R-curves of an yttria- and alumina-doped hot-pressed silicon nitride ceramic at 1200°C and room temperature

An energy approach has been utilized to measure theR-curves of an Y2O3~A3-doped hot-pressed silicon nitride ceramic at 1200C in an argon atmosphere in three-point bending. In order to evaluate theR-curves at 1200C, a low constant displacement rate of =5 m min^–1 was applied in cyclic loading to obtain the cyclic loading/ unloading-displacement curves during controlled-crack propagation. Propagated crack lengths were measured directly by a microscope and they were compared to compliance-calculated crack lengths. After digitizing the cyclic load-displacement and crack length-displacement curves, crack-resistance parameters,R-curves andK-curves, were calculated by computer. At 1200C this material behaved non-elastically and the crack parameters, obtained here, represent the non-elastic ones. For comparison, at room temperature, continuous loading was applied to obtain the load-displacement curves. At room temperature, linear-elastic fracture mechanics behaviour was observed.     

Effects of heat treatments on the microstructure of a yttria/alumina-doped hot-pressed Si3N4 ceramic

The effects of post-sintering heat treatments on the microstructure in an Y₂O₃-Al₂O₃-doped hot-pressed silicon nitride ceramic in an argon atmosphere were studied. The degree of crystallization of the secondary crystalline phase depended more on the time than the temperature of the heat treatments. Analytical transmission electron microscopy studies revealed a spencite-(Y, N)-apatite solid solution as the secondary crystalline phase, while the aluminium content in the residual glass was high.     

Performance of ground blast furnace slag and ground basaltic pumice concrete against seawater attack

The aim of this research work is to investigate the seawater resistance of the concrete incorporating ground blast furnace slag (GBS) and ground basaltic pumice (GBP) each separately or both together. The variable investigated in this study is the level of fine aggregate replacement by GBS and GBP. Compressive strength measured on 150 mm cubes was used to assess the changes in the mechanical properties of concrete specimens exposed to seawater attack for 3 years.

Differential scanning calorimeter was used to evaluate the microstructure of the specimens under seawater attack. The effects of exposure were determined by direct measurement of the mass loss of steel bars, embedded in the mortar after 1, 2 and 3 years. The abrasion of concrete was also determined according to mass loss of specimens.

The test results showed that the presence of GBS and GBP had a beneficial effect on the compressive strength loss due to seawater attack and abrasion value. The results create perspectives of forecasting the durability of concrete depending on the types and amount of additives. Furthermore, specimen CSP80 was found to have higher seawater attack resistance than that of the reference concrete. This improvement can be explained partly by the decrease in the permeability of the specimen and partly by the seawater resistance of the additives. Additionally, the corrosion percentage obtained in the reference specimen was higher than all other specimens.     

A new ZVT–ZCT quasi-resonant DC link for soft switching inverters

In this article, the new ZVT–ZCT Quasi-Resonant DC Link, which ensures zero crossings at any time required for soft switching (SS) and provides zero voltage transition (ZVT) turn-on and zero current transition (ZCT) turn-off together for the main switch of active snubber cell in pulse width modulated or space vector modulated operation of inverter is presented. The new circuit combines the most desirable features of the circuits presented previously and overcomes most drawbacks of these circuits by using only one auxiliary switch with fewer other components. Consequently, new ZVT–ZCT Quasi-Resonant DC Link, which is verified by a prototype of a 1.2 kW and 50 kHz circuit, is analysed in detail. All semiconductor devices operate under SS, the main switch is subjected to no additional voltage and current stresses, and the stress on the auxiliary switch is very low in the proposed new inverter.     

A study on the photostabilizer additives on the textile fiber reinforced polymer composites: Mechanical,thermal, and physical analysis

The effect of photostabilizers on the mechanical, thermal, and physical properties of textile fiber reinforced polymer (T‐FRP) composites was investigated. In the first phase of this study, the effect of different concentrations of ultra violet absorber (UVA), hindered amine light stabilizers (HALS) and antioxidants (AOs) into T‐FRP composites for unweathering condition are examined. Mechanical tests were performed as well as differential scanning calorimetry (DSC) analysis for thermal properties. According to test results, there is no significant effect of photostabilizers on the mechanical and thermal properties of the T‐FRP composites. In the second phase of the study, the influence of the photostabilizers on the durability performance of T‐FRP composites is focused under the accelerated UV weathering condition by the help of tensile testing, thermal analysis, and color measurements. According to test results, only about 5% loss in mechanical properties (25% loss for composites without additives) can be observed after 240 h of UV weathering with HALS and UVA addition at adequate concentrations. In addition, AOs can be considered as a strong stabilizer on physical properties with lower color change values. This work shows that the efficiency of the photostabilizers is highly dependent on the type, concentration, and weathering time. POLYM. ENG. SCI., 58:1082–1090, 2018. © 2017 Society of Plastics Engineers     

The effect of reprocessing on the mechanical properties of the waste fabric reinforced composites

In this study, waste cotton fabric reinforced polymer matrix composite plate has been processed by a-custom-made recycling extruder. Two different (12.5% and 25% fibers by weight) waste fabric reinforced composite plates were produced and reprocessed six times to assess repetition effect of processing on the mechanical and rheological properties on plates. Effects of reprocessing were evaluated by the tensile testing and impact testing besides SEM, DSC, XRD and MFI rheological and characterization analysis. Test results of composite plates were compared with the pure low density polyethylene (LDPE) plate. Test results show that the tensile strength was increased till the 4th reprocessing step while reducing impact properties. In further reprocessing, tensile properties have been decreased as a consequence of the fabric/fiber damage. Thermal effect of reprocessing was limited according to the comprehensive characterization and rheological analysis.     

A detailed analytical analysis of a passive resonant snubber cell perfectly constructed for a pulse width modulated d.c.–d.c. buck converter

In this paper, a detailed analytical analysis of a passive resonant snubber cell that is perfectly constructed for a pulse width modulated (PWM) d.c.-d.c. buck converter is proposed. This snubber cell provides a larger overall efficiency and a wider load range than most of the active snubber cells presented previously, and has a simple structure and low cost. The operation principles and a detailed steady-state analysis of a PWM buck converter implemented with this snubber cell are presented. The theoretical analysis is verified with a prototype of a 5-kW and 50-kHz insulated gate bipolar transistor-(IGBT)-PWM buck converter. All of the semiconductor devices in the converter operate under soft switching conditions. Additionally, at 80% output power, the overall efficiency of the proposed soft switching converter is increased to about 98% from the value of 91% in its counterpart hard switching version.     

A new ZVT-PWM DC-DC converter

In this paper, a new active snubber cell that overcomes most of the drawbacks of the normal "zero voltage transition-pulse width modulation" (ZVT-PWM) converter is proposed to contrive a new family of ZVT-PWM converters. A converter with the proposed snubber cell can also operate at light load conditions. All of the semiconductor devices in this converter are turned on and off under exact or near zero voltage switching (ZVS) and/or zero current switching (ZCS). No additional voltage and current stresses on the main switch and main diode occur. Also, the auxiliary switch and auxiliary diodes are subjected to voltage and current values at allowable levels. Moreover, the converter has a simple structure, low cost, and ease of control. A ZVT-PWM boost converter equipped with the proposed snubber cell is analyzed in detail. The predicted operation principles and theoretical analysis of the presented converter are verified with a prototype of a 2 kW and 50 kHz PWM boost converter with insulated gate bipolar transistor (IGBT). In this study, a design procedure of the proposed active snubber cell is also presented. Additionally, at full output power in the proposed soft switching converter, the main switch loss is about 27% and the total circuit loss is about 36% of that in its counterpart hard switching converter, and so the overall efficiency, which is about 91% in the hard switching case, increases to about 97%     

Hydro-abrasive erosion of concrete incorporating ground blast-furnace slag and ground basaltic pumice

In this research work, an attempt has been made to find the suitability of the ground blast-furnace slag (GBS) and ground basaltic pumice (GBP) as a possible substitute for conventional crushed fine aggregate. The main purpose of this investigation is to determine the hydro-abrasive erosion (HAE) characteristics of concrete with GBS and GBP as fine aggregates.The results create perspectives of forecasting HAE of concrete structures depending on the types and amount of additives. It was found that the HAE characteristics of concrete had improved when some of the fine aggregates were replaced by GBS and GBP. As the amount of these additives increased, the mass loss of the concrete incorporating GBS + GBP decreased. This improvement can be explained partly by the decrease in the permeability and partly by the HAE resistance of the additives. In addition to these results, the HAE of concrete was strongly influenced by its compressive strength. Furthermore, the increase in the percentage of additives increased the chloride penetration depths, sharply. The results of this investigation suggest that a joint incorporation of GBS and GBP could conveniently be used to improve its HAE characteristics of concrete.