Heterogeneous gradient modeling and experimental verification: Enhancing prediction accuracy for metal mechanical properties

Homogeneity is one of the three fundamental assumptions in solid mechanics and serves as the theoretical basis for analyzing the mechanical property of metallic materials. However, most metal components do not exhibit a traditional “uniform structure”, but instead develop thin “heterogeneous structures” after processes such as casting, forging and welding. This deviation from homogeneity reduces analytical accuracy. To address this limitation, this paper proposes a heterogeneous gradient model for common metals with a thin heterogeneous surface layer. By quantifying gradient effects in heterogeneous structures, the elastic-plastic stress-strain relationship has been modified, and theoretical prediction models for tensile, torsional and bending deformations have been established. The proposed model of heterogeneous structure performance was verified by a series of heat treatment and mechanical property tests using an automotive front axle made from 42CrMo, and the underlying mechanisms of heterogeneous structural effects was elucidated through microstructure analysis. The experimental results demonstrate excellent agreement with the modeling, with deviations remaining within 5%. The results demonstrate that the heterogeneous gradient model can effectively predict the tensile, bending, and torsional properties of forged components. This framework provides a systematic approach to predict heterogeneous microstructure properties within traditionally assumed homogeneous systems.