Key Engineering Materials Vols. 471-472

Abstract: In this study, the impact responses of sandwich structure with both FML and aluminum skins were compared. The force-time histories from the low-velocity drop weight impact tester were recorded under various impact energies. Energy absorbed from the two types of sandwich structures under various impact energies were also calculated by measuring its initial velocity before impact from a series of recorded high speed camera pictures and force-time histories. Based on results obtained, pure aluminum skins with PP honeycomb core that being impacted by lower impact energies shows higher absorbed energies as compared to FML skins. However with higher impact energies the FML skins shows improvement over the aluminum with higher energy absorption capacity. Damages created were also being characterized under optical microscope for further investigation.

Abstract: The improvements of buckling and post-buckling behaviours of laminated composite plates were done by changing the composite related parameters such as the level of anisotropy, thickness to width ratio and boundary condition. In recent years, shape memory alloy has been used to achieve such improvements. A study is conducted on the buckling and post-buckling improvements of composite plates due to the combined effects of composite and shape memory alloy related parameters. Shape memory alloy wires are embedded within laminated composite plates and the amount of recovery stress induced by the shape memory wires is predicted using the Brinson’s model. A geometric non-linear finite element method is used to model the buckling and post-buckling behaviours of shape memory alloy composite plates and source codes are developed to solve the model. It is found that significant improvements in buckling and post-buckling behaviours of composite plates can be attained by combining the effect of shape memory alloy and composite related parameters.

Abstract: 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.

Abstract: Resistive relative humidity (RH) sensors were fabricated by nano composites of nylon-6 and titanium dioxide nanopowders. The results indicated that these sensors can be fabricated as a reliable, low cost and fast response instruments. Different percentages of nylon-6 and TiO2 were studied and average diameters of the resultant nanofibers were found the 80 to 120 nm. The nano composite of nylon-6/TiO2 nanofibers was electrospun on the interdigital gold electrode on the glass substrate. It was found that the impedance of the mat ranged from 107 Ω to 102 Ω while the relative humidity was increased from 11% RH and 97.3% at room temperature. Transition electron microscopy (TEM) and scanning electron microscopy (SEM) were used to study the morphology of the nano composite.

Abstract: The purpose of the present study is to obtain the least strength reduction and uttermost healing efficiency in a typical [(90/0)/(90/0)Hollow/90/(0/90) Hollow/90/(0/90) Hollow/(0/90)] self-healing laminate. It has been done using a hollow glass fiber (HGF) with a given diameter and an individual method to distribute the HGF in the host laminate. The results of three-point bend flexural strength testing indicated that for the investigated distribution, the inclusion of HGF imparts little reduction in undamaged strength (4%) which is due to the non-integrity of self-healing laminate related to the host laminate. After healing it was found that the laminate had a residual strength of 97% compared to the undamaged control and 100% compared to an undamaged self healing laminate.

Abstract: Composite metal decking has become one of the prevalent forms of Fast Track Construction for multi-story steel buildings. The in-plane stiffness of composite metal decks however is of considerable importance as they typically act as a diaphragm in lateral-load- resisting systems and thus attract a large in-plane shear. The diaphragm action or the in-plane shear capacity of composite metal decks remained a concern for structural engineers and designers. The present work aims to investigate the in-plane shear behavior of fiber reinforced composite metal decks and compare it to that reinforced with welded wire mesh. A comprehensive experimental program involving testing large scale slabs was conducted. Steel decking of trapezoidal profile with a sheet thickness of 0.9 mm was used to construct the composite slabs. Conventional WWF mesh reinforcement and synthetic macro fibers at different reinforcing rates were considered in the test program. The slabs were tested under monotonically increasing in-plane shear force until failure. Load-deflection responses were plotted and cracking pattern and sequence were recorded. The test results show that fibers provide comparable deck behavior as that with steel mesh. Both imparted similar ultimate in-plane shear capacity and enhanced the ductility and the post peak behavior of the composite metal decks relative to the control slab. The results demonstrate the viability of synthetic macro fibers to replace the steel mesh in this type of composite flooring systems.

Abstract: In this paper, injection molding parameters are optimized using the L18 Taguchi orthogonal array for mechanical strength and surface quality of the green part. The feedstock used consists of stainless steel powder (SS316L) with the powder loading of 63 vol. %, 63.5 vol. % & 64 vol. %. The binder compositions used are polyethelene glycol (PEG-73 wt.%), polymethyl methacrilate (PMMA-25 wt.%) and stearic acid (4 wt.%). Mould temperature, injection temperature, injection pressure, injection time, holding time and powder loading ware selected as signal factors using Taghuci’s method based on literature, where these parameters were significant in MIM. Results showed that the optimum parameters are: mold temperature at 650C, injection temperature at1450C, injection pressure at 650 bar, injection flow rate at 20 m3/s, holding time at 5 s and powder loading of 64 vol.%. Analysis of Variance (ANOVA) result shown that mold temperature is the most influence in order to produce good green part’s surface quality while powder loading give the best result for green part’s strength.

Abstract: An aircraft radome usually refer to radar transparent, dome-shape structures which protects radar antennas on aircraft from aerodynamic loading, weather as well as impacts from bird strikes. Materials that are used for small aircraft radome usually have low dielectric constant and high toughness. Current composite material using high strength fibers such as glass fiber, carbon and aramid are commonly used in aerospace structures. However, the need for biodegradable materials has prompted the usage of natural fibers. Natural fibers have comparable mechanical properties such as low weight, low cost, renewable and biodegradable. In this preliminary work, comprehensive reviews of biocomposites materials are discussed in term of their properties for the purpose of evaluation for aircraft radome application. The present review will cover five local natural fibers namely bamboo, banana, kenaf, oil palm and pineapple leaf fiber.

Abstract: In this paper a solid like interface element along with a fatigue constitutive law is used to study the damage behaviour of holed composite laminates under cyclic loading. For this purpose a user element routine and a material routine was developed include the interface element and to handle the formulation of progressive fatigue damages. The developed procedure is used to predict delamination initiation and growth in mixed-mode condition for a typical composite laminate. The obtained results for damage and stresses are compared with the available results in the literature.

Abstract: The residues of tea factory and waste hardboards are generally incinerated without utilizing their heat performances. The first objective of this study was to manufacture cement bonded particleboard using residues of tea factory (Camellia sinenses L.) and waste hardboards. The second objective was to evaluate modulus of rupture (MOR), modulus of elasticity (MOE), internal bonding strength (IB), water absorption (WA) and thickness swelling (TS) properties of the boards produced. The boards were produced at two density levels of 800 and 1200 kg/m3 and at five lignocellulosic mixture ratios of poplar chips/hardboards/tea residues (1/0/0; 1/1/0; 1/0/1; 0/1/0; 0/0/1, based on weigth). All the boards were produced at lignocellulosic material/cement ratio of 1:2.75 on a weight to weight basis. As cement curing accelerators, Al2(SO4)3 and Na2SiO3 were used at ratios of 1.5% and 3.5%, based on cement weight, respectively. The MOR values ranged from 0.8 to 10.99 MPa and MOE values ranged from 254 to 2979 MPa. The mean values of WA and TS after 24 h of water soaking of the cemen bonded particleboards ranged from 28% to 43.5% and 1.3% to 8.08%, respectively.