Zainudin A. Rasid

Thermal Buckling and Post-Buckling Improvements of Laminated Composite Plates Using Finite Element Method

Thermal buckling and thermal post-buckling behaviours of laminated composite plates are improved by embedding shape memory alloy wires within laminates of composite plates. The procedure is to use the recovery stress that is induced when the reverse transformation of the shape memory alloy from martensite to austenite phases is constrained. For aerospace applications where the source of the shape memory alloy heating is the high temperature environment itself, a study is conducted to see the effect of shape memory alloy in improving the thermal buckling and post-buckling of composite plates. Due to the temperature dependent nature of the composite matrix and the shape memory alloy, the finite element formulation developed here is in the incremental form. Solving this non-linear model using the developed in-house source code, critical loads are determined and the post-buckling paths of the shape memory alloy composite plates are traced. This study shows that by embedding the shape memory alloy within composite plates, the thermal buckling and post-buckling behaviours of composite plates can be improved substantially.

The instability improvement of the symmetric angle-ply and cross-ply composite plates with shape memory alloy using finite element method

Shape memory alloy (SMA) wires were embedded within laminated composite plates to take advantage of the shape memory effect property of the SMA in improving post-buckling behavior of composite plates. A nonlinear finite element formulation was developed for this study. The plate-bending formulation used in this study was developed based on the first order shear deformation theory, where the von Karmans nonlinear moderate strain terms were added to the strain equations. The effect of the SMA was captured by adding recovery stress term in the constitutive equation of the SMA composite plates. Values of the recovery stress of the SMA were determined using Brinsons model. Using the principle of virtual work and the total Lagrangian approach, the final finite element nonlinear governing equation for the post-buckling of SMA composite plates was derived. Buckling and post-buckling analyses were then conducted on the symmetric angle-ply and cross-ply SMA composite plates. The effect of several parameters such as the activation temperature, volume fraction, and the initial strain of the SMA on the post-buckling behavior of the SMA composite plates were studied. It was found that significant improvements in the post-buckling behavior for composite plates can be attained.

The natural frequency of the shape memory alloy anti-symmetric angle-ply composite plates using finite element method

Shape memory alloy (SMA) wires were embedded within laminated composite plates to take advantage of the shape memory effect (SME) property of the SMA. Active modal modification of SMAC plates was studied using the finite element method (FEM). A linear FEM formulation was developed based on the first order shear deformation theory. The effect of SMA was captured by adding the geometric stiffness matrix to the stiffness matrices of composite plates. Two methods of frequency improvements are considered here: The active property tuning (APT) and the active strain energy tuning (ASET) methods. The values of recovery stress for the ASET analysis were determined from Brinson’s model. The effects of several parameters on the natural frequencies of the SMAC plates were studied. It was found that the effect of SMA is similar for couples of frequency modes where frequencies of mode I and IV seems to have affected the most by SMA.

The post-buckling improvement of the shape memory alloy composite plates through the active strain energy tuning using finite element method

Shape memory alloy has been used as actuator parts in aerospace industry since the 1970s. In recent years, this smart material has been used to improve structural behaviours. Due to environmental heating, the problem of buckling of thin composite structures of aerospace vehicles becomes significant. A numerical study on the buckling and post-buckling improvements of composite plates due to shape memory effect behaviour of the shape memory alloy is presented. The shape memory alloy wires were embedded within laminated composite plates to exploit the recovery stress induced by the shape memory alloy to improve the stiffness of the plates. The study was conducted on symmetric and anti-symmetric angle-ply and cross-ply composite plates. The methods of active property tuning and active strain energy tuning were applied to show the various effects of the shape memory alloy on the studied behaviours. A geometric non-linear finite element model of the shape memory alloy composite plates and its source code were developed. It was found that significant improvements occurred in the critical loads and the post-buckling paths of the symmetric and anti-symmetric angle-ply and the symmetric cross-ply composite plates due to the active strain energy tuning method. In the case of the anti-symmetric cross-ply composite plate where bifurcation point did not exist, the post-buckling path improved substantially too.

Enhancing Ride Comfort of Quarter Car Semi-active Suspension System Through State-Feedback Controller

The objective of this study is to simulate the road disturbance toward suspension in quarter car system. Suspension consists of the system of springs, shock absorbers, and linkages that connects a vehicle to its wheel and allows relative motion between the car body and the wheel. This paper shows the mathematical modeling in order to design the quarter car suspension system using Simulink and MATLAB software. The work shows the effect of suspension travel in quarter car system toward road profile by using state-feedback controller. The state-feedback controller’s purpose is to decrease the continuous damping in suspension system. The inconsistency condition of the road is the main element that affects the ride comfort which is in this paper represented by different heights of road profile. In suspension principles, the road wheels and vehicle body produce vertical forces which are rotational motions. Therefore, state-feedback controller must be able to reduce body deflection caused by road disturbance to achieve the ride comfort of driver and passengers. The results show that the proposed controller is capable of reducing the vibration of suspension after experiencing the bumps with different heights.

Improvement on Ride Comfort of Quarter-Car Active Suspension System Using Linear Quadratic Regulator

The goal of this paper is to investigate the performance of an active suspension system via linear quadratic regulator (LQR) control and proportional–derivative–integral (PID) control. This project presents the mathematical models of the two degrees of freedom of a quarter-car active suspension system. This project introduces the design of a controller performance used for an active suspension system. The equations of motion of the quarter-car active suspension system model are developed. In the passive suspension system, there are huge oscillations or vibrations that occur in the suspension system. This phenomenon will lead to uncomfortable ride among the passengers or the driver. Besides, it takes longer time to reduce the vibration. Therefore, a good controller design must be able to reduce the vibration and produce a fast settling time. This project is focused on designing a controller for active suspension system by using MATLAB and Simulink software for both PID and LQR controllers to enhance the performance of ride comfort. This research also aims to study the effect of disturbances such as road bump and holes to the response time of the vibration of the vehicle. The result shows that the response of LQR control gives the best output performances in minimizing the vibration and gives faster settling time than that of the PID control.

The effect of changing disk parameters on whirling frequency of high speed rotor system

The requirement for efficiency improvement of machines has caused machine rotor to be designed to rotate at high speeds. It is known that whirling natural frequency of a shaft changes with the change of shaft speed and the design needs to avoid points of resonance where the whirling frequency equals the shaft speed. At high speeds, a shaft may have to carry a huge torque along and this torsional effect has been neglected in past shaft analyses. Whirling behaviour of high speed rotating shaft is investigated in this study with consideration of the torsional effect of the shaft. The shaft system under study consists of a shaft, discs and two bearings, and the focus is on the effect of the disc parameters. A finite element formulation is developed based on Nelsons 5 degrees of freedom (DOF) per node element that includes the torsional degree of freedom. Bolotins method is applied to the derived Mathieu-Hill type of equation to get quadratic eigenvalues problem that gives the forward and backward frequencies of the shaft. Campbells diagrams are drawn in studying the effect of discs on the whirling behaviour of the shaft. It is found that the addition of disks on the shaft decreases the whirling frequency of the shaft and the frequency is lower for mass located at the centre of the shaft compared to the one located near to the end. The effect of torsional motion is found to be significant where the difference between critical speed of 4DOF and 5DOF models can be as high as 15%.

Parametric instability of shaft with discs

The occurrence of resonance is a major criterion to be considered in the design of shaft. While force resonance occurs merely when the natural frequency of the rotor system equals speed of the shaft, parametric resonance or parametric instability can occur at excitation speed that is integral or sub-multiple of the frequency of the rotor. This makes the study on parametric resonance crucial. Parametric instability of a shaft system consisting of a shaft and disks has been investigated in this study. The finite element formulation of the Mathieu-Hill equation that represents the parametric instability problem of the shaft is developed based on Timoshenkos beam theory and Nelsons finite element method (FEM) model that considers the effect of torsional motion on such problem. The Bolotins method is used to determine the regions of instability and the Strut-Ince diagram. The validation works show that the results of this study are in close agreement to past results. It is found that a larger radius of disk will cause the shaft to become more unstable compared to smaller radius although both weights are similar. Furthermore, the effect of torsional motion on the parametric instability of the shaft is significant at higher rotating speed.

The Thermal Stability Property of Bio-composites: A Review

Composite material has played important role as an alternative material to metal in many industries. However as the growing of environmental concern throughout the world becomes so high, the interest on the green or bio-composite as to replace fossil based composite has also increased. Bio-composite, a type of composite materials that constitutes of natural fibres and bio-polymers, comes with the environmental advantages of being renewable, biodegradable and sustainable. However green composites also come with several disadvantages such as low in mechanical properties, low in thermal stability and high in water absorption. The level of these disadvantages vary from one bio-composite to another since there are lots of factors that determine these properties. Due to this, a large number of researches have been conducted to improve these properties with the aim of applying bio-composites as structural components. In this paper, a review is made on the thermal stability property of the bio-composites. The review includes the discussion on tests conducted to study the instability behavior of the bio-composites and factors that will improve the thermal stability of bio-composites. It was found that the addition of the high volume fraction of fibres to the bio-composites may not increase the thermal stability of the bio-composite. However, thermal stability can be improved by giving chemical treatments to the bio-composites that improves the compatibility of the fibres and the polymers of the bio-composites.

The Instability Improvement of the Shape Memory Alloy Composite Plates Subjected to In-Plane Parabolic Temperature Distribution

The designs of thin structure components of aerospace vehicles require the consideration of thermal buckling and post-buckling problems. Thermal buckling of the structures in the aerospace environment may occur due to non-uniformly distributed temperature field. A finite element method study on the post-buckling of composite plates with embedded shape memory alloy wires was conducted. The plates were subjected to in-plane and through-thickness non-uniform thermal loadings where the non-uniform temperature distributions considered were parabolic in-plane and linearly varying through-thickness thermal loadings that may act separately or in combination. Recovery stress induced by the shape memory alloy was exploited to improve the thermal buckling behaviours of the composite plates. A non-linear finite element model along with its source codes that considered the recovery stress of the shape memory alloy, the non-uniform temperature field, the temperature dependent properties of the SMA and the composite matrix were developed. The post-buckling paths that showed the effect of the shape memory alloy on the thermal post-buckling behaviour of composite plates were generated using the source codes. It was found that the strain energy tuning method of the shape memory alloy greatly improved the post-buckling behaviour of composite plates subjected to the non-uniform temperature distributions.