Key Engineering Materials Vols. 334-335

Abstract: The main purpose of this study is to evaluate the interfacial reaction between titanium matrix composites (TMCs) and A380 alloy in aluminum die-casting. In-situ synthesized titanium matrix composites and H13 tool steel were immersed in molten A380 alloy in a mold at 993 K for times varying from 0 to 1200 s. In-situ synthesis TMCs and interfacial reaction between TMCs and A380 alloy were examined by X-ray diffraction, optical microscope, scanning electron microscope and electron probe micro-analyzer. The reaction behavior shows that TMCs can a substitution for H13 tool steel.

Abstract: Liquid molding processes are becoming more popular among the composite manufacturing industries due to their versatility and economy among other merits. In analyzing the flow during the process, permeability is the most important parameter. Permeability has been regarded as a property of the porous medium. However, in many practical cases, the value may vary depending on the flow conditions such as the flow rate. It is speculated that this deviation is caused by inhomogeneous microstructure of the medium. In this study, numerical simulations as well as experimental measurements have been done to investigate the cause of deviation. Microstructure of porous medium was modeled as an array of porous cylinders. Resin flow through the array was simulated numerically. Simulations were performed for two different flow conditions, namely saturated flow and unsaturated flow. Based upon the results, permeabilities were estimated and compared for the two flow conditions. In addition, a model was proposed to predict the permeability for different flow conditions. Results showed that experimental data were in agreement with the prediction by the model.

Abstract: To meet the demands of technology for the development of new materials with tailormade properties, we propose the use of smart materials of nanostructure synthesized by solidifying a poorly conducting alloy in a microgravity environment in the presence of an electric field and surface tension. Energy method combined with a single term Galerkin expansion is used to find the condition for the onset of Marangoni marginal electroconvection (MMEC) in a composite material modeled as a porous layer. It is shown that a proper choice of electric parameter
and the ratio of Brinkman viscosity to viscosity of the fluid λ control Marangonielectroconvection (MEC).

Abstract: This paper is concerned with the fatigue life prediction of CFRP laminates under variable cyclic loading using the linear cumulative damage (LCD) rule with statistical approach. Three-point bending fatigue tests for plain-woven CFRP laminates were carried out under
various cyclic loading with constant and variable stress amplitude and frequency.
As results, the applicability of LCD rule to the flexural fatigue life was confirmed for this CFRP laminates.

Abstract: Interlaminar fracture behavior of carbon fabric/epoxy composite, which is one of the candidate composites for the Korean tilting train carbody, was investigated. Specimens were made of a CF3227 plain fabric with an epoxy resin. An initial starter crack was formed by inserting a 12.5
thick Teflon film at the one end of the specimen. Interlaminar fracture toughness was evaluated using the mixed mode flexural fixture, which provides a wide range of mixed mode deformation by varying the length of lever arm. According to the results, the crack growth was progressive and stable under mode I dominantly mixed mode ratio and was relatively rapid and unstable under mode II dominantly mixed mode ratio. The mixed mode interlaminar fracture behavior can be predicted by a mixed mode fracture criterion depending on the point at which the crack growth was associated.

Abstract: In the traditional iterative design process for composite structures, it is difficult to achieve an optimal solution even though a great effort is made. A genetic optimization system based on grid technology offers an automatic and efficient approach for composite structure redesign and optimization. A genetic algorithm system, which integrates Genetic Algorithm Optimization (GAO) software and a Finite Element Analysis (FEA) based commercial package, has been developed as a tool for composite structure design and analysis. The GAO is capable of tailoring large number of composite design variables and taking the time-consuming FEA results to calculate objective function value and conduct optimization in high accuracy. By operating the system employing the Grid technology and Artificial Neural Network (ANN) method, significant time saving in numerical analysis can be achieved. A user friendly interface has also been built in the system. In the paper, aeroelastic tailoring of a composite wing has been taken as a numerical example to demonstrate the optimization approach. The numerical results show that an optimal design has been achieved to meet the design requirement.

Abstract: Satellite structural components must be able to withstand various loading and environments that will experience during integration, tests, transportation, launch, and on-orbit operation. A polymeric composite optical bench that fixes delicate optical payloads such as a camera or a telescope was developed based on static strength, thermal deformation, and vibration. The optical bench consists of composite sandwich panels with and without a hole and composite struts with end fittings. In this paper, the optimum stacking sequence of the composite optical bench was calculated to minimize severe thermal deformations during orbital operation using a genetic algorithm and the finite element analysis. Then, the optimum design is evaluated whether it withstands launch loads (high inertia, vibration, etc.), that are not usually significant compared to orbital thermal loadings, or not. The thermal deformation of sandwich panels was minimized at the stacking sequence of [0/±45]s and that of composite struts was lowest at the angle of [02/90]s. There was no buckling in the compressive loading. By vibration analysis, the natural frequencies of the composite components were much higher than aluminum structures (i.e., sandwich panel: 10.7%; strut: 27.79%) and the stiffness condition expected was satisfied. Then, a composite optical bench was fabricated for tests and all analyses results were verified by structural testing. There were good correlations between two results. To increase the structural stiffness, several Nitinol shape memory alloy wires installed on it and the natural frequencies were measured.

Abstract: Targeted at improving the overall integrity of functionalised composite structure, an embedded sensor network technique was developed using circuited piezoelectric wafers. The technical difficulties due to sensor embedment, such as electrical insulation, were addressed. With Hilbert transform-based signal processing and a correlation-based identification algorithm, Lamb wave signals, excited and captured by the integrated sensor network, were evaluated for damage assessment. Effectiveness of the sensor network and proposed identification algorithm was demonstrated by identifying delamination in orthotropic woven fabric CF/EP composite laminates. Excellent identification capacity of the built-in sensor network indicates its considerable application potential in providing high-fidelity data acquisition/condition monitoring for composite structures.

Abstract: This study provides a practical method regarding the development of a complete self-diagnostic technique for monitoring the bearing damage of bolted composite or metallic joints. The basic concept is based on making BG (Bolt Gauge) measurements that has been proposed in earlier work [1,2]. That is, bonding a strain gauge onto the surface of bolt head to monitor the bolt strain changes that would identify bearing damage. Extensive tests using double lap bolted joint specimens are performed to verify the health monitoring technique, including the effects of the bolt clamp-up, material response, joint geometry and loading history. The results have shown that the bearing damage detected by BG measurements agreed well with acoustic emission (AE) measurements. Finite element analysis is performed to discuss the monitoring mechanisms.

Abstract: This paper presents experimental results on the mechanical performance of advanced carbon/epoxy composites with embedded polymeric films. The composite laminates with polymeric films, which are potentially used as a sensor/actuator carrier for structural health monitoring applications, were investigated under various mechanical loadings including low velocity impact, single lap shear and short beam shear. The preliminary work showed that embedment of those polymeric films does not degrade, but could significantly improve, the mechanical properties of the composite laminates.