bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carrier Lifetime Measurements for Process Monitoring During Device Production
Authors: Graff K , Pieper H 
Published: March 2009

Carrier lifetime measurements were performed in silicon crystals in order to characterize the quality of the material and to control the device production process. For process monitoring, floating-zone n-type silicon of high resistivity was used, since p-type silicon in general exhibits pronounced axial and radial profiles of carrier lifetime.
The influence of various atmospheres during heat treatment on the final carrier lifetime in n-type silicon was investigated. Oxygen with and without additional hydrochloric acid increased the carrier lifetime, while hydrogen, in comparison with inert gas atmospheres, decreased it. Gold, copper, and iron were found to be the main heavy metal impurities introduced into silicon specimens by heat treatment. The iron content varied considerably with the atmosphere used during annealing, showing the highest concentrations for hydrogen. Fast cooling of specimens after heat treatment produced carrier lifetimes that were unstable with the time elapsed after quenching.
Radial Lifetime Profiling on Silicon Specimens by the Photoconductivity Decay and Photocurrent Methods—A Comparison
Authors: Vieweg-Gutberlet FG , Siegesleitner PF , Stallhofer M 
Published: March 2009

Radial profiles of the minority carrier lifetime of silicon specimens, obtained by the photoconductivity decay (PCD) method and the photocurrent method have been compared. The photocurrent method used on slices gives more or less the same spatial resolution as a modified PCD setup reported by Graff, used on cross-sectional bars. Some problems occur when the photocurrent method is applied to p-type silicon samples.
For each of the methods a typical application exists: the photocurrent method is an important and relatively easy-to-handle tool for the investigation of the lifetime behavior of silicon wafers during the heat treatment and oxidation process, and the PCD method enables a very fast test of the lifetime (and lifetime profiles) to be made on the starting ingot material.
Solid-Particle Erosion of High-Technology Ceramics (Si3N4, Glass-Bonded Al203, and MgF2)
Authors: Gulden ME 
Published: March 2009

Four “engineering” ceramics were subjected to impact (single particle) and erosion (multiple impacts) under conditions which simulate a natural dust environment in the subsonic velocity regime. The target materials are hot-pressed silicon nitride (Si3N4), reaction-bonded Si3N4, a glass-bonded aluminum oxide (Al2O3), and hot-pressed magnesium fluoride (MgF2). Tests were performed with six narrow size ranges of natural quartz between 10 and 385 μm average, and five velocities for each particle size. Hot-pressed Si3N4 was also impacted with silicon carbide (SiC) under the same particle size-velocity conditions.
The results are discussed in terms of current erosion and impact models by considering particle size-velocity dependencies, appearance of the impact damage, and the basic properties and structure of the targets.
Under these erosion conditions, the four target materials exhibited widely different behavior not only in absolute amount of material removed, but also in mechanism of removal. The systems hot-pressed Si3N4-SiC particles and MgF2-quartz particles were characterized by a highly deformed, permanent surface crater with associated lateral and radial crack formation, and erosion loss was proportional to particle mass and velocity, both to the fourth power. Erosion of hot-pressed Si3N impacted with quartz particles was proportional to the third power of particle size and the first power of velocity, and loss occurred by minor chipping with no secondary crack formation. Erosion of glass-bonded A12O3 and reaction-bonded Si3N4 did not show a consistent particle size-velocity dependence. The variation is related to the two-phase structure of these materials. It was found that strength is not necessarily reduced for erosion conditions which produce appreciable material removal.
Erosion Damage in Carbon-Carbon Composites at Hypersonic Impact Velocities
Authors: Adler WF , Evans AG 
Published: March 2009

The damage to three-dimensional orthogonal carbon-carbon composites created by particle impacts ranging from 1800 to 6000 ms-1 has been characterized for three weave constructions at both ambient and temperatures up to 3600¼C. The subsurface damage modes in the vicinity of the impact crater are described for the range of conditions investigated. Hypotheses are advanced concerning the failure modes and kinetics for the material ejected from the crater based on examination of sectioned specimens and high-speed photographic sequences.
Kinking of the longitudinal and lateral fiber bundles is found to be the primary damage mode. Kinking of the longitudinal fiber bundles under the impact site (which controls the depth of the impact crater) displays a relatively minor dependence on the bundle dimensions. The lateral extent of the impact crater is dependent on the longitudinal fiber bundle content—decreasing as the bundle dimensions increase. It is hypothesized that kinking of the longitudinal fibers leads to this removal, which is related to kinking of the adjacent lateral fiber bundles which increases with the particle impact velocity.
CAVIJET Coal-cutting parameters
Authors: Conn AF , Rudy SL 
Published: March 2009

Laboratory coal-cutting experiments with CAVIJET cavitating waterjets have demonstrated the feasibility of this technology for hydraulic coal mining applications. The objective of the first phase of a developmental program, as described in this paper, was to determine the system and operating parameters required to cut coal with CAVIJETS, and to compare the results with those observed for noncavitating jets.
Comparable coal cutting was achieved with the CAVIJET, relative to high-pressure, noncavitating jets, using one-fifth the pressure and one-half the specific energy. These results suggest that CAVIJET-augmented mining devices can be developed with compact, low-pressure pumps. Thus, CAVIJET should be capable of operating with safer, lighter, more suitable support equipment, while providing all of the advantages (reduction of dust and sparks; decreased damage to cutters) of conventional hydraulic mining methods.
An Elastic-Plastic R-Curve Description of Fracture in Zr-2.5Nb Pressure Tube Alloy
Authors: Simpson LA , Clarke CF 
Published: March 2009

An R-curve approach was investigated with the aim of establishing a means of predicting critical crack lengths in Zr-2.5Nb pressure tubes using small fracture-mechanics specimens. Because of the elastic-plastic nature of the fracture process and limitations on the maximum specimen size, conventional R-curve methods were not applicable. The crack growth resistance was therefore expressed in terms of the crack opening displacement (COD) and R-curves were plotted for several sizes of specimens and crack lengths at 20°C and at 300°C. The effect of hydrogen on R-curve behavior at these two temperatures was investigated as well.
Conventional clip-gage methods were not suitable for this work. Crack length was determined from electrical resistance, and COD, at the actual crack front, was determined from photographs of the specimens taken during testing. Crack length and specimen size had little, if any, effect on the R-curve shape. A method for expressing crack growth resistance in terms of the J-integral was also investigated and appears to be consistent with the COD approach. The effects of hydrogen and temperature on R-curve shape are consistent with their known effects on the mechanical behavior of Zr-2.5Nb. Finally, predictions of critical crack length in pressure tubes obtained by matching R-curves to crack driving force curves are consistent with published burst-testing data.
Flight-by-Flight Spectrum Development
Authors: Denyer AG 
Published: March 2009

A method of developing the design flight-by-flight sequenced stress spectrum at any location within the primary airframe structure is presented.
The procedure commences with the applicable procurement specifications for the aircraft and concludes with the detail's local stress spectrum suitable for fatigue and fracture mechanics analyses or testing. The stress spectrum is created within a computer program that utilizes input data comprising mission profiles, structural location data, libraries of load factor exceedance data, balanced external load conditions, and corresponding internal loads solutions. The output consists of the spectrum in tabular form and the time trace graphs of the stress amplitude.
Included is a typical spectrum developed for a variable geometry bomber with terrain-following capability, and discussion as to load sequence effects and the structural internal loads solutions necessary to describe the stress trace on a mission-by-mission basis.
Finally, the system-generated spectrum is discussed in terms of its effect on fatigue and fracture mechanics analysis.
Derivation of Flight-by-Flight Spectra for Fighter Aircraft
Authors: Kaplan MP , Reiman JA , Landy MA 
Published: March 2009

The importance of predicting the durability and damage tolerance capability of aircraft structures has underscored the need to derive a realistic flight-by-flight stress spectrum. This stress spectrum is generated from an analysis of the projected usage (mission profiles), combined with load factor exceedance curves that are obtained either from MIL-A-8866B or recorded data. The mission profiles are defined by the using command (the organization which flies the aircraft) and contain such information as mission length, number of times flown per aircraft lifetime, fuel load, weapons configuration, and a breakdown of the mission by segment, for example, takeoff, climb, cruise, descent, etc.
This paper describes two different approaches for obtaining load factor exceedance curves: (1) MIL-A-8866B and (2) data recorded from a different aircraft flying a similar mission. In the first example, the spectrum is derived for a ground-attack fighter that is in the design phase (that is, has never flown) and in the second case, the spectrum is derived for an aircraft that has already been built but is being used in a new mission (flight demonstration squadron). In this second case, a large amount of recorded load factor exceedance data exists from a different aircraft flying the same mission. Using either exceedance curve approach, these data are combined with the mission profile data to develop a stress-exceedance curve for each mission. The stress-exceedance information then is input to a computer program, along with some additional data such as the number of times a given mission is flown. The computer program first generates a random mission ordering and then randomly orders the stresses within each mission. The final result is a random flight-by-flight stress spectra suitable for use in performing damage tolerance and durability analyses and tests.
Direct Observation and Mechanism of Fatigue Crack Propagation
Authors: Kikukawa M , Jono M , Adachi M 
Published: March 2009

Fatigue crack propagation tests were carried out by using a specially designed testing apparatus in a scanning electron microscope. A grain-oriented silicon iron was used as a testing material and it was found that a nearly plane-strain state could be realized up to the specimen surface by selection of the loading axis to the specific orientation of the material. From the sequential observations of crack opening and closure behavior the mechanism of fatigue crack propagation by Mode I opening was confirmed to be an alternating slipping-off process at the crack-tip apex.
Quantitative evaluation of a relationship between crack-tip opening displacement and crack growth length is given by considering the slip direction, crack tip angle, and the amount of rewelding. Also, a relation between crack growth length and slipped length in Mode II fatigue cracks is discussed.
Fatigue Damage Mechanisms in Composite Materials: A Review
Authors: Stinchcomb WW , Reifsnider KL 
Published: March 2009

Some of the earliest investigations concluded that the basic mechanisms of fatigue in composites and fatigue in homogeneous materials differ greatly. Instead of the initiation and propagation of a fatigue crack traditionally identified with homogeneous materials, fatigue in composites consists of various combinations of matrix, fiber, and interfacial cracks and debonds to form a very complex damage state. Furthermore, fatigue mechanisms are dependent upon a number of parameters, including the material system, stacking sequence of plies, geometry, stress state, and environment.
The variety of damage modes, the complexity of their interactions, and the subsequent effect on engineering properties make it difficult to interpret fatigue damage in order to define and predict fatigue failure or lifetime for composite materials. A brief synopsis of the current knowledge of fatigue damage mechanism in fiber-reinforced composite materials is presented along with some suggestions to help advance the level of understanding of the fatigue response of composite materials.
Delrin as a Material for Joint Prostheses—A Review
Authors: Dumbleton JH 
Published: March 2009

Delrin acetal resins are thermoplastic polymers manufactured by the polymerization of formaldehyde. The use of Delrin in total hip prostheses was first suggested in the mid-1960s. The attraction of Delrin is that the creep resistance is ten times that of ultrahigh molecular weight polyethylene, the most usually used plastic material. In addition, Delrin is about five times harder than ultrahigh molecular weight polyethylene and thus will resist the abrasive action of bone chips and acrylic cement particles.
Since 1970, Delrin acetal polymer has been used in the Christiansen total hip prosthesis and in the Christiansen endoprosthesis. Up to the end of 1977, approximately 7000 surgical procedures had been carried out with the prosthesis. The results have been very good. Prostheses removed for cases of infection or loosening have not shown wear on the articulating Delrin components. Furthermore, histological studies of the surrounding tissue show a benign tissue response similar to that seen around polyethylene implants. The Christiansen prosthesis has been recommended as a Class II device by the U.S. Food and Drug Administration.
Studies on the performance of Delrin in the Christiansen total hip prosthesis have been carried out in a hip joint simulator at the University of Cincinnati. These investigations showed that the Delrin wear rate was similar to the wear rate of polyethylene in the Charnley or Charnley-Müller hip prosthesis configuration. In addition, studies on the simulator showed that although acrylic cement fragments caused deformation and scarring of polyethylene when entrapped between the joint surfaces, a similar phenomenon did not occur for Delrin.
The mechanical properties of Delrin have been investigated over many years, and a comparative table is shown, demonstrating the superiority of Delrin over ultrahigh molecular weight polyethylene, in relation to hardness, creep resistance, and strength.
Wear studies on Delrin in the laboratory have been carried out at several locations. The wear of Delrin has been shown to depend upon the test environment, the wear rate being lower with blood plasma as a lubricant than with distilled water. There is agreement on this between tests carried out at the University of Cincinnati and at the Royal National Orthopaedic Hospital in London. However, tests carried out at the Orthopedics Department of the University of California at Los Angeles (UCLA), show that the wear rate of Delrin does not depend upon the liquid test environment, although much higher wear rates will be obtained if the wear test is carried out under dry conditions. However, the tests at UCLA indicate that the wear rate of Delrin is acceptable for total hip prosthesis end use.
The results, taken in conjunction with the clinical findings, suggest that Delrin performs well in the Christiansen total hip prosthesis configuration. Work is at present under way to study the use of Delrin for a tibial plateau in an unconstrained knee prosthesis.
Fracture and Corrosion in Stainless Steel Total Hip Replacement Stems
Authors: Dobbs HS , Scales JT 
Published: March 2009

Thirty-two stainless steel Charnley total hip replacements were examined; 23 of these had been removed from patients after a period of implantation, twelve as a result of fracture. All the components were forgings produced by the same manufacturer. The majority of the components (Type 1) were about eight years old and were manufactured from air-melted EN58J stainless steel with a maximum permitted carbon content of 0.06 percent (this steel is similar to Type 316 stainless steel). The remainder (Type 2) were about four years old and were manufactured from vacuum-melted material with a maximum permitted carbon content of 0.03 percent (similar to 316L stainless steel). The following results were noted:
1. The material in the Type 1 implants was often sensitized and contained many inclusions. The material in the Type 2 implants was never sensitized and contained fewer inclusions but had a larger grain size than the Type 1 material.
2. In both types of implant, fracture initiation was not obviously associated with corrosion, and the influence of the patient' weight and activity seemed to be more important than that of metallurgical defects.
3. In the Type 1 components, intergranular corrosion occurred in sensitized regions. and the severity of the corrosion increased with the period of implantation. The incidence of corrosion of all kinds was 35 percent for an average implantation time of 46 months. In the Type 2 material, pitting corrosion occurred, but the sample size was too small to allow a meaningful estimate to be made of the incidence of this kind of corrosion.
4. Other surface markings were observed, including fretting due to abrasion by acrylic cement.
5. It is the authors' opinion that the main consequence of corrosion may be an eventual undermining of the integrity of the clinical procedure rather than the destruction of the component itself.
Moisture Diffusion Analysis of Microstructure Degradation in Graphite/Expoxy Composites
Authors: Leung CL , Dynes PJ , Kaelble DH 
Published: March 2009

Directional diffusion coefficients, that is, D1, D2, and D3, for the principal axis i = 1, 2, 3 of a unidirectional fibrous composite were determined by moisture absorption measurements. It was shown that the initial moisture absorption of a cured dry composite is non-Fickian and may relate to microstructural relaxation of internal stresses.
Moisture effusion rates of the specimens were also evaluated. Absorption-desorption kinetics over several cycles showed that there exists a damage mechnism in the composite which enhances moisture uptake from the dry state but does not enhance moisture release from the water-equilibrated state.
Analysis of Sets of Two-Parameter Weibull Data Arising in Rolling Contact Endurance Testing
Authors: McCool JI 
Published: March 2009

Frequently in conducting rolling contact endurance tests, several small samples are subjected to some kind of “treatment.” It is shown herein that if the treatment affects the rating life but not the Weibull shape parameter the data can be analyzed as a set rather than as individual samples, with considerable improvement in the precision with which the rating lives can be estimated.
Methods and supporting tables are given for the detailed analysis of sets of such data under the assumption that they represent censored data samples drawn from two-parameter Weibull populations.
The complete analysis consists of the following: (a) a test for the equality of shape parameters among the populations, and, when a common shape parameter is found to be plausible, (b) two tests for the equality of scale parameters or any fixed percentile, (c) an interval and bias-corrected point estimation of the common shape parameter and the tenth percentiles of the individual groups, and (d) a procedure for assessing which of the populations differ in their scale parameter and, hence, any percentile values.
The numerical values of key percentage points of the relevant distributions required for carrying out the analyses cover the range from k = 2 samples of size n = 5, censored at the third (r = 3) failure, to k = 5 and n = r = 30. As an illustration, the analyses are applied to two sets of rolling contact endurance data obtained with various steel materials fabricated into cylindrical rod and ball test specimens.
Two procedures for the selection of sample size are discussed, and illustrative examples are given of their use.
Crack Propagation Measurements on Glass: A Comparison Between Double Torsion and Double Cantilever Beam Specimens
Authors: Champomier FP 
Published: March 2009

A simple and rapid method of measuring crack propagation in glass was sought. Double torsion (DT) and double cantilever beam (DCB) specimens that allow KIc values as well as (K, V) diagram determinations were tested successively, using relatively large testpieces (250 by 100 by 6 mm).
In the case of DT specimens, it is shown that relaxation experiments do not require the prior determination of specimen compliance. Excellent reproducibility thus is obtained. The technique is easy to master, but the crack front profile is not taken readily into account.
Relaxation of DCB specimens reveals the important role played by the specimen compliance compared to the testing machine compliance. Experiments are not conducted as easily as in the previous case.
In both cases, it is shown that the minimum speed that can be achieved practically during a relaxation experiment on glass is of the order of 10 −7 ms−1.
Results were obtained on float glass in ambient air. They are in satisfactory agreement and compare favorably with published data.
Fracture from Controlled Surface Flaws
Authors: Petrovic JJ , Mendiratta MG 
Published: March 2009

The use of controlled surface flaws to examine fracture properties of brittle materials is reviewed. Surface flaws are introduced by microhardness indentation. Such flaws are semi-elliptical in shape, with dimensions dictated by the indentation load.
A single flaw of proper size placed on the tensile surface of a conventional four-point bend specimen initiates fracture because it is the “worst flaw” in the specimen. Presence of the flaw reduces both the fracture strength and its associated scatter. Because controlled surface flaw dimensions are generally visible on the fracture surface, the critical stress intensity factor, KIc , may be calculated using fracture mechanics analyses for surface flaws in bending.
Such a fracture mechanics test is experimentally convenient, adaptable to testing in severe environments, and requires a relatively simple test specimen geometry. Also of importance is the fact that the fracture flaw dimensions are close to those of the natural flaws in the material. For silicon nitride (Si3N4) and silicon carbide (SiC) the technique has been employed to determine KIc at room and elevated temperatures, as well as under dynamic loading conditions. It has also been used to study slow crack growth, environmental effects, and mixed-mode fracture in these materials. Disadvantages of the controlled surface flaw technique as well as potential new applications are discussed.