A Flexible Syntactic Foam For Shock Mitigation

This dissertation focused on the development and assessment of flexible microballoons filled elastomeric foam for shock mitigation applications. The overall goal of the research was to develop a flexible syntactic foam that has controllable bulk modulus, compressibility and shock mitigation characteristics and to validate these characteristics by experiments. Elastomer LP-2 with solid manganese dioxide and uncured BJO-093 hollow Pμb were chosen for making the syntactic foam. Hand mixing and room temperature curing was used to make foams of 0 to 30% weight of filler, which amounts to 0 to 60% of volume of the filler. Analysis using gas laws and simple elasticity equations showed that the compressibility of the foam and the resulting bulk modulus vary as a function of microballoon content. Confined compression tests confirmed these results and demonstrated that the bulk modulus can be changed from 19 MPa to 9 MPa as the filler content was increased from 0 to 30% by weight. The compressive high strain rate behavior of the foam was determined using the Split Hopkinson Pressure Bar test apparatus at strain rates ranging from 3,000/s to 4,600/s. The peak strain and strain rate values remain unaffected irrespective of the amount of filler. Both peak stress and stress rise rate decreased with increased filler content. Decrease in peak stress and stress rates were as high as 50% of the base material for filler content of 20% by weight. These characteristics show the potential of this material for shock mitigation applications

Development of Carbon Fibre Metal Laminates (CFML): Design, Fabrication and Characterisation

Abstract Fibre Metal Laminates (FMLs) are hybrid materials consisting of metal layers bonded to fibre-reinforced polymer layers. CFML is an FML developed at NAL consisting of thin aluminum foil combined with carbon-epoxy and glass-epoxy prepreg materials. CFML is proposed as the candidate material for the leading edges of wing and empennage of an aircraft as it has superior characteristics in terms of shape retention (due to highly linearly elastic material like carbon/epoxy), energy absorption capability (due to layered structure and plastic deformation), lightning protection (due to the presence of aluminum layers), and also due to its cost effectiveness (lightweight construction and simple production techniques). An important design issue is the internal residual stresses built into the laminate during curing due to differential coefficients of thermal expansion of the different material systems. This report discusses the methods and issues involved in the fabrication of CFML. CFML laminates were fabricated and Tensile, Compression, ILSS and Flexure testing of standard specimens for different lay-ups were done. The failure modes exhibited during these tests indicate that these materials could be better in energy absorption. However, these conclusions need to be validated with the experiments to quantify their energy absorption capability

Assay of sulfur compounds with 1-​chlorobenzotriazole

A simple but accurate potentiometric method for the estn. of certain sulfur contg. org. compds. has been developed, based on their oxidn. with 1-​chlorobenzotriazole. A back-​titrn. procedure can also be used. The nature of oxidn. in different media is discussed and the oxidn. products have been identified

Performance of Distributed CFAR Tests in Nonhomogeneous Background

We evaluate the performances of several distributed CFAR tests operating in nonhomogeneous background conditions. The analysis considers the detection of Rayleigh target in Rayleigh clutter sith the possibility of differing clutter power levels in the test cells of distributed radars. The tests considered include the previously defined maximum order statistic detector (MOS), belonging to a class of signal-plus- order statistic (S+OS) detectors, a new normalized test statistic (NTS), also belonging to the S+OS class, the OR and the AND fusion rules. Numerical results studied for a two radar system show how the false alarm rate of the MOS test changes with differences in the clutter power levels of the test cells. Results also indicate that, with differing test cells\u27 power levels, the OR fusion rule can be quite competitive to more complex tests, viz. NTS and MOS

Development of CGLARE: Design, Fabrication and Characterisation

Fibre Metal Laminates (FMLs) are hybrid materials consisting of metal layers bonded to fibre-reinforced polymer layers. CGLARE is an FML developed at NAL consisting of thin aluminum foil combined with carbon-epoxy and glass-epoxy prepreg materials. CGLARE is proposed as the candidate material for the leading edges of wing and empennage of an aircraft as it has superior characteristics in terms of shape retention (due to highly linearly elastic material like carbon/epoxy), energy absorption capability (due to layered structure and plastic deformation), lightning protection (due to the presence of aluminum layers), and also due to its cost effectiveness (lightweight construction and simple production techniques). This paper describes the issues regarding the development of CGLARE such as surface preparation of aluminum foils and bonding of aluminum with glass. Tensile, Compression, ILSS and Flexure testing of ASTM standard CGLARE specimens for different layups have been done. An important design issue is the internal residual stresses built into the laminate during curing due to differential coefficients of thermal expansion of the different material systems. The paper presents these results that indicate some properties of these material systems that could be exploited for energy absorption in the leading edges of the aircraft

Investigation of electrochemical behavior of plasma nitrided Ti-6Al-7Nb alloy in Hanks’ Solution

Titanium alloy Ti-6Al-7Nb was plasma nitrided using inductively coupled RF Plasma with 100% Nitrogen at 750, 800 and 850°C for 4 h. Micro Raman studies show the formation of titanium nitrides. Potentiodynamic polarization studies in Hanks’ solution show the corrosion resistance of the untreated samples to be better than the treated samples. Electrochemical Impedance Spectroscopy (EIS) studies show higher charge transfer resistance and lower double layer capacitance for the substrate compared to the nitrided samples. FESEM images of samples immersed in SBF show that growth of apatite is more and the size of deposits are larger on nitrided samples as compared to that on the untreated substrate. Nitrided samples immersed in Hanks’ solution for 7 days show higher amount of calcium, phosphorous and oxygen than the substrate

Influence of Pongamia, Mahua and Neem cakes on finger millet productivity and soil fertility

A field experiment conducted at Bio-fuel park, Agricultural Research Station, Madenur, Hassan in Kharif season of 2009 to asses the performance of finger millet (Eleusine coracana L.) under different organic manure treatment consisting of four treatments viz., recommended FYM and NPK through inorganic fertilizers as control, Pongamia, Mahua and Neem cake with 5 replications laid in randomized complete block design. The results revealed that application of recommended FYM along with neem cake equivalent to 100% recommended N performedbetter in respect of finger millet productivity and maintenance of soil fertility followed by recommended FYM with 100% NPK through fertilizers. Nutrient supplementation with different oilcakes proved superior in respect of soil sustainability

Diversity Combining in Antenna Array Base Station Receiver for DS/CDMA System

This paper analyses few schemes for combining base station antenna array signals in wireless DS/CDMA. The performances of equal gain combining (EGC), likelihood rank test (LRT) and a modified rank test (MRT) are evaluated using simulation studies. The results indicate that, under certain assumptions on multiple access interference statistics, the probability of error of MRT is lower than that of EGC, if a few high power interfering users are present along with a low power user of interest. If there are a moderately large number of users and if the received power of all the users are nearly the same, then EGC outperforms MRT. In fact, under this condition, the performance of EGC is close to that of the optimal likelihood ratio test

Torsional strengthening of thin-walled tubular reinforced concrete structures using NSM-CFRP laminates: experimental work

Torsional strengthening of thin walled tubular reinforced concrete elements, such as bridge box girders and spandrel beams, has received only limited attention, and investigations generally focus on the use of conventional strengthening methods such as span shortening, steel encasing, member enlargement, shotcrete etc. However, research on the use of innovative fibre reinforced polymers (FRP) as near surface mounted (NSM) reinforcement for torsional strengthening is still very limited and more work should be undertaken to examine the full potential of the NSM technique over more traditional solutions. The current paper assesses experimentally, four different strengthening configurations using NSM technique applied on three faces of two beams using straight CFRP laminates, and on four faces of two beams using special L-CFRP laminates. The results show that the proposed strengthening configurations can effectively control crack propagation and increase the torsional moment carrying capacity of the RC element, thus resulting in increased performance and durability.Marie Curie Initial Training Network “Endure” for the grant received and also the Portuguese Foundation for Science and Technology for the current FCT grant. The author would also like to extend the acknowledgements to the industries CASAIS and CiviTest for performing the experimental work. The authors acknowledge the support provided by the FCT for the project StreColesf, POCI-01-0145- FEDER-02948