Relationship between mechanical-property and energy-absorption trends for composite tubes
U.S. Army helicopters are designed to dissipate prescribed levels of crash impact kinetic energy without compromising the integrity of the fuselage. Because of the complexity of the energy-absorption process it is imperative for designers of energy-absorbing structures to develop an in-depth understanding of how and why composite structures absorb energy. A description of the crushing modes and mechanisms of energy absorption for composite tubes and beams is presented. Three primary crushing modes of composite structures including transverse shearing, lamina bending, and local buckling are described. The experimental data presented show that fiber and matrix mechanical properties and laminate stiffness and strength mechanical properties cannot reliably predict the energy-absorption response of composite tubes.
Numerical simulation of the crushing process of composite materials
Abstract Components in composite materials are progressively replacing metals for crashworthy applications in the automotive, railway and aeronautical industries. The numerical simulation of the crushing process for composite structures is a recent research area. Due to the complex mechanical behaviour of advanced composites, the capability of the existing analytical and numerical models to predict the crushing behaviour of composite materials is still limited. A numerical model for the crushing simulation of fibre-reinforced composite materials is proposed in this work. The progression of the main cracks is modelled using a new formulation of finite decohesion elements, that allows to correctly account for the energy involved in the cracking process. The intralaminar damage is modelled taking into account the specificities of each material system, degrading the elastic properties in accordance with the different predicted physical damage phenomena. After the validation of the decohesion element, this is used as part of a model for simulation of composite tubes crushing. A good agreement between the numerical results and the experimental data is achieved. The need for further improvements on the physical basis of the intralaminar failure criteria used, as well as on the numerical solution methods for the non-linear problem, is identified.
Fully Integrated Bidirectional CMOS-MEMS Flow Sensor With Low Power Pulse Operation
Leveraging More-than-Moore technology, we demonstrate an integrated CMOS MEMS flow sensor via a very compact system on chip (SoC) that can sense the bidirectional N2 gas flow. Our SoC features a very low-noise instrumentation amplifier that is implemented on a CMOS wafer and serves as a readout integrated circuit for a thermoresistive micro-calorimetric flow sensor which is fabricated on a MEMS wafer. A compact heterogeneous integration is achieved by combining the two wafers via the proprietary InvenSense AlN process. The measured sensitivity of our CMOS MEMS flow sensor is 98 mV/sccm which is three times better than the state-of-the-art counterpart. The flow range measured by our SoC is from −26 to 26 m/s (from −50 to 50 sccm). Moreover, the pulsed heater operation makes this proposed SoC flow sensor a very low power (<9 mW) and, thus, a promising candidate for the Internet-of-Things applications in smart home/green buildings.