7.7 Modellierung und Simulation
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Erscheinungsjahr
- 2019 (2)
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- Dissertation (2) (entfernen)
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- Englisch (2)
Referierte Publikation
- nein (2)
Schlagworte
- Concrete (1)
- Damage (1)
- Explicit dynamics (1)
- Fatigue failure (1)
- Impact simulation (1)
- Isogeometric analysis (1)
- Mesoscale (1)
- Mortar method (1)
- Spectral elements (1)
Organisationseinheit der BAM
The simulation of the structural response for impact scenarios strongly requires an accurate simulation of both the impact event as well as the subsequent wave propagation. The numerical modeling of the impact event is intrinsically ill-posed due to the instantaneous changes of velocities in the contact area, leading to unbounded accelerations for decreasing time steps which causes oscillations in the contact stresses. These oscillations then propagate into the bulk material. Using a rate dependent material model, like concrete, they might lead to significant errors and a wrong prediction of the structural response. A regularization is thus required to avoid oscillations in the contact stresses. Another issue is related to the numerical computation of the contact conditions. In impact simulations, the nonlinear contact computation needs to be evaluated in every time step. A segmentation technique of the contact area is accurate but time consuming and may result in a bottleneck for the simulation and implementation, especially for 3D problems. The modeling of the subsequent wave propagation requires small time steps, which is primarily due to accuracy reasons. Implicit schemes are thus not affordable. Explicit time integration schemes are efficient only for diagonal mass matrices, as in this case no solution of a linear system is required. In this work, a coupled finite element - Non-Uniform Rational B-Spline (FE-NURBS) approach is applied to impact problems. The coupled approach uses an intermediate NURBS layer to compute the contact forces between the contacting bodies discretized by FEs. The advantages of a smooth isogeometric contact formulation are used to compute the contact forces. A segmentation of the contact area is avoided and an efficient element-based integration is used. The impact event is regularized using a mesh dependent nonlinear penalty approach. The penalty function is a polynomial which ensures a smooth transition between the noncontact and the contact state during the impact. For finer meshes, the penalty regularization becomes stiffer while still avoiding artificial oscillations in the contact stresses. Efficient higher order space and time discretizations are used to model the wave propagation. Explicit time integration is combined with higher order spectral element spatial discretization.
Concrete is a complex material and can be modeled on various spatial and temporal scales. While simulations on coarse scales are practical for engineering applications, a deeper understanding of the material is gained on finer scales. This is at the cost of an increased numerical effort that can be reduced by the three methods developed and used in this work, each corresponding to one publication.
The coarse spatial scale is related to fully homogenized models. The material is described in a phenomenological approach and the numerous parameters sometimes lack a physical meaning. Resolving the three-phase mesoscopic structure consisting of aggregates, the mortar matrix and the interfaces between them allow to describe similar effects with simpler models.