Christine Espinosa

Modelling Strategies for Simulating Delamination and Matrix Cracking in Composite Laminates

The composite materials are nowadays widely used in aeronautical domain. These materials are subjected to different types of loading that can damage a part of the structure. This diminishes the resistance of the structure to failure. In this paper, matrix cracking and delamination propagation in composite laminates are simulated as a part of damage. Two different computational strategies are developed: (i) a cohesive model (CM) based on the classical continuum mechanics and (ii) a continuous damage material model (CDM) coupling failure modes and damage. Another mixed methodology (MM) is proposed using the continuous damage model for delamination initiation and the cohesive model for 3D crack propagation and mesh openings. A good agreement was obtained when compared simple characterization tests and corresponding simulations.

Metal cutting modelling SPH approach

The purpose of this work is to evaluate the use of the smoothed particle hydrodynamics (SPH) method within the framework of high speed cutting modelling. First, a 2D SPH based model is carried out using the LS-DYNA® software. The developed SPH model proves its ability to account for continuous and shear localised chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Then, the SPH model is used in order to improve the general understanding of machining with worn tools. At last, a hybrid milling model allowing the calculation of the 3D cutting forces is presented. The interest of the suggested approach is to be freed from classically needed machining tests: Those are replaced by 2D numerical tests using the SPH model. The developed approach proved its ability to model the 3D cutting forces in ball end milling.

Experimental and Numerical Investigation of Delamination in Curved-Beam Multidirectional Laminated Composite Specimen

Composite corners are generally tested under four point-bending to identify Inter-Laminar Tensile Strength design values. Hereafter several lay-ups have been defined in order to characterize very different damage evolution processes. Damage monitoring has been performed with the help of Digital Image Correlation, Acoustic Emission and Fast Video Recorder. The different processes leading to final failures have been identified. A deterministic continuous composite material model is used to investigate these phenomena. Initiation and evolution up to saturation and fracture are implemented for various damage mechanisms and for delamination. A first comparison between experiments and numerical simulations is presented.

Modelling Strategies for Predicting the Residual Strength of Impacted Composite Aircraft Fuselages

Aeronautic Certification rules established for the metallic materials are not convenient for the composite structures concerning the resistance against impact. The computer-based design is a new methodology that is thought about to replace the experimental tests. It becomes necessary for numerical methods to be robust and predictive for impact. Three questions are addressed in this study: (i) can a numerical model be “mechanically intrinsic” to predict damage after impact, (ii) can this model be the same for a lab sample and a large structure, and (iii) can the numerical model be predictive enough to predict the Compression After Impact (CAI)? Three different computational strategies are used and compared: a Cohesive Model (CM), a Continuous Damage Model (CDM) coupling failure modes and damage, and a Mixed Methodology (MM) using the CDM for delamination initiation and the CM for cracks propagation. The first attempts to use the Smooth Particle Hydrodynamics method are presented. Finally, impact on a fuselage is modelled and a numerical two-stage strategy is developed to predict the CAI.

Modelling Aeronautical Composite Laminates Behaviour under Impact Using a Saturation Damage and Delamination Continuous Material Model

We show that the behavior of T700/M21s and T800/M21s composite panels are affected by the influence of strain rates together with local shear and crush punch or global flexural strengths of the structure. A deterministic continuous composite material model has been developed as a LS-DYNA user defined material model for unidirectional composites on the basis of the Matzenmiller model widely used for woven composites. Initiation and evolution up to saturation and fracture are implemented for various and coupled damage mechanisms including delamination. Quasi-static and dynamic characterization tests laminates have been carried out on balanced angle ply [±θ] and used for calibration of numerical values. Impact induced damage from experiment’s measures and numerical predictions are compared for T800/M21S aeronautical samples impacted at 15J.

Inner Damage and External Dent in Composite Structures after Impact – Part I: Experimental Observations

The damage tolerance methodology is used here to compare impact damage from experimental testing and virtual (numerical) testing. The first part of the study aims to identify links between experimental internal (delaminated area) and external measurable damage (dent depth) for a typical aeronautical T800S/M21e laminate. Effects of the mass/velocity ratios at some level of impact energy are evaluated. It is shown that a big mass generates denser and larger delamination with about the same dent than a small mass, which is a critical case for damage tolerance analysis. A relation between the external dent depth and internal delaminated area is proposed.

Numerical Prediction of Damage Interaction during L-Shaped Laminated Composite Structures Unfolding

The Low through-the-Thickness Strengths of Composites make them Prone to Delamination and Brutal Rupture. for Primary Aircraft Structural Components, it is Necessary to Predict Failure with Adequate Criteria for any Structure of Various Thicknesses and in Zones of Material or Geometric Discontinuities. the Purpose of the Present Work is to Evaluate the Ability of our Continuous Damage Model to Predict at which Interface Delamination will Occur in any Geometrical or Material Configuration. Numerical Predictions of Delamination Onset Computed by our CDM Model Show a Good Agreement with Theoretical Estimations and Experimental Results of an L-Shape Structure Reference Case. Comparisons between 2D and 3D Models Show no Effect of Free Boundaries on Delamination Onset and Growth.