There is an increasing drive toward the monitoring of the structural health of costly and safety critical infrastructure. Quite often, however, this does not require the cost and nuisance of active monitoring, and a simple passive system will suffice. One of the most robust, cost effective, and neat methods of passive peak monitoring involves the use of strain memory alloys; which are ferrous alloys that display paramagnetism in the unstrained state, but transform proportionally to display varying degrees of ferromagnetism depending on the level of peak strain induced in the material. This effect is achieved using a transformation in crystal structure from a metastable austenitic structure to a stable strain-induced martensitic structure. Because of the physical properties and the relatively low cost of strain memory alloys it is actually possible to manufacture complete components from this family of materials, and the materials can be tailored in terms of physical as well as transformation properties using alloying chemistry and prior deformation of austenite in the ausforming temperature range. Several dual purpose components have been developed for a variety of different applications, using strain memory alloys: a smart composite laminate, a smart rock anchor, and a smart aircraft bolt among others. This paper presents the general principles involved in using strain memory alloys for structural health monitoring, as well as specific application designs and results.

The increasing inclusion of composite laminates in safety critical structures has prompted the development of a variety of damage assessment or structural health monitoring techniques. Among the new technologies is a method suited to peak strain measurement by the use of strain memory alloy films embedded in the laminate at primary manufacturing stage. The metastable alloys that comprise the group known as strain memory alloys, are all ferrous based, relatively cheap to produce, and operate on the principle of crystal transformation from austenitic parent phase to martensitic product phase [1,2]. The martensite forms in direct proportion to the peak strain induced in the material, and the magnetic susceptibility changes in direct proportion to the amount of martensite that has nucleated within the material. The correlating change in magnetic susceptibility can therefore be monitored as an indication of peak strain, since the transformation is irreversible.

The increasing use of composite laminates in safety critical structures has prompted the development of a robust structural health monitoring system for laminates, which uses metastable ferrous alloy inserts embedded within the laminate during component construction to provide an indication of the peak tensile strain encountered by the laminate. The metastable ferrous alloy insert has an austenitic crystal structure at room temperature, but upon application of strain, this transforms to a thermodynamically stable martensite, resulting in a change in magnetic susceptibility, which can be correlated with the peak strain experienced by the material (strain memory effect). This paper presents the test results that show that it is possible to manufacture a smart laminate in this fashion, and that sufficient strain is experienced by the insert to provide a significant change in magnetic susceptibility, thereby warning of a high strain level in the laminate. Various insert geometries and laminate thicknesses are also tested for their effect on the susceptibility measurements.

The problem of quantitative characterization of damage accumulation during hydrothermal aging of polymer matrix composites is addressed. Effective elastic stiffnesses and thermal diffusivities of glass fiber reinforced thermoplastic are measured at several steps of aging. Anisotropic damage accumulation is identified. It is shown that both elastic and thermal properties of the composite degenerate with the accumulation of damage. The extents of degenerations are linked to each other using the methods of micromechanics. The established cross-property connection is in a good agreement with the experimental measurements.

A state of the art of the problem of buckling in sandwich structures is discussed and the shortcomings of some existing theories shown. A specified classification of the forms of stability is given and, in accordance with it, a refined theory for the study of the mixed forms of stability is formulated. Different models of the fillers are classified according to their stress–strain state. For the transversely soft model of the filler a set of geometrically nonlinear refined relations is derived. These relations are used to describe the subcritical instantaneous equilibrium of the sandwich plates in the case of both large and small changes in the shear stresses.

Composite laminates are finding increasing use in load bearing structures of a safety critical nature. This trend means that it becomes increasingly important to be able to measure the accumulated damage within safety critical composite panels. The current research approaches include the use of piezoelectric patches, fibre optics, and even the intrinsic piezoresistive properties of carbon fibres themselves. The aforementioned methods do, however, suffer various difficulties in terms of manufacturing considerations, as well as the complexities associated with some of the monitoring equipment needed to interpret damage levels. A more robust concept has however recently seen development, which relies on embedding metastable ferrous elements or wires within the laminate. Not only can this smart material easily withstand the processing temperatures; but if correctly used, the elements may impart significant load-bearing capacity to the laminate. The damage assessment equipment is simple and can in fact be operated by a person with no specialised training.

A new higher-order theory for the analysis of laminated orthotropic plates and shells subject to both mechanical and thermal loads is developed. Using the variational approach the system of governing differential equations and corresponding boundary conditions are derived. Two refined models of the stress and strain state are considered, their application and accuracy are discussed. The analytical solution is obtained for plates and shells with the Navier boundary conditions on the side surfaces. The results of calculations are given and compared with an exact three-dimensional solution available in the literature. The influence of the laminated structure upon the exactness of results and the characteristics of stress–strain state is studied and discussed.