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A combined numerical-experimental method that enables accurate prediction of not only the elastic moduli and tensile failure strengths of syntactic foams, but also accounts for the experimentally observed scatter in these measurements is presented. In general, for the systems studied, an increase in microsphere content resulted in an increase in tensile modulus and a decrease in tensile strength. At low particle loading ratios, the variance in the measured experimental strength can be almost entirely attributed to the distribution of inter-particle distances between the microspheres, whilst at high particle loadings, geometric variance in the microstructure is shown to be only partially responsible for the observed scatter in strength data. Thus, for the first time, a direct link between the underlying microstructure and the experimentally observed scatter in fracture strength is drawn and substantiated with modelling.

In the current work, the fracture properties of epoxy polymers containing poly-siloxane core shell rubber (CSR) nano-particles were studied. The effect of different cure rates and curing temperatures on the epoxy resin was also investigated. Single edge notched bend tests were performed to evaluate the fracture energy of the polymers. The fracture energy of the unmodified epoxy polymer increased significantly from 339 J/m 2 to 3,922 J/m 2 due to the addition of 9 wt% of CSR nano-particles. Similarly, the fracture toughness for the unmodified polymer increased from 1.27 MPa m 1/2 to 3.42 MPa m 1/2 for an epoxy polymer containing 9 wt% of CSR nano-particles. Faster rates of curing, which can be achieved at higher cure temperatures are found to be detrimental to the toughness of the modified epoxy polymers.

Composite sandwich materials have yet to be widely adopted in the construction of naval vessels despite their excellent strength-to-weight ratio and low radar return. One barrier to their wider use is our limited understanding of their performance when subjected to air blast. This paper focuses on this problem and specifically the strength remaining after damage caused during an explosion. Carbon-fibre-reinforced polymer (CFRP) composite skins on a styrene–acrylonitrile (SAN) polymer closed-cell foam core are the primary composite system evaluated. Glass-fibre-reinforced polymer (GFRP) composite skins were also included for comparison in a comparable sandwich configuration. Full-scale blast experiments were conducted, where 1.6×1.3 m sized panels were subjected to blast of a Hopkinson–Cranz scaled distance of 3.02 m kg−1/3, 100 kg TNT equivalent at a stand-off distance of 14 m. This explosive blast represents a surface blast threat, where the shockwave propagates in air towards the naval vessel. Hopkinson was the first to investigate the characteristics of this explosive air-blast pulse (Hopkinson 1948 Proc. R. Soc. Lond. A 89, 411–413 (doi:10.1098/rspa.1914.000810.1098/rspa.1914.0008)). Further analysis is provided on the performance of the CFRP sandwich panel relative to the GFRP sandwich panel when subjected to blast loading through use of high-speed speckle strain mapping. After the blast events, the residual compressive load-bearing capacity is investigated experimentally, using appropriate loading conditions that an in-service vessel may have to sustain. Residual strength testing is well established for post-impact ballistic assessment, but there has been less research performed on the residual strength of sandwich composites after blast.

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