bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties and Applications of Molybdenum
Authors: Burman R
Published: December 2008

Molybdenum (“Moly”) is the most readily available and least expensive refractory metal. Massive ore reserves and many refinement facilities are located within the United States. The major application for Moly, over 80% of total markets, is that of alloy additions to irons and steels.

Metallic Moly is consolidated into commercial products by the powder-metallurgy process (P/M) and by the consumable electrode vacuum-arc casting process (VAC). Moly's high melting point and low vapor pressure at extreme temperatures justify its applications to cold wall vacuum or inert atmosphere furnace equipment. These properties, as well as Moly's high thermal conductivity and good electrical and chemical properties, lead to applications in glass-making manufacture of fibers and containers. Moly is also widely used in electronics, solid-state devices, X-ray tubes, crystal growing, heat pipes, photoetched masks, etc.

TZM Moly Alloy is the best commercial high strength, high temperature material for hot-work tool applications such as die casting (even ferrous metals), hot extrusion (non-ferrous and ferrous metals), hot piercing stainless steel tubes, isothermal forging tools, isothermal shape rolling, hot gas valves and seals, and hot turbine components. The Moly-30% tungsten alloy (Mo-30W) is commercially employed for its high melting temperature of 2829°C (5125°F) and its chemical inertness in corrosive molten zinc, especially the high purity grades. Moly and Moly-base alloys are commercially used for principally high temperature applications in hot equipment, hot working tools, and hot operating machines.
Tantalum and Niobium in Some Electronic Applications
Authors: Belz LH
Published: December 2008

The evolution of tantalum and niobium capacitors is reviewed. Present tantalum capacitor technology and commercial activity are summarized. Superconducting materials are reviewed, with specific discussion of niobium alloys and intermetallics. The use of tantalum and niobium oxides is described in the production of tantalate and niobate piezocrystals.
Use of Refractory Metals in Chemical Process Industries
Authors: Smallwood RE
Published: December 2008

The chemical process industry utilizes many different materials of construction to contain and to instrument the many varied and often aggressive chemical processes. Molybdenum, niobium, tantalum, and tungsten, known as the refractory metals, see limited use in the chemical process industry. A summary of the corrosion resistance, mechanical properties, fabricability, economic factors, and special properties of the refractory metals for chemical process applications is given. The various refractory metals are compared to more traditional materials used in the process industry.
Effect of Process Conditions on Autodoping in Silicon Epitaxy
Authors: Chang H-R
Published: December 2008

Vertical and lateral autodoping in silicon epitaxy deposited in a vertical pancake type reactor using dichlorosilane has been examined as a function of pre-epitaxial bake cycle, dopant type, and growth parameters. Phosphorus and arsenic were used as dopant elements to form a localized buried layer at the center of substrates. The results show that higher prebake temperature produces more lateral autodoping for phosphorus while the opposite holds for arsenic. Autodoping in both vertical and lateral directions decreases with increasing prebake time. A continual decrease in autodoping was found with increasing growth rate for phosphorus while for arsenic, only slight difference was noticed in the growth rate range studied. Both phosphorus and arsenic show a similar trend on the deposition temperature dependence of autodoping, i.e., autodoping decreases at first, then increases with increasing temperature.
Control of Gain Variations in Shallow Junction Ion Implanted Bipolar Transistors Caused by Planar Channelling
Authors: Bazley DJ
Published: December 2008

Ion implantation is a widely used technique for the fabrication of high performance bipolar transistors giving good control of dose and junction depth. Precautions are normally taken to reduce the effects of axial channelling by orientating the slices off axis from the ion beam. The effects of planar channelling can also be significant however, particularly in the case of bipolar transistors where the result can be large variations in the gain of the transistors across the slice. This paper considers the causes of these variations and the ways in which they can be alleviated by modifying the transistor structure and by orientating the slices during the base implant.
The Effect of Wafer Flatness on Yield by Off-Line Computer Simulation of the Photolithographic Process
Authors: Denes L
Published: December 2008

This paper describes a powerful new computer program which has the ability to directly simulate virtually all popular projection and stepper type aligners. The effects on yield of such metrologies as global wafer retilting, exposure by exposure retilting and autofocusing will be analyzed. Three point and the new seven point mirror projection aligner image plate geometries will also be characterized.

The results of several process simulations will be presented using the new program's powerful graphic displays which yield a view of wafer shape never seen before.
Forms of Contamination Affecting Device Processing
Authors: Rapa AC
Published: December 2008

Semiconductor devices are known for their sensitivity to particulate contamination during manufacture. This sensitivity is increasing as device features shrink and circuit densities increase. Current VLSI (Very Large Scale Integration) devices are also sensitive to many other forms of contamination besides particles. This paper examines the various forms of contamination and their interactions which affect the yield and performance of VLSI devices.
Problems Associated with Submicrometre Contaminant Measurement
Authors: Lieberman A
Published: December 2008

Special problems in measuring submicrometre particulate contaminants in liquids are discussed. These include the need for standards and specifications in the pertinent particle size and concentration ranges that can be associated with effects of concern in semiconductor processing. Problems in controlling artifact introduction from sample handling and transport systems are discussed. The need for better understanding of statistical effects on data validity in measurements of clean liquids is pointed out. Operation of present-day particle sizing and counting instruments for submicrometre particles is described with some reference to both capabilities and limitations.
Precipitation Behavior of Deposited Metals in Cz-Silicon
Authors: Suga H , Shimanuki Y , Murai K , Endo K
Published: December 2008

Precipitation behaviors of metallic impurities in CZ-silicon single crystals were investigated with a transmission electron microscope equipped with an energy dispersive x-ray spectrometer. Results show bulk precipitates only for Au, Cu, Ni. Effect of near-surface denudation of SiOx micro-precipitates to suppress the metal precipitation in the denuded zone was explicit both Cu and Ni cases. But Au precipitated uniformly. Fe and In precipitates were localized in the near-surface region. The other metals (Cr, Mo, Al, Te, Ta and Pb) remained on the wafer surface and did not seem to segregate to the deliberately introduced defects (stacking faults, dislocation and SiOx) nearby the deposit. Among those metals impurity precipitation on stacking faults and dislocations was observed significantly only in Cu contaminated wafer. Most of metals seemed to be less mobile under oxidizing atmosphere by oxygen trapping of the metal at the wafer surface.
Extrinsic Gettering Via the Controlled Introduction of Misfit Dislocations
Authors: Salih ASM , Kim HJ , Davis RF , Rozgonyi GA
Published: December 2008

As an alternative, or a complement, to existing gettering techniques, extrinsic gettering by misfit dislocations is described and the gettering efficiency evaluated. Uniform arrays of misfit dislocations were produced at epitaxial Si interfaces by introducing GeH4 into a SiH4/H2 epitaxial deposition system. The dislocation density was controlled by adjusting the magnitude of lattice mismatch due to the expansion of the Si matrix by Ge. The dislocation properties were determined using conventional and cross-section transmission electron microscopy and optical microscopy coupled with angle polishing and preferrential etching. The dislocation bands were found to be confined to the epi/substrate interface and were used as “extrinsic” gettering sinks. Surface metallic contamination was introduced deliberately and diffused towards the dislocations with a high temperature furnace operation. TEM analyses showed metallic precipitation at the dislocations as a result of gettering. Depth profiles of gold were determined by SIMS. The Au peaks were found to coincide with the dislocation bands and to be proportional to the dislocation density.
The Effect of Si-SiO2 Interface on the Excess Point Defect Distribution in Silicon
Authors: Shin Y-S , Kim C-K
Published: December 2008

Lateral diffusion enhancement of boron and phosphorus by excess point defects, excess interstitials during thermal oxidation of silicon and excess vacancies during high concentration phosphorus predeposition, has been investigated experimentally and numerically. Two-dimensional steady state excess point defect concentration profiles were obtained by a finite difference method. Numerical result was compared with the experimental data and the values of excess point defect recombination velocity (S) at the unoxidizing Si-SiO2 interface divided by the point defect bulk diffusivity (D), S/D, were found out to be about 0.7/μm for excess interstitials and about 1.3/μm for excess vacancies.
Fracture Tracing in Semiconductor Wafers
Authors: Dyer LD
Published: December 2008

From the beginning of their shaping until their final assembly into useful devices and systems, semiconductor wafers are subject to several kinds of failure, one of which is brittle fracture. The purpose of this paper is to describe the method of tracing cracks in silicon slices back to their origins and of further analyzing the fracture by means of characteristic fracture markings. Some background material in fracture theory and the causes of various markings is also presented.
Oxygen Determination in Silicon Using Fourier Transform Infrared Spectroscopy
Authors: Shive LW , Schulte BK
Published: December 2008

Silicon wafer users must often test non-ideal one-side polished slices for oxygen content. This data is usually biased with respect to the true value. However, this bias can now be eliminated for some types of one-side polished wafers by using calibration programs that are provided with most commercial FTIR instruments. These programs require a calibration wafer of known oxygen content and with a thickness and a backside surface similar to those of the unknown. The effectiveness of this procedure for eliminating bias for several non-ideal sample types is described.
A Method to Determine the Initial Phosphorus and Boron Concentrations in Float-Zoned Polysilicon Rods
Authors: Chiou H-D
Published: December 2008

A simple method to determine the initial dopant concentrations in polycrystalline silicon rods used in the floating-zone process is described in this paper. The technique is to grow a single crystal in the taper region of the first float-zoned pass. The net carrier concentration, the concentration difference between the donor and acceptor, in the taper region is obtained by four-point probe resistivity measurements. From the slope of the net carrier concentration versus the distance plot in the taper region, the initial phosphorus and boron concentration are calculated. Experimental data show that the calculated values are in good agreement with the frozen-end average dopant concentrations measured on the second-pass zero-dislocation crystals.
Dopant Profiling in Silicon
Authors: Pawlik M
Published: December 2008

The developments necessary to implement a comprehensive research programme aimed at understanding dopant incorporation in silicon are described. The two experimental techniques used, and possessing the required dynamic range and depth resolution, are high resolution Spreading Resistance and Secondary Ion Mass Spectrometry. Comparative studies of samples with both techniques lead to a greater understanding of dopant incorporation and dopant activation and provide a wealth of data for the refinement of process models such as SUPREM.

Data are presented on a number of different samples, including boron and arsenic implantations and anneals (furnace, and electron beam) in silicon and in silicon-on-sapphire.
New Applications of Tape Bonding for High Lead Count Devices
Authors: Marshall JF , Sheppard RP
Published: December 2008

There are two primary forces which drive the interconnect market: the first is manufacturing cost, and the second is system performance. In the past, tape automated bonding (TAB) was viewed as an interconnection technology which offered a cost advantage; however, only a handful of semiconductor manufacturers with high volume, low lead count product lines were able to demonstrate a cost savings with TAB over conventional automatic wirebonding.

Recently, however, development work and usage of TAB has been accelerating due to performance considerations in the interconnection of increasingly complex VLSI devices. VHSIC speeds are forcing new approaches to packaging and interconnection. TAB offers a practical solution to many of these performance problems. TAB leads offer improved electrical, thermal and mechanical properties in addition to doubling the I/O density capability for perimeter pad configurations compared to conventional wirebonding. Furthermore, TAB technology affords the potential to accommodate I/O pads anywhere on the surface of the device through the use of a multilayer “area array” or “decal” tape interconnect pattern.
Production of Detector-Grade Silicon by Neutron Transmutation Doping
Authors: Ammon Wv , Kemmer J
Published: December 2008

High ohmic n-type silicon was produced from over-compensated, neutron transmutation doped P-type silicon. It was found that compensation levels of even more 70 % do not lead to the formation of p/n junctions across the wafer so that resistivities of up to 10 KOhmcm can be produced on a fairly reliable basis. The properties of NTD and conventionally doped silicon as well as their detector suitability are compared.
Neutron Transmutation Doping in Hydrogenated Amorphous Silicon
Authors: Hamanaka H , Kuriyama K , Yahagi M , Iwamura K , Kim C , Shiraishi F , Tsuji K , Minomura S
Published: December 2008

A neutron irradiation for thermal neutron flux density of 5 × 1011/cm2s and irradiation time of 10 hr was applied to hydrogenated amorphous silicon (a-Si:H). The density of 31P produced by the neutron transmutation doping (NTD) was estimated to be 1012/cm3. Dark and photo conductivities were measured before and after NTD in parallel with ESR measurements. The annealing behavior of the irradiation damage was studied up to the growth temperature of a-Si:H. Dark conductivity of the well-annealed NTD a-Si:H shows an activation type conduction above room temperature with activation energy of 0.69 eV.
Equalization of Axial Neutron Flux Density for the Transmutation Doping of Silicon in a Heavy Water Reactor
Authors: Andresen K , Heydorn K , Nonbøl E
Published: December 2008

New irradiation facilities for the neutron transmutation doping of silicon crystals with a diameter of up to 110 mm have been installed in the Danish heavy-water reactor DR 3. Cross-sectional uniformity is easily achieved by rotation, but axial variation is affected by different reactor operating conditions. A computer program has been developed as an aid in designing a stainless steel absorber that limits the maximum deviation with a minimum reduction of the average neutron fluence. Comprehensive experimental verification has been carried out to ascertain the quality of the NTD silicon within close specifications.
Advanced Test Reactor Ntd Silicon Production Hardware
Authors: Schell MJ
Published: December 2008

The Advanced Test Reactor (ATR) is a 250-MWth materials testing and nuclear research facility operated for the United States Department of Energy (DOE) by EG&G Idaho, Inc. The unique capabilities of the ATR can be readily adapted via hardware to produce large quantities of large-diameter (20 cm plus) doped silicon crystals. Conservative estimates place the production eapability in excess of 15 metric tons per year. The proposed hardware is based upon a closed-loop, hydraulic-shuttle-tube system.
Rapid Extraction Methods for Organics in Soil
Authors: Petros JK , Alsop GM , Conway RA
Published: December 2008

This article presents rapid methods for the extraction and subsequent analysis of organics in soils potentially contaminated from chemical wastes. A methylene chloride extraction, on both a micro scale in a syringe and a macro scale in a shaken flask, with subsequent gravimetric analysis are described. On wet soils, anhydrous sodium sulfate is added to bind the water before adding methylene chloride and mixing with a vortex touch mixer. A baseline procedure is the direct gravimetric determination of volatile organics corrected with a Karl Fischer determination of water. Estimates of time saved by using the rapid methods, as well as precision and accuracy data, are presented.
Recovery of Chromium from Plating Wastes
Authors: Bolto BA , Kotowski M , Pawlowski L
Published: December 2008

Recovery of chromium from a plating sludge is discussed. The process consists of two parts: roasting the sludge with sodium carbonate (Na2CO3) and calcium oxide (CaO), followed by leaching. The optimal parameters for roasting are a temperature range of 950 to 1000°C and Na2CO3 and CaO contents of 2.4 and 2.8 mol per mole of chromium oxide (Cr2O3) respectively.

Demineralized water is recommended for the leaching of sodium chromate (Na2CrO4) from the agglomerate formed during roasting. The leached water is recycled through a strongly acidic cation exchanger followed by a weakly basic anion exchanger. A solution of chromate or chromic acid having a concentration up to 60 kg Cr/m3 is obtained.
Comparison of Analytical and Experimental Stress-Intensity Coefficients for Chevron V-Notched Three-Point Bend Specimens
Authors: Bar-On I , Tuler FR , Roman I
Published: December 2008

Chevron-notched specimens in a number of configurations have been recently used to determine plane-strain fracture toughness. Most researchers have employed tensile short-rod and short-bar specimens, while the three-point bend configuration has been used only to a limited extent despite its convenience for testing at ambient and high temperatures.

In the present study, both experimental and analytical K-calibrations for three-point bend chevron-notched specimens were carried out. Fracture toughness tests were performed in accordance with ASTM Standard of Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E 399-81) to determine plane-strain fracture toughness, KIc, for polymethyl methacrylate (PMMA), 60/40 brass, 7075-T651 aluminum, and quenched and tempered 4140 steel. In parallel, three-point bend chevron-notched specimens of these materials were loaded to failure. The ratio (KIc/Pmax) B · √W is the dimensionless quantity Y*. This quantity was found to be 11.6 for the specimen geometry employed in the present study.

Three analytical models, which have been used successfully for the short-bar and shor t-rod configurations were used to calculate the stress-intensity coefficient and the critical crack length for the three-point bend configuration. The predicted stress intensity coefficients are 20 to 60% higher than the experimental value, and the predicted critical crack length is at least 20% lower than the directly measured critical crack length.
Specimen Size Effects in Short-Rod Fracture Toughness Measurements
Authors: Barker LM
Published: December 2008

Short-rod fracture toughness specimens of various sizes were used in toughness measurements on six different metals. The toughness values were observed to be independent of the specimen size, within experimental scatter, whenever the specimen diameter exceeded 1.25(KIcSR/σys)2. The test records were analyzed by a linear elastic fracture mechanics (LEFM) method and also by an elastic-plastic method. When the specimen size was too small to yield a size-independent result, the LEFM analysis always tended toward conservative (smaller) toughness values, while the elastic-plastic analysis always tended toward nonconservative values. Thus, the two analysis techniques apparently establish upper and lower bounds for the toughness when the specimen is too small for a valid test. It was also found that the slots which form the chevron in the specimen must either be very thin or have sharply pointed slot bottoms (≤60° included angle) to maintain good plane-strain constraint along the crack front.
Compliance and Stress-Intensity Factor of Chevron-Notched Three-Point Bend Specimen
Authors: Shang-Xian W
Published: December 2008

An analytical dimensionless compliance formula and normalized load versus load-point displacement plot of chevron-notched three-point bend specimen are derived by use of Bluhm's slice model. The stress intensity factor coefficients are calculated for specimen geometries of W/B = 1.5 and 2, θ = 40° to 90°, and are fitted as polynomials. Fracture-toughness values KIcv of two heat-treatment conditions of GCr15 bearing steel are determined by chevron-notched specimens and compared with the ASTM E 399 valid fracture-toughness values. The comparisons show that for GCr15-I specimens with flat R-curves, KIcv and KIc are in agreement, but for the GCr15-IV specimens with rising R-curves, KIcv are near to Kmax, instead of KIc. The effect of machining tolerance of chevron notch on the measurements is analyzed.
An Investigation on the Method for Determination of Fracture Toughness KIc of Metallic Materials with Chevron-Notched Short-Rod and Short-Bar Specimens
Authors: Chizhi W , Maochan Y , Tzeguang C
Published: December 2008

By means of an expression proposed by the authors, dimensionless critical crack lengths and stress-intensity factor coefficients for chevron-notched short-rod specimens were calculated based on the straight-through crack assumption. Calculation was also done for chevron-notched short-bar specimens in an extended range including short bar with rectangular cross section. Three configurations of chevron-notched specimens were used to test fracture toughness KIc for eight metallic materials. Some results were compared with values from standard compact tension and three-point bend specimens. Good agreement was obtained when both stable crack extension and a very small plasticity factor were achieved. The role of load-displacement plot is emphasized. A discussion about some specimen parameters such as dimensionless initial crack length and width to half height (or width to radius) ratio is given.
Specimen Size and Geometry Effects on Fracture Toughness of Aluminum Oxide Measured with Short-Rod and Short-Bar Chevron-Notched Specimens
Authors: Shannon JL , Munz DG
Published: December 2008

Plane-strain fracture toughness measurements were made on aluminum oxide using short-rod and short-bar chevron-notched specimens previously calibrated by the authors for their dimensionless stress intensity factor coefficients. The measured toughness varied systematically with variations in specimen size, proportions, and chevron notch angle apparently due to their influence on the amount of crack extension to maximum load (the measurement point). The toughness variations are explained in terms of a suspected rising R-curve for the material tested, along with a discussion of an unavoidable imprecision in the calculation of KIc for materials with rising R-curves when tested with chevron-notched specimens.
Fatigue Crack Growth Behavior in a Nitrogen-Strengthened High-Manganese Steel at Cryogenic Temperatures
Authors: Ogawa R , Morris JW
Published: December 2008

The fatigue crack growth rate (FCGR) of a nitrogen-strengthened high-manganese stainless steel of nominal composition 18Mn-5Ni-16Cr-0.02C-0.22N was determined in the intermediate stress-intensity factor range (20–70 MPa√m) at 77 and 4 K. Fractographic investigations were performed on the fracture surfaces. The FCGR at 4 K was very nearly the same as at 77 K and substantially below the FCGR for AISI 304LN steel. The fracture surfaces of both the high-manganese alloy and the 304LN showed a transgranular failure mode, but the detailed fractographic features varied with temperature and alloy type. The fractography was closely related to changes in the FCGR.
Correlation of the Parameters of Fatigue Crack Growth with Plastic Zone Size and Fracture Micromechanisms in Vacuum and at Low Temperatures
Authors: Verkin BI , Grinberg NM , Serdyuk VA
Published: December 2008

Much attention has been paid recently to the kinetics and micromechanisms of fatigue crack growth in various materials. Of particular interest are magnesium alloys, which find expanding applications in structures requiring high specific strength. This paper reports experimental results on Mg-Nd-Zr, Mg-Y-Cd, and Mg-Y-Cd-Zn alloys in different structural states. We measured the fatigue crack propagation rates and the values of the threshold point Kth, the transition points K1−2, K*, and K2−3, and the critical point Kfc in air at 293 K and in a vacuum of 10−4 Pa at 293 and 140 K. The plastic zone size around a fatigue crack was studied by X-ray diffraction and the micromechanisms of its growth by electron fractography.

Vacuum is shown to produce a decrease in the rate of fatigue crack growth in the whole range of Kmax values, while Kth and Kfc remain undergoing. The effect of vacuum was most prominent in thermally hardened alloys undergoing cyclic softening. A reduction in temperature from 293 to 140 K produced an increase in Kth and a decrease in the rate of fatigue crack growth in Region I and at the beginning of Region II for all alloys. In Region III, however, the rate of fatigue crack growth and Kfc changed ambiguously.

The plastic zone size was found to be larger in vacuum than in air; a reduction in temperature produced a decrease in its value regardless of the alloy structural state. The micromechanisms of fatigue crack growth were found to be dependent on composition and initial structural state of alloys, and variations in these parameters with low temperature correlated with the plastic zone size and the rate of fatigue crack growth. Our studies show the existence of certain structural and substructural criteria for the transition points K1−2, K*, and K2−3.
Spectroscopic Probing of Solvation Interactions
Authors: Wirth MJ , Koskelo AC , Mohler CE , Hahn DA , Sanders MJ
Published: December 2008

Three spectroscopic methods have been developed to probe structures of solvation environments in organic solutions: electronic band broadening measurements, two-photon perturbation studies, and fluorescence depolarization experiments. The results of each spectroscopic study indicate that the method does sense solvation structural effects rather than a completely amorphous liquid. The application of these probes is especially promising for investigations of liquid chromatographic retention mechanisms, and a preliminary study of the separation of aromatic isomers is discussed.
Global and Nonglobal Rotations in Proteins Detected by Fluorescence Polarization
Authors: Chen RF , Scott CH
Published: December 2008

Fluorescence polarization methods have been used to assess protein motion for about three decades. These methods are still evolving, but basically can be divided into three classes: (1) steady state methods, (2) time-resolved anisotropy measurement, and (3) differential polarized phase fluorometry. A brief overview of these methods is given, and data are presented on proteins that are unlabeled, or conjugated with dansyl (1-dimethylaminonaphthalene-5-sulfonyl) group. The experiments show that the dansyl label exhibits a fast thermally activated motion, which is viscosity independent, as well as a slower motion characteristic of the global rotation of the protein as a whole. Data on the intrinsic ultraviolet fluorescence of proteins show that the global rotation rate can be obtained from steady state data, which also can detect independent motion of the tryptophan residues. Time-resolved anisotropy data are presented showing directly the rapid rotation of the dansyl group. These data illustrate the ease with which polarization data detect global and nonglobal rotations in proteins.
Some Photoacoustic Studies of Consequence in Luminescence Spectroscopy
Authors: Kirkbright GF
Published: December 2008

In photoacoustic spectroscopy (PAS) the signal response with respect to wavelength of incident radiation is detected as heat at the surface of the sample that results from nonradiative relaxation of the excited states produced on absorption by the molecular species in the sample. This process is complementary to radiative relaxation via luminescence, and study of photoacoustic signals can give information concerned with the quantum efficiency of luminescence processes. The manner in which absolute quantum efficiencies can be determined for both solid and liquid samples with simple instrumentation and without reference to luminescence standard materials is described.
Synchronous-Excitation Fluorescence Applied to Characterization of Phenolic Species
Authors: Purcell FJ , Kaminski R , Obenauf RH
Published: December 2008

Synchronous-excitation fluorescence (SEF) spectroscopy promises to be a quick, sensitive, and highly selective technique for the determination of hazardous contaminants. This work concentrates on detection of the phenols that pervade many areas of everyday life. Phenols frequently found in streams and groundwater as industrial pollutants also result as degradation products of green plants. The primary concern for these phenols is their known carcinogenic nature. In conjunction with derivative spectroscopy, synchronous-excitation fluorescence detects phenols in the parts per billion range and discriminates between common variants. By scanning the excitation and emission monochromotors with a 3-nm offset between them, each phenol species is characterized by a single peak. The water-Raman band, the prime interference at dilute concentrations in normal fluorescence, is also eliminated with the synchronous technique. Further, when derivatization is applied to the data, isomers, whose synchronous peaks occur within 5 nm of one another, can be separated from a mixture.
Fracture Behavior of SiC Matrix Composites Reinforced with Helical Tantalum Fiber
Authors: Kagawa Y , Nakata E , Yoshida S
Published: December 2008

The present study was started to examine the effect of ductile metallic fiber on the toughness and fracture behavior of engineering ceramics. Helical fibers were used for the purpose of better ensuring stress transfer from the matrix to the fiber than straight fibers.

A length of tantalum fiber 0.4 mm in diameter was formed into two types of helix. Helical or straight fibers were incorporated in a silicon carbide (SiC) matrix. The fibers were unidirectionally aligned to the longest axis of a specimen with uniform spacings. Specimen dimensions were 10 by 10 by 55 mm. Specimens were prepared by means of vacuum sintering. The volume fraction of the fiber was varied from 0.01 to 0.04. Three-point bending tests were carried out at room temperature in air. Measurement of the acoustic emission signal was made to investigate the fracture process of the composites. Results were compared with three kinds of specimens: helical fiber reinforced composites, straight fiber reinforced composites, and SiC matrix alone.

It was found that the fracture of the composites reinforced with tantalum fiber, whether straight or helical, was not so catastrophic as to be shattered to pieces like that of the SiC matrix alone. This arises because in fiber reinforced composites, fibers bridge the crack surfaces which have occurred in the matrix and carry the load which the matrix supported before fracture. But the fracture behavior of both types of composites differs in detail depending on their fiber geometry. The maximum load supported by the specimen after the matrix fracture was larger in the helical fiber composites than in the straight fiber composites. This seems to be due to the fact that the stress-transfer effect between the matrix and fiber was better for the helical fiber composites than for the straight fiber composites. Also, multiple fracture of the SiC matrix was observed in the helical fiber composites. Moreover, the total work done up to the complete fracture of a specimen, which was estimated from the load-displacement relation, was different by the fiber geometry and this was due to the differences of the energy absorption mechanism of the composites.
Damage Initiation at Curved Free Edges: Application to Uniaxially Loaded Plates Containing Holes and Notches
Authors: Klang EC , Hyer MW
Published: December 2008

This paper extends two ideas that have been used in the study of straight free edges to the case of curved free edges. The first idea is based on the notion that it is the differences in material properties of adjacent laminae that are responsible for initial free-edge interlaminar damage. To extend this to curved free edges the idea must be interpreted in terms of differences in shear and elongation strains of adjacent laminae. This interpretation involves both the material property differences and the spatial distribution of laminate strain at the hole edge. It is shown that a large strain level and a small difference in material properties can be as damaging as a small strain level and a large difference. From this it is evident interlaminar damage will probably begin at some circumferential location other than the net section. To explore these findings, the second extension was necessary. Specifically, the edge replication technique, using acetate film, was extended to record damage at a curved free edge. For a curved free edge the standard polishing technique was modified, as were the steps necessary to actually make a replica. These points are discussed in the paper. Finally, the damage recorded from uniaxially loaded plates containing central circular holes and semicircular edge notches are compared with the predictions of the difference theory.
An Evaluation of the Effects of Stacking Sequence and Thickness on the Fatigue Life of Quasi-Isotropic Graphite/Epoxy Laminates
Authors: Harris CE , Morris DH
Published: December 2008

A test program has been conducted in which the effect of specimen thickness on the fatigue lives of quasi-isotropic, graphite/epoxy lamintes was investigated. Three replicate specimens for each notched and unnotched geometry at 16, 32, and 64-ply thicknesses of a [90/45/0/–45]ns and [45/0/–45/90]ns laminate were tested in compression-compression fatigue. The fatigue lives of the notched specimens did not appear to be a strong function of laminate stacking sequence or specimen thickness. The stress concentration at the hole dominated over the interlaminar stresses at the straight free edge. The unnotched specimens of the [90/45/0/–45]ns laminate with tensile interlaminar normal stresses delaminated more readily than did the [45/0/–45/90]ns laminate with compressive interlaminar normal stress. The life of the 16-ply unnotched specimens was lower than was the life of the 32 and 64-ply specimens. Delaminations were located at the interface where the maximum τxz shear stress occurred regardless of the sense of magnitude of the interlaminar normal stress. Finally, a specially designed antibuckling fixture was found to be effective in preventing out-of-plane motion without overconstraining the specimen.
Fatigue Response of Notched Graphite/Epoxy Laminates
Authors: Kress GR , Stinchcomb WW
Published: December 2008

Although composites have gained widespread use, we do not, as yet, have a precise and complete understanding of the mechanisms of damage development in composite materials. Recent research results have pointed out the need to treat damage as a collective condition—that is, a damage state, rather than as an assembly of discrete and independent damage modes. This paper presents the results of an investigation to determine the damage states which develop in two quasi-isotropic graphite/epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Damage was monitored nondestructively throughout the loading history using X-ray radiography, moiré interferometry, and stiffness change. Some specimens were deplied after specific numbers of cycles to determine the distribution of damage in each ply around the hole and to confirm the components and size of the damage state observed nondestructively. Fatigue life and residual strength tests were also performed.

Fatigue damage in the two laminates included matrix cracks in all plies followed by delaminations. The density of matrix cracks and the distribution of the damage zone (matrix cracks plus delaminations) in laminates cycled at the same percent of notched tensile strength were strongly dependent on the local constraint and distribution of interlaminar stresses as governed by the stacking sequence. The distinctly different damage states which developed in the two initially quasi-isotropic laminates due to similar load histories produced stiffness changes of 15% to 20%, different rates of change in residual strength (an initial increase followed by a decrease), and a factor of two to four difference in fatigue life.
Analysis of Behavior of Fibrous Composite Compression Specimens
Authors: Rehfield LW , Armanios EA , Changli Q
Published: December 2008

Unidirectional laminated composite specimens reinforced with end tabs are analyzed. The stress field in the laminate-tab interface and within the laminate is predicted using a new analysis method. The method is simple and does not require extensive numerical computations. Results are obtained in closed form. Selected examples are modeled also by finite elements in order to verify that the simple analysis method yields good results. Analyses of previously tested specimens provide a plausible explanation of observed behavior. The present analysis method facilitates specimen design and data interpretation and, therefore, aids in overcoming many of the difficulties associated with the compression testing of composite laminates.
Dynamic Response of Flat Integrally Stiffened Graphite/Epoxy Panels Under Combined Acoustic and Shear Loads
Authors: Soovere J
Published: December 2008

This project involved an experimental investigation into the effect of a high random acoustic loading, in combination with a static shear load near initial buckling, on the dynamic response of integrally stiffened graphite/epoxy panels. The program covered the design, fabrication, finite-element analysis, and testing of a J-stiffened monolithic panel and a J-stiffened minisandwich panel. The minisandwich panel had a syntactic core containing glass micro-balloons. The panels were designed to an initial shear buckling load of 17.51 kN/m (100 lb/in.). The predicted initial shear buckling load was, generally, in good agreement with the measured load. The damping, in all of the modes, increased significantly on approaching buckling. The root-mean-square strain, at the critical panel location, increased by as much as 30% in the vicinity of panel buckling, in spite of the increase in the damping.
Dispersive Wave Propagation in Random Particulate Composites
Authors: Kinra VK
Published: December 2008

Propagation of ultrasonic waves has been studied in random particulate composites at low, intermediate, and high frequencies. The principal objective of this experimental work is to demonstrate the existence of two separate branches of wave propagation: a low-frequency acoustical branch where the inclusions move essentially in phase with the matrix and a high-frequency optical branch where inclusions move essentially out of phase with the matrix. The two are separated by a well-defined cutoff frequency which corresponds to the rigid-body-translation resonance of the relatively heavy inclusions. The measured values of the cutoff frequency were found to be in excellent agreement with an elementary model of Moon and Mow. To the best of our knowledge this is the first experimental observation of the optical branch and of the cutoff frequency.
Ferrite-Resin Composite Material for Vibration Damping
Authors: Yamauchi F , Emoto S
Published: December 2008

Newly developed ferrite-resin composite materials have high rigidity (E = 1.8 × 109 N/m2) and high mechanical damping constant (in a logarithmic decrement, Δ = 1.1). The composite materials were used effectively for loudspeaker enclosure humming suppression. It is also convenient to use the composite materials in a paste state. They were applied to a hopper and a machine base for vibration control.
Finite-Element Analysis of Interlaminar Shear Stress Due to Local Impact
Authors: Ross CA , Malvern LE , Sierakowski RL , Takeda N
Published: December 2008

Interlaminar delamination may occur as a result of a nonperforating low-velocity impact of a foreign object against a continuous-fiber composite laminate. Experimental evidence shows that for a crossplied laminate consisting of three lamina and subjected to a central localized impact, one delamination region will extend farther from the impact point than the second region.

To establish a quantitative value for the interlaminar shear stress of a crossplied fibrous composite plate subjected to a central impact, a finite-element computer program has been utilized. Specifically, a three-dimensional dynamic-elastic-orthotropic-material finite-element program has been used in which the interlaminar shear stress can be calculated directly. This program was used to evaluate the interlaminar shear stresses for a [05/905/05] glass/epoxy plate with built-in edges, and subjected to a load simulating a central localized impact of 45.7 m/s by a cylindrical steel projectile.

Results of the calculations show a region of large shear stress (exceeding the estimated shear strength of the matrix material) extending from the impact point toward the boundary in the 0-deg direction while a region of large shear stress in the transverse 90-deg direction was found to be much smaller. Also, only minor differences in calculated shear stresses were evident in the interlaminar plane immediately below the impact point when compared with the interlaminar plane farthest from the impact point. The high-shear-stress regions agreed qualitatively with the areas observed in experiments.
Short Fiber Reinforced Magnetic Powder Cores
Authors: Morita M , Ochiai K , Kamohara H , Arima I , Aisaka T , Horie H
Published: December 2008

Short fiber reinforced magnetic powder cores were investigated. The powder cores were made of iron powders and insulating resin by a compression molding process. Aramide fiber (Kevlar) chopped strand reinforced cores show very tough characteristics compared with those made without the fiber, and also show that they have suitable magnetic properties for magnetic wedges.
Manufacture of Carbon-Carbon Composites by Using Fine Coke and Its Properties
Authors: Cho T , Okura A
Published: December 2008

A fabrication of a carbon-carbon (C/C) composite, in which fine pulverized coke is used as carbon material of matrix, was carried out using three types of carbon fibers, that is, short fibers, long fibers, and cloth. The bending strength of the composite is highest with long fibers 3 to 5 times as high as of ordinary carbon material, then cloth and short fibers. A still stronger C/C composite could be obtainable with long fibers by improving dispersion of these fibers in the matrix. Accordingly, the C/C composite obtained through this study imply a success in development of such composite materials by means of a simple process.
Toward Process Optimization by Monitoring the Electrical Properties During the Cure Cycle for CFRP
Authors: Minoda Y , Sakatani Y , Yamaguchi Y , Niizeki M , Saigoku H
Published: December 2008

Application of advanced composite materials, namely carbon fiber reinforced plastic (CFRP) (graphite/epoxy) to aerospace structures is currently expanding from simple components to complex-shape integrated structures. The objective of this study is to establish the feasibility of optimizing the cure cycle of integrated CFRP structure by in-process direct measurement of electrical properties of the article in an autoclave.

An instrumentation technique that included material and shape of electrodes and an insulator and bleeder system was investigated. Experimental studies using the above test setup attempted to determine correct pressurization timing under certain preprogrammed heating patterns thus resulting in cured CFRP laminates, which were practically voidless, with proper fiber volume fraction and thickness per ply.
Work of Fracture in Metal Matrix Composites
Authors: Daimaru A , Hata T , Taya M
Published: December 2008

When one talks about “fracture toughness” of composites, one must be careful in distinguishing the energy release rate for the initiation of a crack (γI) and the energy absorbed during the fracture averaged over the whole history of fracture process (γF). Unlike metals, the value of the critical stress intensity factor KIc of composite was found not to reflect any basic material property. Instead, the measurement of γF seems to represent a meaningful toughness property of composite when the composite is a mixture of brittle and ductile phases, such as metal matrix composites (MMCs).

We have recently conducted experimental and analytical study on the value of γF of unidirectional fiber MMC and obtained a good agreement between the experiment and theory. In this paper, we report the experimental and theoretical results on a particulate MMC. The results of two different types of MMCs have revealed that three-point bending test of the MMC specimen with center notch can be used as a reasonable method to measure γF.
Liquid Crystal Film Visualization Approach to Fracture in Composites
Authors: Kobayashi A , Suemasu H
Published: December 2008

The cholesteric liquid crystals indicate a change of color in response to the temperature change by reflecting the specified wavelength of light due to the pitch alternation caused by the temperature change in the molecular layer of a liquid crystal, indicating red at lower temperature and blue at higher temperature.

Using these liquid crystals, heat evolution during rapid crack propagation can be estimated. However, rather much errors have been introduced due to poor response of liquid crystals.

In the present study, the heat evolution produced during rapid fracture in composites will be calculated through the improved dual-layer liquid crystal film method, which is to improve the response and to increase the accuracy in measurement of isothermal colored boundaries appeared in the liquid crystal film during fracture by obtaining two isothermals, T1 and T2, necessary for heat evolution calculation, at an earlier period of time after fracture, and by making the spacing between isothermals larger, leading toward the easier discrimination of colored boundaries, resulting in fewer errors. The results show that the time required to obtain two isothermals is reduced even by 50% for the glass-fiber composites. A videotape recorder system is used to record the colored isothermals, and velocity gages to measure the crack propagation velocity.

Thus obtained heat evolution is correlated with the crack propagation velocity.