welded Blanks Based on the Johnson–Cook Damage Model

## TL;DR

This study uses the Johnson–Cook model to analyze how high-strength steel laser-welded blanks fracture during forming, combining experiments and simulations to improve predictions.

## Contribution

The study introduces a calibrated Johnson–Cook damage model for predicting fracture behavior in high-strength steel TWBs during forming.

## Key findings

- The Johnson–Cook model was successfully calibrated for TWB welds and high-strength steels using experimental and simulation data.
- The calibrated model accurately predicted fracture behavior during forming, validated by bulge tests and FLD comparisons.
- Stress triaxiality, strain rate, and temperature effects were systematically analyzed to improve damage prediction.

## Abstract

This paper, based on the Johnson–Cook damage model, investigates the damage mechanism of high-strength steel tailor welded blanks (TWBs) (Usibor1500P and Ductibor500) during the forming process. Initially, specimens with varying notch sizes were designed and fabricated to perform uniaxial tensile tests to determine their mechanical properties. Then, the deformation process of the notched specimens was simulated using finite element software, revealing the distribution and variation of stress triaxiality at the fracture surface. By combining both experimental and simulation data, the parameters of the Johnson–Cook (J–C) damage model were calibrated, and the effects of temperature, strain rate, and stress triaxiality on material fracture behavior were further analyzed. Based on finite element analysis, the relevant coefficients for stress triaxiality, strain rate, and temperature were systematically calibrated, successfully establishing a J–C fracture criterion for TWB welds, Usibor1500P, and Ductibor500 high-strength steels. Finally, the calibrated damage model was further validated through the Nakajima-type bulge test, and the simulated Forming Limit Diagram (FLD) closely matched the experimental data. The results show that the analysis based on the J–C damage model can effectively predict the fracture behavior of tailor welded blanks (TWB) during the forming process. This study provides reliable numerical predictions for the damage behavior of high-strength steel laser-customized welded sheets and offers a theoretical basis for engineering design and material performance optimization.