A Modified Microhardness Based Approach to Damage Characterization for Fracture Prediction Under Biaxial Stresses in SPIF

• Published in: Experimental techniques (Westport, Conn.) Conn.), 2023-10, Vol.47 (5), p.1097-1109
• Main Author: Shrivastava, P.
• Format: Article
• Language: English
• Subjects: Axial stress; Characterization and Evaluation of Materials; Chemistry and Materials Science; Damage assessment; Deformation analysis; Digital imaging; Ductile fracture; Finite element method; Forming techniques; Hardness tests; Materials Science; Mathematical models; Microhardness; Model accuracy; Parameter identification; Parameter modification; Plastic deformation; Research Paper; Strain; Thickness
• ISSN: 0732-8818; 1747-1567
• DOI: 10.1007/s40799-022-00615-z

Single Point Incremental Forming process is subjected to the complex state of stresses that lead to plastic deformation instabilities during the process. Apart from formability and deformation analyses, the characterization and prediction of damage and or fracture in SPIF is of utmost importance. Prediction of fracture in SPIF by continuum-based models is satisfactory for low triaxiality conditions. However, fracture prediction under high stress triaxiality conditions i.e., under biaxial stresses in SPIF still needs attention. For this purpose, an accurate identification and characterization of damage model parameters is of utmost importance as the prediction accuracy of damage model majorly depends on it. In this work, a modified microhardness-based approach to damage parameter characterization is presented for predicting ductile fracture under biaxial stresses in SPIF. Strategy has been proposed to evaluate damage parameter (D) for Lemaitre continuum damage models by evaluating micro-hardness in the through-thickness direction of the fractured SPIF samples. Additionally, a methodology is proposed to evaluate hypothetical hardness by precisely obtaining the plastic stress–strain characteristics of the AA1050 H14 material subjected to biaxial straining. Prior to indentation test, in SPIF, Digital Image Correlation (DIC) technique is utilized to evaluate true plastic strain and thickness strain values. The values of damage parameter obtained from conventional as well as revised approaches are used to simulate fracture in SPIF by incorporating Lemaitre damage model as a user subroutine (VUMAT) in Abaqus software. Experimentally obtained maximum plastic strain and wall thickness are compared to simulated maximum plastic strains subjected to conventional and revised methodology.