# Failure Modelling of CP800 Using Acoustic Emission Analysis
## 4 Summary and Outlook  
In this paper, the AHSS CP800 was characterised regarding its flow behaviour using tensile and hydraulic bulge tests. It was further modelled using an analytical approach. The failure behaviour was experimentally analysed using butterfly tests and evaluated using three methods: a mechanical evaluation method using the drop of the forming force, the common optical evaluation method with optical measurement, and a new acoustical evaluation method using acoustic emission analysis. The butterfly tests were numerically modelled using the determined flow behaviour and the specific failure displacement from each evaluation method, which served as the boundary condition for each simulation. Therefore, the butterfly specimen's exact stress state at the failure area and the equivalent failure strain at failure onset could be calculated and used to parametrise and compare the JC failure model for each evaluation method. As to be expected, the equivalent plastic strain at failure is highest for the mechanical evaluation method and lower for the other two methods. Due to the low sensitivity of the mechanical evaluation method to material failure it is detected later, resulting in high equivalent plastic strains. Therefore, the JC failure model from the mechanical evaluation method shows the highest curve. The equivalent plastic strain at failure derived for the optical evaluation method shows higher values than the acoustical evaluation method for the most loading angles, except for 74.5\({}^{\circ}\) and 90\({}^{\circ}\). This is because the acoustical evaluation method derives the material failure mostly earlier and at a different area than the optical method. While the failure for the optical evaluation method is evaluated on the specimen surface of the simulation model, the failure for the acoustical evaluation method is analysed inside the specimen. Therefore, the course of both JC failure models varies due to the different area of material failure and hence stress state. A more accurate estimation of the material failure is assumed using the JC failure model created by the acoustical evaluation method. In future investigations, B-pillar demonstrators, as shown in [27], will be produced using the CP800 material. The experimental tests will be reproduced numerically using the presented material model. The three created JC failure models will be used in the simulations and the impact of modelling quality, regarding failure prediction, will be analysed. Figure 12: JC failure models of the three evaluation methods for CP800. **Author Contributions:** Conceptualization, B.-A.B., H.W. and E.S. ; methodology, E.S. ; software, E.S. ; validation, E.S. ; formal analysis, E.S. ; investigation, E.S. ; resources, B.-A.B. and H.W. ; data curation, E.S. ; writing--original draft preparation, E.S. ; writing--review and editing, B.-A.B. and H.W. ; visualization, E.S. ; supervision, B.-A.B. and H.W. ; project administration, B.-A.B. and H.W. ; funding acquisition, B.-A.B. and H.W. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the DFG (Deutsche Forschungsgemeinschaft/German Research Foundation) within the project \"Improving the failure characterisation of advanced high-strength steel sheets by coupling measuring systems for optical forming analysis with acoustic emission technology\" with the grant number \"385276585\". **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable. **Acknowledgments:** The authors would like to express gratitude to the company voestalpine Stahl GmbH for providing the steel CP800 for the experimental investigations. Furthermore, the authors would like to thank [PERSON] from the Institute of Forming Technology and Machines for the support regarding the realisation of the experiments.