## 1 Introduction
The registration and analysis of changes in these properties allow the identification of areas willing to crack. Examples of this type of approach are included the works of [PERSON] and [PERSON] [25], [PERSON] [26], [PERSON] [27], who developed material evolution algorithms depending on the deformation history. The models take into account the fact that ductile cracking is preceded by a sudden local material density drop. Based on this assumption, areas exposed to cracking and porosity can be determined. [PERSON] [28] was one of the first to attempt to model ductile cracking. He assumed that the measure of material damage is a variable that characterizes the material with regard to the formation of internal porosities which ultimately lead to the separation of the material. This variable may be a stress-strain function ([PERSON] model [29]) or, for example, may be dependent on the Lode parameter (Xue and Wierzbicki model [30]). It should be noted that the coupled fracture criteria include many material constants that must be experimentally determined. On the other hand, in the uncoupled models, the accumulated damage is considered not to affect the plastic conditions of metals, with fracture occurring when an external vari able reaches a limit value [23]. The uncoupled ductile fracture criteria in many cases involve the measurement of a specific stress configuration based on the deformation history. In this group of criteria, it is characteristic that the calculated value of the criterion (often called the \(C\) variable) has no influence on the mechanical properties of the material. This means that the crack is not related to the local deterioration of properties, which contributes to their frequent use in numerical modeling of material damage [22; 31]. The indirect approach to some extent combines both previously described methods. It is based on the analysis of the change in properties with the increase in the \(C\) variable [22]. Uncoupled models have a simple formulation and can be easily implemented in software [23]. Several authors have carried out relevant comprehensive works comparing different ductile fracture criteria [21; 32; 33] or have proposed modified or new fracture criteria such as [PERSON] et al., who introduced a modified Xue and Wierzbicki model with a linear damage accumulation law in order to find the location and time of fracture occurrence [34], [PERSON] et al., who proposed a hybrid Pater criterion [35], [PERSON] et al., who developed a new fracture criterion based on cross-wedge rolling tests [36], [PERSON] et al. [37], who proposed an anisotropic damage model and [PERSON] et al., who proposed a modified Cockcroft-Latham model [38]. In the literature, there are a number of independent fracture criteria that are commonly used to analyze the risk of ductile cracking during plastic deformation of metals [31; 39; 40]. In order to correctly apply the criteria, it is necessary to know the deformation history of a given material. Critical parameters at which a crack occurs are determined during laboratory tests, the type of which is selected depending on the specificity of the technological process and the type and number of constants included in a given criterion. Apart from the usual tests, real material-forming experiments such as cross-wedge rolling [41; 42] can also serve for the determination of fracture occurrence. In the present work, a combined experimental and numerical study is performed regarding the prediction of crack initiation during plastic deformation processes. For that reason, the hot forging process is considered as a modified compression test, enabling us to evaluate the conditions for crack initiation. Two different aluminum alloys were selected for the tests and strain distribution was determined by the DIC method. Then the numerical model was validated by the experimental results, whereas after the validation, it was applied successfully for the prediction of possible fracture areas during the process of backward extrusion.