# Failure Prediction for the Tearing of a Pin-Loaded Dual Phase Steel (DP980) Adjusting Guide
## 1 Introduction  
As an efficient means to reduce weight and increase safety, advanced high-strength steel (AHSS) sheets have become widespread in the automotive industry. The AHSS used here, DP980, is a dual phase steel consisting of a soft ferrite matrix containing tough islands of mainly martensite. Due to its very high strength of at least 980 MPa, good strength-to-weight ratio, and low cost but still relatively good formability, it has become an attractive sheet material for automobile components such as bumpers. However, its rather low elongation to failure poses a challenge to forming, and accurate knowledge of their deformation behavior--in particular, that between incipient necking and failure--is thus of paramount importance in order to exploit its full potential. Numerous ductile damage models have been developed over the past decades. They can be categorized into micromechanics-based (e.g., the maximum stress-based Cockcroft-Latham model [1], its modification by [PERSON] et al. [2], the volumetric strain limit-based model by [PERSON] [3], the porous plasticity-based Gurson model [4], the monotonic function-based Johnson-Cook model [5], which is in this regard similar to the older [PERSON] [6] and Rice-Tracey [7] models) and phenomenological models (e.g., Bai-Wierzbicki [8] and generalized incremental stress state-dependent damage model(GISSMO) [9]). All recent models have in common that the fracture strain, \(\varepsilon_{f}\), is considered a function of triaxiality, \(\eta\), defined as the ratio of mean stress to equivalent stress. Models differ by the shape of the \(\varepsilon_{f}\)-\(\eta\) function (exponential, polynomial, mixed functions, etc.) and the number of additional variables (Lode angle, strain rate, and temperature) and fitting coefficients. Generally, the accuracy of these models increases with the number of coefficients and variables. Still, these models are deficient, as they cannot accurately cover a larger range of triaxiality (e.g., Cockcroft-Latham), may falsely predict fracture for other triaxialities, cannot handle strain path changes, are linked to a certain constitutive model, cannot account for shear-dominated failure (e.g., Gurson model), cannot handle non-linear damage growth, and cannot tackle the problem of mesh-dependence arising in numerical simulations once strains become close to the fracture limit. In a phenomenological model, the generalized incremental stress state-dependent damage model (GISSMO) meets many of these demands in an elegant and straightforward manner by tabulating \(\varepsilon_{f}\)-\(\eta\) data, and thus allowing for any triaxiality failure diagram (TFD) shape [10]. It has consequently been developed, integrated into the commercial finite element (FE) code LS-Dyna [11], and successfully applied to structures under diverse loading scenarios (e.g., [12]). However, there is still a lack of validation examples. Furthermore, \(\eta\) was often not determined experimentally, but assumed based on finite element analysis or theory. In this study, we attempted to predict the failure through the tearing of an adjusting guide loaded by a pin. To do so, we obtained force-displacement data for diverse stress states, represented through stress triaxiality, \(\eta\), induced in the material by using diverse specimens (shear, uniaxial tension, and notch specimens). For the local strain measurement, especially for the post-necking region, digital image correlation (DIC) was employed, and representative \(\eta\)-values corresponding to the single specimen types were calculated from the strain fields. Damage was accounted for by applying GISSMO; the damage parameters were obtained through reverse engineering-based optimization with the commercial graphical optimization tool LS-Opt.