It is well known that laminated composite materials are prone to impact damage caused by foreign objects and exhibit poor damage resistance in through the thickness direction. By drawing inspiration from naturally occurring impact resistant structures, such as dactyl clubs of mantis shrimp, enhanced damage tolerance and impact energy absorption can be achieved with traditional CFRP layers by creatively arranging them into bio-inspired configurations, called helicoidal or Bouligand structures. Through an extensive numerical analyses of low velocity impact (LVI) supported by the experimental results, a further insight into the possibilities that these structures can offer in terms of damage resistance was attained. By comparing the results of three square plates with different planar sizes, it was shown that the helicoidal layups are more effective at absorbing energy while minimising through the thickness failure than standard quasi-isotropic and cross-ply laminates. Although the helicoidal composites generally exhibited a higher degree of delamination in LVI tests, the standard lamination schemes displayed higher degree of perforation, which resulted in a reduced residual strength in the compression after impact (CAI) testing of a quasi-isotropic laminate compared to several helicoidal ones subjected to 40 J and 80 J impact energy. Furthermore, using advanced finite element analysis (FEA) code LS-DYNA® for simulating LVI and CAI events, it was revealed that the helicoidal arrangement endured the least amount of fibre damage.

Bistable energy harvesting has become a major field of research due to some unique features for converting mechanical energy into electrical power. When properly loaded, bistable structures snap-through from one stable configuration to another, causing large strains and consequently power generation. Moreover, bistable structures can harvest energy across a broad-frequency bandwidth due to their nonlinear characteristics. Despite the fact that snapthrough may be triggered regardless of the form or frequency of exciting vibration, the external force must reach a specific snap-through activation threshold value to trigger the transition from one stable state to another. This aspect is a limiting factor for realistic vibration energy harvesting application with bistable devices. This paper presents a novel power harvesting concept for bistable composites based on a "lever effect" aimed at minimising the activation force to cause the snap through by choosing properly the bistable structures' constraints. The concept was demonstrated with the help of numerical simulation and experimental testing. The results showed that the actuation force is one order of magnitude smaller (3-6%) than the activation force of conventionally constrained bistable devices. In addition, it was shown that the output voltage was higher than the conventional configuration, leading to a significant increase in power generation. This novel concept could lead to a new generation of more efficient bistable energy harvesters for realistic vibration environments.

No abstract

No abstract

Detection of visible crack, delamination etc. in composite structures can be fulfilled by several techniques. However, the problem is of greater complexity in the case of nonvisible defects such as barely visible impact damage and microcracks.The objective of this research work was to create and validate a low cost smart-sensor for NDT and structural health monitoring (SHM) to be used for complex geometries. The smart-sensor presents a dual function, i.e. it determines the presence of delamination and cracks within the cross-section but it also provides information on surface damages due to fatigue or impacts. In the latter case the damage could induce the breakage of the sensor that could still work with a different resonant frequency.The sensor utilizes a passive wireless resonant telemetry scheme based on an inductor capacitor (LC). The use of a passive system eliminates the need for onboard power and exposed interconnects, increasing the life of the device and the reliability due to the continuous operation even in case of damage results from the sensor.The sensor design, the signal processing and the experimental setup that validate the remote interrogation of the antenna sensor are presented. Two different designs were investigated, one for conductive surface and one for nonconductive surface (fiberglass-composite).