Stating Failure Modelling Limitations of High Strength Sheets: Implications to Sheet Metal Forming

Abstract

This article discusses the fracture modelling accuracy of strain-driven ductile fracture models when introducing damage of high strength sheet steel. Numerical modelling of well-known fracture mechanical tests was conducted using a failure and damage model to control damage and fracture evolution. A thorough validation of the simulation results was conducted against results from laboratory testing. Such validations show that the damage and failure model is suited for modelling of material failure and fracture evolution of specimens without damage. However, pre-damaged specimens show less correlation as the damage and failure model over-predicts the displacement at crack initiation with an average of 28%. Consequently, the results in this article show the need for an extension of the damage and failure model that accounts for the fracture mechanisms at the crack tip. Such extension would aid in the improvement of fracture mechanical testing procedures and the modelling of high strength sheet metal manufacturing, as several sheet manufacturing processes are defined by material fracture.

Understanding the Fatigue Notch Sensitivity of High-Strength Steels through Fracture Toughness

“…The stress concentration factors (K t ) were calculated through numerical modelling, and their values are presented in Figure 3. Both geometries in conventional tensile and in the normal location of failure onset exhibit a stress triaxiality of 0.33 at maximum force, which is in agreement with the results reported by several authors [39,40]. The shearing clearances specified in Table 3 are commonly used in chassis parts to avoid burrs and excessive deformation of the edge [21,41].…”

A Review of Sheet Metal Forming Evaluation of Advanced High-Strength Steels (AHSS)

“…Moreover, physical time scaling and both homogeneous and mass scaling are managed to control CPU time. Sandin et al [227] used explicit time integration to efficiently handle the high non-linearity caused by material fracture and element erosion.…”

“…When thoughtfully formulated, these diverse models may converge towards consistent predictions concerning damage location [244]. Sandin et al [227] as well as Khameneh et al [196] evolved the MMC model with the GISSMO model.…”

“…Additional details about the GISSMO model were provided by Andrade et al [234]. GISSMO is a phenomenological damage model that uses stress state-dependent equivalent plastic strain as fracture criteria [227]. It is uncoupled from the plasticity model.…”

Prediction of sheared edge characteristics of advanced high strength steel

“…where The MMC fracture locus was used as initial estimate for an inverse modelling scheme that scaled the fracture surface and calibrated the GISSMO parameters n and m. The aim of the inverse modelling was to obtain correlation between simulation and experiments in terms of material failure of the R3.75 tensile specimen. A more detailed description of the inverse modelling procedure for the hardening curve in Section 2.1 and the GISSMO damage-and failure model was given by Sandin et al [13].…”