Jaafar Sahari

Thermal–mechanical model of warm powder compaction process

Abstract A coupled mechanical and thermal analysis of powder during the warm compaction process has been investigated. This paper presents the development of the numerical model to generate a green compact through uniaxial die compaction. The powder is considered to be the rate independent thermo-elastoplastic material. The constitutive laws are derived based on a continuum approach and the governing equations are developed where the thermal strain is taken into account together with elastic and plastic strains. The Elliptical Cap failure criterion is considered to model the yielding of the material during the process. A large displacement based finite element approach is used considering an updated Lagrangian strategy. The non-linear systems of equations are solved employing the staggered-incremental-iterative solution strategy.

Effect of Acid- and Ultraviolet/Ozonolysis-Treated MWCNTs on the Electrical and Mechanical Properties of Epoxy Nanocomposites as Bipolar Plate Applications

Carbon nanotubes (CNTs) have a huge potential as conductive fillers in conductive polymer composites (CPCs), particularly for bipolar plate applications. These composites are prepared using singlefiller and multifiller reinforced multiwalled carbon nanotubes (MWCNTs) that have undergone a chemical functionalization process. The electrical conductivity and mechanical properties of these composites are determined and compared between the different functionalization processes. The results show that UV/O3-treated functionalization is capable of introducing carboxylic functional groups on CNTs. Acid-treated CNT composites give low electrical conductivity, compared with UV/O3-treated and As-produced CNTs. The in- and through-plane electrical conductivities and flexural strength of multifiller EP/G/MWCNTs (As-produced and UV/O3-treated) achieved the US Department of Energy targets. Acid-treated CNT composites affect the electrical conductivity and mechanical properties of the nanocomposites. These data indicate that the nanocomposites developed in this work may be alternative attributers of bipolar plate requirements.

Electrical Properties of Carbon Nanotubes-Based Epoxy Nanocomposites for High Electrical Conductive Plate

Electrical properties of carbon nanotubes-based epoxy nanocomposites for high electrical conductive plate were investigated. Dispersion and incorporation mechanism between two conductive fillers with different sizes (CNTs and Graphite) in the polymer matrix are the key factors in the fabrication of high electrical conductivity plate. Different variation of carbon nanotubes (CNTs) (1~10 wt %) and Graphite (G) (60 ~ 69 wt %) loading concentration were added into the epoxy resin. Dispersion of CNTs and G in epoxy resin were conducted by the internal mixer with a Haake torque rheometer. The mixture of G/CNTs/EP was poured into the steel mold, and G/CNTs/EP nanocomposites had been fabricated through compression molding. The electrical conductivity of nanocomposites in terms of variation of G and CNTs concentration were measured by the four point probe for in a plane electrical conductivity. The results revealed that addition of G/CNTs and increasing curing temperature are effective ways to produce high electrical conductive nanocomposites. The highest electrical conductivity was reached on 104.7 S/cm by addition 7.5 wt% of CNTs. Dispersion quality of G and CNTs in the epoxy matrix was observed on the fractured surface by scanning electron microscopic.

Effect of Carbon Black Addition on the Rheology Properties of Electrically Conductive PP-Graphite Composite

This investigation gives attention on the rheology characteristics of polymer composites based on graphite and carbon black as fillers for further processing using an injection molding machine. In such a high solid loading system, the particles exhibit a very strong tendency toward agglomeration. This rapidly increases the viscosity of the mixture and decreases moldability. The presence of agglomerates in the mixture in particular may result in defect within the microstructure in the final product, even though it is sometime necessary in electrical conductivity. Composite materials in this study are polypropylene (PP) as matrix, and graphite (G) and carbon black (CB) as fillers, with a varied composition according to the percentage weight (% wt) of CB. Twin screw co-rotating extruder was used for mixing materials in order to achieve the best homogeneity of this compound. The measurement results obtained using capillary rheometer equipment showed that the addition of CB to the mixture of PP/G increase the viscosity of the materials, increase the activation energy and generally reduce the fluidity of composite materials. The value of the mixture viscosity increases with increasing the number of CB, reducing the ability of materials to be formed (moldability). Material viscosity, activation energy, fluidity and moldability shows how suitable the compound material to be processed by using injection molding machine.

Simultaneous Optimization for Multiple Responses on the Compression Moulding Parameters of Composite Graphite – Polypropylene Using Taguchi Method

This research concerns the effect of compression molding parameters on conducting polymer composite (CPC) properties such as electrical conductivity and flexural strength. In the present work on CPC, focus is given to graphite (G) as filler and polypropylene (PP) was use as the binder. The Taguchi’s L9 orthogonal array has been used as design of experiment (DOE) while the electrical conductivity and flexural strength were assumed to be quality characteristic (responses). The electrical conductivity was measured using four point probes and flexural strength was measured using three point tests according to ASTM D638. Classical analysis of variance (ANOVA) was used to investigate the significant of each compression molding parameters and finally propose the optimum compression molding parameters. But for several responses, the optimum condition for one response is not very likely to the optimum condition for other response.

Optimization Mixing Parameters on the Electrical Conductivity of Polymer Nanocomposites Based on the Taguchi Method

The objective of this paper is optimization mixing parameters in terms of mixing process of polymer nanocomposites using Taguchi method. Considering the mixing parameters such as rotational speed, mixing temperature and mixing time were performed to reveal the electrical conductivity data. Taguchi method was used by electrical conductivity analyses based on three level factorial designs. Orthogonal arrays of Taguchi, the signal-to-noise (S/N) ratio, and the analysis of variance (ANOVA) were utilized to find the optimal levels and the effect of mixing parameters on electrical conductivity. Confirmation analysis measurements with the optimal levels of mixing parameters were carried out in order to show the optimum electrical conductivity of Taguchi method. The result shows that Taguchi method is effective in solving the quality problem occurred on the mixing parameters of the polymer nanocomposites.

Taguchi Method for the Determination of Optimised Sintering Parameters of Titanium Alloy Foams

Sintering is a key step in the preparation of metal foams. The present work focuses on the sintering effects on the properties of titanium foam prepared using the slurry technique. Sintering affects the density as well as the mechanical properties of the sintered parts. To achieve a high density of the titanium alloy foam, the effects of various parameters including temperature, time profile and composition have to be characterized and optimized. This paper reports the use of the Taguchi method in characterizing and optimizing the sintering process parameters of titanium alloys. The effect of four sintering factors: composition, sintering temperature, heating rate and soaking time to the density has been studied. The titanium slurry was prepared by mixing titanium alloy powder, polyethylene glycol (PEG), methylcellulose and water. Polyurethane (PU) foam was then impregnated into the slurry and dried at room temperature. This was later sintered in a high temperature vacuum furnace. The various factors were assigned to an L9 orthogonal array. From the Analysis of Variance (ANOVA), the sintering temperature was found to give the highest percentage of contribution (34.73) followed by the composition of the titanium alloy powder (26.41) and the heating rate (0.64). The optimum density for the sintered titanium alloy foam was 1.4873±0.918 gcm-1. Confirmatory experiments have produced results that lay within the 90% confidence interval.

Mathematical modelling of thermoplastic natural rubber melt flow in a double feed extrusion system

A mathematical model for investigating the melt flow behaviour of thermoplastic natural rubber (TPNR) in a double feed system of a single-screw reciprocating injection unit using a specially written software is presented. The model enabled the prediction of processing parameters in the feed and main extruders, from which the optimum conditions for processing TPNR were obtained. The introduction of the double feed system also contributed to better mixing in the main extruder.

Effects of Different Particles Sizes of Graphite on the Engineering Properties of Graphites/Polypropylene Composites on Injection Molding Aplication

The injection molding of polymer composite is one of the promising and practical methods in the manufacturing of bipolar plates in mass production. Graphite filler with higher loading concentration is mainly used for this purpose. The particle size and composition (wt. %) of graphite filler material influences on the mechanical properties and electrical conductivity of composite materials. The main challenge is the reduction of flow ability during injection of high load filler material. Flow ability of feedstock material is an important factor in the process of injection molding. This paper presents a development of the rheology approach on the effect of particle size in material flow ability occurs in the injection molding process. Polypropylene (PP) as polymer matrix and graphite as conductive filler mixed together with different size to form feedstock material. Graphite purchase from local Asbury Graphite Mills, Inc, grade 3243 with particle size in average after sieve of ≤40, ≤100, and ≤150 μm. Proportions of polymer matrix and graphite at (PP / G) 25 / 75 wt. %. Mixing of graphite in PP matrix is done using an internal mixer (Thermo Haake) at 50 rpm, temperature at 200 oC. Rheology behaviors of graphite composite were measured using a capillary rheometer type Shimadzu CFT-500D, with a diameter 1 mm and length 10 mm. The fracture surface morphology was examined using scanning electron microscopy (SEM). The electrical conductivity of composite materials was measured by the four point probe. The hardness property measurement of conductive material composite was performed using a Dynamic ultra micro hardness tester using a Vickers typed diamond indenter. The results indicate that the level of viscosity and shear rate on all eligible mixed particle size capable of injectable. The properties of composite materials is the highest in three mix particle size (40/100/150 μm) for the electrical conductivity of 9.13 S.cm-1 and hardness at 34.3 HV. Viscosity of 56 Pa.s at a temperature of 200 oC and shear rates generated in 3231 s-1. The highest electrical conductivity for a single particle size is 49.2 S.cm-1 at 150 μm and hardness of Vickers to 47.2 HV at 100 um. The highest electrical conductivity and hardness due to the packing density and reinforcement different particle size.

Analysis of Energy Absorption on Pultruded Composite Tube under Oblique Loading

The capability of structures to absorb as much amount energy, particularly in automotive structures to reduce the damages due to impact energy during collision attract attention of many reserachers. During the actual collision, the crash box is not only experienced axially crash, but also in oblique crash. In this study, an experiment was carried out to study the crashworthiness parameters and behaviour of pultruded fibre E-glass/polyester pultruded composite tubes under oblique loading. Quasi-static loadings were applied axially and oblique on the pultruded composite to investigate the response of force-displacement during progressive collapses. The pultruded wall thickness of 6 mm tubes were used and four oblique angles of 0˚, 5˚, 10˚ and 15˚ were selected to study their effect on crushing behaviours and collapse modes using compression moulding. All specimens were chamfer 45˚ on top end for purpose to work as a collapse trigger mechanism. The results showed that the energy absorption of the structures increasing with decrease of the loading angle.