Key Engineering Materials Vol. 856

Abstract: Barkhausen noise (BHN) measurement is one of electromagnetic testing methods that is suitable for ferromagnetic materials. It has a sensitivity to different material properties such as microstructure, composition, residue stress, hardness, etc. which can also be used to determine the hardness case depth of a hardened layer. The measurement is intriguing because of its time and cost-effectiveness. The aim of this work was to study and select a suitable method to evaluate and predict the hardness case depth of induction hardened S50C steel based on Barkhausen noise measurement. Signal processing of BHN signal was performed and extracted features were validated with the actual hardness case depth according to the destructive method of Vickers hardness and metallography in order to achieve the most accurate hardness case depth evaluation model. The results showed that the hardness case depth prediction model could be used to indicate the hardness case depth of induction hardened steel significantly at the correlation coefficient (R) of 0.97 and root mean squares error of estimation (RMSEE) of 3.56%.

Abstract: Poly(lactic acid) (PLA) is a potential biodegradable polymer to replace petroleum-based plastic, however, its main drawback is brittleness because of slow crystallization rate. To overcome this limitation, compounding with some additives is the most chosen choice due to easy and effective preparation. In this study, an epoxidized soybean oil (ESO) and a microcrystalline cellulose (MCC) were applied as a plasticizer and a nucleating agent, respectively. The PLA was compounded with ESO and MCC by using a twin-screw extruder. The product sheets were prepared by using a chill-roll cast film extruder. Change of thermal property after adding ESO and MCC was investigated by a differential scanning calorimeter. Mechanical property of the prepared sheet was carried out by using a universal testing machine in a tensile mode. Microstructure of the sheets was also studied by wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) techniques. The results showed that ESO assisted plasticization while the MCC induced crystallization of PLA. Also, ESO and MCC eased flowability and alignment of PLA microstructure in machine direction.

Abstract: This research is firstly presented the thermal resistance of a ceramic backing made from metakaolin-based geopolymer for stainless steel welding. The general problems such as lack of fusion, hydrogen inclusion, porosity and corrosions of stainless steel welded specimens were found because, largely, stainless steel presents an affinity to gases as oxidation. Therefore, during welding, if these gases do not escape from the weld pool before solidification of weld metal, it results in porosities or hydrogen inclusions. In this case, it can be solved by properly using inert gas backing. The welder usually uses the steel backing plate with a gas release hole to support weld root and gas transmission for completed weld penetration and superior weld quality. Since the geopolymer shows a good property of thermal resistance, researchers are interested in using the ceramic backing made from geopolymer instead of the commercial ceramic backing. The ceramic backings from the geopolymer were designed merely in 3 types as follows: Narrow curved groove without gas release hole, narrow curved groove with gas release holes and wide curved groove with gas release holes. Consequently, two pieces of stainless steel were welded by gas tungsten arc welding and then the weld quality such as defects, porosity and root penetration of welded specimens was inspected. Moreover, the surface failure of ceramic backing after the welding process was also considered. The results revealed that ceramic backing from a geopolymer with wide curved groove and gas release holes gave completed penetration at the root when inspecting with non-destructive testing such as visual test, penetration test, and radiography test. It was concluded that the geopolymer could be used as ceramic backing in stainless steel welding by gas tungsten arc welding. Moreover, it could be used as backing for aluminum and steel welding as well.

Abstract: 4D-printing has been emerged and developed from 3D-printing. The 4D-printing technology creates sophisticated structures in which can change over time to perform programmed functions. In this research, simply programmable 4D-printed responsive structures were designed, prepared and studied. The designed structures are influentially inspired by creatures and the customized 3D-printer was used. Magnetic crosslinked PVA was prepared and used as programmable 4D-printed responsive samples. Effect of PVA concentration on gel fraction was elucidated for the prepared crosslinked PVA. Fe₃O₄ particles were incorporated to the crosslinked polymer before manufacturing. Effect of speed of platform and effect of rate of syringe pump on the 4D-printed magnetic crosslinked PVA structure were investigated. Furthermore, the responsive property of the magnetic crosslinked PVA was determined.

Abstract: Vulcanization or curing process is a very important process in producing useful rubber products. The quality, performance as well as manufacturing cost of a rubber product are largely affected by the curing process. The curing process takes place when heat is transferred to the rubber compounds inside a heated mould. Curing of a thick article, such as a solid tire, often occurs under transient non-isothermal conditions. The temperature distribution in the rubber significantly affects the cure level distribution throughout the part, especially in a large rubber component. Therefore the ability to predict the distribution of cure level in a rubber part during curing is of great importance for improving the process efficiency and the quality of the final product. In this work, simulations of the curing process of a solid tire, consisting of three layers of different rubber compounds, were performed and the cure level distribution results were evaluated. The simulations are carried out using the commercial finite element software ABAQUS with the cure kinetics model for rubber implemented through the user subroutine UMATHT. The effects of the mold temperature and initial temperature of the solid tire on the cure level distribution and cure time were investigated.

Abstract: This research has focused on the effect of modified cellulose and clay on the thermal and mechanical properties of PLA bio-nanocomposite. Cellulose was chemically modified with silane coupling agent in order to enhance compatiblization with PLA. Successful modification was confirmed by Fourier Transform Infrared Spectroscopy and EDX-SEM. PLA was compounded with various amounts and ratios of the modified cellulose and clay by a twin-screw extruder. Thermal properties of the bio-nanocomposites were characterized by Thermogravimetric Analysis and Differential Scanning Calorimetry. Glass transition temperature of the bio-nanocomposite slightly decreased whereas melting temperature remained constant when the amount of both fillers was increased. In addition, crystallization behaviour of PLA has been influenced by the type and amount of the fillers. Clay showed a greater effect on the crystallization of PLA than the modified cellulose and unmodified one, respectively. The flexural modulus of the composite containing equal amount between clay and cellulose was increased with an increasing in fillers contents. But the flexural and impact strength of composite were gradually decreased with an increase in fillers contents. Variation of clay and cellulose ratio resulted in the change of mechanical properties. The composite containing higher ratio between clay:cellulose or cellulose:clay showed a better mechnical properties comparing to the ratio of clay:cellulose equal to 1:1.

Abstract: Many researches concentrated on development of antimicrobial membranes for many applications such as air or water filtration. Disk diffusion was well-known conventional method for antimicrobial assay. However, this method is preferable to hydrophilic materials, where inhibition zone was easily observed. For hydrophobic materials, negative test was always shown, except increase in antimicrobial loading. In this study, glucose fermentation was introduced as a new method for antimicrobial assay. The survived and viable bacteria either at the surface or attached inside the membranes could ferment glucose resulting in acid production and changing color of indicator in the glucose solution from pale orange to pink. FU8M and FA8M nanofiber membrane, loading with AgNO₃ and Benzalkonium chloride (0.3-1.0%) were used as hydrophobic and hydrophilic membrane, respectively. The water absorption of these membranes took 2 h and 2 min, respectively, showing that the latter membrane improved its wettability. It is found that FU8M membrane showed no inhibition zone when the antimicrobial loading less than 1%, whereas the FA8M membrane showed inhibition zone from 8.6-14 mm, depending on antimicrobial loading. However, when glucose fermentation method was used, membranes showed the positive test after 9 hours of incubation at the antimicrobial concentration of 0.5%. Hence, this new method can be used as antimicrobial testing for membrane with simple and cost effective.

Abstract: The amount of plastic wastes and tire wastes were continuously increasing. The old tires and polymer which was low-density polyethylene (LDPE) were used to create polymer-modified pavement to get rid of plastic wastes and tire wastes replacing asphalt road. LDPE of 15 wt% was the main matrix material of the modified road pavement instead of asphalt; moreover, ground tire rubber (GTR) at various concentration of 3, 5, 7 and 10 phr was used as the additive mixed with mineral aggregates of 85 wt%. In this study, the Marshall method was used to prepare the sample. The properties of Marshall stability, Marshall flow, bulk specific gravity and voids of the polymer-modified pavement were studied for comparing to commercial asphalts. The results showed that the strength of the modified pavement increased which was higher than commercial asphalts although void concentration increased. The bulk specific gravity decreased as increasing amount of GTR. The percentage of water absorption increased as addition of GTR content. This study might be benefits in reduction of waste and valuable resources as bitumen, and also recovery an environment

Abstract: This research investigated the use of water treatment sludge (WTS) as an geopolymerized material. WTS with an initial SiO₂:Al₂O₃ ratio of 3.25 was thermally treated at temperatures of 105, 500, 650 and 850 °C for 1 h. The powdered WTS after calcinations was reacted with alkaline-silicate solution (ASS) with different proportion between NaOH and Na₂SiO₃ solutions. The effect of calcining temperatures on the strength’s development of WTS geopolymer was determined. Without thermal treatment of the WTS, no strength was gained during the early stages. Samples prepared from WTR calcined at 850 °C exhibited the highest strength at all curing times. When WTS geopolymer was prepared as solid plate, the test in noise reduction was explored at various sound frequencies between 1000-10000 Hz. The average noise reduction efficiency of WTS geopolymer was 63.5% closed to the case of commercial light-weight brick at the same paste’s thickness.

Abstract: An improvement of flexural strength of cement stabilized soils using geogrid designated as compacted cement-geogrid-sand (CCGS) is investigated in this research. The studied material performance of the CCGS includes postpeak behavior, toughness, and equivalent flexural strength ratio. The geogrid inclusion significantly improves the postpeak flexural behavior, which is a requirement for bound pavement materials. The first peak flexural strength f₁ and stiffness of both compacted-cement-sand (CCS) and CCGS are essentially the same for the same cement content. The tested soils were obtained from Ayutthaya province, Thailand, and is commonly used as a construction material for backfill and pavement applications. The backfill soils were used sand. In this study, Type I Portland cement was used as a cementing agent and geogrid two type were used as a reinforcement material. Properties of the cement and the geogrid, which were obtained from the manufacturers. The specimens were subjected to a flexural performance test according to ASTM C1609/C1609M-10 (2010). The results showed that in the flexural performance of the CCGS includeing postpeak behavior, toughness, and equivalent flexural strength ratio depends on the type and shape of apertures of the geogrid. It was found that the triaxial geogrid with shape of triangular apertures was more effective in reinforcing and provided the high equivalent flexural strength over uniaxial geogrid.