## 1 Introduction  
In recent years, the wide usage of advanced lightweight materials such as high-strength steels, magnesium alloys and aluminum alloys has been leading to an evolution in manufacturing methods for components and parts in the automotive industry [1]. As a typical metal forming technology, the die-casting process can satisfy various requirements of structural parts, particularly for complex shapes with high production efficiency and molding accuracy [2]. The die-casting process is used to produce automotive body and many cross components, such as suspension systems, transmission systems, wheels and brake systems. As an essential part of the safety design and operation for whole vehicles, the safety evaluation of die-cast components must be taken seriously [3]. The strength and fracture properties of die castings need to be accurately characterized to ensure the safety of each component before the whole vehicle safety evaluation by crash testing and simulation. Finite element simulation plays an important role in whole safety analysis [4]. Numerical simulation provides the capability to evaluate the performance and reliability of components, thus optimizing the entire vehicle design process. For example, [PERSON] et al. [5] established a coupled gas-liquid-solid multiphase flow model through ANSYS software to analyze and control the quenching deformation of lightweight cast aluminum alloy wheels. [PERSON] et al. [6] investigated the effects of microdefects and the stress state on the failure behavior of cast aluminum alloy A356 by experimental and numerical methods. Considering the distribution of porosity within the die-cast components, [PERSON] et al. [7] investigated the failure characteristics of the die-cast aluminum alloy Aural-2 by experimental and numerical methods. They proposed a probability-dependent damage model to represent the behavior of the fracture under a wide range of stress states, and found a significant dependence of the initiating fracture strain on the stress triaxiality. Up to now, the simulation of die-cast structural parts has mostly focused on the simulation of the casting process and the effects of casting defects on the service performance of the parts. From the viewpoint of die-cast components application, high-stress conditions are inevitable. The fracture behavior of cast aluminum materials must especially be characterized through a reasonable failure model to ensure the simulation accuracy of the whole vehicle crash. When assessing safety performance, the fracture moment and fracture location are important indicators for evaluating the reliability of structures and components. Traditional fracture mechanics, represented by the stress intensity factor criterion, J-integral criterion, etc., cannot explain the fracture characteristics of uncracked solid materials under the assumption of preexisting initial cracks. At the microscopic level, the material failure process is the process of formation, growth and the coalescence of voids within the material [8]. Most studies [9; 10; 11] have suggested that void growth and aggregation-type microscopic fracture mechanisms can accurately illustrate the macroscopic fracture behavior under monotonic loading conditions. According to the interaction of plasticity and damage criteria, the currently applied damage mechanics models can be divided into two groups: coupled models and uncoupled models [6; 12; 13]. Among the coupled models, the Gurson-Tvergaard-Needleman (GTN) model considers the formation and growth process of voids, and has been widely applied in various applications [14; 15]. In this model, material damage occurs once the void volume fraction of the material reaches a limiting value during deformation. However, the complicated parameter calibration process is the main reason that limits the further application of GTN models when compared to uncoupled damage models [16]. When using uncoupled damage models, the failure criterion is usually characterized by the failure strain.