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排序方式: 共有259条查询结果,搜索用时 15 毫秒
1.
2.
The tensile deformation and fracture behaviour of aluminium alloy 2124 reinforced with different amounts of silicon carbide particulates was studied, in the as-extruded and heat-treated conditions, with the objective of investigating the influence of heat treatment and composite microstructural effects on tensile properties and quasi-static fracture behaviour. Results indicate that for a given microstructural condition, the elastic modulus and strength of the metal-matrix composite increased with reinforcement content in the metal matrix. For a given volume fraction of reinforcement, the heat-treated composite exhibited significantly improved modulus and strength-ductility relationships over the as-extruded counterpart. The increased strength of the Al-SiC composite is attributed to the competing and synergistic influence of strengthening precipitates in the matrix metal, residual stresses generated due to intrinsic differences in thermal expansion coefficients between components of the composite and strengthening from constrained plastic flow and triaxiality in the ductile matrix due to the presence of brittle reinforcement. Fracture on a microscopic scale is initiated by cracking of the individual or clusters of SiC particles present in the microstructure. Particle cracking was dominant for the as-extruded composite microstructure. For both the as-extruded and heat-treated conditions, particle cracking increased with reinforcement content in the matrix. Final fracture of the composite resulted from crack propagation through the matrix between clusters. Although these composites exhibited limited ductility on a macroscopic scale, on a microscopic scale the fracture mechanism revealed features reminiscent of ductile failure. 相似文献
3.
Understanding the Influence of Copper Nanoparticles on Thermal Characteristics and Microstructural Development of a Tin-Silver Solder 总被引:1,自引:0,他引:1
D.C. Lin T.S. Srivatsan G-X. Wang R. Kovacevic 《Journal of Materials Engineering and Performance》2007,16(5):647-654
This paper presents and discusses issues relevant to solidification of a chosen lead-free solder, the eutectic Sn-3.5%Ag,
and its composite counterparts. Direct temperature recordings for the no-clean solder paste during the simulated reflow process
revealed a significant amount of undercooling to occur prior to the initiation of solidification of the eutectic Sn-3.5%Ag
solder, which is 6.5 °C, and for the composite counterparts, it is dependent on the percentage of copper nanopowder. Temperature
recordings revealed the same temperature level of 221 °C for both melting (from solid to liquid) and final solidification
(after recalescence) of the Sn-3.5%Ag solder. Addition of copper nanoparticles was observed to have no appreciable influence
on melting temperature of the composite solder. However, it does influence solidification of the composite solder. The addition
of 0.5 wt.% copper nanoparticles lowered the solidification temperature to 219.5 °C, while addition of 1.0 wt.% copper nanoparticles
lowered the solidification temperature to 217.5 °C, which is close to the melting point of the ternary eutectic Sn-Ag-Cu solder
alloy, Sn-3.7Ag-0.9Cu. This indicates the copper nanoparticles are completely dissolved in the eutectic Sn-3.5%Ag solder and
precipitate as the Cu6Sn5, which reinforces the eutectic solder. Optical microscopy observations revealed the addition of 1.0 wt.% of copper nanoparticles
to the Sn-3.5%Ag solder results in the formation and presence of the intermetallic compound Cu6Sn5. These particles are polygonal in morphology and dispersed randomly through the solder matrix. Addition of microsized copper
particles cannot completely dissolve in the eutectic solder and projects a sunflower morphology with the solid copper particle
surrounded by the Cu6Sn5 intermetallic compound coupled with residual porosity present in the solder sample. Microhardness measurements revealed the
addition of copper nanopowder to the eutectic Sn-3.5%Ag solder resulted in higher hardness. 相似文献
4.
Tejaswi Thunugunta Aswath Channa Reddy Shivashankara Kodthalu Seetharamaiah Laxman Ramanna Hunashikatti Satisha Gowdra Chandrappa Narayana Cherukatu Kalathil Lakshmana Reddy Dhoranapalli Chinnappa Reddy 《IET nanobiotechnology / IET》2018,12(6):706
The increasing use of nanoparticles and their occurrence in the environment has made it imperative to elucidate their impact on the environment. Although several studies have advanced the authors’ understanding of nanoparticle–plant interactions, their knowledge of the exposure of plants to nanoparticles and their effects on edible crop plants remain meager and is often paradoxical. The aim of this study was to increase their knowledge on the effect of zinc oxide (ZnO) nanoparticles on eggplant seed germination and seedling growth. ZnO nanoparticles had a negative effect on the growth of eggplant in plant tissue‐culture conditions, as the growth of seedlings decreased with the increase in the concentration of ZnO nanoparticles. In contrast, ZnO nanoparticles enhanced eggplant growth under greenhouse conditions. The accumulation of ZnO nanoparticles in various parts of eggplant was observed through scanning electron microscopy of both plant tissue‐culture and greenhouse‐raised eggplant seedlings. To the best of their knowledge, this is the first study to report on ZnO nanoparticle accumulation in eggplant and its effect on seed germination and seedling growth.Inspec keywords: crops, zinc compounds, scanning electron microscopy, II‐VI semiconductors, nanoparticles, agriculture, cellular biophysics, nanofabricationOther keywords: plant tissue‐culture, greenhouse‐raised eggplant seedlings, ZnO nanoparticle accumulation, seedling growth, ZnO nanoparticles, nanoparticle–plant interactions, zinc oxide nanoparticles, eggplant seed germination, eggplant growth, ZnO 相似文献
5.
Laxman U. S. Nayak Lee Priest Allan P. White 《Universal Access in the Information Society》2010,9(4):367-374
In this cross-sectional study, the principles of a technology acceptance model were used to identify variables related to
the level of Internet usage by older adults. Community-dwelling older adults aged 60–88 years completed a postal questionnaire
survey that elicited responses on the use of the Internet. Out of a sample of 592 older adults (236 males and 356 females),
50.7% used the Internet. A multiple linear regression analysis was carried out on the Internet users sample using the self-reported
number of hours of Internet usage per week as the dependent variable. The results indicated that attitude toward using the
Internet and good health status were statistically significant predictors of the level of Internet usage. A second multiple
regression analysis using Internet activity as the dependent variable showed that attitude, usefulness, good health, and gender
(males) were significant predictor variables. 相似文献
6.
Debprakash Patnaik Srivatsan Laxman Naren Ramakrishnan 《Knowledge and Information Systems》2011,29(2):273-303
Mining temporal network models from discrete event streams is an important problem with applications in computational neuroscience,
physical plant diagnostics, and human–computer interaction modeling. In this paper, we introduce the notion of excitatory
networks which are essentially temporal models where all connections are stimulative, rather than inhibitive. The emphasis
on excitatory connections facilitates learning of network models by creating bridges to frequent episode mining. Specifically,
we show that frequent episodes help identify nodes with high mutual information relationships and that such relationships
can be summarized into a dynamic Bayesian network (DBN). This leads to an algorithm that is significantly faster than state-of-the-art
methods for inferring DBNs, while simultaneously providing theoretical guarantees on network optimality. We demonstrate the
advantages of our approach through an application in neuroscience, where we show how strong excitatory networks can be efficiently
inferred from both mathematical models of spiking neurons and several real neuroscience datasets. 相似文献
7.
S. Jayalakshmi S. V. Kailas S. Seshan K. Kumar T. S. Srivatsan 《Materials and Manufacturing Processes》2005,20(5):747-760
A growing impetus to enhance our understanding of the behavior of magnesium-based alloys for use in weight critical applications resulted as a consequence of the low density of magnesium. In an attempt to enhance the applicability of magnesium for a wide spectrum of performance-critical applications, the addition of reinforcement to the alloy was considered as an economically affordable and potentially viable scientific alternative. In this paper are reported the results of a study aimed at understanding the influence of saffil alumina short fiber reinforcement on microstructural development of a squeeze-cast magnesium alloy. Preliminary results confirm promise of the reinforced alloy, which retains hardness, strength, and stiffness better at elevated temperatures compared to the unreinforced counterpart. However, impact strength and toughness of the reinforced alloy are inferior. The importance of the matrix alloy in governing the overall mechanical response of the composite microstructure is discussed based on fractographic observations. The importance of volume fraction of the reinforcing phase on properties of the composite microstructure is highlighted. 相似文献
8.
In this technical paper the role of alloy chemistry and secondary processing on tensile response and final fracture behavior of four high strength steels is presented and discussed. The conjoint influence of composition, secondary processing and intrinsic microstructural features in governing stress versus strain response and tensile properties is highlighted. The macroscopic mode and intrinsic microscopic features that result from final fracture of the four high strength steels is discussed. The intrinsic microscopic mechanisms governing tensile deformation and final fracture behavior of the high strength steels are outlined in light of the specific role played by composition, intrinsic microstructural effects and nature of loading. 相似文献
9.
10.
Therese Hurtuk C. C. Menzemer A. Patnaik T. S. Srivatsan K. Manigandan T. Quick 《Journal of Materials Engineering and Performance》2012,21(11):2363-2374
In this article, the influence of bolt holes, specifically their number and layout on strength, deformation, and final fracture behavior of titanium alloy gusset plates under the influence of an external load is presented and discussed. Several plates having differences in both the number and layout of the bolt holes were precision machined and then deformed under quasi-static loading. The specific influence of number of bolt holes and their layout on maximum load-carrying capability and even fracture load was determined. The conjoint influence of bolt number, bolt layout pattern, nature of loading, contribution from local stress concentration, and intrinsic microstructural effects in governing the macroscopic fracture mode and intrinsic microscopic mechanisms is presented and discussed. 相似文献