L.S. Sutherland

Size and scale effects in composites: I. Literature review

This paper is concerned with a review of the size and scale effects involved in the prediction of strength of fibre-reinforced-plastic (FRP) composite materials and structures. The review covers the basic principles in the establishment of scaling laws and the application of the Buckingham-Pi theorem. An analysis of various theories used in categorising size effects, such as the weak link, extended weak link and fracture mechanics approaches, is presented. This is followed by an examination of the literature devoted to scaling issues in FRP composites.

The effects of test parameters on the impact response of glass reinforced plastic using an experimental design approach

An instrumented falling weight machine was used to investigate the effects of test parameters on the impact response of low fibre-volume E-glass woven-roving reinforced polyester coupons. Statistical experimental design techniques were used to plan the experiment and to analyse the data. All the parameters considered were found to affect the responses in a complex and interacting manner. Multiple damage modes occurred and the damage mechanisms were seen to vary with the test parameters. Identification of the important parameter effects above the experimental variation using statistical methods combined with graphical representation of these effects and the failure modes simplified the interpretation of the results. It was demonstrated that the techniques of statistical design of experiments are powerful to identify the interaction among parameters that govern the structural response in particular when there are many parameters.

Effects of laminate thickness and reinforcement type on the impact behaviour of E-glass/polyester laminates

A large number of impact tests have been carried out on woven-roving and chopped-strand-mat glass reinforced, hand laid-up polyester laminates of different thicknesses and weights. Deflection, force, absorbed energy and damaged area results for these tests have been presented and compared, and the failure modes described. A simple analysis assuming shear-dominated deflection gave good correlation with the experimental data. Prediction of the damaged area proved to be more difficult, although some correlation was seen. Further investigation into the nature of the damage is required.

Size and scale effects in composites: II. Unidirectional laminates

This paper is concerned with the scale and size effects in the strength characterisation of composite materials with particular reference to hand laid-up unidirectional laminates. Attention has been focused on the tensile and flexural strengths of glass/epoxy and carbon/epoxy laminates. The experiments have been designed through the use of statistical, factorial-based techniques, whereby a more comprehensive analysis of the inter-relationship between different parameters and their influence on strength can be made. The work highlights the importance of fabrication factors and the distinguishing difference between scale effects and size effects.

Numerical simulation of transversely impacted, clamped circular aluminium plates

This paper presents experimental and numerical results of a series of drop weight impact tests examining the dynamic response of fully clamped aluminium 5083/H111 circular plates struck laterally at the centre by a mass with a spherical indenter. The impact velocity varied from 1.0 to 6.0 m/s. The plates showed no visible damage at the very low incident energies but suffered both indentation and global deformation as incident energy was increased. The numerical modelling was performed using the LS-DYNA non-linear, dynamic finite element software. Both shell and solid element models of progressively refined mesh sizes were used and the results compared with the experimental data. The numerical calculations used can accurately predict the response of deflections, forces and absorbed energies, even for the models with coarse meshes. However, finer meshes and solid elements were required to obtain a satisfactorily accurate prediction of the deformed shape.

Size and scale effects in composites: III. Woven-roving laminates

This paper is concerned with scale and size effects in the strength characterisation of composite materials with particular reference to woven-roving laminates. Attention has been focused on the tensile and flexural strengths of glass/polyester laminates fabricated by hand lay-up techniques. Factorial experiments have been designed to allow investigation of the joint influence of different factors on strength. The work highlights the importance of fabrication factors and the distinguishing difference between scale effects and size effects.