R.A. Shenoi

Free vibration analysis of composite sandwich plates based on Reddy's higher-order theory

Two new C0 assumed strain finite element formulations of Reddys higher-order theory are used to determine the natural frequencies of isotropic, orthotropic, and layered anisotropic composite and sandwich plates. The material properties typical of glass fibre polyester resins for the skin and HEREX C70 PVC (polyvinyl chloride) foam materials for the core are used to show the parametric effects of plate aspect ratio, length-to-thickness ratio, degree of orthotropy, number of layers and lamination scheme on the natural frequencies. A consistent mass matrix is adopted in the present formulation. The results presented in this investigation could be useful for a better understanding of the behaviour of sandwich laminates under free vibration conditions and potentially beneficial for designers of sandwich structures.

Size and scale effects in composites: I. Literature review

This paper is concerned with a review of the size and scale effects involved in the prediction of strength of fibre-reinforced-plastic (FRP) composite materials and structures. The review covers the basic principles in the establishment of scaling laws and the application of the Buckingham-Pi theorem. An analysis of various theories used in categorising size effects, such as the weak link, extended weak link and fracture mechanics approaches, is presented. This is followed by an examination of the literature devoted to scaling issues in FRP composites.

Probabilistic strength analysis of rectangular FRP plates using Monte Carlo simulation

Abstract Probabilistic strength analysis of simply supported rectangular anti-symmetric cross-ply and angle-ply fibre reinforced plastic laminated plates is performed by applying the Monte Carlo simulation method. Various limit state equations are derived from non-linear laminate theory with different anisotropic plate failure criteria. Transverse lateral pressure load, elastic moduli, geometric and ultimate strength values of the laminates are considered as basic design variables and assumed to follow both normal and two-parameter Weibull probability distributions. Reliability of the laminates is estimated and the sensitivities of basic design variables to the estimated reliability is viewed by varying their mean values systematically.

Dynamic analysis of composite sandwich plates with damping modelled using high-order shear deformation theory

The dynamic behaviour of fibre reinforced plastic sandwich plates with PVC foam core is investigated in this paper. Recently, the authors have developed an analytical method based on Reddys refined high-order shear deformation theory to study the dynamic behaviour of undamped fibre reinforced plastic (FRP) sandwich plates. The present paper explains how the dynamic constitutive material properties (obtained by carrying out DMTA tests) are introduced into the analytical model using the elastic–viscoelastic principle. The obtained equations of motion are used to carry out steady state analysis and to determine the natural frequencies and modal loss factors of specific composite sandwich plates.

Radial flow permeability measurement. Part A: Theory

This paper deals with permeability measurement in the context of Resin Transfer Moulding (RTM). A new approach to two-dimensional radial flow permeability measurement with constant inlet pressure is proposed. It allows principal permeability to be measured even if the experimental axes are not aligned with the principal direction. This part of the paper looks at the underlying theory of the new approach while part B reports on validation experiments. Formulae are derived which allow to calculate principal permeability and the orientation of the principal axes from flow front measurements in three directions. Transient effects of the developing flow front caused by the circular inlet are discussed and its influence on the measured permeability is illustrated. Numerical studies are performed which show that the shape of the flow front is dependent only on the size of the inlet diameter and the degree of anisotropy. This leads to the development of a formula for estimating the minimum required mould size for permeability measurement.

Measurement of three-dimensional permeability

This study investigates the possibility of using a three-dimensional radial flow test to measure permeability. As part of this investigation, compaction tests have been conducted to determine the fibre volume fraction as a function of the compaction pressure. Results from permeability tests are reported. The flow front in these tests is measured using thermistors. The dependence of the flow front shape on the injection pressure has been demonstrated. In the case of three-dimensional flow the capillary pressure can become more important than the externally applied injection pressure. As a consequence, the sharp flow front becomes a flow front zone. Permeability measurement is no longer possible. This has been confirmed experimentally. Finally, new possible applications for the flow measurement sensors are discussed.

Progressive failure and ultimate collapse of laminated composite plates in bending

A method is presented to study the non-linear behaviour, first ply failure and ultimate collapse of laminated composite plates with clamped edges, subjected to transverse pressure. Several failure criteria, including Hashins and Tsai-Wus, are used to predict the failure mechanisms. The effect of aspect ratio on the strength and stiffness of laminated composite plates is studied. Non-linear strain-displacement relations that contain large strain and large rotation are used in the analysis. The general purpose finite element program ABAQUS is used for the analysis. The stiffness reduction is carried out at the Gauss points of the finite element mesh depending on the mode of failure. The predictions of the model correlate well with experimental data for different aspect ratios.

Influence of material and geometry variations on the behaviour of bonded tee connections in FRP ships

Abstract This paper is concerned with the design of tee connections in single skin FRP ships and boats. A brief review of the problem is first presented and reference is made to current practice towards the design of such joints. Areas of principal interest, especially those with most influence on joint behaviour, are identified. These are used in a systematic manner in physical and numerical modelling of the joint. Load/deflection graphs from the mechanical tests are presented and physical characteristics of the joint under load are noted. Numerical finite element models have then been used to provide an insight into the internal load dissipation and failure mechanisms. The modelling is used to highlight significant influences of geometry and material variations on the performance of the tee joints.

A Study of Structural Composite Tee Joints in Small Boats

The paper examines the influence of joint geometry on the ability to transfer out-of-plane loads for a hull bulkhead joint in small boats. The hull bulkhead assemblies have been designed on the basis of sandwich beam and laminated plate theories. An analytical solution has also been developed to predict the failure load. Experimental speci mens have been produced and tested to failure in order to be compared with the analytical method. Finally, a design tool based on the analytical model and the factors affecting cost and weight efficiency of the joint has been produced for practical engineering purposes.

Fatigue Behaviour of Polymer Composite Sandwich Beams

The static and flexural fatigue characteristics of foam cored polymer composite sandwich beams are investigated. The skins of the beams are made from hybrid glass-aramid fibres set in epoxy resin and the core materials are linear and cross-linked polymer foams. The applied load in a ten-point configuration approximates a uniformly distributed load throughout the span of the beam which is simply supported at the ends. The testing frequencies are 0.33-0.91 Hz. Failure modes relate to both core shear and skin failure.