The roadmap to the efficient design of composites for structural integrity
Event details
| Date | 30.11.2015 |
| Hour | 14:00 › 15:00 |
| Speaker | Dr. Carlos González & Dr. Cláudio S. Lopes |
| Location | |
| Category | Conferences - Seminars |
This presentation proposes a systematic strategy to design composite materials for structural integrity (damage resistance, damage tolerance) using a multiscale numerical approach. A virtual design/testing strategy that takes into account the physical mechanisms of damage at the different length scales has been developed and validated and IMDEA Materials. The multiscale approach describes systematically the material behaviour at different length scales from ply microstructure to laminate, and to composite structure.
At microscale level, the representation of the mechanical behaviour of a composite material is achieved by means of a Representative Volume Element (RVE) which accurately describes the mechanical behaviour of the different phases by means of constitutive equations. The matrix behaviour is modelled by a coupled damage-plasticity law in order to handle the non-linearity due to plasticity in the matrix under compressive stress states and the quasi-brittle behaviour under tensile loads. On the other hand, a cohesive model is adopted to address decohesion and friction between fibres and matrix. The relevant material properties of the matrix and interfaces are measured by means of instrumented nanoindentation and direct observation of the damage mechanisms and events (Figure 1a).
At mesoscale level, laminates are simulated by means of thermodynamically-consistent damage models for plies and ply-interfaces defined in the context of the mechanics of continuum media (Figure 1b). The ply model use physically-based criteria to predict the onset of matrix cracking and fibre fracture under tensile, compressive and shear loadings and take into account the effect of ply thickness on the strength. The model parameters (e.g. ply elastic constants, tensile and compressive strength in the longitudinal and transverse directions, shear strength, etc.) are determined by means of micromechanical simulations. The interface model, to simulate delamination and friction between plies, is implemented as a surface interaction.
At structural level, the laminate is modelled by means of shell elements which contain as many integration points through the thickness as the number of plies in the laminate in each region of the component but different plies are not modelled independently. Thus the analyses are limited to bidimensional stress states, and do not take into account delamination, but are very efficient from the numerical viewpoint and can capture the structural failure modes of large structures (impact, buckling, etc.). Nevertheless, accurate models for the onset and evolution of damage at the laminate level are necessary in order to ensure the fidelity of the simulations.
Besides the simulation of the actual physical mechanisms in composites, one of the
advantages of this bottom-up multiscale approach is that changes in the properties of the
constituents (fibre, matrices), the fibre architecture or laminate lay-up can be easily
incorporated to provide new predictions of the macroscopic behaviour of the composite.
Also, the observed scatter in material properties can be easily studied as well as its
influence on the failure mechanisms.
This presentation includes examples of the application of the multiscale virtual testing
approach such as the prediction of in-situ effects in composite laminates; failure of openhole
and bearing specimens; low-velocity impact response of laminates (Figure 1b); bird
impact on aircraft leading edge (Figure 2); and design of non-conventional composite
laminates.
At microscale level, the representation of the mechanical behaviour of a composite material is achieved by means of a Representative Volume Element (RVE) which accurately describes the mechanical behaviour of the different phases by means of constitutive equations. The matrix behaviour is modelled by a coupled damage-plasticity law in order to handle the non-linearity due to plasticity in the matrix under compressive stress states and the quasi-brittle behaviour under tensile loads. On the other hand, a cohesive model is adopted to address decohesion and friction between fibres and matrix. The relevant material properties of the matrix and interfaces are measured by means of instrumented nanoindentation and direct observation of the damage mechanisms and events (Figure 1a).
At mesoscale level, laminates are simulated by means of thermodynamically-consistent damage models for plies and ply-interfaces defined in the context of the mechanics of continuum media (Figure 1b). The ply model use physically-based criteria to predict the onset of matrix cracking and fibre fracture under tensile, compressive and shear loadings and take into account the effect of ply thickness on the strength. The model parameters (e.g. ply elastic constants, tensile and compressive strength in the longitudinal and transverse directions, shear strength, etc.) are determined by means of micromechanical simulations. The interface model, to simulate delamination and friction between plies, is implemented as a surface interaction.
At structural level, the laminate is modelled by means of shell elements which contain as many integration points through the thickness as the number of plies in the laminate in each region of the component but different plies are not modelled independently. Thus the analyses are limited to bidimensional stress states, and do not take into account delamination, but are very efficient from the numerical viewpoint and can capture the structural failure modes of large structures (impact, buckling, etc.). Nevertheless, accurate models for the onset and evolution of damage at the laminate level are necessary in order to ensure the fidelity of the simulations.
Besides the simulation of the actual physical mechanisms in composites, one of the
advantages of this bottom-up multiscale approach is that changes in the properties of the
constituents (fibre, matrices), the fibre architecture or laminate lay-up can be easily
incorporated to provide new predictions of the macroscopic behaviour of the composite.
Also, the observed scatter in material properties can be easily studied as well as its
influence on the failure mechanisms.
This presentation includes examples of the application of the multiscale virtual testing
approach such as the prediction of in-situ effects in composite laminates; failure of openhole
and bearing specimens; low-velocity impact response of laminates (Figure 1b); bird
impact on aircraft leading edge (Figure 2); and design of non-conventional composite
laminates.
Practical information
- Expert
- Free
Organizer
Contact
- Géraldine Palaj