Investigation of Test Methods, Material Properties, and Processes for Solar Cell Encapsulants

Encapsulant materials and processes for the production of cost effective, long life solar cell modules are identified, and evaluated. Ethylene vinyl acetate lamination pottant studies are conducted with respect to the time/temperature cure requirements for successful use of this compound. The time needed to produce successful gel contents are redetermined at a variety of temperatures and are related to the peroxide half life temperature curve. Formulation of the butyl acrylate syrup casting pottant is complete. The formulation contains an ultraviolet stabilizer system and is cured with an initiator that presents no shipping or handling hazards. The catalyzed syrup is stable at room temperature and has a pot life of at least an eight hour period of time. The syrup cures to a transparent rubber in 18 minutes at a temperature of 60 C

The response of glass window systems to blast loadings: An overview

The failure of glass windows in terrorist bombing attacks and accidental explosion incidents has been cited as one of the major causes to the vast casualties. Many studies have been carried out to investigate the response and vulnerability of glass windows against blast loadings. These include laboratory and field tests that have been carried out to experimentally study glass window performance under explosion scenarios and development of analytical and numerical models to analyze and predict glass window responses. This article reviews literatures on the studies of the response of glass window systems to blast loadings. Over 100 papers and documents that are available in the open literature are reviewed. The background and history of the studies on the topic are also briefed. Understandings about the dynamic material properties of glass and available material models are summarized. Popularly used analysis methods and design standards for monolithic and laminated glass windows are outlined, and their accuracies are discussed. Recent studies including analytical solution, numerical simulation, and experimental investigations on glass window systems are summarized. Mitigation measures for blast-resistant windows are also briefly discussed

Methods of condition monitoring and fault detection for electrical machines

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Mild Traumatic Brain Injury: Combined in Silico and in Vitro Studies

Mild traumatic brain injury (TBI) is a significant public health concern worldwide and has attracted significant attention due to high-impact sport as well as improvised explosive devices used in military conflicts. The earliest sign of mild TBI is associated with cognitive, behavioral and physical/somatic changes, which are commonly invisible to existing medical techniques. Thus it is essential to target mechanisms of mild TBI and its associated damage measures for earlier diagnosis/treatment and enhanced protection strategies. In this work, the mechanism of blast-induced mild TBI was inspected through integrated in silico and in vitro models. A three-dimensional (3D) human head model with anatomical details was reconstructed from high-resolution medical images, and positioned in three different directions with respect to the blast wave. The effects of head orientations as well as cerebral blood vessel network in brain mechanics were investigated. The dynamic responses of the brain were monitored by the maximum principal strain (MPS), shear strain (SS), and intracranial pressure (ICP). The developed numerical model was validated by the shock tube experiment using a surrogate head, i.e., water-filled polycarbonate shell. Results demonstrated that the ICP alternations in the brain was initially dominated by the direct blast wave propagation and the skull flexure took effect at a later time. It is worth noting that cerebral blood vessel network induced larger MPS and SS in the brain, which were influenced by vessel diameter and density. Moreover, the contour of the head and its orientation significantly altered the flow dynamics around the head, resulting in different spatial and temporal distributions of brain mechanics. Excessive mechanical stain sensed by brain cells, especially abundant cortical astrocytes, could be a potential index factor for the brain injury. An in vitro injury model for primary cortical astrocytes was developed to identify the injury threshold. Rat cortical astrocytes cultured on silicone membrane were subjected to equibiaxial pulse stretch. The blast pressure profile on the membrane was monitored and the membrane deformations were captured through the high-speed imaging system. The simulated membrane strain, validated by experimental measures, was used to construct an exposure-response curve. It was observed that live cells declined sharply in the strain range from 18% to 35%, which was identified as the injury threshold of cortical astrocytes. The obtained damage threshold of rat cortical astrocytes could be inferred about the level of brain injury in a rat. A 3D rat head model was constructed with an impactor mimicking the loading conditions of contact sports. Results revealed that impact depth and impactor shape were the two leading factors affecting brain dynamics. The influence of impactor diameter was region-specific and an increase in impactor diameter could substantially increase brain strains in the region which located directly beneath the impactor. The lateral impact could induce higher strains in the brain than the central impact. Results suggested that indentation depth instead of impact depth would be appropriate to characterize the influence of a softer impactor. Advisor: Linxia G

Advanced Underground Space Technology

The recent development of underground space technology makes underground space a potential and feasible solution to climate change, energy shortages, the growing population, and the demands on urban space. Advances in material science, information technology, and computer science incorporating traditional geotechnical engineering have been extensively applied to sustainable and resilient underground space applications. The aim of this Special Issue, entitled “Advanced Underground Space Technology”, is to gather original fundamental and applied research related to the design, construction, and maintenance of underground space

Methods for testing high voltage connectors in vacuum, measurements of thermal stresses in encapsulated assemblies, and measurement of dielectric strength of electrodes in encapsulants versus radius of curvature

Internal embedment stress measurements were performed, using tiny ferrite core transformers, whose voltage output was calibrated versus pressure by the manufacturer. Comparative internal strain measurements were made by attaching conventional strain gages to the same type of resistors and encapsulating these in various potting compounds. Both types of determinations were carried out while temperature cycling from 77 C to -50 C

Experimental analysis of disc thickness variation development in motor vehicle brakes

Over the past decade vehicle judder caused by Disc Thickness Variation (DTV) has become of major concern to automobile manufacturers worldwide. Judder is usually perceived by the driver as minor to severe vibrations transferred through the chassis during braking [1-9]. In this research, DTV is investigated via the use of a Smart Brake Pad (SBP). The SBP is a tool that will enable engineers to better understand the processes which occur in the harsh and confined environment that exists between the brake pad and disc whilst braking. It is also a tool that will enable engineers to better understand the causes of DTV and stick-slip the initiators of low and high frequency vibration in motor vehicle brakes. Furthermore, the technology can equally be used to solve many other still remaining mysteries in automotive, aerospace, rail or anywhere where two surfaces may come in contact. The SBP consists of sensors embedded into an automotive brake pad enabling it to measure pressure between the brake pad and disc whilst braking. The two sensor technologies investigated were Thick Film (TF) and Fibre Optic (FO) technologies. Each type was tested individually using a Material Testing System (MTS) at room and elevated temperatures. The chosen SBP was then successfully tested in simulated driving conditions. A preliminary mathematical model was developed and tested for the TF sensor and a novel Finite Element Analysis (FEA) model for the FO sensor. A new method called the Total Expected Error (TEE) method was also developed to simplify the sensor specification process to ensure consistent comparisons are made between sensors. Most importantly, our achievement will lead to improved comfort levels for the motorist

Investigation of the effects of high pressure pulses on biological samples

The increase in survivability in modern conflict has been accompanied by an increase in casualties with multiple and complex blast injuries which are associated with long term complications such as heterotopic ossification. Improving treatments for these complications requires the development of a cellular and molecular understanding of the effects of blast on live biological samples which in the past has been limited by the lack of experimental capabilities. This thesis describes the development and characterisation of experimental platforms to study the effects of high intensity pressure waves on cells and tissues. A confined Split Hopkinson Pressure Bar (SHPB) system has been developed, allowing cells in suspension or in a monolayer to be subjected to pressure waves in the order of tens of MPa and duration of hundreds of microseconds. The confinement chamber has been designed to enable recovery of the biological samples for cellular and molecular analysis, such as cell survivability, viability, metabolic activity and morphological changes post compression. The SHPB platform, coupled with quasi-static experiments, has also been used to determine stress-strain curves of porcine skin tissue samples under uniaxial compression at low, medium and high strain rates. Three phenomenological models have been used to fit the experimental data at different strain rates and the results compared. The recovered samples have been examined using histological techniques to study morphological changes induced by uniaxial compression. Finally, a shock tube-bio set up has been developed and characterised to replicate primary blast damage on cell monolayers by generating single air blast in the order of kPa and few milliseconds duration. This platform permits investigation of a different pressure-time regime compared to the SHPB system and to analyse post-traumatic changes induced in biological samples. To conclude, different experimental platforms have been successfully developed to study the effects of pressure pulses on biological samples.Open Acces

NASA Tech Briefs, April 1987

Topics include: NASA TU Services; New Product Ideas; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Fabrication Technology; Machinery; Mathematics and Information Sciences; Life Sciences