An improved M–K model coupled with different ductile criteria for fracture limit predictions of Inconel 718 alloy

Abstract

Fracture Forming Limit Diagram (FFLD) is gaining special attention for high strength materials like Inconel 718 alloy where the substantial necking tendency rarely seen. The present study mainly aims at accurate evolution of forming limits for Inconel 718 alloy with an improved Marciniak–Kuczynski (M–K) model coupled and various ductile fracture criteria. Firstly, uniaxial test has been performed for analyzing material properties and anisotropic parameters. The stretch forming tests have been conducted to evaluate the limiting forming limits of Inconel 718 alloy. Subsequently, an improved M–K model coupled with ductile fracture criteria has been developed for the theoretical prediction of the fracture strains. The different ductile fracture criteria, namely; Clift, Cockcroft and Latham, Oyane and Brozzo, have been implemented in the improved M–K model. A Newton–Raphson method has been used to solve improved M–K model. The improved M–K model coupled with Oyane's fracture criterion has shown good predictability of the fracture loci with the least average absolute errors and root-mean-square deviation (Δavg = 0.075 and RMSD = 0.105).

Keywords

• Fracture limits
• Stretch forming
• Fracture criteria
• Improved M–K model
• Inconel 718 alloy