Murray L. Scott

A Review of Explicit Finite Element Software for Composite Impact Analysis

As explicit finite element (FE) codes improve and advanced material models become available, such tools will find more widespread application within the aerospace industry, as ‘what-if ’ simulations become more manageable with increasing computing power and greater modeling realism. This paper describes the investigation of three commercial explicit FE analysis packages, LS-Dyna, MSC.Dytran, and Pam-Shock, to determine their capabilities in predicting barely visible impact damage (BVID) in composite structures. The investigation is conducted by first determining the suitability of the codes in constructing an FE model of a stiffened panel, solving for BVID and retrieving results. The results are in turn compared to experimental data in order to gauge the suitability of the codes for composite design and analysis. Comparisons of the FE simulations to experimental data include damage development and degradation, as well as the time-history responses. The Chang-Chang failure theory with brittle degradation was used for both LS-Dyna and MSC.Dytran, while the biphase model was used for Pam-Shock. Results indicated that the general shape of the force-time curves as well as the peak forces were predicted reasonably well. However, all simulations predicted a trough that was much less significant than the test results, as well as a shorter impact duration.

Engineering solutions for complex composite material behaviour spanning time and temperature scales

The issue of time and temperature dependencies is considered in the behaviour of advanced fibre-reinforced polymer composite materials. Currently, for the vast majority of analyses of composite structures, time and temperature are considered invariant. In an effort to further improve the design of composite structures, more advanced analyses are now being developed to accurately capture the behaviour under a range of conditions. Various events and load cases in which time and temperature are critical are described in general terms. The specific cases of viscoelastic distortion under mechanical and thermal loading, the behaviour of adhesive joints and the structural response of composites to fire are discussed in detail. The key material response, characterisation methods and analysis approaches developed are described. It is observed that key challenges in the development of improved predictive models are measurement of time- and temperature-dependent material properties and the implementation of efficient multidisciplinary analysis methods.

An investigation into an advanced composite finite element explicit biphase model: Part II - Damage parameters

The elastic and damage parameters of the ‘‘biphase’’ composite material and degradation model contained in the explicit finite element code, Pam-Shock, have been investigated in Parts I and II, respectively. The biphase analysis is a relatively new methodology aiming at accurately predicting the complex damage responses of composite structures to dynamic loading conditions. The intricacy of the damage mechanism dealt with hence calls for a broad range of elastic and damage parameters to be defined within the analysis before a solution corresponding to real case scenarios can be achieved. This investigation focuses on the unknown effects of such parameters and has been successful in identifying the significance and sensitivities that the variation of the parameters impose on the predicted outputs. It was established that the variation of some of the parameters, such as Poisson’s ratio, can cause a considerable deviation from the reference run, thus making it imperative to concentrate on deriving accurate empirical values to be used against such material properties within the analysis. A brief tabulated summary demonstrates the strengths and limitations of the model in predicting the response of advanced composite structures to impact events.

Voxel modelling of 3D through-thickness reinforced composite laminates

Publisher Summary Market and regulatory pressures on the aircraft industry continually drive improvements in performance, noise, emissions, safety, reliability, comfort, and the total cost of ownership. Advanced fiber composite materials are being used in aircraft at an ever-increasing rate as one of the avenue to achieve some of these improvements. The adoption of new composite structures in civilian aircraft must be justified on performance and through-life cost considerations. Through-thickness reinforcement (TTR) has the potential to improve the damage tolerance of composite structures and reduce manufacturing costs. With the introduction of TTR into a laminate, the local misalignments of the fibers around the reinforcement result in reduced in-plane stiffness and strength. The voxel model calculates the effective properties of such laminates. The model captures the effect of TTR type, volume fraction, and direction.

Non-linear finite element modelling of an integrally stiffened composite panel

Abstract The progressive introduction of advanced fibre composite materials into aerospace structures has enabled significant performance improvements to be achieved. Structures using these materials are generally designed so that their behaviour is essentially linearly elastic through to failure. The realisation of further significant weight reductions in light-weight aerospace structures is highly dependent on design technologies which will enable postbuckling stiffened panels to be utilised in primary structures. The capabilities of the finite element code, MSC/NASTRAN, to predict the onset of buckling and subsequent postbuckling behaviour of a blade-stiffened fibre composite panel have been investigated. The panel consists of T300/914 carbon/epoxy unidirectional tape and is reinforced by integral stiffeners. Basic modelling techniques for the efficient analysis of such postbuckling assemblies are presented. It is concluded that the prediction of their performance requires specialist modelling skills and a sound understanding of the behaviour of the composite materials used in the structure.