Materials Science Forum Vol. 1101

Abstract: Mechanical properties of graphene nanoplatelets (GNPs) reinforced aluminum matrix composite fabricated by the semi-solid stir casting method were investigated. Aluminum alloy A356 is selected based on being widely used in automotive and aircraft industries. Recently, graphene has attracted wide attention from a scientific committee due to its outstanding properties. GNPs are an ideal reinforcement for nanocomposites' productions due to their excellent mechanical properties for strength enhancement. In this study, the effect of different weight fraction of GNPs content (0,0.3,0.5,1.0,and 1.5 wt.%) reinforced with A356 aluminum alloy was analysed. A 45-degree carbide impeller performed the stirring process of 500 rpm for 5 minutes. The samples were then characterised by microscopic examination, Vickers hardness, and tensile test Morphology of the fracture surface of the composite were observed using scanning electron microscopy..The microstructure revealed a homogenous distribution of nanoparticles in the matrix alloy. The composite exhibits improved mechanical properties, maximum tensile strength and hardness of 236MPa and 83 HV are obtained respectively. The composite has shown significant enhancement in the tensile and hardness which is 20% times higher than unreinforced A356 alloy. The hardness increased as the weight fractions of GNP in the A356 matrix has increased. However, when the content of GNPs used above 1.0 wt%, its tensile strength is reduced. Meanwhile, the fracture sample is ductile with a fine dimple structure. These findings may contribute to the process field of semi-solid stir casting, particularly on the GNPs addition to aluminium alloy as their primary material.

Abstract: In the automotive industry, parts are mostly made from aluminium alloy due to its lightweight properties and high corrosion resistance. However, the drawback is that the aluminium alloy is easily worn due to wear and friction and will end up in the scrap yard. In order to salvage the aluminium component, the worn part can be repaired. Currently, wire arc additive manufacturing (WAAM) offers flexible remanufacturing of the worn part. However, the wear behaviour of the additively manufactured part needs to be studied first to improve the wear performance of the material. In this study, the gas metal arc welding (GMAW) or MIG-based WAAM machine was utilised to produce a 3D profile from the available aluminium alloy wire grade ER 5356. The wear test was carried out in accordance with ASTM G-99, using a pin-on disc in both dry and wet sliding conditions. It was found that on dry sliding, the specific wear rates are decreasing from 5.3632 x 10^-11 mm³/Nm to 4.3496 x 10^-11 mm³/Nm and 4.1513 x 10^-11 mm³/Nm as the speed increases from 200 to 400 RPM at the constant 20 N load. Meanwhile, for wet sliding, it has been observed that the specific wear rate increases as similar speed values are used in dry sliding conditions, which are 6.8122 x 10^-12 mm³/Nm, 1.1931 x 10^-11 mm³/Nm and 3.7561 x 10^-11 mm³/Nm with a similar constant 20 N load. Next, the coefficient of friction for dry sliding shows that as the speed decreases. In contrast, for wet sliding, it is observed that the coefficient of friction increases.

Abstract: Aluminum composite panel cores are usually found to be combustible. At the present, most buildings that installs combustible aluminum composite panel’s (ACP) core as part of the wall cladding are suspected to accelerate the spread of fire and act as fuel during burning. The purpose of this study is to develop thermogravimetry analysis test (TGA) using FDS which is widely used by fire researchers to study the fire behavior of polymer composite. A pyrolysis model was being developed using FDS. The pyrolysis model developed has tested 5 type of ACP commercial core which includes 3 different fire retardant (FR) ACP from various manufacturer, A2 ACP and 100% polyethylene ACP. All the samples shall be simulated at a maximum of 800 °C, a heating rate of 10 °C per minute and 20mL per minute nitrogen air flow to ensure that the pyrolysis process take place. In the same time, a TGA test was conducted experimentally to compare the result from the simulation. The result from the model developed and experimental testing was closely identical. Results obtained from fire dynamic simulation indicate the same decomposition point and residue for the mass fraction. Relative error was calculated to compare the result and the highest error obtained was 9.69% for A2 type and the lowest recorded was 2.59% for FR1 type. To summarize, FDS manage to reflect the exact pyrolysis process that occurs on the 5 type of ACP that was being tested experimentally.

Abstract: In the current paper, composites with both thin and thick plies are designed to meet specific criteria and tested under both in plane and out of plan critical loading conditions. The tests adopted are bolted joint, drop-weight impact, compression after impact, Charpy impact, bending, and bending after thermal aging. The results of the proposed design are compared with that of the traditional composites and show higher improvement in most of the load cases by using thin plies inside the lamination process with the traditional ones. The results showed that the two proposed alternatives with thin plies are of higher advantage for the bolted joints problem. On the other hand, the alternative with thin plies distributes to be surrounding each traditional ply is of high advantages for both the impact and the bending problems. The alternative with a core of thin plies at the middle of the laminate is of high advantage for the compression after impact.

Abstract: Glass Fiber Reinforced Polymer (GFRP) Composite are increasing rapidly in Aerospace Industry, Civil and Wind energy sectors, where they can frequently be exposed to different temperature conditions. As the constituent polymer matrix is highly affected by temperature, extreme temperature conditions are critical for GFRP composite structural design. Researchers have recently found nanofillers such as graphene and carbon nanotubes with excellent multifunctional mechanical properties. Graphene Nanoplatelets (GnP) consist of several layers of graphene. GnP is considering an attractive nanofillers as it has improved polymer matrix properties. In this study, the weight percentage of GnP added in GnP-GFRP laminate is 0.25% and 0.5%.GFRP and GnP-GFRP laminates are fabricated by using the hand lay-up method, and the specimens are subjected to a three-point bending test in a thermal chamber with varying the temperature, i.e., 30°C, 50°C, 75°C, and 100°C. This paper investigates the effect of graphene nanoplatelets on the flexural behavior of glass fiber-reinforced polymer composites subjected to different temperatures. Flexural strength and modulus are evaluated, and the appropriate conclusions are determined. GFRP with 0.25% GnP shows higher strength than the neat and 0.5% GnP-GFRP. Here, it has also been shown that flexural strength and modulus decrease significantly with increasing temperature.

Abstract: Rolling Contact Fatigue (RCF) caused crack propagation, flaking, and wear. We focused on the wear in the present study because in recent years it was found that PPS thrust bearings under the RCF in water caused wear. The RCF test was performed under a thrust load of 2300 N in water to investigate the effect of the number of cycles on surface roughness in detail. We obtained the experimental results that R_a and R_z values decrease with the number of cycles. This means the bottom surface is worn down at the early stage of wear fatigue.

Abstract: The rolling contact fatigue of PEEK-alumina ball bearings in non-lubrication was tested under 500 N and 600 N. During the tests, the friction torque was measured. The retainers under both conditions broke during the tests, and rubbed on the upper and bottom races. The friction features were not different between 500 N and 600 N. However, the black colored surfaces on the races and retainer were identified only in the test under 600 N. The wear loss of the bearing tested under 600 N was larger than that under 500 N. From these results, the specimen under 600 N received the heavier wear damages than that under 500 N, and the worn surface was not related to the friction torque. The wear damages of the inner elements and the outer rings in the retainer were larger than those of the races and 9-alumina balls in both specimens.

Abstract: In our previous paper[6], the effects of the retainer wear failure on the friction torque were investigated. In the present paper, to research the failure of the retainers of the PEEK-alumina ball bearings tested under dry rolling contact, the upper and bottom surfaces and the sections of the retainer pockets were observed. The wear damage was found on the surface of the upper and bottom surfaces. On the sections of the pocket, the changes due to wear at the pocket edge was found. On the worn curves of the sections, large scatter of the curvature center positions were numerically calculated in both specimens. The balls moved relatively for the retainer unit to the upper or bottom sides. These results indicate that the wear changed the pocket shape, and the ball could not become to keep the position for the retainer unit. The wear of the pocket caused the failure of the retainer.

Abstract: In recent years, self-healing research has been actively carried out to increase the life and stability of concrete structures. A representative method of concrete self-healing is a method using a bacterial substrate and a capsule. Bacteria-based self-healing is greatly influenced by the external environment, and sleeping structures are more suitable for capsule-based methods. In this study, the mechanical properties of the bonding surface of the photocurable resin are used to grow cracks in the capsule so that the self-healing capsule pops out and the healing liquid inside the capsule can be diffused efficiently. We proceeded with research to form pathways. The study analyzed the concordance rate of the bonding surface of the capsule and the judging position, and analyzed the factors affecting the concordance rate. As a result, by adjusting the number of bonding surfaces and the degree of air bubble removal, the rate of coincidence between the bonding surfaces and the fracture position was increased from 15.48% to 63.18% by a factor of 4.08.