Key Engineering Materials Vols. 471-472

Abstract: In this paper, the experimental results on the structural behaviors of the pultruded fiber reinforced plastic (PFRP) cantilevered channel beams under tip point load are presented. The dimensions of the beam specimens are 76 22 6, 102 29 6 and 152 43 10 mm. The span-to-depth ratios of the specimens are in the range of 10 to 46. A total of 36 specimens were tested to investigate the effect of unbraced length of the beam on the behavior of lateral-torsional buckling and buckling load. Then, the obtained buckling loads were compared to the critical buckling loads calculated by using the modified classical beam theory. From the tests, it was found that the beams have linear elastic responses up to 90-95% of their buckling loads. The mode of failure of the specimens is in the form of lateral-torsional buckling. The modified Timoshenko and Gere’s equation unsatisfactorily predicts the critical buckling loads of the beams. Finally, by using a curve fitting, a modification factor was proposed, and the obtained test results and those calculated by the proposed modified equation are in good agreement.

Abstract: Polyurethane (PU)/Clay nanocomposite rigid foams were synthesized with modified layered silicate clay (organoclays, Cloisite 30B). PU foams were prepared by a batch reaction injection molding process. Organoclay was dispersed first in the isocyanate component using an ultrasonic homogenizer and then mixed with polyol and physical blowing agent mixture to produce nanocomposite PU foams. To study the reaction possibility between cloisite 30B and isocyanate as well as the effect of sonication on the reaction, Fourier transfer infrared (FTIR) analysis was conducted. The dispersion of organoclay in the rigid PU/clay nanocomposite foams was analyzed by wide angle X-ray diffraction (XRD). The microstructure of the foams was studied by an optical microscope and image analysis software. It was concluded that with increasing of nanoclay content the cell size is decreased and the cell size distribution is narrowed. The mechanical properties of pure and nanocomposite foams were examined by compression test. The data obtained from the compressive stress-strain curves reveals that the strength and modulus of polyurethane foam increase by addition of organoclay up to 1wt% and then decrease. Thermal conductivity coefficient (k-factor) of rigid PU nanocomposite and neat foams was measured by a simple transient method. The thermal conductivity results demonstrated that the polyurethane foam k-factor continuously decrease by addition of organoclay. It can be attributed to the reduced cell size as well as narrow cell size distribution in of nanocomposite foams.

Abstract: This paper presents the experimental and numerical studies on the flexural strengthened steel I-beams by using Carbon Fiber Reinforced Polymer (CFRP) strips. Nowadays, strengthening existing steel structures by using CFRP has been widely interested. One of the common usages of CFRP to strengthen steel beams is the flexural upgrading. In this case, CFRP strips are pasted on the tensile flange to improve flexural behaviors. The problems that are frequently reported for CFRP strengthened steel beams are the debonding, delaminating (peeling), and splitting. Identification these failure modes are essential to provide an appropriate level of safety for strengthened steel beams. To investigate the CFRP failure modes, four strengthened steel I-beams were chosen. The CFRP plates with different thicknesses in single and double (splice) layers were used. Both experimental test (four-points bending test) and numerical simulation (full 3D simulation with ANSYS) were employed. The incremental loading was applied until failure while deformations in the critical regions were recorded. The results reveal that for the CFRP flexural strengthened steel beams the following failure modes occurred: (a) debonding at the CFRP plate tips, (b) debonding below point loads, (c) delaminating at the ends of CFRP plate, and (d) splitting below point loads. The sequence of failure modes depended on the specifications of CFRP plate. Some recommendations are provided to overcome/retard these failures.

Abstract: This work focuses on synthesis of MWCNT-alumina hybrid compound via methane decomposition process using nickel catalyst. The catalysts prepared through in situ process by using nickel salt and aluminium powder which then calcined at 900oC followed by methane decomposition process to grow MWCNT on alumina surface. The Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM) images confirmed the formation of MWCNT with homogenous dispersion on alumina particles.

Abstract: Computer simulation is widely used and conventional in manufacturing as a way to improve the manufactured goods quality as at same time plummeting invention costs, development time and scrap. In this study, three-dimensional model have been developed to simulate the filling and the solidification pattern in an aluminum casting with “AnyCasting” software. Using this software, solidification of aluminium 11.8% Si alloy in sand and metal mould was simulated and the results were compared with the experimental results. The solidification time and temperature was experimentally determined from thermocouple located at diverse distances. A data logger is used in experiment to gain the temperature division contour during the process of solidification of the aluminium 11.8% Si alloy. Experiments were set up to legalize the simulation results and it is confirm that the results from the two mould methods be in good agreement and the solidification of cast aluminium alloy using copper mould was much faster compared to the one cast sand mould. From this work it is concluded that simulation using AnyCasting software can be use to initially calculate. The simulation shows result that matches with the experimental data qualitatively and therefore the validation procedure is successful.

Abstract: In spite of a vast background on cohesive constitutive law and its use for various analyses such as delamination in composite laminates, some numerical aspects of that have been less explored and reported in the literature. The aim of this paper is to study the phenomenon of spurious stress oscillation and also dominant process zone (where damage has its most significant evolution) in delamination modeling. For this purpose, distribution of normal stress and damage parameter of different DCB specimen are analyzed. Distribution of stress around the process zone indicates spurious oscillation just ahead of the delamination tip where damage parameter is zero and no effect of this phenomenon is seen on results of applied load versus opening displacement. Additionally, it is shown that larger values of penalty stiffness lead in smaller length of dominant process zone and very large values of penalty stiffness pushes the distribution of damage parameter to become step-like function. Authors believe that this effect is in fact the main reason of un-converged solution of models with too large penalty values.

Abstract: Past and on-going research works on adhesive bonding in composite and sandwich were reviewed. Discussion was emphasized on critical failure mechanisms (e.g. mechanism of peel fracture) to enhance the performance of the bonding. This paper also focused on the application of good adhesive bonding in the application of sandwich structures. Debonding between skin and core is one of the failure mechanisms that should be given more attention in fabrication of sandwich structures. Incorporating fillet in composite bonding is one of the alternative ways to reduce the stress concentration at the edges of overlap length and to produce high peel strength for bonding. Basic understanding of the designs, theories and manufacturing of adhesive bonding were also presented. Several important parameters in the design such as the strain energy release rate (SERR) and formation of fillet also discussed. The analysis of SERR using virtual crack closure technique (VCCT) has also been highlighted to achieve high strength of adhesive bonding, providing the key element for optimization of the delamination resistance in maximizing energy absorption during fracture. Significant challenges or limitations in improving and optimizing the design were also highlighted.

Abstract: In this paper, free and forced vibrations of symmetric laminated composite plates are studied analytically by using a perturbation method where the analytical results for transverse displacement are compared with the numerical results. The external force is taken to be harmonic in time and having uniform amplitude.

Abstract: In this article, halloysite nanotubes (HNTs) and precipitated silica were replaced by recycled polyethylene terephthalate powder (R-PET) in natural rubber composites. Five different compositions of NR/HNTs/R-PET and NR/Silica/R-PET composites [i.e. 100/20/0, 100/15/5, 100/10/10, 100/5/15, and 100/0/20 parts per hundred rubber (phr)] were prepared on a two-roll-mill. Comparison of the curing behavior, tensile properties, and morphological characteristics of natural rubber composites was studied. The results indicated that the replacement of HNTs and silica by R-PET decreased the tensile strength, tensile modulus, and elongation at break of composites, but NR/Silica/R-PET composites showed the lower trend than that NR/HNTs/R-PET did. The negative effect of these properties could be explained by the decrement of crosslink density, R-PET is unable to be transferred the stress due to the weal rubber-fillers interactions, and the reducing of ductility of rubber matrix. The curing results revealed that, with replacement of HNTs and Silica by R-PET, the scorch time (ts2) and cure time (tc90) were decreased. Scanning electron microscopy investigation of tensile fracture surfaces confirmed that co-incorporation of NR/HNTs/R-PET would improve the dispersion of R-PET and enhanced the interactions between fillers and NR matrix rather than NR/Silica/R-PET composites.

Abstract: In this paper, the influence of recycled polyethylene terephthalate powder (R-PET) on fatigue life, thermal properties and micro-fracture surfaces of halloysite nanotubes (HNTs) and silica filled natural rubber composites have been studied. The total amount of hybrid filler in each formulation was kept constant at 20 parts per hundred rubber (phr). The final properties of HNTs/R-PET and Silica/R-PET compounds are considered separately and comparatively. Results indicated that the fatigue life of the natural rubber composites decreased with the replacement of these two fillers by R-PET powder. This observation might be due to the R-PET itself, which reduces the interfacial adhesion and wettability between rubber matrix and fillers. By replacing of HNTs and silica with R-PET powder, the thermal degradation of natural rubber composites was shifted to a lower temperature and the char residues was decreased, in which HNTs/R-PET composites expressed the higher temperature and char residues than silica/R-PET composites. This findings may be due to the HNTs/R-PET has less volatile matter than silica/R-PET that might enhance the degradation temperature of the natural rubber composites. SEM micrographs also exhibited weak interfacial adhesion when these two fillers were replaced with R-PET powder in NR composites.