bluuebunny/crossref_metadata_2025_split huggingface dataset:
Energy Absorption by Expanded Bead Polystyrene Foam: Dependence on Fracture Toughness and Bead Fusion
Authors: Stupak P. R. , Donovan J. A. 
Published: March 2011

AbstractIncreased energy absorption and load result when the contact area between an object and a foam cushion is less than the foam area because of an increased foam deformation volume (i.e. “Load Spreading”). The deformed volume is trapezoidal (i.e. not prismatic) and is a function of the foam dimensions and the object geometry. The load spreading effect is greatest when the ratio of the object area to the foam thickness is smallest; a common configuration in commercial packages (Figure 1).
Scaling Laws for Transport, Mechanical and Fracture Properties of Disordered Materials
Authors: Sahimi Muhammad , Arbabi Sepehr 
Published: March 2011

AbstractWe discuss scaling laws for scalar and vector transport properties of, and fracture processes in, disordered materials. Random resistor networks, and elastic and superelastic percolation networks are used to model the disordered material. While scalar transport properties of such systems (e.g. conductivity or diffusivity) obey universal scaling laws near the percolation threshold, vector transport properties (e.g. elastic moduli) may not follow such universal laws, and the critical exponents characterizing such scaling laws may depend on the microscopic force laws of the system. On the other hand, fracture processes in such systems appear to obey universal scaling laws. In particular, the external stress F for the fracture of the system scales with its linear size L as F ˜ Ld-1/(ln L)ψ, where d is the dimensionality of the system and ψ is a small critical exponent (ψ ≃ 0.1). Moreover, as the macroscopic fracture point of the system is approached, the ratio of various elastic moduli of the system approaches a universal fixed point, independent of the microscopic details of the system. Finally, the distribution of fracture strength in a randomly reinforced system, or in a system near its percolation threshold with a broad distribution of elastic constants, is in the form of a Weibull distribution, rather than the recently-proposed Gumbel distribution.
Optimal Selection of Foams and Honeycombs in Packaging Design
Authors: Zhang J. , Ashby M. F. 
Published: March 2011

AbstractThe volume of foams used in packaging is enormous. Proper design requires identifying the right material and selecting the right density for each particular application. A new approach to package design is presented in the form of “the Packaging Selection Diagram”, from which the optimal density of a cellular material can be obtained once the maximum permitted stress of the packaging is known. This approach offers greater generality and simplicity than the existing methods such as the Janssen factor or the Energy Absorption Diagram.
Fracture Behavior of Open Cell Ceramics
Authors: Brezny Rasto , Green David J. 
Published: March 2011

AbstractCellular ceramics constitute a class of materials where the properties may be optimized against the weight. These materials may be potentially useful in both structural and non-structural applications. In order to broaden the utilization of the currently- available materials, the mechanical properties must be improved. The objective of this paper is to review several recent studies on the strength and toughness of open cell brittle materials. The work was aimed at understanding the mechanisms involved in the failure of these materials and the relationship between the properties and the microstructure.
The Indentation and Nailing of Cellular Materials
Authors: Vaz M. Fátima , Fortes M. A. 
Published: March 2011

AbstractAn experimental study was carried out on the indentation of cellular materials under quasi-static conditions. The study concentrated on a closed cell rigid polyurethane foam, but other cellular materials were tested. Load (F) - penetration depth (x) curves were obtained for various types of indenters which fall into two main types: sharp indenters (e.g. normal nails) and blunt indenters (e.g. flat ended nails). The F(x) curves are similar for the two types with an initial high slope region followed by a lower slope region in which F increases linearly with x. Nevertheless, the mechanisms of indentation are completely different, with a blunt indenter pushing the material under it and a sharp indenter pushing it radially as it penetrates. The effect of dimensions and shape of the indenters on the F(x) curves was investigated and scaling relations could be derived. Penetration-removal cycles clarify the differences between the two types of indenters, and give additional information on the mechanics of indentation. The experiments were complemented with scanning microscope observations of sections of the indented material. Two approaches are advanced for modelling indentation: a discrete approach in which the cellular structure is taken into account and a continuum approach.
Fracture Properties of an Anisotropic Biological Cellular Material - Apple Flesh
Authors: Khan Ali A. , Vincent Julian F. V. 
Published: March 2011

AbstractThe texture of apple flesh is important in assessing its eating qualities. The texture in turn is related to the structure of the parenchyma. The parenchyma cells of the fruit are arranged in radial quasi-columnar form with radial spaces in between. This anisotropy has a marked effect on the fracture properties such that it is much easier to drive a crack between the columns (radially) than to drive it across them (tangentially). The fracture tests used were simple crack-opening tests under tension or using a wedge. This difference was also detected by a taste panel. The radial spaces ease the passage of cracks travelling along them, and act as crack stoppers for cracks travelling at right angles to them. They also allow the cells to deform more in one orientation more giving the structure ductility and making the apple tougher in that orientation. It is possible to increase this effect by controlled damage such as slow freezing which causes the intercellular spaces to expand increasing the crack-stopping mechanisms and increasing the ductility, therefore increasing the fracture toughness. Toughness first increases, then decreases with increasing damage. This effect can be mimicked with brittle paper: fracture toughness of tracing paper initially increases if holes are punched randomly in it.
Fracture and Yield of a Porous Composite of Trinitrotoluene and Cyclotrimethylene Trinitramine
Authors: Wiegand Donald A. , Pinto J. 
Published: March 2011

AbstractComposites of trinitrotoluene and cyclotrimethylene trinitramine have been studied in uniaxial compression and in triaxial confined compression. Failure by crack propagation and fracture was observed in all uniaxial studies while failure by yield and plastic flow was found for all triaxial confined compression work. The yield strength is approximately a factor of 2 greater than the uniaxial compressive fracture strength. The relationships between the fracture and yield strengths and Young's modulus indicate that all three decrease with increasing porosity. Based on this porosity interpretation, the compressive strength, the yield strength and Young's Modulus may be increased significantly by reducing the porosity.
Representation of the Microstructural Dependence of the Anisotropic Elastic Constants of Textured Materials
Authors: Cowin Stephen C. 
Published: March 2011

AbstractThis paper addresses the question of representing the dependence of the elastic coefficients in the anisotropic form of Hooke's law upon the microstructure of a material. The concern is with textured material symmetries, that is to say materials such as natural and man-made composites whose material symmetry is determined by microstructural organization. The approach is to relate the anisotropic elastic coefficients to local geometric or stereological measures of the microstructure. The predictions of micromechanical models and continuum mechanical models are compared and are found to be consistent with each other.
Digital-Image-Based Study of Circular Holes in an Elastic Matrix
Authors: Day A. R. , Thorpe M. F. , Snyder K. A. , GarBoczi E. J. 
Published: March 2011

AbstractUsing a digital-image-based representation of a continuum composite, we apply computer simulation techniques to obtain the elastic moduli of a matrix containing randomly-centered circular voids. As the area fraction of the voids increases, the elastic moduli of the composite decrease until they eventually vanish at the percolation threshold. We compare our results with an effective medium theory, which predicts that Poisson ratio tends to a fixed value as the percolation threshold is approached, independent of the values of the elastic moduli in the pure system. Our results are also compared with recent experimental results.
Impact Resistance of Post-Tensioned Concrete
Authors: Wang Nianzhi , Mindess Sidney 
Published: March 2011

AbstractImpact tests were carried out on post-tensioned beams, prepared both with plain concrete and fibre-reinforced concrete. It was found that post-tensioned beams might be less resistant to impact loading than were ordinary reinforced concrete beams. However, the addition of fibres to the concrete greatly increased the impact resistance of these beams.
Fracture Properties of Fiber Reinforced Concrete Subjected to Impulsive Loading
Authors: Ansari Farhad , Navalurkar Rajendra K. 
Published: March 2011

AbstractThe need to accurately predict the response of structures under impact loadings has led to an interest in the mechanical properties of component materials at high rates of loading. The mechanism of cracking and its propagation play an important role in evaluation of the response of fiber reinforced concrete structures subjected to impulsive loading. In the present study, single–edge notched beams were tested under high velocity impact loads. A computer assisted instrumented Charpy test system was employed in performing the impact tests. Development and testing of a new fiber optic sensor, for the determination of internal Crack Opening Displacements (COD) in fiber reinforced concrete is described.
Testing of SFRC by the Schmidt Rebound Hammer
Authors: Šušteršič Jakob , Rebić Milenko , Urbančič Stanislav 
Published: March 2011

AbstractThe rebound number, its relationship to fundamental frequency and correlations with compressive strength and erosion - abrasion resistance are discussed. Nine mix proportions were used. The w/c ratios were varied from 0.30 to 0.65. The volumetric percentage of hooked steel fibres was varied from 0.25 to 2.0 vol.% at the w/c of 0.30; at the others the quantity of fibres was constant. In addition, mixes without fibres were made at each w/c.The rebound number and the fundamental frequency are decreased by an increase of steel fibre content. The rebound number correlates with erosion - abrasion resistance. It does not correlate with compressive strength of concretes with constant w/c and different contents of fibres.
Ceramic Fiber Composites, Processing and Performance
Authors: Rice Roy W. 
Published: March 2011

AbstractCeramic fiber composites (mainly with continuous fibers) are reviewed, in part, from the perspective of the pertinence of such results to cementitious construction materials. While there is a large gap in the density, stiffness, etc., of the matrices and of the types and volume fraction of fibers used in these two types of material systems, the fact that for any of these systems fiber-matrix friction/pull-out are important suggests some useful transfer of information. Fiber coatings, which can have spectacular benefits in ceramic fiber composites by controlling fiber-matrix interfaces are discussed. Matrix conformance to the fibers and fiber bending and shape are also probable factors about which less is known, but are discussed because of their potential importance. Similarly, issues of fiber size and fibermatrix property differences are briefly discussed, as are effects of matrix porosity.
Fracture Energy Optimization in Synthetic Fiber Reinforced Cementitious Composites
Authors: Li Victor C. , Wang Youjiang , Backer Stanley 
Published: March 2011

AbstractA study has been carried out on cementitious composites reinforced with various synthetic fibers, focusing on their tensile behavior, toughness, and fracture mechanisms. A model is formulated to predict the tensile behavior and fracture energy of fiber reinforced cementitious composites (FRC) with short, randomly distributed fibers. The model accounts for the pull-out of fibers oblique to the fracture surfaces (including snubbing friction effect), and the variation of the fiber/matrix interfacial shear stress during pull-out. Experimental and analytical results are shown to be in close agreement for the one class of fiber reinforcement which best satisfies the assumptions of the model. Systems which violate the assumptions exhibited different failure mechanisms and were observed to show less satisfactory reinforcement performance, especially the composite fracture energy. The model is used to examine the effect of fiber properties on composite post-cracking behavior and is useful in design of such material systems with optimum performance and cost effectiveness.
Dependence of Substrate Orientation on the Synthesis of CoSi2 Layers Formed by Ion Implantation & Rapid Thermal Annealing
Authors: Gwilliam Russell M , Reeson Karen J , Webb Roger P , Spraggs Russell S , Sealy Brian J 
Published: March 2011

Abstract200 keV Co+ ions have been implanted into (100), (110) and (111) single crystal silicon substrates to doses of 2 × 1017 Co+ cm−2 and 5 × 1017 Co+ cm−2. During implantation the substrates were tilted at an angle of 70 to the incident ions and maintained at a temperature of 350°C. The experimental results, after implantation, are in close agreement with those obtained by computer simulations, which allow the single crystal orientation of the target and its position with respect to the incident ions to be specified. 5s RTA treatment at 1100°C was found to give CoSi2 layers of similar crystalline quality and resistivity to those produced by conventional furnace annealing.
Low Resistivity CoSi2 Surface Layers for Use as Contacts in CMOS Processes
Authors: Audet Sarah A. , Rafferty Conor S. , White Alice E. , Short Ken T. , Hsieh Yong-Fen 
Published: March 2011

AbstractUniform CoSi2 surface layers 30nm thick have been realized through room temperature implantation of Co+ through a resist or an oxide mask and low temperature (600°C) annealing. TEM studies show that the surface layers are polycrystalline with large, uniformly thick grains. Resistivity values as low as 181µΩ-cm have been obtained. Surface layers of TiSi2 have also been synthesized using a similar process. The ease of formation, the low resistivity and the smooth interfaces of the CoSi2 and TiSi2 surface layers make this technique a promising candidate for contacting source and drain junctions in sub-half-micron CMOS processes.
Nucleation, Transformation and Agglomeration of C54 Phase Titanium Disilicide
Authors: Mann R.W. , Racine C.A. , Bass R.S. 
Published: March 2011

AbstractThe transformation of TiSi2from the C49 phase to the C54 crystallographic phase is an irreversible, polymorphic transformation that occurs by a nucleation and growth process. Typical of polymorphic transformations, the transition occurs readily once a stable embryo of the thermodynamically favored phase is formed. Future VLSI applications requiring control of the resistivity and thermodynamic stability of thin TiSi2films formed on submicron features will necessitate understanding this nucleation and transformation process to a greater extent. We have found that the C54 phase nucleation site density, the resulting microstructure and thermal stability of the film can be strongly influenced by the initial silicide formation conditions. Rapid thermal processing (RTP) has been found to offer a significant advantage over conventional furnace annealing for the silicide formation process.
Rapid Thermal Annealing of Titanium in an Ammonia Ambient: Kinetics and Film Properties
Authors: Srikrishna K. , Jairath R. , Huglin G. 
Published: March 2011

AbstractThe reaction between titanium and ammonia to form titanium nitride in a rapid thermal annealer has been studied as a function of process temperature and substrate conditions. The films produced have been characterized by Rutherford Backscattering, Sputtered Neutral Mass Spectroscopy and four point probe electrical resistivity measurements. On oxide substrates, below 720°C only dissolution of nitrogen within the titanium is observed leading to an increase in the specific resistance of the film. Above 720°C, stoichiometric titanium nitride begins forming leading to a drop in the specific resistance of the film. Only in the vicinity of 800°C is all the titanium consumed to form TiN. However, temperatures beyond 700°C cause dissolution of oxygen within the titanium. On silicon substrates, the competing reactions of nitridation and silicidation at the two interfaces govern the extent of nitridation.
Optical Properties of Growth Phases Formed by Rapid Thermal Annealing of MoSix thin Films on Si (100)
Authors: Srinivas G. , Rastogi R.S. , Vankar V.D. 
Published: March 2011

AbstractAmorphous thin films were deposited by co-sputtering Mo and Si on Si(100) single crystals. Rapid thermal annealing at 700, 800 and 1050°C for 30 sec. resulted in the growth of hexagonal and tetragonal phases of MoSi2 as revealed by glancing angle x-ray diffraction. The optical properties of these films were studied by spectroscopic ellipsometry in the range 1.0 to 5.0 eV. As deposited films showed both metallic and semiconducting features in the <ε1> and <ε2> spectra. As a result of annealing at 700 and 800°C, pronounced increase in <ε1> was obtained. Annealing at 1050°C resulted in decrease of the values of <ε2>. Surface morphology, density changes and stress variations associated with recrystallization and compound formation are proposed to account for these observations. The peaks in <ε2> spectra are found to be interband transitions in the MoSi2 structures. These results are in confirmity with the EELS and UPS studies and theoretically calculated band structure of MoSi2.
In-Situ Fabrication and Process Control Techniques in Rapid Thermal Processing
Authors: Moslehi Mehrdad M. , Kuehne John , Yeakley Richard , Velo Lino , Najm Habib , Dostalik Bill , Yin David , Davis Cecil J. 
Published: March 2011

AbstractAdvanced rapid thermal processing (RTP) equipment and sensors have been developed for in-situ fabrication of semiconductor devices. High-performance multi-zone lamp modules have been applied to various processes including rapid thermal oxidation (RTO), chemicalvapor deposition (CVD) of tungsten and amorphous/polycrystalline silicon, silicide formation, as well as high-temperature rapid thermal annealing (RTA). Concurrent use of multizone lamps and multi-point temperature sensors allows real-time wafer temperature control and process uniformity optimization. Specific experimental results will be presented on the multi-zone lamp modules, in-situ process control sensors, and single-wafer fabrication processes.
Impacts of Temperature and Reactant Flow Rate Transients on LPCVD Tungsten Silicide Film Properties
Authors: Cale T. S , Park J.-H. , Raupp G. B. , Jain M. K. 
Published: March 2011

AbstractA transient model of a stagnation point flow, single wafer reactor is used to predict the concentrations of tungsten hexafluoride and dichlorosilane as a function of position along the surface of a six inch wafer during the transient and steady state operating phases of tungsten silicide deposition in trenches having an initial aspect ratio of five. We analyze two startup protocols: 1. The susceptor temperature setpoint is changed from just above room temperature to its steady state value after the reactant flows are established. 2. The reactant flowmeter setpoints are changed to their steady state values after the wafer temperature is established in a flow of inert gas. A ballistic transport and reaction model is used to predict film thickness and composition profiles of these tungsten silicide films as a function of deposition time. The transient portions of the two startup protocols do not affect film profiles or average composition as much as the inherent increase in aspect ratio as the fill proceeds.
Role of Photoeffects in Integrated Rapid Isothermal Processing
Authors: Singh R. , Sinha S. , Thakur R.P.S. , Hsu N.J. 
Published: March 2011

AbstractRapid isothermal processing (RIP) based on incoherent radiation as the source of energy is emerging as a practical alternative to furnace processing. In this paper, we show that in addition to the well established short time processing feature, RIP can also be used as a reduced substrate temperature processing technique.
Microstructure and Kinetic Analysis of the Initial Stages of SiC Formation in a Rapid Thermal Processor
Authors: Kim Ki-Bum , Liao Jimmy C. , Burrow Brad J. , Sullivan Eileen A. 
Published: March 2011

AbstractWe have investigated the evolution of the microstructure, growth modes, and growth kinetics of β-SiC in a rapid thermal processor using FTIR, ESCA, and TEM. SiC layers were formed by reacting C2H4 with Si substrates between 900 and 1300°C at 5 torr. We found that SiC forms discrete nuclei at 900°C, a mixture of discrete nuclei with a thin β-SiC layer in between those nuclei at around 1000°C, and a continuous β-SiC layer above 1100°C. In all cases, β-SiC grows epitaxially on Si substrates. In addition, we identified that a graphitic carbon layer is formed on top of a continuous β-SiC layer. The thickness of the SiC layer was deduced from the integrated absorption spectra of FTIR and measured from the high resolution cross-sectional TEM micrographs. Kinetic data indicate that SiC grows rapidly at the initial stages of reaction. The growth rate, however, is retarded significantly as the reaction proceeds.
Single-Wafer RTCVD of Polysilicon: a Complementary Step in Front-End Integrated Processing
Authors: Kermani Ahbmad 
Published: March 2011

AbstractPolycrystalline silicon is used in the fabrication of integrated circuits in various applications. These include a MOS gate material, bipolar emitter and base contacts, trench refill, complementary material for elevated source / drain structures, solid diffusion source for formation of shallow junctions and the active material in thin film transistors. The deposition of polysilicon as the MOS gate electrode or the bipolar emitter contact follows the most critical processing steps in fabrication of these devices. Maximum reproducibility and highest device performance are achieved when the interfaces between the polysilicon and the underneath substrate are well controlled. This level of control can be obtained by combining the compatible processing steps under a controlled environment. Single-wafer RTCVD of polysilicon was introduced to complement the emerging front-end integrated processing technology for MOS, bipolar and BICMOS devices.
Demonstration of Multiprocessing by Silicon Epitaxy Following In-Situ Cleaning
Authors: Apte Pushkar P. , Venkatraman Ramnath , Saraswat Krishna C. , Moslehi Mehrdad M. , Yeakley Richard 
Published: March 2011

AbstractConventional semiconductor manufacturing techniques may be unable to meet technological demands in certain cases, and alternatives need to be investigated. We propose in situ sequential processing, which we define as ‘multiprocessing’, as a possible innovation. We demonstrate a specific manifestation of multiprocessing, namely the integration of a novel in situ pre-clean using anhydrous hydrogen fluoride with chemical vapor deposition of silicon, leading to the growth of high-quality single-crystal silicon epitaxy. Further, we show that the multiprocessing technology is viable for manufacturing, since it is simple, rapid, has a low thermal budget and does not suffer from cross-contamination. Finally, we discuss the possible role of multiprocessing in semiconductor manufacturing.