Materials Science Forum Vol. 1091

Abstract: In this work, the improvement of SiC power MOSFET performance achieved using high-κ gate-dielectrics instead of the standard SiO2 is investigated by means of advanced gate-impedance characterization. The benefit of using high-κ gate-dielectrics with high dielectric constant is demonstrated by comparing SiC MOSFETs with pure high-κ, a stack of SiO2/high-κ, as well as pure SiO2. Namely, the fabricated high-κ SiC MOSFETs show a superior performance to commercial SiC MOSFETs with SiO2/SiC interface with respect to channel resistance and interface quality. The proposed characterization approach is non-destructive and applicable to packaged power devices.

Abstract: We show the superior threshold voltage V_th and on resistance R_on stability of a SiC DMOStechnology at bipolar gate-drive operation. Therefore, the defect parameters of a two-state non-radiativemulti-phonon model to capture the charge trapping kinetics of oxide and interface defects is calibratedwithin our simulation framework Comphy by data extracted from measure-stress-measure (MSM) se-quences. An extrapolation of the device degradation at operating conditions renders bias temperatureinstabilities (BTI) a minor threat to on-state loss increase.

Abstract: The shear strength of rocks was influenced by internal and external factors whose presence can reduce the shear strength of rocks. Therefore, it was important to analyze the shear strength of rock that has joints in carrying out mining planning in excavations. This study was focused on determining the shear stress of rock samples resulting from direct shear tests by considering the joint roughness coefficient (JRC) so the relationship between the two can be determined and validated using numerical modeling. In this case the author uses the finite element method using Phase2 software. Determination of surface roughness using the Z₂ coefficient, the sample was grouped into several sets based on the roughness value. Other tests carried out are physical properties test, compressive strength test, and Brazilian test, the results of which were used as rock characteristics in modeling. Numerical modeling requires rock characteristics in the form of compressive strength, Young's modulus, Poisson's ratio, tensile strength, internal friction angle, cohesion, normal joint stiffness, and joint shear stiffness. Laboratory test results analyzed using linear regression showed that at peak conditions, JRC’s influences on shear stress was very strong at each loading (R² = 0.93 to 0.97). For the residual condition, a very strong influence occurs only at the highest loading of 640 N (R² = 0.91). The results of the comparison of the weak plane shear test with the modeling results showed the error percentage of 1.4% - 41.7%, this error percentage value was estimated because the analysis used was 2D-based numerical modeling so that the interpretation results only included the cross section of each sample 3D-based laboratory test covering the entire surface of the shear plane.

Abstract: Failure due to shear deficiency in reinforced concrete (RC) structures, particularly RC beams, is one of the most common problems encountered in RC structures. As a result, the effectiveness of using externally anchored geopolymer fiber mortar panels were investigated in the scope of this experimental study. The variable of the test programmed herein was the change in anchor bolt spacing. Two strengthened beams with 200 mm and 300 mm anchor bolt spacings, respectively, were tested. In addition, one un-strengthened beam was prepared as the reference beam to compared the load-deflection behavior, shear capacity, and failure mode of the strengthened beams. All the beams were tested under monotonic loading until reached the failure load. The experimental results of all strengthening beams showed an increase in the shear strength of the RC beams by 34.9% (spacing 200 mm) and 22.8% (spacing of 300 mm) compared to the reference beam. In addition to increasing shear capacity, the failure mode of the strengthened beam with 200 mm anchors spacing changed from brittle shear failure to ductile flexural failure with increased stiffness. This indicated that geopolymer fiber mortar panel is considered a promising technique that could be utilized to repair and rehabilitate shear deficient RC beams.

Abstract: The objectives of this study are to analyze the pattern crack and failure mode of the GFRP concrete beam by using GFRP sheet as shear reinforcement (GFB) compared with the two types of the conventional reinforced concrete beam (CB and GB). One of the conventional reinforced concrete beams is reinforced with the steel bar (CB) and the other is the GFRP bar (GB) as longitudinal reinforcement. The nine beams were cast from one concrete batch with dimensions of 150 mm width, 250 mm depth and 3300 mm length. This study focuses on a simply-supported beam using a roller and pinned supports at the end of the beam. Control beam (CB) that using steel reinforcement shows three phases of deformation based on the deflection load curve, ie before crack, after crack, and after yield, while GB and GFB beams that use GFRP bar reinforcement only show two phases of linear deformation namely the deformation phase before cracking and after cracking. From the crack pattern, CB beams experience the flexural cracks which starting from the mid-span on the tensile side of the constant moment region and propagated to the compression region along with the increase in load. All GB beams show the crack starts from the mid-span and then propagates towards the support. Whereas GFB beam show the flexural cracks that occur in the constant moment region and in the shear span, also diagonal cracks that divide the GFRP sheet occurred. From the failure mode, CB experienced flexural failure, while GB experienced compression failure and shear failure in all GFB beams.

Abstract: In certain scenario, seawater maybe the only mixing and curing water available. Normally, concrete mixing requires freshwater, a resource which is expected to vastly deplete as a result of global water scarcity. Seawater which covers more than 70 percent of earth surface has potential to replace the freshwater in concrete. Hence, it is necessary to optimize conditions for its application in concrete, because freshwater reserves are either limited or its transport is costly. Further, the effect of various replacement ratios of fly ash needs further studies to determine applicability on concrete with seawater mixing in particular. Thus, this study aims to examine by which seawater can be employed as mixing water for making concrete, especially for plain concrete. The main objective of this study is to investigate the effect of seawater as mixing and fly ash as supplementary binder at 10%, 20% and 30% for Portland Composite Cement replacement on compressive strength, respectively. The water-to-binder ratio was varied at 40%, 50% and 60%. The specimens were cured (continuous immersion) in freshwater and seawater for 91-days. The results indicated that seawater can be used as mixing and curing water. Compressive strength of concrete increase when using seawater as mixing water and freshwater as curing water especially for w/b of 40%. Also, significant strength development up to 91-days was shown by fly ash concrete when using seawater as curing water and freshwater as mixing water . Effectiveness of seawater curing on strength development of fly ash concrete with w/b of 40% is larger in concrete with freshwater mixing than seawater mixing. The results obtained in this study provide an information in development for applicability seawater in concrete.

Abstract: The use of industrial waste materials as a substitute for cement in the manufacture of mortar is an alternative approach to reduce carbon dioxide emissions in building construction. In this study, processed waste tea ash (PWTA) obtained from the extraction tea plant was used to partially replace 0-40% cement in the manufacture of mortar. The effects of PWTA on the basic engineering properties of mortar are evaluated and compared to mortar without PWTA. Test results showed that workability and density of mortar decreased with increases in the PWTA content. Furthermore, no decline in compressive strength of concrete was observed up to 20% replacement of cement with PWTA at 7, 28 and 90 days and beyond that, the compressive strength decreased. Results obtained from this study indicate that PWTA can be used as partial replacement of cement up to 20% with comparable strength with normal mortar. This approach helps to minimize the usage of cement in mortar production and can reduce the negative impact of PWTA on the environment.

Abstract: This study aims to determine the relationship between variations in the depth of bamboo twigs with the sound absorption coefficient. The sample consisted of 12 bamboo twigs made up of three types of depth variations. Measurement of sound absorption of bamboo twigs using two microphone impedance tubes and B & K Lab shop software version 16. Standardization ISO 10534-2:1998 [1] was used to test parameters between 100 and 1600 Hz. This type of research is a comparative quantitative approach, data processing using Pulse Lab shop version 16 and visualized into a curve graph using Microsoft Excel. The results showed that the bamboo twig material with a depth of 50 mm was better than 25 mm with an absorption coefficient (α) of 0,68 at a frequency of 1600 Hz. While the material with a thickness of 75 mm only absorbs at a frequency of 1100 Hz with a maximum absorption coefficient of 0,57. According to ISO 11654 [2], it shows that bamboo twigs have the potential to be used as sound-absorbing materials. The sound absorption coefficient value of bamboo twigs rises from low to high frequency with increasing twig depth.

Abstract: Bamboo twigs are branches of the bamboo plant. This study intends to confirm the potential of bamboo twigs as an alternative sound absorbing material in acoustic applications. The pieces of bamboo twigs are arranged according to their edges: hollow edges (RR) and node edges (BB), creating five upper-bottom surface combination patterns. The acoustical characteristics were examined through absorption coefficient (α) and standard deviation measurements. The result shows the best surfaces combination is the RB-RR specimen. RB-RR specimen is a combination of hollow and node edges on the upper surface and hollow edges on the bottom surface. Although narrower in frequency ranges, the specimen performs approximately equivalent to the well-known Glass wool in terms of maximum absorption coefficients (α). Refers to the measurement results, the abundant bamboo twigs can be qualified as a potential alternative for sound absorption material in the future.

Abstract: In the construction industry, wood is frequently used as a form material in large quantities. Wood in form is only used three to six times before being discarded, resulting in non-recyclable wood waste. This can be avoided by substituting wood as a formwork material. One of the efforts to reduce the number of wood forms is to use a permanent formwork. This permanent form has a number of benefits, including a low cost, environmental friendliness, the ability to increase the strength of building elements, and efficiency. Therefore, it is of interest to investigate the effects of Permanent Formwork on the strength of building elements. Permanent Formwork, geopolymer mortar, and normal concrete are used to create six test specimens with dimensions of 600 x 150 x 150 mm, cubes of 50 x 50 x 50 mm, and cylinders of 100 x 200 mm. There are two test beams in each variant. This Permanent Formwork can withstand loads of up to 12.2 MPa, according to the test results. These findings show that Permanent Formwork can effectively increase the strength of structural elements that are nearly half the strength of control beams.