Advanced Materials Research Vols. 264-265

Abstract: The effects of isothermal temperature on the microstructure evolution of semisolid A6070 alloy produced by strain-induced melt activation process were investigated. The results showed that high semisolid isothermal temperature could make the semisolid particles more globular, but the size of the particles would grow larger and accelerate the spherical evolution of the solid particles. It was found that the optimal process temperature should be 620 °C and 10 min of isothermal temperature based on the conditions of this paper.

Abstract: Laser gas assisted nitriding and TiN coating of Ti-6Al-4V alloy is carried out. The microstructures developed in the laser irradiated region are examined using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). The laser nitrided surfaces are coated with TiN using the PVD facility to enhance the tribological properties. The heating model incorporating the lump parameter analysis is used to predict the melt layer thickness during the laser treatment process. It is found that laser nitrided surfaces posses δ-TiN+ε-TiN phases and TiN coating of laser nitrided surfaces improves the microhardness at the surface.

Abstract: The effects of weld nugget size, base metal strength, mode of loading and pre-strain of base metal on the load bearing capacity of spot-welds have been investigated using two varieties of interstitial free steel sheets. The effect of bake hardening treatment after spot-welding of prestrained sheets has also been examined using an ultra low carbon bake hardening grade steel. The major results infer that: (i) the load bearing capacity of spot-welds increases with increasing nugget size and base metal strength, (ii) the load bearing capacity of spot-welds increases with increasing pre-strain of base metal, (iii) the remnant dislocation density around the spot-weld increases with increasing pre-strain, (iv) the strength of spot-welds on pre-strained sheets does not alter significantly after the baking treatment, but baking treatment increases the strength of pre-strained base metals, and (v) the location of failure is commonly at the interface of HAZ/base metal for tensile-shear specimens and at the HAZ for cross-tension specimens.

Abstract: In an injection moulded part, warpage is the distortion caused by non-uniform shrinkage within the plastic part. When looking critically at the causes of warpage, it is found that several key parameters of the moulding process have some effect on the warpage. However, the two major categories that contribute to warpage include the part design and the mould design. In mould design, the gate location, runner/gate system and cooling system design are the major factors affecting not only the warpage and part quality but also the injection moulding cycle time. This paper presents an investigation of using different cooling system configuration on warpage and shrinkage of an industrial plastic part with the aim of determining which cooling configuration will provide minimum warpage and cycle time. As conventional injection mould cooling design is based on straight drilling, it limits the geometric complexity of the cooling design, especially curved shape cooling channels. Nowadays, new technology of advanced rapid tooling based on solid freeform fabrications can be been used to provide conformal cooling channels in injection moulds. In this paper, several type of cooling channels are analysed to compare the performance in terms of warpage and shrinkage and to determine which configuration is suitable for minimizing warpage. Autodesk Moldflow Insight (AMI) simulation software is applied to examine the results of the cooling performances and warpage analysis.

Abstract: The elongation and the strength of rolled steel are severely affected by cracks in production. Reduction of cracks is important for the improvement of slab quality. In this paper, a series of experiments on internal crack healing in slab during rolling was carried out on the experimental rolling mill. The crack shape and the fracture morphology of the crack healing zones were observed by using the scanning electron microscope, and the shear strength of crack healing zone was tested through the tensile testing machine. With increase of the reduction ratio during rolling, the crack healing degree increases.

Abstract: Natural fibers are widely used as “reinforcing agents” in polymer composites. The aim of the current study is to evaluate the effect of span length on the tensile properties of several natural fibers (Vietnamese coir and bamboo and Bangladeshi jute). Tensile testing of jute, bamboo and coir fibers was carried out by varying span length (5, 10, 15, 25 and 35 mm). The Young’s modulus and strain to failure were corrected by using newly developed analytical equations in order to correlate the Young’s modulus and strain to failure of natural fibers. Scanning electron microscopy of the fibers was also carried out. It is clearly observed that the Young’s modulus increased with an increase in span length. Whereas tensile strength and strain to failure decreased with an increase in the span length of single fibers. The correction method resulted in a high Young’s modulus for larger span, while strain to failure found was lower compared to smaller span. This is because larger span length helps to minimize the machine displacement compared to smaller ones. Among all fibers, the Young’s modulus of bamboo fiber was highest, followed by jute and coir respectively. Jute fiber had smoother surface and compact structure compared to other two fibers.

Abstract: Charpy impact tests were conducted on carbon reinforced epoxy composites fabricated by hand lay-up method using 0.47, 0.56 and 0.66 carbon fiber volume fractions; tests were conducted at temperatures between -60oC to 60oC. The impact strength was found, in general, to increase when the samples were fractured at temperatures above 0oC and the impact strength decreased with the increase of fiber content. The impact energy absorption was highest of 270 KJm-2 with 47 vol% fiber when fractured at +60oC and it reduced to 130 KJm-2 at -60oC. With decreasing the fracture temperature and increasing the fiber content the impact strength reduced significantly. The reduction of impact energy was from 235 KJm-2 to 107 KJm-2 for 56 vol% fiber and from 196 KJm-2 to 90 KJm-2 for 66 vol% fiber when fractured at +60oC and -60oC, respectively. Failure occurred mostly by fiber delamination; fiber splitting and matrix cracking were also present. Delamination was more in specimens tested at -60oC while fiber splitting and matrix cracking were more when fractured at +60oC.

Abstract: Hybrid jute-carbon/ epoxy composites, fabricated by hand lay-up method with fiber volume fractions of 0.47, 0.58 and 0.68 were used to investigate water absorption behavior as a function of immersion time and fiber content. The effect of moisture content on impact strength and failure modes was also studied. Results show that the moisture absorption increased with increasing the immersion time in water and it was more with higher fiber fraction specimens. Maximum moisture contents of 0.45%, 0.52% and 0.61% were recorded for the specimens containing fiber volume fractions of 0.47, 0.58 and 0.68, respectively. The impact strength reduced with increasing moisture absorption in all specimens containing different fiber fractions. Composites with higher fiber content gave reduced impact strength under all test conditions. Composites of different fiber fractions and of highest moisture content produced impact strengths about 20 to 28% less than those strengths obtained without water immersion. The 47 vol% fiber specimen was least affected by water immersion and impact strength reduction was only 17% after immersion till saturation. Failure occurred by mainly by delamination and it was evident in all fractured specimens. Results of the effect of impact energy on moisture content have been evaluated using ANOVA ANALYSIS and the results gave errors of 1%, 0.6 % and 0.8 % for 0.47, 0.58 and 0.68 fiber volume fraction specimens, respectively.

Abstract: Polyaniline (PAni) film was successfully electrodeposited on the surface of steel substrates in oxalic acid electrolyte by cyclic voltammetry at different potential sweep rates (dE/dt) (10, 20 and 30 mVs-1) and different pH values (1.55, 2.55 and 3.55). The coated steel with PAni was characterized by Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The corrosion resistance of the electrodeposited layers was evaluated by potentiodynamic polarization in 0.1 M NaCl aqueous solution. The results showed that with increasing pH and sweep rate the amount of corrosion rate decreased and increased respectively. Moreover, the correlation between variation of anodic charge (Qa) with pH and sweep rate has been evaluated. The variation of anodic charge confirmed that the growing rate of polymer decreased with increasing sweep rate and pH. The result of potentiodynamic polarization showed that the coated steel with synthesized PAni in pH 3.5 and sweep rate 0.01Vs-1 had better protective properties against corrosion.

Abstract: In the present study, lignocellulosic-epoxy composites were prepared from Kenaf bast fiber at different loadings using resin infusion method. Montmorillonite (MMT) was used as a filler which would be mixed in the epoxy resin before the mixture (resin, hardener and MMT) was infused to the Kenaf fiber mat. The effect of modification on MMT was also studied in this work. MMT was modified using grafting process, which the oxygen in MMT were grafted with isocyanates group from Hexamethylene Diisocyanate (HMDI). The mechanical properties of the composites prepared were improved as Kenaf fiber loadings increased. This indicated that the reinforcement effect by additional of Kenaf fiber was evident. The mechanical properties of the composite can be further enhanced by additional of MMT or HMDI-MMT.