# Failure Modelling of CP800 Using Acoustic Emission Analysis
## 1 Introduction  
With electro mobility, lightweight construction continues to have a high priority in production technology. Electric cars, for example, are designed to be as light as possible in order to maximise the range of the battery. Meanwhile, the demand on comfort and passenger safety has not declined, leading to more systems being installed in the car and contributing to an increase in weight. As a result, AHSS such as CP800 are still frequently used to replace conventional steel grades and increase lightweight designs [1]. Nowadays, finite element simulation is used standardly for efficient process and component development. This can significantly reduce cost- and time-intensive experimental tests, as well as reworking of the tools. For the correct numerical modelling of a process, material data sets are needed. The data sets are usually described with suitable analytical functions and implemented in the numerical model. Depending on which aspects are to be predicted numerically, different material data sets are required. In forming technology, the flow and failure behaviours are often necessary to describe the forming processes. For conventional sheet metal forming processes, flow curves and forming limit diagrams are determined experimentally [2]. Since multistage or shear-stressed processes exceed the range of validity of strain-based failure models such as the forming limit diagram, stress-state-based failure modelsare increasingly used. Unfortunately, there is still no standardised procedure for the stress-state-based material failure characterisation, so different specimen geometries and evaluation methods are used to parametrise various failure models. Frequently, tensile tests with different specimen geometries are performed and evaluated by means of an optical measuring system [3]. [PERSON] et al. characterised the failure behaviour of additively manufactured stainless steel 316L and titanium alloy Ti-6 Al-4V with varying pore sizes [4]. For both materials' cylindrical notched tensile, butterfly shear tensile and biaxial punch tests were performed and tracked using an optical measuring system. The experimental tests were numerically modelled to parametrise and compare the failure models from Mohr-Coulomb [3] as well as Hosford-Coulomb [5] for different pore sizes. A strain-rate-dependent Hosford-Coulomb model was developed by [PERSON] et al. in [6] and parametrised for the AHSS sheets DP980, CP980, and CP1120. Uniaxial tensile, notched tensile, central hole tensile, smiley shear tensile, and punch specimens were tested using optical measurement and numerically mapped for the model parametrisation. In [7] [PERSON] et al. investigated the fracture behaviour of the aluminium alloy 6061 from an extruded tube using circular arc, shear, arc-shaped notched, and V-shaped notched tensile specimens. The tests were performed using optical measurement, numerically modelled, and evaluated to fit the JC failure model [8]. The hot formability of aluminium alloy 7075 sheet material was studied by [PERSON] et al. [9]. Tempered tensile tests with uniaxial tension, notched tension, and shear tension specimen were performed as well as measured optically. Numerical models of the tests were created and a temperature as well as strain rate dependent JC failure model was determined. [PERSON] et al. also performed uniaxial tensile, shear tensile, holed tensile, grooved tensile, and notched tensile tests with different notch radii for a 7075 sheet material [10]. The specimens were taken in different rolling directions, optically measured while testing, and numerically mapped. Based on the simulations, the anisotropic failure model from [PERSON] and [PERSON] was calibrated [11]. The use of optical measuring and digital image correlation is common to all presented research. The optical measuring system offers the following advantages: the failure location can be precisely determined and, with sufficiently high measuring frequency, the moment of failure can be accurately detected.