Carbon Fiber Reinforced Plastic Skins Research Articles

The Bending Responses of Sandwich Panels with Aluminium Honeycomb Core and CFRP Skins Used in Electric Vehicle Body

The aim of this paper was to investigate bending responses of sandwich panels with aluminium honeycomb core and carbon fibre‐reinforced plastic (CFRP) skins used in electric vehicle body subjected to quasistatic bending. The typical load‐displacement curves, failure modes, and energy absorption are studied. The effects of fibre direction, stacking sequence, layer thickness, and loading velocity on the crashworthiness characteristics are discussed. The finite element analysis (FEA) results are compared with experimental measurements. It is observed that there are good agreements between the FEA and experimental results. Numerical simulations and experiment predict that the honeycomb sandwich panels with ±30° and ±45° fibre direction, asymmetrical stacking sequence (45°/−45°/45°/−45°), thicker panels (0.2 mm∼0.4 mm), and smaller loading velocity (5 mm/min∼30 mm/min) have better crashworthiness performance. The FEA prediction is also helpful in understanding the initiation and propagation of cracks within the honeycomb sandwich panels.

Inspections of Helicopter Composite Airframe Structures using Conventional and Emerging Nondestructive Testing Methods

This paper presents nondestructive testing (NDT) results and analysis from the inspection of composite specimens representing typical helicopter parts. The specimens include monolithic laminates produced from carbon fiber reinforced plastic (CFRP), Nomex honeycomb core sandwich panels with CFRP skins, and CFRP frame-skin joint panels. External protection layers comprising copper mesh and fiberglass were also included in the specimens. These panels were fabricated with a wide range of defects to simulate helicopter in-service damage including delamination and skin-core disbond along with barely visible impact damage. The study aims to assess a number of conventional and emerging NDT techniques suitable for rapid in situ and off-site inspection of helicopter composite structures. The techniques considered are flash and sonic thermography, radiography, and different ultrasonic inspection modes including pulse-echo, through-transmission, and phased array. These techniques are compared on their ability to detect and characterize the fabricated defects.

Lightweight Actuator Structure With SMA Honeycomb Core and CFRP Skins

The authors proposed a sandwich structure that consists of a shape memory alloy (SMA) honeycomb core and carbon fiber reinforced plastic (CFRP) skins as a shape-controllable structure. The proposed lightweight actuator structure can be bent by heating even though it has a moderate bending stiffness. First, unidirectional CFRP skins were bonded to the SMA honeycomb core made of thin SMA foils, and residual shear strain was applied to the SMA core. Then, the ends of the upper and lower skins were fixed to other cores. The length, thickness, and width of the sandwich beam specimen were 180 mm, 16 mm, and 13 mm, respectively, and its weight was 9.6 g. Hence, the effective density of the entire beam was only 0.26 g/cm3. When the specimen was heated, the beam either bent upward, taking the form of a sigmoid curve, or generated a moderate blocking force. When the specimen was cooled to room temperature, the beam regained its initial straight shape. Therefore, a two-way actuation is possible. This method has a better ability to bend skins with high in-plane stiffness because the recovery shear force has an out-of-plane stress component and is applied uniformly to all the skins from the inner core. In addition, the microscopic mechanism of this bending deformation can be clarified by a numerical simulation with a finite element method. Furthermore, the proposed actuator structure can possibly be used as a member that suppresses resonance since the natural frequency of the beam can be controlled by increasing the elastic moduli of SMA on heating.

Vibration damping in sandwich panels

Currently, there is incomplete knowledge of the damping level and its sources in satellite structures and a suitable method to model it constitutes a necessary step for reliable dynamic predictions. As a first step of a damping characterization, the damping of honeycomb structural panels, which is identified as a main contributor to global damping, has been considered by ALCATEL SPACE. In this work, the inherent vibration damping mechanism in sandwich panels, including those with both aluminium and carbon fibre-reinforced plastic (CFRP) skins, is considered. It is first shown how the theoretical modal properties of the sandwich panel can be predicted from the stiffness and damping properties of its constituent components using the basic laminate theory, a first-order shear deformation theory and a simple discretization method. Next, a finite-element transcription of this approach is presented. It is shown to what extent this method can be implemented using a finite-element software package to predict the overall damping value of a sandwich honeycomb panel for each specific mode. Few of the many theoretical models used to predict natural frequencies of plates are supported by experimental data and even fewer for damping values. Therefore, in a second, experimental part, the Rayleigh–Ritz method and NASTRAN (finite-element software used by ALCATEL SPACE) predicted modal characteristics (frequency and damping) are compared with the experimentally obtained values for two specimens of typical aluminium core honeycomb panels (aluminium and CFRP skins) used by ALCATEL SPACE as structural panels. It is shown through these results that the method (theoretical and finite element) is satisfactory and promising.

Experimental Investigation of Elastodissipative Characteristics of Carbon-Fiber-Reinforced Plastics

A procedure is described for the experimental study of elastodissipative properties of carbon-fiber-reinforced plastic (CFRP) structures. Experimental values of dissipation factors are given for angle-ply structures with a reinforcing angle varying from 0 to 90°. Elastodissipative characteristics of two types of CFRP are identified. The values obtained can be used for predicting the properties of complex CFRP structures. It is shown that the energy absorption in sandwich structures with CFRP skins and a honeycomb core is mainly governed by properties of the skins.