Polymer composites subjected to cyclic loading would exhibit damage precursors, such as crazes and microcracks, during the first few load cycles. However, damage precursors are not readily detectable with existing sensing techniques, and as such current service life prediction methods depend on macroscopic damage measures. For critical airframe structures, information on macroscopic damage does not provide adequate warning time for corrective actions. This article explores the feasibility of embedding particulate magnetostrictive particles for sensing damage precursors during the early stage of fatigue damage. The sensing is based on the notion that magnetostrictive particles undergo irreversible changes in magnetization intensity when subjected to cyclic loading, and that this change can be captured with an induction coil sensor. In the sequel, Terfenol-D particles are embedded between layers of pre-preg AS4/3501-6 material system. The specimen is then subjected to fatigue loading while monitoring the change in the strength of the magnetic flux density using pickup coil. Results show that the embedded system exhibits a change in magnetic state, in tens to hundreds of millivolts of pickup coil, starting from the first few load cycles. Scanning electron microscopy and acoustic emission data were used to validate the observed results.

Defects in composite laminates are difficult to detect because of the conductive and paramagnetic properties of composite materials. Timely detection of defects in composite laminates can improve reliability. This research illustrates the preliminary analysis and detection of delaminations in carbon fiber laminate beams using a single layer of magnetostrictive particles and noncontacting concentric magnetic excitation and sensing coils. The baseline analytical models also begin to address the intrusive nature of the magnetostrictive particles as well as relate the applied excitation field with the stress and magnetic flux densities induced in the magnetostrictive layer. Numerical methods are used to begin to characterize the presence of magnetostrictive particles in the laminate and the behavior of the magnetostrictive particles in relationship to the magnetic field used during sensing. Unidirectional laminates with embedded delaminations are used for simulations and experimentations. A novel, yet simplified fabrication method is discussed to ensure consistent scanning and sensing capabilities. The nondestructive evaluation scanning experiments were conducted with various shapes and sizes of damages introduced into carbon fiber-reinforced polymeric composite structures. The results demonstrate high potential for magnetostrictive particles as a low-cost, noncontacting, and reliable sensor for nondestructive evaluation of composite materials.

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This paper presents a methodology toward designing, analyzing, and optimizing piezoelectric interdigitated microactuators using multiphysics finite element analysis. The models used in this paper were based on a circularly interdigitated design that takes advantage of primarily the d33 electromechanical piezoelectric constant coefficient. Because of the symmetric nature of the devices, a small number of 2D axisymmetric parametric models were developed to characterize the behavior of the diaphragms. The parametric models offered a large range of possible results from a very small number of models. The variations in the design parameters and their effects on deflection were captured using these models. The models also showed that several of the design parameters were naturally coupled. Discrete models were then used to capture the variations in the key design parameters during fabrication. The numerical models correlate well to the maximum deflection of the experimental devices.

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