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Computational Process for Recurring Loads In principle, the effect of any change in stiffness on local stresses must be calculated throughout the model. While this is, in principle, numerically possible, the pure number of stress cycles make it practically infeasible. It is more logical to take the global effect of stiffness changes into consideration when significant changes occur, while always taking local effects into consideration. A closer look at the special case of block loads (i.e. the repetition of the same load stress cycle) allows the local effect of the stress cycle to be first calculated, then extrapolated using the stiffness fall-off curve. This extrapolation also allows an estimate of when a recalculation (a so-called N-Jump) is required at the global level. Good results have been achieved over the last 15 years for composite materials with woven fibers using this method. Complex Loads As already mentioned in the introduction, the load collectives to be investigated in the vehicle industry are complex, with varying amplitude and multiple, non-proportional loads. A simple approach with extrapolation no longer possible here, which is why a typical estimate is often made using SN-curve- based methods and all the aforementioned disadvantages (layup-dependent, high test scattering). In this case there is now an extension to the n-jump method for complex loads that uses cumulative damage based on hysteresis operator theory [6,7] for local damage accumu- lation (local stiffness fall-off calculation). These methods can accurately map typical non-linear accumulation when calculating stiffness reduction, while considering correctly the effects on other damage modes. One special aspect is the ability to implement any linear and non-linear damage accumulation methods using this method. An open interface allows research institutes and research departments to add their own extensions. This methodology was developed alongside extensions to stiffness reduction rules and newmethods for determining material curves. Details of the methodology and correspond- ing test method insights are presented in [7]. Damage between the Layers CDM can also be used for accurate predictions when calcu- lating delamination between layers and taking damage within the layers into account [9,10]. The complex calculations involved in delamination simulation induce that the focus for fatigue calculation is not on the delamination process itself but on the statement question- ing whether delamination occurs. The first tools measuring whether an existing short crack between the layers continues to grow during an operating load collective are undergoing tests. They take into account the damage, or stiffness in the

layers, that prompts a change to the intermediate layer load. Further investigations into delamination from the border and the behavior of larger cracks are what follow, to round off the computational tool. Conclusion and Outlook Switching frommetal to composite materials is far more complex than switching from one metal to another metal. Retaining a testing and simulation level equivalent to that for metals and treating a composite material as a “black metal” would result in restricting the effect of many of the positive composite material characteristics. The goal of lightweight design would remain elusive. This is why the damage simula- tion methods and process chains need to be adapted. Open- ness allowing extensions to the various simulation scales is key, given the considerable potential for development here. Firstly, the right simulation tools can be used such that many tests can be performed more efficiently. Secondly, produc- tion processes and designs can be simulated from an early stage. This allows design and production studies to achieve better and also lighter vehicles in the simulation phase. References [1] Küssner, M. E. N.: Simcenter for the predictive validation of com - posite materials. Simulation von Composites – Bereit für Industrie 4.0? Hamburg, NAFEMS DACH, 2016 [2] v. Paepegem, W.: Fatigue DamageModelling with the phenom- enological residual stiffness approach. In: A. Vassilopoulos, Fatigue Life Prediction of Composites and Composite Structures, 2010, pp. 102-138 [3] Ladevèze, E.; Le Dantec, P.: Damage modelling of the elementary ply for laminated composites. Composite Science and Technology, 43,1992, pp. 252-267 [4] M3, S., 2014, M3 - SIM-Flanders. Retrieved from SIM-Fladers: www.sim-flanders.be/research-program/m3 [5] Jain, A.; v. Paepegem, W.; Verpoest, I.; Lomov, S.: A feasibility study of theMaster SN curve approach for short fiber reinforced compos- ites. I Journal of Fatigue, 2016, pp. 264-274 [6] Brokate, M.; Sprekels, J.: Hysteresis operators. 1996, New York, Springer [7] Carrella-Payan, D.; Magneville, B.; Hack, M.; Naito, T.; Urushiyama, Y.; Yamazaki, T.; v. Paepegem, W.: Implementation of fatigue model for unidirectional laminate based on finite element analysis: theory and practice. Frattura ed Integrita Strutturale 38, 2016, pp. 184-190 [8] v. Paepegem, W.: Development and finite element implementation of a damage. PhD Thesis, 2002, U Gent [9] Bruyneel, M.; Delsemme, P.; Groupil, A.; Jetteur, J.; Lequesne, C.; Naito, T.; Urushiyama, Y.: Damage modeling of laminated composites: validation of the inter-laminar damage law in SAMCEF at the coupon level for UD plies. World Congress of CompMechanics, 2014, Barcelona [10] Bruyneel, M.; Delsemme, P.; Groupil, A.; Jetteur, J.; Lequesne, C.; Naito, T.; Urushiyama, Y.: Damage modeling of laminated composites: validation of the intra-laminar damage law in SAMCEF at the coupon level for UD plies. European Conference on CompositeMaterial ECCM16, 2014, Sevilla

CAEWissen by courtesy of Dr. Michael Hack, Siemens PLMSoftware in Kaiserslautern.

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