bluuebunny/crossref_metadata_2025 huggingface dataset:
Pitfalls to Avoid in Threshold Testing and its Interpretation
Authors: Bush RW , Donald JK , Bucci RJ
Published: April 2008

The impact of a number of testing variables on the measurement of fatigue crack growth thresholds is discussed. References are made to the original works from which the current recommendations for measurement of threshold in ASTM E 647 were derived. The applicability of these original recommendations in light of advances made since that time is discussed. In addition, the effects of some commonly overlooked parameters and features, such as residual stress and environment, on the measurement and interpretation of crack growth thresholds are presented.
Use of Small Fatigue Crack Growth Analysis in Predicting the S-N Response of Cast Aluminum Alloys
Authors: Caton MJ , Jones JW , Allison JE
Published: April 2008

The development of a material model to estimate the S-N response of a cast aluminum alloy is described. An important requirement of such a model is sensitivity to processing effects such as solidification time and subsequent material characteristics such as secondary dendrite arm spacing (SDAS), strength, and porosity. It has been speculated that the fatigue properties of aluminum castings are dominated by the propagation of cracks which initiate from microshrinkage pores ranging in size from ∼ 10 to 1000 μm. A model was developed that calculates fatigue life based on small crack growth rates measured in cast 319 aluminum specimens with two different solidification times. Results from this small crack model are compared with predictions from a traditional LEFM model using long-crack data and measured thresholds.
Prediction of Fatigue Limits of Engineering Components Containing Small Defects
Authors: Akiniwa Y , Tanaka K
Published: April 2008

The propagation and arrest behavior of fatigue cracks under various stress ratios was investigated using structural carbon steel specimens having single edge or small surface pre-cracks with lengths ranging from 0.16 to 4.33 mm. The threshold condition of crack extension from pre-cracks was given by a constant value of the effective stress intensity range irrespective of pre-crack length and stress ratio, and the value was equal to the threshold value obtained for long cracks. Cracks extended from pre-cracks were arrested under low stress amplitudes because of the development of crack closure with crack growth. A cyclic resistance curve was constructed in terms of the maximum stress intensity factor which was the sum of the range of the threshold effective stress intensity and the crack opening stress intensity factor, and was used for predicting of fatigue thresholds. The predicted values of the fatigue limit for crack extension, the fatigue limit for fracture, and the length of non-propagating cracks agreed very well with the experimental results. The cyclic resistance-curve method was further applied to predict the effect of the mean stress on the endurance limit of smooth specimens. Haigh diagrams for the endurance limit were successfully derived from the arrest condition of nucleated small cracks in smooth specimens.
ASTM Committee D09—A History of Success
Authors: Mathes KN
Published: April 2008

Historical Aspects: A long history of continued, active use is in itself a measure of success. Methods D 149 (1922), D 150 (1922), D 257 (1925) on electrical tests have been used extensively and even today are being periodically revised and updated. Much the same is true for D 115 (1941) varnish, D 202 (1924) paper and D 229 (1925) rigid sheet and plate plastics. D 495 (1938) dry tracking is generally now recognized as a technical failure, but a commercial success. This standard is still widely used and referenced! Standards D 69 (1920) friction tape, D 295 (1928) varnished cotton fabric and D 748 (1961) shellac, were once very important, are still needed, but today are seldom used.

Technical Concepts and Materials: In 1948 two technical papers, one by Ken Mathes on functional tests and another by Tom Dakin on thermal aging provided a basis for the adequate acceptance and use of the many new insulating materials that were becoming available. First, the Electrical Institute of Electrical Engineers, AIEE (now the Institute of Electrical and Electronic Engineers, IEEE), and then ASTM committee D09 followed with the much needed new approaches and standards—then and still outstanding successes. Tremendous growth in the use of plastics led to the formation of Technical Committee ASTM D20 from subcommittee status in D09. Committee D27 on Insulating Liquids and Gases also split away from D09. New elastomeric materials for cable led to their incorporation as Subcommittee 18 of D09 from their origins in ASTM D11 on rubber.

The subjects of treeing and surface failure (tracking) are extremely important, but today are still, to some extent, goals rather than completed accomplishments.

Instrumentation: The Electronic revolution has been successfully incorporated by D09 in many electrical, mechanical, and physical tests for insulating materials. Methods for very high resistance are an example. Organizational and Government Support: Public Utilities, the Electrical Industry, NIST (originally NBS), the US Navy, NEMA, NASA, and UL have periodically been responsible for outstanding accomplishments in D09. UL continues in the forefront especially in thermal aging. D09 participation in the International Electrotechnical Commission (IEC) is of particular importance. Publications: Symposia, Publications like STPs and Research Reports have often highlighted D09 activity and success.

Individuals: Success is possible only with the technical and organizational skills of dedicated individuals. Many ASTM awards have recognized such accomplishment.

Summary: This abstract can only touch on the foregoing aspects, which are described with more detail in the following paper.
Fire Hazard Testing in the International Electrotechnical Commission Standards: An Overview of IEC TC 89 Activities
Authors: Maennling NN
Published: April 2008

This paper presents an overview of the activities of IEC TC 89—Fire hazard testing. It covers the history of the committee, its status within the IEC and its philosophy of risk reduction. It describes the current publications and projects of IEC TC 89, plus new work as well as the description and activities of its eight working groups.
New Ways of Disruptive Discharge Recognition in Insulation Testing Devices
Authors: Mathis H-J , Baur M , Blank R , Woschitz R , Überfall T
Published: April 2008

The dielectric testing of gaseous and liquid insulation has a long tradition and devices for breakdown testing have improved during the past 40 years. Special liquids like silicone oil, have made it necessary to develop special methods. As a result, methods to recognize the disruptive discharge have changed, as have methods to determine switchoff characteristics and to generate test voltages.

The dielectric breakdown voltage is a variable with a statistical distribution. The test procedure involves a number of single test sequences. To get reliable results, it is of paramount importance to have a minimum of influence from one sequence to the next. This depends on breakdown energy and therefore on breakdown recognition, maximum short-circuit current and also on the switch-off characteristic of the testing device. The development of new, sensitive testing devices enable the energy which is sent into a test sample to be kept at a very low level. This permits a clear differentiation between partial discharge and disruptive discharge.

Investigations in breakdown characteristics and switch-off methods of devices with different techniques across several gaseous and liquid samples with special consideration of the comparability of testing results have been made to improve testing. This article describes new ways of breakdown recognition and switch-off techniques, discusses advantages and disadvantages of the new and better-known methods and discusses the problems of standardization.
Geosynthetic Stress-Strain Curves: Practical Features and Observations
Authors: Peggs ID
Published: April 2008

The features of the ideal elastic-plastic stress-strain curve compared with practical curves are discussed with reference to conventional materials engineering and geosynthetic materials testing practices. Uniaxial and biaxial test curves are compared and referenced to the modes of failure of the two types of test specimens. A comparison of the well-defined yield points in HDPE geosynthetics with the smoother elastic-plastic transitions in LLDPE and PP is presented, together with methods that define artificial yield points. Considerations for the use of one, rather than two, gage length values for the determination of yield and break strain properties during uniaxial tension tests are presented. Plane stress and plain strain behavior of geosynthetics in laboratory uniaxial tests and in the field are compared together with their significance in the stress crack testing and elongation performance in HDPE geomembranes. Reference is also made to the measurement of strain and its significance during the shear testing of seams.
Wide-Width Geomembrane Testing
Authors: Koerner GR
Published: April 2008

Geomembranes are the most widely used components of liner and cover systems throughout the world. Arguably they are the most critical components of such systems. Millions of square meters of geomembrane have been used as liquid barriers over the past 20 years. However, there is debate over how to properly determine the performance tensile characteristic of these materials. This paper attempts to shed some light on obtaining uniaxial performance responses of commercially available geomembranes via ASTM D 4885, Standard Test Method for Determining Performance Strength of Geomembranes by the Wide Strip Tensile Method.

Over the past ten years since the test method was issued, several inconsistencies have been identified with the method. Such inconsistencies make it difficult for laboratories to generate comparable results while utilizing the standard. Areas of concern are specimen preparation, clamping, strain rates and data reduction. It is hoped that the paper may help promote uniform and consistent wide-width geomembrane testing. This paper contends that wide-width geomembrane testing is a performance test and that it should only be used for the purpose of design and research.
Tensile Strength and Clamping of Geogrids
Authors: Müller-Rochholz J , Recker C
Published: April 2008

Through the development and application of high strength geosyntetics, the problem of clamping during the tensile test has become an important theme. The construction of clamping systems is decisive for obtaining a value as close as possible to true tensile strength. For this purpose the theoretical demands on an ideal clamping system are depicted and the development stages of the clamps are shown. The results of tensile tests with different clamping systems are given in Table 1. Infrared images are given to show stress/strain inhomogenity.
Strain Gauging Geotextiles Using External Gauge Attachment Method
Authors: Chew SH , Wong WK , Ng CC , Tan SA , Karunaratne GP
Published: April 2008

Measurement of geotextile deformation allows an in-depth understanding of the behaviour of geotextiles. However, attaching strain gauges to geotextiles poses a challenge as geotextiles are soft and have a fibrous surface. A properly installed strain gauge must not only adhere firmly to the geotextile, but also the method of strain gauge attachment must not change the surface properties of the geotextile significantly. Two common methods of geotextile strain measurement are attaching strain gauges directly to the geotextile with an adhesive agent and mounting electronic sensors by means of two end plates fixed to the geotextiles. The first method will inherently stiffen the localized area of the geotextile due to the introduction of the adhesive agent. In the second method, the electronic sensors are generally large, bulky and expensive. Therefore, a new strain gauging method is proposed which is intended to minimize or eliminate the limitations of the present strain measurement methods. This new method makes use of the idea of attaching gauges “externally” to a thin plastic strip whose ends are connected to the geotextile via two end plates. Hence, the geotextile region where the strain is measured remains virtually unaffected. Because of the relatively low modulus of the plastic strip, its strain is nearly the same as that of the geotextile. The results show that the proposed method is able to measure the true global strain developed in the geotextile with a correction factor of about 1.1. This method allows registration of strains up to about 10% and has very little stiffening effect on the geotextile.
The Influence Factors Study for Geogrid Pullout Test
Authors: Chang DT-T , Chang F-C , Yang G-S , Yan C-Y
Published: April 2008

The interaction coefficient of pullout (μ) between the interface of soil and geosynthetic is known the major parameter for designing the details of the reinforced soil. To obtain this coefficient (μ), it is suggested to perform the pullout test. Some researchers followed GRI or the like to guide the procedures for running this test. However, details of the test have not been clearly identified. In this study, factors that could affect the pullout resistance are subject to further evaluation. One type of thick HDPE, stiff geogrid was used with confinement of sand soil in the confining box. Factors focused in this study include the pullout rates, sleeve lengths, frictional effect of the box wall, and specimen widths. Findings indicated that the optimum pullout rate is 1.0 mm/min for fully mobilizing the pullout resistance and is used for the entire program. Sleeve length of 15 cm is ideal for eliminating the effect of the front wall of the box. With a specimen width of 20 cm, the boundary effect can be reduced to a minimum. Moreover, the results of pullout behavior as in the case of wall with low friction angle (3.7°) is not much different from that of wall with high friction angle (24.7°).
Gate Oxide Reliability Assessment and Some Connections to Oxide Integrity
Authors: Dumin DJ
Published: April 2008

Most characterizations of oxide reliability involve extrapolation of high voltage results to low voltage operation. Wearout at high voltages tends to be global while many reliability attributes, such as breakdown and stress-induced-leakage-currents (SILCs), tend to be local. This paper will explore several oxide reliability assessment attributes, including oxide breakdown, stress-induced-leakage-currents, and trap generation. These attributes will be described and an attempt will be made to associate them with oxide integrity.
Localized Charging Damage in Thin Oxides
Authors: Bersuker G , Werking J
Published: April 2008

In the proposed model, breaking of the oxide chemical bonds is assumed to result from the combined effect of electric field and electron fluence in the oxide during electrical stress. Collision between the injected electron and oxide atoms may excite the bond to an unstable electronic state that can lead to the formation of a structural defect. Electric field polarizes, and thus weakens the defect bonds causing bond breakdown. The model describes charge-to-breakdown dependence on electric field, temperature and oxide thickness. The difference in positive and negative gate bias charge-to-breakdown data is attributed to the presence of the structural strained layer at the Si/SiO2 interface. This approach is used for analysis of the effects of process induced charging stress on transistor parameters. It is shown that leakage current may increase or decrease with oxide thickness depending on the magnitude of the stress induced charging damage.
COCOS (Corona Oxide Characterization of Semiconductor) Metrology: Physical Principles and Applications
Authors: Wilson M , Lagowski J , Savtchouk A , Jastrzebski L , D'Amico J
Published: April 2008

During the past five years great progress has been made in CV replacement metrology which utilizes precise dosing of electric charge on dielectric surfaces achieved with a corona discharge in air. This charge produces controlled changes of electric field in the dielectric film and in the space charge region of semiconductor substrate. The response of the dielectric and semiconductor is monitored in a non-contact manner using three measurements: the contact potential difference (CPD) in the dark, CPD under strong illumination, and the small signal ac-surface photovoltage (ac-SPV). In COCOS metrology these measurements are performed as a Junction of the corona charge placed on the whole wafer. A near equipotential, whole wafer surface is maintained while the semiconductor space charge is transferred from accumulation — through flat band — to deep inversion. Data analysis based on electrostatic equations and charge neutrality gives a total set of electrical parameters, equivalent to those obtained in MOS-CV metrology, characterizing the space charge, the semiconductor-dielectric interface and the dielectric film. The equipotential condition is crucial for reducing charge transport along the surface without creating guard-rings. Using a blanket of corona charge placed over the wafer surface and whole wafer mapping of CPD and SPV, the COCOS metrology enables one to obtain whole wafer maps of almost all parameters. Examples are given, illustrating COCOS application to Si/SiO2, with an emphasis on thin gate oxide reliability.
Application of Quantox Measurements to Identify Phosphorus Contamination in Silicon Wafers
Authors: Dexter MA , Hasslinger KM , Fritz JR , Ullo CA
Published: April 2008

During a three-year period, MOS fab experienced a 0.3% parametric failure rate on LOCOS devices. The observed failure mode is high N- and low P-channel current leakage. Only wafer number five of a lot was affected. This selective (believed) phosphorus contamination was appropriately named the “Phantom Wafer Failure”. MOS fab implemented routine monitoring on all oxidation furnaces using the Keithley Quantox characterization tool in December 1997. Flatband voltage and mobile ion concentration were monitored using this tool. It was only after implementing this monitoring that the fab was able to identify the source of the phosphorus contamination. This report illustrates using the Keithley Quantox to identify the source of this phosphorus contamination.
Application of Gate Oxide Integrity Measurements in Silicon Wafer Manufacturing
Authors: Seacrist MR
Published: April 2008

The contribution of silicon starting material to device yield potential via gate oxide breakdown performance has grown in importance with the continually increasing levels of device gate area. Gate oxide integrity (GOI) testing is applied in silicon wafer manufacturing to determine the material-related capacitor defect density. GOI testing is used as a research tool and as part of a standard test set for evaluating and qualifying process changes from crystal pulling through final wafer cleaning. GOI measurements are also used to monitor finished wafer product quality. Other parallel material measurements are made for comparison and examined for correlation with GOI. Applications and results of GOI measurements in silicon wafer manufacturing are reviewed.
Silicon Substrate Related Gate Oxide Integrity at Different Oxide Thicknesses
Authors: Grann ED , Huber A , Grabmeier J , Hölzl R , Wahlich R
Published: April 2008

Gate oxide integrity (GOI) testing is a valuable tool for the characterization, development and optimization of tailor-made silicon (Si) substrates for the integrated circuits industry. Different Si substrates with various numbers of grown-in defects have been evaluated using charge-to-breakdown measurements. Yield and defect density analyses are studied for oxide thicknesses in the range from 40 nm down to 5 nm. The sensitivity and impact of grown-in defects, here predominantly crystal-originated particles (COPs), for different material groups on gate oxide reliability are shown in detail. In addition, results are presented on gate oxide degradation due to intentional metallic (Ni, Cu, Fe) contamination of various wafer types.
High Resolution Gate Oxide Integrity (GOI) Measurement in Near-Perfect Silicon
Authors: Murakami Y , Yamazaki T , Itou W , Shingyouji T
Published: April 2008

Gate Oxide Integrity (GOI) measurements are performed for various types of silicon wafers: Pure Silicon™, Epitaxial, Hydrogen Annealed, Low COP CZ, and Conventional CZ wafers. A clear dependence of GOI parameters is observed with Time Zero Dielectric Breakdown (TZDB) and Time Dependent Dielectric Breakdown (TDDB) measurements. Using multisource measurement units can perform high resolution GOI measurements. Time Dependent Dielectric Breakdown (TDDB) measurements on 5300 MOS capacitors on a 200 mm wafer have been made successfully with this technique. High resolution GOI measurements, in particular, make clear the correlation between grown-in defects and oxide defects in CZ wafers. It is also demonstrated that this technique is highly suitable for the evaluation of various types of near-perfect silicon, which inherently has no defects.
Strength of a G-10 Composite Laminate Tube Under Multiaxial Loading
Authors: Socie D , Wang J
Published: April 2008

An experimental study of the strength and failure behavior of an orthotropic G-10 glass fiber-reinforced epoxy laminate has been conducted. Tubular specimens were loaded in combinations of tension, compression, torsion, internal pressure, and external pressure to produce a variety of stress states. Previous work involved the loading of two simultaneously applied in-plane stresses. This investigation furthers the previous work by simultaneously applying three in-plane stresses. One interesting observation from this work is that combined axial compression and torsion loading results in a much lower failure strength than combined hoop compression and torsion even though the stress state is identical. For the same torsion stress, axial compression is more damaging than hoop compression because torsion loading rotates fibers aligned in the axial direction to accommodate the shear strains. Hoop fibers do not rotate and remain aligned in the compressive loading direction. A simple failure mode dependent maximum stress theory that considers low-energy compressive failure modes such as delamination and fiber buckling provides a reasonable fit to the experimental data.
Analysis of Characterization Methods for Inelastic Composite Material Deformation Under Multiaxial Stresses
Authors: Ahmad J , Newaz GM , Nicholas T
Published: April 2008

Off-axis tension (OAT) tests and biaxially loaded cruciform-shaped specimen (BC) tests on unidirectional fiber-reinforced metal matrix composites are subjected to detailed analyses using a newly developed model. The results indicate that the off-axis tension test is a viable method for biaxial stress-strain characterization of composites in the nonlinear deformation range. It is found that, besides being much more expensive to conduct, the specific cruciform-shaped specimen test considered in the study is less amenable to unambiguous interpretation.
Deformation and Fracture of a Particulate MMC Under Nonradial Combined Loadings
Authors: Rees DWA , Au YHJ
Published: April 2008

Nonradial, elastic-plastic cyclic loading paths have been applied to a 17% SiC particulate/2124 aluminum alloy metal matrix composite at room temperature. By combining axial loading with torsion these cycles involve stepped loading and reversals through zero with successively increasing peak stresses through to failure. Strain data taken from a three-element rosette strain gage, bonded to the outer diameter of the tubular test piece, are processed to enable an examination of the axial and shear surface strain response to the loading paths. The component stress-strain plots and the total strain paths are given for the elastic-plastic deformation preceding fracture in this composite. The behavior is complex although it permits an assessment of the existence of a yield surface and the appropriateness of the concepts of the normality rule, isotropic and kinematic hardening. A qualitative judgment is offered in the form of rotation and distortion accompanying a translating yield surface. It is shown how a rigid translation can admit reversed softening and ratchet strain. The particulate arrangement offers greater resistance to tensile plasticity so that strain ratcheting occurs predominantly under compressive stress. This alloy offers no preference to shear flow from forward and reversed torsion other than the usual appearance of a Bauschinger effect within the metal matrix when one torsional mode follows the other. However, cyclic torsional ratcheting appears with simultaneous axial tension. The rotation and distortion features are implied from an examination of the strain paths. Their gradients are a guide to the direction of a plastic strain increment vector lying normal to the yield surface. Further plots reveal the degree to which the principal axes of stress rotate and deviate from the principal strain axes. This composite is light and strong but the SiC particulates sacrifice the available tensile ductility of the matrix alloy. Under cyclic loading the likelihood of an early brittle tensile failure appears to be offset by the prior compressive flow that occurs under a comparable stress magnitude. The compressive residual strain can lessen the severity of a subsequent tensile strain, thus contributing to survival when cycling to combined stress levels of ±500 MPa in torsion and ±200 MPa in tension/compression.
Experiences with Lifetime Prediction Under Multiaxial Random Loading
Authors: Pötter K , Yousefi F , Zenner H
Published: April 2008

A number of multiaxial fatigue criteria have been developed during the past decades. They can be subdivided into hypotheses of the critical plane approach, hypothesis of integral approach, as well as empirical criteria. In the case of the integral approach the equivalent stress is calculated as an integral of the stresses over all intersection planes, whereas in the case of the critical plane approach only the intersection plane with the critical stress combination is considered. The difference between the two approaches is insignificant with proportional in-phase loading, but becomes clearly visible in the case of noncorrelated or phase-shifted loading. In the present paper the two approaches are compared. For the model verification, variable-amplitude tests under combined bending and torsion with smooth and notched specimens are applied. The integral approach was found to be superior to the critical plane approach under varying principal stress directions.
Laboratory Techniques for Service History Estimations of High Strength Fastener Failures
Authors: Gaudett M , Tregoning R , Focht E , Zhang XJ , Aylor D
Published: April 2008

Two fastener failures have been analyzed to determine both failure mode and service loading history. The analyses were conducted through careful fractographic investigation and laboratory simulation to assess the integrity of the assembly design and to evaluate the role of unintended environmental effects in these failures. The first case involves Monel K-500 bolts that failed due to fatigue loading, terminated by overload fracture. The fatigue mode was intergranular (IG) at initiation, and then transitioned to classical transgranular fatigue prior to overload failure. Intergranular cracking in Monel K-500 is usually associated with environmentally assisted cracking (EAC). However, simulated service testing of several bolts under both fatigue and slow strain rate loading revealed that IG fatigue cracking could occur at low applied ΔK in air. Transgranular fatigue is associated with higher ΔK levels. Therefore, EAC was not the root cause of these failures.

The second case examines the fatigue failure of several IN625 studs. The stud stresses are estimated from fatigue striation measurements using a representative fatigue crack growth behavior and driving force equation. The inferred applied stress is greater than the material yield strength, which is indicative of a basic deficiency in the original joint design. Laboratory testing verifies the relative accuracy of this stress estimation method for both simple and complex loading histories. The accuracy can be most significantly improved through fatigue crack growth testing of the actual failed material under relevant service conditions.
Fatigue Testing of Low-Alloy Steel Fasteners Subjected to Simultaneous Bending and Axial Loads
Authors: Alexander DF , Skochko GW , Andrews WR , Briody RS
Published: April 2008

Fatigue testing of high strength, low-alloy steel fasteners has been completed with simultaneous unidirectional bending and axial loads that demonstrates a potentially beneficial effect on fatigue life by accounting for bending. Fatigue tests were performed in load control on fasteners with failures in rolled and cut/machined threads. The objective of the testing was to determine if the fatigue strength of steel fasteners subjected to high bending and axial stresses is higher than in conventional axial, load controlled tests. Test results in the range of 104 to 106 cycles indicate that the fatigue lives of fasteners with a 2:1 ratio of bending to axial stress is from two to ten times as great as that of fasteners subjected to axial loading only. A special fixture design was used for the testing. The fixture permits an adjustable offset between the fastener and clevis centerlines, thus producing an eccentric loading. The eccentric load results in simultaneous application of bending and axial loads. The magnitude of the bending and axial loads was verified by strain gage measurements on the reduced shank diameter of the test specimens. Fatigue life was determined based on failure cycles (specimen separation). Stresses corresponding to failure cycles were based on the sum of the alternating axial and bending stresses at the half-life of the test specimen. A low degree of data scatter and good agreement with published data were observed for the axial load tests performed with the fixture set at zero offset between the clevis and fastener centerlines.
Stress Intensity Factor Solutions for Cracks in Threaded Fasteners
Authors: Oster DM , Mills WJ
Published: April 2008

Nondimensional stress intensity factor (K) solutions for continuous circumferential cracks in threaded fasteners were calculated using finite-element methods that determined the energy release rate during virtual crack extension. Assumed loading conditions included both remote tension and nut loading, whereby the effect of applying the load to the thread flanks was considered. In addition, K solutions were developed for axisymmetric surface cracks in notched and smooth round bars. Results showed that the stress concentration of a thread causes a considerable increase in K for shallow cracks, but has much less effect for longer cracks. In the latter case, values of K can be accurately estimated from K solutions for axi-symmetric cracks in smooth round bars. Nut loading increased K by about 50% for shallow cracks, but this effect became negligible at crack depth-to-minor diameter ratios (a/d) greater than 0.2. An evaluation of thread root acuity effects showed that the root radius has no effect on K when the crack depth exceeds 2% of the minor diameter. Closed-form K solutions were developed for both remote-loading and nut-loading conditions, and for a wide range of thread root radii. The K solutions obtained in this study were compared with available literature solutions for threaded fasteners as well as notched and smooth round bars.
Thread Lap Behavior Determination Using Finite-Element Analysis and Fracture Mechanics Techniques
Authors: Hukari RJ
Published: April 2008

A new aerospace bolt thread lap inspection criterion is proposed based on fatigue crack propagation trajectories predicted by finite-element analysis (FEA) and fracture mechanics techniques.

Fastener producers and end users incur high costs due to thread lap problems. Current thread lap inspection criteria are 30 to 40-years-old, and are based on an intuitive understanding of potential thread lap behavior. These inspection criteria are ambiguous and make inspection difficult. Some costs can be avoided and quality can be improved by redefining acceptable and unacceptable thread laps. Specifically, these inspection criteria can be improved by using fracture mechanics and FEA techniques developed in the last 30 years.

Two-dimensional, axisymmetric, full nut-bolt-joint geometry, FEA models with elastic-plastic material properties, and contact elements at the thread interfaces were analyzed using ANSYS FEA software. Singular crack tip elements were used. Laps of expected geometries were built into the models, and then assumed to propagate as fatigue cracks. Cracks were iteratively grown using the maximum tangential principal stress criterion to determine the direction of crack propagation. Certain types of thread laps were shown to propagate in such a way that bolt failure would not occur. Conversely, other types of laps were predicted to propagate in such a way that bolt failure would be expected.

A simpler, less subjective criterion for inspecting laps is presented. This criterion takes advantage of the benign laps. The proposed method allows any lap contained entirely within a particular zone to be acceptable.
Fatigue Acceptance Test Limit Criterion for Larger-Diameter Rolled Thread Fasteners
Authors: Kephart AR
Published: April 2008

This paper describes a fatigue lifetime acceptance test criterion by which studs having rolled threads, larger than 1.0 in. (25 mm) in diameter, can be assured to meet minimum quality attributes associated with a controlled rolling process.

This criterion is derived from a stress-dependent, room temperature air fatigue database for test studs having 0.625 in. (16 mm) diameter threads of Alloys X-750 HTH and direct aged 625. Anticipated fatigue lives of larger threads are based on thread root elastic stress concentration factors which increase with increasing thread diameters. Over the thread size range of interest, a 30% increase in notch stress is equivalent to a factor of five (5x) reduction in fatigue life. The resulting diameter-dependent fatigue acceptance criterion is normalized to the aerospace rolled thread acceptance standards for a 1.0 in. (25 mm) diameter, 0.125 in. (about 3 mm) pitch, Unified National thread with a controlled root radius (UNR). Testing was conducted at a stress of 50% of the minimum specified material ultimate strength, 80 ksi, (552 MPa) and at a stress ratio (R) of 0.10. Limited test data for fastener diameters of 1.00 to 2.25 in. (25 to 60 mm) are compared with the acceptance criterion.

Sensitivity of fatigue life of threads to test nut geometry variables was also shown to be dependent on notch stress conditions. Bearing surface concavity of the compression nuts and thread flank contact mismatch conditions can significantly affect fastener fatigue life. Without improved controls these conditions could potentially provide misleading acceptance data. Alternative test nut geometry features are described and implemented in the rolled thread stud specification, MIL-DTL-24789(SH), to mitigate the potential effects on fatigue acceptance data.
Accelerated Small Specimen Test Method for Measuring the Fatigue Strength in the Failure Analysis of Fasteners
Authors: Raymond L
Published: April 2008

In conducting a failure analysis on a fastener, measuring fatigue strength or endurance limit is often the time-limiting factor in the analysis. The classical approach to measure the fatigue strength, which often takes as much as 3–4 months to 3–4 years using several machines, cannot be tolerated from an operational cost perspective, especially if the failure closes down production.

This paper presents an accelerated method of testing for the fatigue strength of a fastener based on measuring the threshold stress for fatigue crack initiation at the root of a thread. The method builds on the work of Prot and Corten in combination with a Rising Step Load™-fatigue testing protocol. Using this new approach, the fatigue strength can be measured in less than one week with one machine.

A case history is presented to illustrate the use of this new method in fatigue to quantify the effect of surface conditions at the root of the threads on the life of a large 3.5-in.-diameter (8.9 cm) bolt. Life analysis is based on a Goodman Diagram modified within the framework of fracture mechanics.
Nondestructive Evaluation of Dimension Stone Using Impulse Generated Stress Waves: Part 3—Microstructure Characterization
Authors: dos Reis HLM , Habboub AK
Published: April 2008

A nondestructive testing and evaluation approach is presented to retrieve the microstructural characteristics and the grain size distribution of dimensional stone. The dimension stone test samples are typical of polycrystalline aggregations that represent quasi-monophasic rock structures with densely packed, elastic, and untextured grains. The grains of the test sample have a size distribution ranging approximately from 4 to 9 mm, and exhibit randomness in shape and in crystallographic axis orientation. Results indicate that this approach has the potential of being used for fast retrieval of microstructural features of dimension stone in the laboratory or in-situ.
Zirconium in the Nuclear Industry: Twelfth International Symposium
Authors: Sabol GP , Moan GD
Published: April 2008

Description

44 papers discuss the history, processing, use, and properties of Zirconium and its alloys. Nearly half are concerned with the corrosion and hydriding of different Zirconium alloys. The techniques used to characterize the oxides and their microstructures and properties have become very advanced. The industry, including producers and users, expects that the work will lead to important conclusions about alloy development, optimization of the processing parameters, and station operating procedures so that the current and new Zirconium materials will continue to operate reliably to very high neutron fluences.

Seven major topics include:

• Properties at High Neutron Fluences

• Hydrogen and Temperature Effects

• Deformation and Fracture Studies

• Processing and Alloy Development

• Effect of Composition and Microstructure on Corrosion

• Corrosion Simulation and the Effect of the Environment

• Effects of Oxides on Oxidation and H Pickup Rates

Audience:Scientists and engineers involved in the production and properties of components for use in nuclear reactors, their behavior during service and the property changes that occur with increasing neutron fluences.
Contribution to a Better Understanding of the Mechanism Causing Dishing Failures of the Carrara Marble When Used for Outside Building Facades
Authors: Erlin B
Published: April 2008

The famed Carrara marble has been used as outside-exposed, thin, facade panels that have failed because of out-of-plane distortions; a phenomenon referred to as dishing, cupping, and bowing. Theories have been advanced to explain that phenomena. This paper expands the explanations, and is based upon the relationships of thermal hysteresis the stone is known to possess and stone dimensions.

The marble consists of a mosaic of fine, essentially equi-axial calcite crystals devoid of defined crystal boundaries. Calcite has a known anisotropic thermal response wherein the crystal expands (as would be expected) in the direction of the ‘c’ crystallographic axis, but contracts (as would not be expected) in the direction of the three ‘a’ crystallographic axes, which are oriented normal to the ‘c’ axis. Very slight repositioning of the crystals result because of dislocations along crystal boundaries, which interfere with the return of the crystals to their original locations. The resulting slight increase in volume of the marble is accumulative with continued thermal cycling.

When the front of panels undergo more thermal cycles and/or reach higher temperatures than the back of panels, the result is a differential volume increase front to back with the front expanding more than the back. Based upon laboratory experimental work, when the ratio of lateral dimensions of the panels to their thickness is appropriate, out-of-plane distortions reconfigure the panels in the form of a permanent slight dish.

The physical effects of the thermal hysteresis on the marble causes; dishing, increased volume, increased porosity, decreased strengths because of stress along crystal boundaries and, ultimately, disintegration of the marble into sugar-like granules.

Marbles having coarser grain sizes and mosaic textures do not undergo similar thermal hysteresis effects as the Carrara marble because there are fewer crystals to interact.
Design and Selection of Exterior Granite Pavers
Authors: Gerns EA , Wonneberger B , Scheffler MJ
Published: April 2008

Over the past several years, thin granite pavers have become commonly used in exterior pavement construction. One- to three-inch-thick granite slabs that are usually more than one foot square are often used in new building deck and plaza construction. Granite pavers are often set on thin-set mortar, a flexible sand and gravel bed, or pedestal supports located at the corners of each paver. This paper provides information and guidance for architects and engineers on the selection of granite types and support systems that are appropriate for use in various pavement applications. It also provides an example of an initial selection of paver thickness for a typical size granite paver. Factors described that are to be taken into account for stone selection include stone strength and durability, safety factors, tolerances, the flexibility and typical detailing of the support system used, type and frequency of service loads anticipated by the designer, and anticipated weathering exposure and environment.

The paper is intended to provide designers topics to consider for initial granite pavement design, including sizing pavers, prior to the designers more detailed evaluation and analysis. Information herein can be useful in helping designers quickly determine whether a granite pavement system is appropriate and which support system is best suited for the site conditions present.
Anchorage Pullout Strength in Granite: Design and Fabrication Influences
Authors: West DG , Heinlein M
Published: April 2008

For the past 10 to 15 years, significant emphasis has been placed on evaluation of the bending strength of stone panels used for thin veneer cladding. However, failures of stone cladding on buildings are more commonly due to problems with the anchor and/or anchorage design or installation than with the bending strength of the granite panel. Judging from the calculations submitted by engineers designing stone cladding systems, many designers of stone cladding panels and anchoring systems are unaware of the issues addressed in this paper.

This paper reports the results of a series of tests according to ASTM Test Method for Strength of Individual Stone Anchorages in Dimension Stone (C1354) using two granites and an assortment of edge anchors. These tests examined possible causes for the variation in anchorage pullout loads. Situations examined included: a) variation for a single stone type tested with the same anchor configuration. b) variation for a single stone type tested with different anchor types and configurations. c) variation between different stone types tested with the same anchor configuration.

The results indicate that the most significant source of variation in anchorage pullout strengths of edge anchors is the thickness of stone material resisting the pullout load. Other sources of variation include the depth of embedment of the anchor, and the geometry of the anchor bracket and anchor cutout in the stone, but these were lower in magnitude.

The conclusions presented in this paper provide a basis for more appropriate consideration of the anchor pullout capacity in stone panels during design. They also provide a basis for possible revision of ASTM C1354 to reflect the key findings of this research.
Repair Methods for Stone Facades
Authors: Hoigard KR , Mulholland GR
Published: April 2008

The dimension stone industry has made significant progress in the last 40 years toward improving the quality and longevity of stone cladding. Material standards have been updated, new tests have been developed, design guides have been published, and a myriad of technical papers have been written discussing everything from connection design to full panel mock-up testing. Despite all of this new information, buildings still get built with, or develop, dimension stone cladding “problems”. This paper discusses practical methods for addressing some of the more common repair issues.

The repair methods presented were developed by the authors for application on a variety of consulting projects, primarily involving marble and granite. Repair methods are discussed for addressing minor chips, spalls, partial missing pieces, cracks, and defective or ineffective anchorages. Guiding concepts behind the repairs are presented, and photographs of actual installations are used for demonstrative purposes.
Common Causes of Failures of Stone Claddings on Buildings
Authors: Chin IR
Published: April 2008

Stone claddings on buildings are often chosen by building owners and designers for their natural aesthetic effect, their historically proven weathering durability, and their inherent low maintenance costs. However, these attributes are quickly eliminated when failure of the stone cladding occurs.

Investigations by the author, of distressed granite, limestone, and marble claddings on over 20 buildings have revealed that the common causes of failures in stone claddings on these buildings include the following: 1. Failure of the stone cladding connections in 45 percent of the buildings due to: a. Inadequate structural design of the connections. b. Corrosion of embedded metals. c. Failure to accommodate anticipated construction tolerances. d. Incompatible contacting materials. 2. Reduction in the strength of the stone due to exposure to the weather in 40 percent of the buildings. 3. Water leakage into the interior of 15 percent of the buildings due to: a. The absence of a flashing and weephole system or of an internal gutter and drainage system in the stone cladding. b. Ineffective flashing and weephole system or ineffective gutter and drainage system in the stone cladding.

Based upon the knowledge gained from the investigations, these common causes of failures in stone claddings are discussed, and recommendations to avoid failures in stone claddings on buildings are presented for consideration.
Marine Atmospheric Corrosion of Reference Metals in Tropical Climates of Latin-America
Authors: Mariaca-Rodriguez L , Almeida E , de Bósquez A , Cabezas A , Fernando-Alvarez J , Joseph G , Marrocos M , Morcillo M , Peña J , Prato MR , Rivero S , Rosales B , Salas G , Uruchurtu-Chavarín J , Valencia A
Published: April 2008

This article presents the results obtained at 16 tropical test sites participating in the “Ibero-American Map of Atmospheric Corrosiveness” (MICAT), a project on atmospheric corrosion carried out during the period 1988–1994 at some 70 test sites distributed across 12 countries of the Latin-American region, Spain and Portugal.

The tropical climate and its different climatic variants are characterized by high average air temperatures, with considerable daily thermal fluctuations, high average relative humidity, and generally high precipitation volumes.

The work is structured in three main blocks: apparently unpolluted atmospheres (i), and marine atmospheres, differentiating between pure marine atmospheres (ii) and those in which both chloride (Cl-) and sulfur dioxide (SO2) pollutants coexist (iii).

In each block an attempt was made to determine the role of the tropical climate in the magnitude of corrosion attack shown by four typical reference metals (mild steel, zinc, copper and aluminum) exposed for one-year periods in tropical atmospheric exposure conditions.