On The Crashworthiness Of Composite Structures And Controllable Trigger Mechanism

Advanced composite materials are widely used in the industry of national defense and civil, especially in the areas of aeronautics and astronautics, due to their superior property of high specific strength and stiffness, high specific energy absorption, and designable capability. The crashworthiness of composite structures has become a hot research topic in recent years because of its importance and complicated nature. In this thesis, the crashworthiness of typical composite components and structure is explored systemically by using numerical simulations together with the experimental research. Special attention has also been paid on the trigger mechanism, an important issue affecting the energy absorption capability of composite structures.The energy-absorbing capability of typical composite structural elements, such as waved beam, cylindrical shell,"T"shape element,"十"shape element,"L"shape element and corrugated board boxes, under quasi-static axial loading is experimentally investigated first. The load-displacements and typical damage patterns and mechanisms of composite structural elements are obtained. Experimental results demonstrate that well-designed composite structural elements do have a good specific energy-absorption capability.A FEM-based numerical strategy and means is proposed to simulate the crashworthiness of composite structures by using the MSC/DYTRAN FE software, including adopting the equivalent material models and using a simple way to model the trigger mechanism. The energy absorption ability of various composite structural elements under axial compressive loads is then simulated. Numerical results are compared well with experimental results, thus the established FEM-based numerical strategy and means is verified. In addition, the effect of different settings of trigger mechanism on the crashworthiness of waved beams is numerically investigated.The SMA (Shape Memory Alloy) -based controllable trigger mechanism is proposed and experimentally verified. Pre-strained SMA wires are embedded into or winded up onto the composite cylinders to form a new kind of trigger mechanism. The pre-strained SMA wire will shrink back to its original length when it is heated to the transformation temperature, consequently will cause the local deformation, thus a controllable trigger mechanism is formed. This controllable trigger mechanism could solve the contradicted requirements between the structural strength (stiffness) and the crashworthiness. Specimens have been made in the Lab and tested. Preliminary test results show that a controllable trigger mechanism does formed and could improve the crashworthiness of composite structures.The dissertation is ended with the summary remarks and the future research topics in this field.