In the present work, polymer-based syntactic foams were studied under cyclic compression in order to investigate their compressibility, recoverability, energy dissipation and damage tolerance. These syntactic foams were manufactured by adding hollow polymer microspheres of various sizes and wall thicknesses into a polyurethane matrix. The associated loading and unloading curves during cyclic testing were recorded, revealing the viscoelastic nature of the materials. SEM images of the samples were obtained in order to study potential damage mechanisms during compression. It was observed that these syntactic foams exhibit high elastic recovery and energy dissipation over a wide range of compressional strains and the addition of polymer microspheres mitigates the damage under compressional loading.

Transverse compression response of tows during processes such as vacuum infusion or autoclave curing has significant influence on resin permeability in fabrics as well as the laminate thickness, fibre volume fraction and tow orientations in the finished composite. This paper reports macro -scale deformations in dry fibre assemblies due to transverse compaction. In this study, influence of weave geometry and the presence of interlacements or stitches on the ply-level compaction as well as nesting have been investigated. 2D woven fabrics with a variety of interlacement patterns -plain, twill and sateen-as well as stitched Non-crimp (NCF) fabrics have been investigated for macro-level deformations. Compression response of single layer and multilayer stacks has been studied as a function of external pressure in order to establish nesting behaviour. It appears that the degree of individual ply compaction and degree of nesting between the plies are influenced by tow architectures. Inter-tow spacing and stitching thread thickness appears to influence the degree of nesting in non-crimp fabrics.

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Meso-scale geometrical changes during transverse compression of aligned tows have a significant influence on resin permeability during infusion as well as on the mechanical properties of the resulting polymer composites. These geometrical changes need to be captured at each and every stage of composite manufacturing and realistic geometrical models verified by accurate experimental data are needed to simulate the changes during forming to predict the mechanical properties of the composite laminates. In the present work, the aligned fibre tows in a dry plain woven glass fabric are simulated by digital element method. A meso-scale compaction study of the tow geometrical changes has been conducted by 3D X-ray computed tomography (CT) under compression loading. The evolution of mesoscale geometrical features such as tow area, thickness, width and waviness has been quantified using high quality CT images. The realistic tow geometrical data by digital element simulation under different compaction levels has been validated by experimental data obtained by CT.

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