Damage signature of fatigued fabric reinforced plastics in the pulsed ultrasonic polar scan

This study investigates the use of both the amplitude and time-of-flight based pulsed ultrasonic polar scan (P-UPS) for the nondestructive detection and evaluation of fatigue damage in fiber reinforced composites. Several thermoplastic carbon fabric reinforced PPS specimens (CETEX), loaded under various fatigue conditions, have been scanned at multiple material spots according to the P-UPS technique in order to extract material degradation in a quantitative way. The P-UPS results indicate that shear dominated fatigued carbon/PPS goes with a reduction of shear properties combined with large fiber distortions. The P-UPS results of the tension-tension fatigued carbon/PPS samples on the other hand reveal a directional degradation of the stiffness properties, reaching a maximum reduction of -12.8% along the loading direction. The P-UPS extracted damage characteristics are fully supported by simulations, conventional destructive tests as well as visual inspection. The results demonstrate the excellent capability of the P-UPS method for nondestructively assessing and quantifying both shear-dominated and tension-tension fatigue damage in fabric reinforced plastics

Nonlinear free vibration of an Euler-Bernoulli composite beam undergoing finite strain subjected to different boundary conditions

In this paper, the free vibration of an orthotropic beam undergoing finite strain are studied. The second Piola-Kirchhoff stress tensor and Green-Lagrange strain tensor according to finite strain assumption were used to obtain Euler-Bernoulli beam governing equations. The Galerkin method and Generalized Differential Quadrature method were employed for solving the governing equations and boundary condition. The effect of beam thickness and different boundary conditions were considered in finite strain formulation of the beam equations. Natural frequencies of different composite materials are obtained and compared. The results revealed that by increasing the beams thickness, the difference between maximum vibration amplitude increased between von Karman and finite strain formulations. Also, in a beam with simply- simply supports, differences between linear and non linear mode shapes was remarkable

Development of beam modal function for free vibration analysis of FML circular cylindrical shells

The free vibration of fiber–metal laminate (FML) thin circular cylindrical shells with different boundary conditions has been studied in this research. Strain–displacement relations have been obtained according to Love’s first approximation shell theory. To satisfy the governing equations of motion, a beam modal function model has been used. The effects of different FML parameters such as material properties lay-up, volume fraction of metal, fiber orientation, and axial and circumferential wavenumbers on the vibration of the shell have been studied. The frequencies of shells have been calculated for carbon/epoxy and glass/epoxy as composites and for aluminum as metal. The results demonstrate that the influences of FML lay-up and volume fraction of composite on the frequencies of the shell are remarkable

Devulcanized rubber based composite design reinforced with nano silica, graphene nano platelets (GnPs) and epoxy for aircraft wing spar to withstand bending moment

This paper aims a new composites design by using devulcanized recycled rubber (90 wt %) and epoxy 20 wt %) based composites reinforcement with nano silica and graphene nano plates (GnPs). The toughening effects of nano-silica/graphene hybrid filler at various ratios on this composite were investigated for aircraft engineering applications especially aircraft wing spar. As well known, wing spar is used two of them; one front, other rear in order to control torsional effect of the wing. Nano-silica and graphene nano plates (GnPs) have been used as the main reinforcing fillers that increase the usefulness of recycled rubber composite. As each filler retains its specific advantages, the use of nano-silica/graphene combinations should improve the mechanical and dynamic properties of recycled rubber composite. In aircraft and aerospace applications, graphene nano plates can be used effectively new design of electrically conductive composites which can improve the electrical conductivity of these composites designed for the fuselages that it would replace copper wire which is generally used for the prevention of damage caused from lightning strikes. There are many advantages and possibilities that graphene nano plates (GnPs) can prevent water entering the wings, which adds weight to the aircraft. In the frame of this present common research, a new devulcanized recycled rubber based composite design for aircraft wing spar has been proposed and wing load due to structure weight was calculated analytically to tolerate bending moment under the service conditions. The toughness properties and tribological behaviour indicating the reinforcement of recycled rubber based composite were evaluated. Microstructural and fractural analyses were made by Scanning Electron Microscopy (SEM)