Low velocity impact energy absorption of fibrous metal-matrix composites using smart materials.

Abstract

In general, the basic concept of an intelligent material is defined as the multifunctional material that has a sensor, a processor and an actuator function in the material that allows it to maintain optimum conditions in response to environmental changes. Despite the fact that these materials have demonstrated varying degrees of success in shape and position control, active and passive control of vibration and acoustic transmission of materials subjected to dynamic loads, impact damage and creep resistance in structures and have been applied in industries from aerospace to biomechanics to civil engineering structures, very little literature is available on the subject. Thus, the objective of this dissertation is to add to the fundamental understanding of the behaviour of these special materials by investigating the possibility of a magnetostrictive SMA hybrid metalmatrix composite beam with piezoelectric actuator, to enhance the materials load attenuation and energy absorption characteristics under low velocity impact loading. The methodology employed in this investigation is driven by two primary factors. The first is the unique approach that the author puts forward to attempt to simplify the characterisation of damage in not just metal matrix composites, but in materials in general. The second factor is the lack of available literature on smart material energy absorption as well as a lack of precise theory for short fibre composites. The methodology includes an extensive literature review, the development of an analytical model, based on the new damage modulus approach, verification of the model using experimental results presented by Agag et. aI., adjustment of the model to include smart material effects and finally numerical simulation using the MATLAB® software to predict the effect of smart materials on the energy absorption capacity of the material under impact. The results show that the damage modulus (ED) is a material characteristic and can be derived from the stress strain diagram. Further, it takes into account degradation of the material through the plastic region, up to the point just before ultimate failure. Thus, ED lends itself to the simplification of many damage models in terms of a reducing sustainable load and energy absorption capacity. Only the energy consumed through material rupture remains to be characterised. The results also show that smart fibres diminish the capacity of the beam to sustain a load, but increase the displacement to failure. Thus, for a compatible substrate material, this increased displacement translates to a significant enhancement of energy absorption characteristics. The effect of prestrain on energy absorption is also considered and there appears to be a definite turning point where the dissertation thus achieves its objective in investigating the ability of smart materials to enhance the energy absorption characteristics of regular fibre reinforced metal-matrix composite materials subject to low velocity impact loading. Of equal importance to the achievement of this objective is the introduction in the dissertation of the unique damage modulus that goes to the foundation of material characterisation for mechanical engineering design and has profound implications in damage theory and future design methodologies. Significant learning has taken place in the execution of this PhD endeavour and this dissertation will no doubt contribute to other investigations in the field of smart materials.