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The very graphic name of 'sandwich composites' adequately describes them as structures with a relatively thick core made of lightweight or low density material separating two thin stiff and strong skins. Such choice of geometry and combination of materials yields a product with reasonable strength and bending stiffness in combination with lightness. This paper presents work in predicting the bending stiffness of a sandwich composite through its equivalent flexural rigidity by modelling the material in the geometry of a cantilever beam. The results are verified experimentally by obtaining, through the laser based optical NDE technique known as Electronic Speckle Pattern Interferometry (ESPI), the displacement curve of the cantilever beam subjected to a point load at its free end. A second experimental technique carried out involved monitoring the dynamic response of a cantilever beam in its first mode of natural vibration. The beam equipped with polyvinyldiene fluoride (PVDF) sensors yielded results which are compared to the values for the flexural stiffness obtained by the prediction and the experimental setup using ESPI.

The paper presents the work that was carried out in the detection and, beyond of what is obviously visible to the naked eye, the extent of impact damage inflicted on composite panels designed and manufactured for structural applications in the aerospace industry. Using a drop-weight impact tester the composite specimens were subjected to controlled impact conditions i.e. relatively low velocity impact levels analogous to those expected from the drop of a heavy tool, collision with a bird etc. The composite specimens consisted of Monex core sandwiched between thin carbon/glass fibre reinforced plastic skins, typically identical to those used in the fabrication of unmanned air vehicles and helicopter rotor blades. The investigation attempted to establish the probability of detecting such barely visible impact damage with optical non-destructive testing methods such as Digital Shearography, Electronic Speckle Pattern Interferometry and Infrared Thermography. These NDT techniques were chosen to be employed in this study, because they are non-contacting, whole field, not limited to particular material types, provide fast and easy results in real-time and have been proven reliable in a large number of applications in the laboratory/factory/field environment.

Energy from the exhaust gas of an internal combus-tion engine is used to power an absorption refriger-ation system to air-condition an ordinary passenger car. The theoretical design is verified by a unit that is tested under both laboratory and road-test condi-tions. For the latter, the unit is installed in a Nissan 1400 truck and the results indicate a successful pro-totype and encouraging prospects for future devel-opment.