Finite element model analysis of thermal failure in connector

Thermal analysis and thermal diagnose are important for small power connector especially in electronic devices since their structure is usually compact. In this paper thermal behavior of small power connector was investigated. It was found that the contact resistance increased due to the Joule beating, and that increased contact resistance produced more Joule heating; this mutual action causes the connector to lose efficiency. The thermal distribution in the connector was analyzed using finite element method （FEM）. The failure mechanism is discussed. It provides basis for improving the structure. The conclusion was verified by experimental results.

Characterization of Failure Mechanisms of Duplex and Graded Thermal Barrier Coatings Exposed to Thermal Shock Test

The beginning of failure of a (ZrO2-7%Y2O3)/(Ni-22%Co-17%Cr-12.5%Al-0.6%Y) duplex andgraded coating systems on lnconel 617 and IN738LC in burner rig tests has been characterized.The test conditions are 40 s heating up to 75O℃ substrate temperature followed by 80 s aircooling. Failure is considered at the appearance of the first bright spot during heating period.Stresses due to thermal expansion mismatch strains on cooling are the probable cause of life-limiting in this conditions of testing.

Failure analysis of a kind of low power connector

A kind of low power connector used e.g. in household appliances was partly burned in routine experiment. The heat sources were four paralleled contacts constructed by springs (Sn/CuSn-alloy) in socket and a plug sheet (Ni/Steel) while mating. The contact interfaces were detected by scanning electronic microscope (SEM) and X-ray energy dispersive spectros- copy (XEDS), obvious wear tracks and various contaminants, including element Si, Al, Na, K, S, Cl, O, etc., were found. The contamination degrees on the four paralleled contacts were different, so that the ratio of average contact resistance on the four contacts was about 5:8:3:1. The maximum contact resistance on contacts of the plug sheet reached 28 ?. The main failure rea- sons were fretting and contamination between the contact interfaces. Fretting simulation showed that connection resistance of connectors was raised up, even to ohms level. When the current increased to 5 A, the socket housing was heated and decom- posed. By the thermal analysis, it was estimated that the connector would be burned under the lower current if the current was not evenly distributed on the four paralleled contacts caused by uneven contamination. Improvement methods for connector failure are also discussed.

Experimental study and numerical analysis of vacuum thermal characteristics of brush DC motor

Brush direct current(DC)motors have several qualities that make them very attractive for space flight applica-tions.Considering the high reliability requirements of aerospace missions,the thermal characteristics and ther-mal failure of the brush DC motor in the space environment were studied.Using a motor thermal resistance network model,a special thermal test method was determined and combined with a thermal conductivity anal-ysis model,the thermal parameters were obtained via item-by-item stripping,and the motor temperature field was constructed.By introducing the arc discharge factor to evaluate the electric-corrosion heat consumption,the numerical analysis results were in good agreement with the test results under the conditions of stalled rotor,nor-mal rotation,single brush,and multiple brushes.The analysis and test results show that continuous operation for 110 s will lead to melting of the brush solder joints,and electrical corrosion heat consumption is one of the main factors that cannot be ignored.The reliability model of vacuum applications should be established in the normal working mode of at least two brushes in both the positive and negative electrodes.To improve the reliability,a sealed air-filled structure of the motor was proposed,a heat-flow co-simulation model of a continuous medium flow with a large curvature and constant without a gravity field was established,and the temperature and ve-locity fields under different sealed pressures were obtained.The results show that the temperature of the single brush reduced to below 140°C from 204.5°C in vacuum,which can meet the long-term continuous working requirement of high reliability of brush motors in space missions.In addition,it was found that with the decrease in pressure,the effect of convective heat transfer gradually weakens,the temperature gradually increases and converges to the unique heat conduction process of the gas,while the effect of convection is negligible.As the pressure continues to decrease,the sealed gas evolves from continuous medium flow to transitional and free molecular flow,and the heat conduction effect of the gas weakens again until it approaches the singleness solid conduction process.

Safer solid-state lithium metal batteries:Mechanisms and strategies

Solid-state batteries that employ solid-state electrolytes(SSEs)to replace routine liquid electrolytes are considered to be one of the most promising solutions for achieving high-safety lithium metal batteries.SSEs with high mechanical modulus,thermal stability,and non-flammability can not only inhibit the growth of lithium dendrites but also enhance the safety of lithium metal batteries.However,several internal materials/electrodes-related thermal hazards demonstrated by recent works show that solid-state lithium metal batteries(SSLMBs)are not impenetrable.Therefore,understanding the potential thermal hazards of SSLMBs is critical for their more secure and widespread applications.In this contribution,we provide a comprehensive overview of the thermal failure mechanism of SSLMBs from materials to devices.Also,strategies to improve the thermal safety performance of SSLMBs are included from the view of material enhancement,battery design,and external management.Consequently,the future directions are further provided.We hope that this work can shed bright insights into the path of constructing energy storage devices with high energy density and safety.

Absorption density control in waveguide photodiode- analysis, design, and demonstration

A modal analysis is conducted for analyzing the absorption profile of high power waveguide photodiodes designed for analog optical link. The excitation of guided modes with large filling factor in the absorber is identified as a limiting factor for the performance of waveguide photodiodes at high optical power, including power handling capability, and bandwidth-efficiency product. A waveguide photodiode design, which spatially separates the input waveguide from the absorber in the lateral direction, is analyzed and experimentally demon- strated to suppress the excitation of mode with large filling factor. Photocurrent 〉 60 mA under - 4 V bias is measured, with 0.80 A/W responsivity. This design illustrates that high power handling capability can be achieved without compromising the bandwidth-efficiency product.

Thermography analyses of rock fracture due to excavation and overloading for tunnel in 30° inclined strata

Large-scale physical model test of 30°inclined strata was conducted to investigate the damage mechanisms during the excavation and overloading using infrared detection.The experiment results were presented with thermal images which were divided into three stages including a full face excavation stage,a staged excavation stage,and an overloading stage.The obtained results were compared with the previously reported results from horizontal,45?,60?,and vertical strata models.Infrared temperature(IRT)for 30°inclined strata model descended with multiple fluctuations during the full-face excavation.For the staged excavation,the excavation damage zone(EDZ)showed enhanced faulting-like strips as compared in the 45?,60?,and vertical models,indicating the intensified stress redistribution occurred in the adjacent rock mass.In contrast,EDZ for the horizontal strata existed in a plastic-formed manner.During the overloading,abnormal features in the thermal images were observed preceding the coalescence of the propagating cracks.The ultimate failure of the model was due primarily to the floor heave and the roof fall.