A Novel Diagnosis Method for Void Defects in HVDC Mass-Impregnated PPLP Cable Based on Partial Discharge Measurement

Mass Impregnated PPLP cable, which is applied to various high-voltage direct current (HVDC) projects due to its excellent dielectric and temperature properties, has a problem wherein voids are formed inside the butt-gap due to cavitation. However, there has been no previous research into technology for void defect identification and insulation diagnosis on HVDC MI-PPLP cables. In this paper, to propose an insulation diagnosis method for void defects in HVDC MI-PPLP cable, the direct current (DC) void discharge patterns were analyzed according to the specimen temperature and the magnitude of applied voltage using the pulse sequence analysis method. In addition, to confirm the pre-symptoms of dielectric breakdown in MI-PPLP cable due to DC void discharge, partial discharge patterns were analyzed continuously until dielectric breakdown occurred. From the experimental results, DC void discharge patterns of the same shape were obtained regardless of the specimen temperature and the magnitude of applied voltage. In addition, it was confirmed that new insulation aging patterns were generated as electrical and thermal aging occurred due to the continuous DC void discharge. Therefore, it is demonstrated that identification and insulation diagnosis of void defects in HVDC MI-PPLP cable is possible through the obtained DC void discharge and insulation aging patterns.

Optimization of Process Parameters on Microstructure and Mechanical Properties of ADC12 Alloy Aptomat Contact Fabricated by Thixoextrusion

The mechanical properties of thixoextrusion components can be improved by controllable processing parameters such as the solid fraction of alloy, holding time, punch velocity, heat treatment and die temperature. In this study, the effects of thixoforming parameters on the microstructures and mechanical properties of thixoextrusion ADC12 alloy Aptomat Contact are studied. ADC12 has excellent castability with high fluidity and low shrinkage rate, so it is widely used in industry, especially in automotive and motorcycle engine part casting. It is a near eutectic alloy with high strength and low ductility (1%). The optimization parameters mechanical properties were investigated by changing the punch velocity, specimen temperature and holding time. The results also indicated optimal value at punch velocity (15 mm/s), specimen temperature (560 °C) and holding time (5 min) which was changed microstructure from eutectic dendrite to globular grain, increasing the ductility (3.3%) of this alloy during the semi-solid forming process while the remaining mechanical properties lead to an increase in the quality of finished parts.

Change of Specimen Temperature during the Monotonic Tensile Test and Correlation between the Yield Strength and Thermoelasto-Plastic Limit Stress on the Example of Aluminum Alloys

This paper presents an attempt to generalize the description of the course of specimen temperature changes during the tensile test and to connect the value of the thermoelasto-plastic limit stress with the value of a clear (physical) or proof strength (offset yield strength) on the example of tests of the following aluminum alloy sheets used in Poland for airplane structures: 2024-T3 and D16 in three grades: D16ATV, D16CzATV, and D16UTV. A thermographic camera was used for specimen surface temperature measurement during the tensile test. The Portevine–Le Chatelier effect (the so-called PLC effect) was observed for tests of specimens cut from sheet plates, which was strongly reflected in the temperature fluctuations. The course of temperature change during tensile tests was divided into four characteristic stages related to the occurrence of a clear or offset yield strength. It was found that if there is a clear yield strength, the value of the thermoelasto-plastic limit stress was greater than this yield strength. If there was an offset yield strength, the value of the thermoelasto-plastic limit stress was lower than this yield strength. The differences in the aforementioned values of individual yield strengths did not exceed several percent. Thus, it can be concluded that the thermoelasto-plastic limit stress determined on the basis of the course of specimen temperature changes during the tensile test is well correlated with the value of the yield strength of the material.

Specimen Temperature Detection on a Clinical Laboratory Pre-Analytic Automation Track: Implications for Direct-from-Track Total Laboratory Automation (TLA) Systems

Clinical laboratory regulations require temperature monitoring of facilities, reagent and specimen storage, as well as temperature-dependent equipment. Real-time specimen temperature detection has not yet been integrated into total laboratory automation (TLA) solutions. An infrared (IR) pyrometer was paired with a complementary metal oxide semiconductor (CMOS) laser sensor and connected to an embedded networked personal computer (PC) to create a modular temperature detection unit for closed, moving clinical laboratory specimens. Accuracy of the detector was assessed by comparing temperature measurements to those obtained from thermocouples connected to battery-operated data loggers. The temperature detector was then installed on a pre-analytic laboratory automation system to assess specimen temperature before and after processing on an integrated thawing and mixing (T/M) robotic workcell. The IR temperature detector was able to accurately record temperature of closed, moving specimens on a pre-analytic automation system. The effectiveness of the T/M workcell was independently verified using the temperature detector. Specimen reroute on the pre-analytic automation track was identified as a potential risk for frozen specimens being inadvertently delivered to future, connected instrumentation. Automated IR temperature detection can be used to verify specimen temperature prior to instrument loading and/or sampling. Such systems could be used to prevent frozen specimens from being inadvertently loaded onto analytical instrumentation in TLA solutions.

Lubricating Performance of Residual Zinc Phosphate Coating on Forged Specimen in Bowden-Leben Sliding Test

The lubricating performance of the zinc phosphate coating employed generally in cold forging is evaluated with Bowden-Leben sliding test by changing friction conditions such as the coating thickness, specimen temperature, the tool surface roughness, contact pressure and sliding speed. A specimen for the friction test is prepared from the inner surface of an extruded square cup and the residual thickness of the lubrication coating on the specimen is controlled by using the surface expansion in forward extrusion of the cup. Experimental results showed that the specimen temperature has the strongest influence on the friction coefficient. With an increase of the specimen temperature, the friction coefficient gradually decreases until 473K, and then increases sharply. With an increase of the tool surface roughness, the friction coefficient increases slightly. Friction coefficient is formulated as a function of the specimen temperature and the tool surface roughness. The anti-galling ability of the coating is affected by the residual thickness of lubrication coating, the specimen temperature and the tool surface roughness.

Influence of Specimen Temperature on Wear Characteristics of AA6063 Aluminium Alloy

Dry sliding wear performance of aluminium alloy (AA 6063) was studied by varying applied normal load, sliding velocity and varying specimen temperatures from 50 to 150 °C. The results signify that the wear increases as the load increases from 10 to 20 N, while it decreases when the sliding velocity of the specimen increases from 1 to 2 m/s at room temperature. As the temperature of the specimen increases, the wear rate increases marginally at initial stage and then increases rapidly for a constant load and velocity. The specific wear was found to be decreased when load and sliding velocity were increased. However, in the case of varying specimen temperature condition, particularly at elevated temperature of the specimen, the specific wear showed an increasing trend. Coefficient of friction (COF) was nearly stable to both load and velocity, but it is marginally vary when temperature of the specimen increases from 50 to 100 °C and it decreases rapidly from 100 to 150 °C.

Fatigue behavior of double-edge notched oxide/oxide ceramic matrix composite in a combustion environment

Tension–tension fatigue tests in a combustion environment were performed on double-edge notched oxide/oxide ceramic matrix composite specimens. The composite, designated as N720/A, constituted woven 0°/90° Nextel™720 fibers in alumina matrix. Monotonic tensile and cyclic loads at a frequency of 1 Hz and a stress ratio of 0.05 were applied on the specimens in a combustion environment. The maximum specimen temperature due to combustion flame impingement in the notch region was 1250 ± 50℃. A stiffness reduction of less than 10% evaluated for the run-out specimens showed the harsh combustion environment had a minimal effect on specimen degradation. The residual strength was evaluated to be ∼75%–85% the strength of non-fatigued (virgin) double-edge notch specimens in room temperature. The monotonic tensile strength and the fatigue limit for 90,000 cycles (run-out) were found to be ∼40 MPa less in the combustion environment when compared to published results for 1200℃ laboratory air environment. The damage mechanisms were also the same in the two environments. Finite element analyses showed that the reduction in strength and fatigue limit in the combustion environment (as compared to the laboratory air environment) was due to the presence of thermal gradient stresses because of non-uniform specimen temperature distribution.