Gin Boay Chai

A review of low-velocity impact on sandwich structures

This contribution is a review of past and current research progress on dynamic response of composites sandwich structures subjected to low-velocity impact. To obtain a comprehensive overview of the current state-of-the-art published works, impact responses on sandwich structures are broadly classified into two main groups, high-velocity and low-velocity impacts, with the focus on low-velocity impact. A summary of some of the commonly used theoretical solutions for low-velocity impact is provided and described in some details. The response of low-velocity impact has been determined based on mass ratio, which is defined as the ratio of the impact mass to effective mass of the structural component. As a result, the response under low-velocity impact was further subdivided into three possible categories, namely, large, small, and medium mass impacts. For each category of impact, currently available suitable solutions are discussed in details. To classify the response of low-velocity impact and also to explore the energy-absorption characteristics as well, the impact duration is identified as the key parameter. The review concludes with detailed discussions on the damage mechanisms and failure criteria for sandwich structures subjected to impact loads.

The effect of varying the support conditions on the buckling of laminated composite plates

Abstract The buckling analysis of laminated composite plates using a semi-numerical approach called the finite strip method is presented. The composite plates are subjected to in-plane compression and their boundary conditions on the unloaded edges are simulated to vary from the free condition to clamp condition using a quintic polynomial function. Along the loaded edges three different support conditions are simulated using single term trigonometric functions. The coupling influence in these laminated plates on the buckling behaviour is accounted for in the analysis through the use of the reduced bending stiffness concept. The validity of the results obtained are verified by comparison with published results and experimental results. Some parametric studies towards the end of this paper give an interesting insight into the effect of changing the support conditions on the buckling behaviour of laminated composite plates. The limitations using the finite strip method found in the present study are also discussed.

Buckling of generally laminated composite plates

Abstract A total potential energy approach has been employed in conjuction with the Rayleigh-Ritz method to study the stability behaviour of generally laminated composite plates with all edges simply supported and subjected to in-plane loading conditions. Thorough comparison with exact solutions for some classes of laminated composite plates subjected to uniaxial compression and biaxial compression are presented to verify the theoretical prediction of the present analysis. Lastly parametric studies on the combination of the various in-plane loads, i.e. biaxial compression and uniaxial compression with shear, on practical laminated composite plates are presented. The buckling results for a symmetric angle-ply laminated composite plate are also discussed.

Thermal deformation measurement of electronic packages using the atomic force microscope scanning moiré technique

In this article, the feasibility of atomic force microscope (AFM) scanning moire on a cross-line diffraction grating has been studied. The AFM scanning moire technique has been applied to measure the thermal deformation of electronic packages successfully. This technique is convenient to perform the mismatch method, also it could obtain a higher resolution than any other moire method.

Buckling strength optimization of laminated composite plates

Abstract An optimization procedure using the Complex technique in conjunction with the finite strip method is presented to find the optimum ply angle in antisymmetric laminated composite plates subjected to in-plane compression. The buckling solution obtained by the finite strip method was compared and verified with published results for the antisymmetric laminated composite plates. The validity of the optimization procedure was also confirmed by comparing the results obtained with published results. The results of this investigation for the optimum ply angle of antisymmetric laminated composite plates which provides the highest buckling strength under various support and in-plane loading conditions, are extensively presented. The effect of variables such as aspect ratio, edge supports and compression factor were discussed in detail.

A review of advances in fatigue and life prediction of fiber-reinforced composites

This contribution is an attempt to provide a thorough review of past and current research work on fatigue and life prediction of fiber-reinforced composites. In order to summarize and present a comprehensive overview of the current state-of-the-art published works, the reviews in this contribution are broadly summarized into four groups of review; (1) fatigue of fiber-reinforced composites, (2) composite damage mechanism, (3) composite failure criteria and, (4) composite fatigue modeling and life prediction. The review will begin with a discussion of inherent and environmental factors affecting the fatigue of composites. This is followed by a rather extensive description of the composite damage mechanism and a summary of commonly used failure criteria for life prediction. And towards the end, models and methods for fatigue and life prediction of composites are summarized and discussed.

Free vibration of generally laminated composite plates with various edge support conditions

Abstract The well known and versatile Rayleigh-Ritz method is employed to study the free vibration behaviour of generally laminated composite plates with various edge support conditions. Classical edge support conditions such as simply-supported, clamped or a combination of both are prescribed along the edges of the plate and the effect of these on the natural frequencies of the plate is presented and discussed. Thorough comparisons with exact solutions for some classes of laminated composite plates are presented to verify the theoretical predictions of the present analysis. Experimental results applied to rectangular C-S-C-S laminated composite plates with symmetric stacking sequence are also presented for verification.

Experimental and analytical investigations of vibration frequencies for centre-loaded beams

Abstract Analytical frequency predictions are verified through experimental investigations on built-in and cantilever beams carrying masses at their centres. Two analytical expressions are derived using eigenfunctions and Rayleighs method, respectively. Results of frequencies obtained through different means are compared and discussed. The qualitative study presented allows one to quickly and accurately predict the vibration frequencies of centre-loaded beams for a large range of mass ratios.

Comparisons of experimental and theoretical frequencies for rectangular plates with various boundary conditions and added masses

Abstract This paper is concerned with a vibration analysis of rectangular plates with masses mounted on various locations. The edges of the plates may either be clamped or simply supported. The study is particularly useful in the understanding of the vibration of printed circuit boards used in the electronics industry. An energy method is developed to obtain analytical frequencies of the plates with various edge support conditions. The analytical procedure using the Rayleigh–Ritz approach is adopted in which each of single and multiple trigonometric series terms is used to represent the shape function. Two experimental methods, a spectrum analyser and a TV-holographic system, are used to study the behaviour of the plate vibrations. The holographic image produced at the corresponding mode frequencies by using the TV-holography technique has been applied to verify the frequency spectra obtained from the spectrum analyser. The experimental results have been used to illustrate the validity of the analytical model. The comparisons show that the analytical model predicts natural frequencies reasonably well, in which the EM 100-term model is suggested for vibration plates with higher modes or heavier loads.

An experimental study on laminated panels in compression

Abstract The theoretical approach adopted in this paper is applied to the buckling and post-buckling behaviour of laminated plates subjected to unidirectional in-plane loading. Full details of the theoretical approach are given in a companion paper ( Comp. Struct. , 19 (1991) 41–65). The membrane boundary conditions considered were those which allowed the unloaded edges to wave in the plane of the plate. The flexural boundary conditions considered were simple supports on the loaded ends with the unloaded edges rotationally restrained, thus giving the theoretical approach more flexibility in allowing the unloaded edges to be simply supported and clamped as the limiting cases. An extensive complementary experimental investigation was carried out to confirm the theoretical findings. The test set-up gave simply supported boundary conditions on the unloaded edges and fully fixed conditions on the loaded ends. Large deflection results and post-buckling strain distributions were obtained for laminated panels composed of 14 layers of Grafil XAS/914C Fibredux, and comparisons are made with the theory.