Tee failure of carbon fibre reinforced plastic laminated plates under biaxial stresses

A new biaxial test procedure, known as the 'plate bending method' is investigated for thin multilayered generally orthotropic laminated plate structures. The method is evaluated with reference to the four criteria for a satisfactory biaxial test. A number of experiments have been performed to determine the applicability of the criteria to the new method. Surface strains, transverse displacements and visual observations have been recorded, from which the bending behaviour and failure mechanisms in the experiments are examined. A classical 2-dimensional thin plate finite element analysis has been developed to predict the stresses generated in the small (linear) and large (non-linear) deformation domains. To minimise computing effort in the analyse of non-linear bending, the formulation omitted the effects of shear deformation, shear stresses, material non-linearities and the exact position of the neutral axis. The omission of these factors has been examined and it is shown that the individual errors are small. Analytical solutions for simple isotropic, and, where available, laminated plate bending examples, have been used to establish the limitations of the finite element analysis. Numerical results have been compared with the measured surface strains and transverse displacements. From the comparison it is shown that the plate bending method can be accurately modelled by the linear analysis. However, the non-linear analysis is shown to be inaccurate when predicting the measured bending for reasons which are discussed

Mechanical and X ray computed tomography characterisation of a WAAM 3D printed steel plate for structural engineering applications

This paper reports an investigation to improve fundamental knowledge and understanding of 3D printing of steel in structural engineering. The process method examined is Wire and Arc Additive Manufacturing (WAAM) for the manufacturing of large-sized components. The mechanical properties of 3D printed Union K 40 - GMAW steel are determined and benchmarked against measured properties of EN 8 carbon medium steel. The results presented and discussed are from tensile coupon testing and X-ray Computed Tomography, with the latter inspecting an internal volume of the WAAM steel for: printing orientation; mapping porosity; interfacial variation between the printed layers. The key finding is that the mechanical properties of the WAAM steel satisfy the requirements for a structural steel grade for building structures as specified by Eurocode 3 (EN 1993–1-1)

Moisture uptake characteristics of a pultruded fibre reinforced polymer flat sheet subjected to hot/wet aging

This paper studies the moisture uptake characteristics of a pultruded E-glass fibre reinforced (isophthalic polyester) polymer after long-term exposure to hot/wet conditions. Both fully exposed samples of varying aspect ratios and selectively exposed samples were immersed in distilled water at 25 °C, 40 °C, 60 °C and 80 °C for a period of 224 days. For the fully exposed condition, bulk and directional diffusion coefficient values were determined. A three-dimensional approach using Fickian theory was applied to approximate the principal direction diffusions at 60 °C by using mass changes from samples having different aspect ratios. This revealed that the diffusion coefficient in the longitudinal (pultrusion) direction to be an order of magnitude higher than in the transverse and through-thickness principal directions. Diffusion coefficients in the three principal directions have also been determined for the selectively exposed condition at 60 °C through the application of one-dimensional Fickian theory. It was found that the size and shape of the samples influences moisture uptake characteristics, and thereby the values determined for bulk and directional diffusion coefficients. Furthermore, the influence of exposure temperature on moisture uptake and mass loss with time was examined. Investigation of the water medium by means of electrical measurements suggested that decomposition of the polymeric composite initiates very early, even after the very first day of immersion. Comparison between the infrared signatures from the pultruded material and the water's residual substances revealed significant decomposition, and this behaviour is verified by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopic (EDS) analysis as well as the recorded mass loss after 224 days of aging

Closed-form equations for flange force and maximum deflection of box-beams of fiber reinforced polymer with partial shear interaction between webs and flanges

Presented in the paper is the formulation of a governing second-order differential equation for the moment distribution along the length of a beam having two interfaces with partial shear interaction where two flange and two web components join to form the box shaped section. For practical applications such a closed-section beam of Fiber Reinforced Polymer (FRP) can be assembled from individual pultruded profiles using mechanical fasteners. This assembly approach can be used to construct deeper section sizes than can be achieved with a single pultrusion, and which can be transported in flat-pack units. In developing the governing equation for flexural response account is made of the finite connection stiffness at the web/flange interfaces by applying conventional elastic beam theory. The differential equation for the partial interaction problem is solved to formulate closed form equations for the flange force and the maximum deflection of a simply supported beam under four-point bending. A numerical parametric study is presented to show changes in beam performance indicators with the degree of shear interaction between the upper and lower bounds of full- and non-interaction. Results from a series of load tests using a three-layered prototype FRP beam are shown to be in good agreement. The theoretical predictions for maximum deflection are however found to be directly linked to the appropriateness of the measured connection stiffness entered into the closed-form equation

Using finite elements in mechanical design/ Mottram

xiv, 264 hal.; ill.; 24 c

Using finite elements in mechanical design/ Mottram

xiv, 264 hal.; ill.; 24 c

Decoupling of the Ericksen-Leslie equations

In this article we show how it is possible to decouple the Ericksen-Leslie equations, thereby allowing us to derive a dynamic equation for the director in which the flow velocity is absent. The flow itself can then be expressed as a function of the director orientation profile. Using this approach, we examine the Freedericksz transition of a nematic liquid crystal and solve the corresponding decoupled dynamic equation numerically. We show how our model still predicts the reduction of the effective viscosity and backflow. More significantly, while kickback is also present, we demonstrate how kick-back can be avoided by an appropriate choice of applied voltage during the switch-on process

Kickback in nematic liquid crystals

We describe a nonlocal linear partial differential equation arising in the analysis of dynamics of a nematic liquid crystal. We confirm that it accounts for the kickback phenomenon by decoupling the director dynamics from the flow. We also analyse some of the mathematical properties of the decoupled director equation