bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of Notched AS4/PEEK Laminates to Tension/Compression Loading
Authors: Simonds RA , Stinchcomb WW
Published: December 2008

The response of notched AS4/PEEK specimens to fully reversed, tension/compression loading has been investigated by examining their fatigue lives, damage initiation and propagation, and their residual strength. AS4/PEEK specimens were subjected to R = -1 tension/compression cyclic loading at 52.4 and 64.3% of their monotonic compression strength. The results indicate a significant difference in the response of the material at the two cyclic stress levels. At the lower fatigue stresses, the predominant damage, as determined by X-ray radiography and by deplying, is characterized by matrix cracking and delamination that initiate at the notch and grow both perpendicular and parallel to the load direction. Stiffness measurements taken during the low-level fatigue history show that compression stiffness and tension stiffness degrade throughout the fatigue lifetime. Further, specimens fatigued at the lower fatigue stresses lost compressive strength as the damage developed while they gained tensile strength. Fatigue life was defined by reduction of compression strength.

Damage to specimens fatigued at higher cyclic stresses developed much more predominantly in the direction perpendicular to the loading and much less in the direction parallel to the loading. Stiffness measurements made on these specimens showed a more rapid degradation of tension stiffness than of compression stiffness throughout the fatigue life. As with specimens fatigued at the lower stress levels, residual compressive strength decreased with damage development. However, the residual tensile strength of specimens fatigued at higher stresses decreased with damage development and the fatigue failure modes were tensile.

The difference in the response of the graphite-PEEK laminates at the two cyclic stress levels suggests that damage initiation and damage propagation play different roles in defining fatigue response.
Investigation into Thermal Conductivity of Composite Materials for Electronics Packaging
Authors: Hoffman RR , Tye RP , Chervenak JG
Published: December 2008

As part of a two-year investigation into the use of composite materials for military electronic equipment enclosures, the thermal conductivity of composite materials was determined by testing and predicted by an analytical technique. The objectives included identifying methods of improving thermal conductivity of composites and utilization of a prediction method. The comparative test and the Lewis-Nielson semitheoretical prediction methods were used and are described. The materials evaluated were a thermoplastic polymer with several discontinuous filler types. The analytical predictions were in good agreement with the test results except at high filler levels, but do not take into account anisotropic material properties or temperature effects. Test and prediction results are presented.
Fiber Orientation and Fracture Morphology in Short Fiber-Reinforced Thermoplastics
Authors: Hahn HT , Jerina KL , Burrett P
Published: December 2008

Spatial fiber distribution and fracture morphology were studied for three injection-molded thermoplastic composites: PPS, PAI, and PEEK reinforced with carbon fibers. Specimens were dog bone-shaped tensile coupons and flex bars. Both optical and scanning electron microscopes were used. In general, most fibers were found to be aligned in the mold-fill direction except in the core. The fibers in the core tended to be normal to the mold-fill direction. Yet, the exact distribution pattern varied from material to material and depended upon the gate design. Examinations of fracture surfaces indicated that the best interfacial bonding was in the PEEK composite followed by the PAI composite. In the core, fracture surfaces generally followed the fiber orientations. The PPS composite showed the most improvement over the matrix properties in both static and fatigue strengths despite poor interfacial bonding. The least improvement was observed of the PAI composite in which matrix cracks were seen to cut through fibers. Nevertheless, the strongest matrix, PAI, yielded the strongest composite, and the weakest matrix, PPS, yielded the weakest composite.
Mechanical Properties of the Carbon Fiber/PEEK Composite APC-2/AS-4 for Structural Applications
Authors: Carlile DR , Leach DC , Moore DR , Zahlan N
Published: December 2008

The mechanical properties of carbon fiber/polyetheretherketone (CF/PEEK) composites have been characterized for structural applications. Stiffness and strength properties were measured on unidirectional laminates in tension, compression, and flexure, enabling the elastic constants for the material to be determined. Stiffness and strength were measured on multidirectional lay-ups in tension. The effect of temperature on strength was examined for fiber- and matrix-dominated lay-ups. Toughness was assessed using fracture mechanics techniques, instrumented falling weight impact tests, and postimpact compression tests to obtain both intrinsic and comparative toughness. Creep and fatigue properties were characterized on fiber- and matrix-dominated lay-ups. The evaluations provide a property data base for CF/PEEK composites.
An Evaluation of the Liquid Oxygen Mechanical Impact Test
Authors: Moffett GE , Schmidt NE , Pedley MD , Linley LJ
Published: December 2008

The ambient liquid oxygen (LO2) mechanical impact test (ASTM method D2512-82) has long been used to screen nonmetallic materials for oxygen service. This method is also used to rank batches or lots of particular materials. This study was conducted to evaluate the repeatability of the ambient LO2 mechanical impact test used by NASA to screen materials for oxygen service (NHB 8060.1B Test 13 Part 1, which is based on the ASTM method). Four materials were tested: Teflon(r), Vespel SP-21(r), Viton A(r), and nylon 6/6. A single batch or lot was used to prepare each polymeric material. Each test material was subjected to several series of tests that were conducted at different impact energy levels. The results show that the variability from series to series in the reaction threshold energy level is within the precision statement of the ASTM method. However, this precision is considerably broader than the reaction threshold implied by the NHB 8060.1B test criteria.
Modeling and Data Evaluation of the WSTF Frictional Heating Test Facility
Authors: Yuen WW
Published: December 2008

A data reduction program and ignition model developed for the analysis of data generated by the frictional heating test facility at WSTF is presented. Based on transient temperature data measured from the stationary cylinder, the model can be used to generate an effective friction coefficient, activation energy and reactive flux constant for different metals/alloys at various test conditions. Data of 15 tests conducted for carbon steel are analyzed to illustrate the capability of the present model.

The effective friction coefficient is observed to decrease with increasing oxygen pressure, suggesting that the formation of oxide layer and the oxide's lubrication property have important effects on the ignition process for carbon steel. The activation energy is estimated to be 46600 cal/gmole. The reactive flux constant is observed to increase with oxygen pressure, suggesting that either the diffusion of ions through an oxide layer or the adsorption of oxygen at the oxide-gas interface is the primary physical process controlling the ignition. The Pv product (which is the mechanical energy input into the system) required for ignition is shown to first decrease and then increase with oxygen pressure, suggesting that at low oxygen pressure, the reactive flux constant is the important parameter controlling the energy input required for ignition while at high oxygen pressure, the reduction in friction coefficient due to the formation of oxide is the dominant physical process.
The Ignition Behaviour of Silicone Greases in Oxygen Atmospheres
Authors: Currie JL , Irani RS , Sanders J
Published: December 2008

Silicone greases are used extensively in oxygen systems at low pressures (0-0.4MPa) on account of their excellent lubricating and sealing properties. However, ignitions have occurred with silicone greases when they have been used in high pressure oxygen systems (>10MPa). The data presented in this paper critically examines the oxygen pressure regimes under which silicone greases can be used safely.

The BS3N100 high pressure oxygen ignition test has been used to evaluate the spontaneous ignition temperature (SIT) in oxygen of a variety of silicone greases. The results of these tests and data on the pressure dependence of the SIT are given.
Promoted Ignition - Combustion Behavior of Selected Engineering Alloys In Oxygen Gas Mixtures
Authors: Zawierucha R , Mc Ilroy K
Published: December 2008

Promoted ignition and more recently promoted combustion are terms which have been used to describe a situation where a substance with low oxygen compatibility ignites and supports the combustion of a more ignition resistant material. A companion paper described the investigation of this phenomenon as it related to carbon steel and 316L stainless steel. In this paper, additional data will be presented on the promoted ignition-combustion behavior of other engineering alloys which may be encountered in or considered for gaseous oxygen applications.

Although a number of papers in recent years have dealt with metal ignition-combustion studies in gaseous oxygen, a standard ASTM test to cover this phenomenon does not currently exist. Due to the range in pressure and purity requirements in oxygen applications, answers to the following issues are needed: (1) applicability of flowing vs. static (fixed) volume approaches, (2) significance of the test volume in static tests, (3) promoter selection, (4) oxygen purity, and (5) test methods for reduced pressures.

In this investigation, alloys have been evaluated via both flowing and static (fixed Volume) approaches using the rod configuration used in the joint ASTM-CGA-NASA program. Static tests have been conducted in a vessel of the same volume as the apparatus used by NASA in the joint ASTM-CGA-NASA test program conducted at WSTF and also in a larger 6.0 liter vessel. Oxygen-nitrogen gas mixtures with purities ranging from approximately 40% to 99.7% at pressures of 0.79 MPa to 34.6 MPa were used in the comparative studies of five alloys from the austenitic stainless steel, aluminum-bronze, cobalt and nickel families.
The Pv Product Required for the Frictional Ignition of Alloys
Authors: Stoltzfus JM , Benz FJ , Homa J
Published: December 2008

New and better metal alloys are needed to advance technologies in propulsion systems and associated hardware for aerospace activities. The National Aeronautic and Space Administration, White Sands Test Facility, developed a frictional heating tester capable of evaluating the ignition properties of alloys in oxygen under rubbing conditions. Sixteen alloys were evaluated in this tester and the mechanical energy (product of the contact pressure and surface speed) required for ignition in oxygen at 6.9 MPa (1000 psig) was determined for each alloy. Alloys that contained large nickel compositions were shown to have the highest resistance to ignition. The effect of coefficient of friction on ignition was evaluated and was shown to have a major effect on the ignition of alloys. The results strongly suggest that for environments where frictional heating is the dominant ignition source alloys must be selected based on data from frictional heating tests.
Oxygen Compatibility of Pressure Regulators for Gas Cylinders
Authors: Barthélémy H , Delode G , Vagnard G
Published: December 2008

Accidents are occasionally reported to occur due to violent ignition of oxygen pressure regulators on opening the gas cylinder valve.

These ignitions can be attributed either to oil contamination, to particle impact or to “adiabatic compression” i.e. rapid pressurization of oxygen when opening the cylinder valve.

Since oxygen regulators, like any oxygen equipment, are normally specially cleaned to remove traces of oil, greasy products and combustible materials, prevention of “oil contamination ignition” mainly consists in advising customers to avoid contamination in service. Particle impact ignitions can be avoided by using dust caps over the cylinder valve outlets during transport, in-line filters and by advising users to momentarily “crack” the cylinder valve before connecting the regulator.

In this paper we concentrate mainly on investigating the conditions which could lead to ignition by “adiabatic compression”. Numerous tests have been carried out in L'AIR LIQUIDE's Laboratory to try to explain how such ignitions occur and how to avoid them. The influence of the materials used in the construction of regulators has been studied, i.e. non-metallic and metallic materials (including aluminum). This influence although very important, has been found to be closely related to and affected by the regulator internal design.

Examples of solutions to prevent such ignition are reported in this paper.

Another important aspect discussed is the influence of the testing equipment and procedure used to establish the ability of a regulator to resist adiabatic compression. There are already some national Standards in Europe (Germany, France, etc) or international Standard (ISO) which specify ignition test methods, however, it has recently been determined that they are not adequately precise or reliable. In fact, some tests carried out according to these Standards have produced different results (regulator acceptable or non-acceptable) depending on which laboratory performed the test. In this paper, we identify the important parameters which must be taken into account when performing the tests.
The Oxidant O2 (Helium) Index of Flammability of Endotracheal Tubes
Authors: Simpson JI , Wolf GL , Schiff GA
Published: December 2008

The effect on flammability of endotracheal tubes exposed to helium diluted oxygen was measured by the Oxidant O2 (He) index of flammability and compared to the corresponding oxidant O2 (N2) indices of flammability. The oxidant O2 (He) index of flammability for PVC (Portex) ETT is 0.274, for RR ETT 0.194, and for Si ETT 0.194. The differences between helium dilution values and the corresponding nitrogen dilution values are statistically significant, the greatest difference being a factor of 1.2. However the common clinical practice of adding helium as a diluent for oxygen in situations with a potential for flammability may not increase patient safety.
Oxygen-Enriched Fires During Surgery of The Head and Neck
Authors: Bruley ME , Lavanchy C
Published: December 2008

Presented is an overview of ECRI's investigations of intraoperative fires concentrating on oxygen- and nitrous oxide-enriched fires, the common medical devices that act as ignition sources, and the combustible substances that are present during surgery. A comparative evaluation of surgical draping materials, specifically including testing for flame spread rates and ignitability in standard atmospheres and ignitabllity in oxygen-enriched atmospheres, was performed and published by ECRI in 1986. A summary of their flammabllity findings is presented, along with a discussion of the oxygen-enriched atmosphere phenomenon of surface fiber flame propagation on reusable surgical textiles. Recommendations are made for minimizing the risk of surgical fires, including special precautions for prevention of fires from surgical lasers.
Effect of Hot Isostatic Pressing on the Mechanical and Corrosion Properties of a Cast, Porous-Coated Co-Cr-Mo Alloy
Authors: Georgette FS
Published: December 2008

The corrosion properties of a cast Co-Cr-Mo alloy were evaluated using anodic and cathodic polarization techniques. These data were compared with those for a Co-Cr-Mo alloy which had been exposed to a porous coating thermal cycle, both with and without a subsequent hot isostatic pressing (HIP) procedure. The thermal exposure during sintering was found to result in the formation of grain boundary precipitates and porosity, accompanied by a reduction in elemental segregation. This resulted in a reduction in mechanical properties, as well as an increase in corrosion resistance. The use of a HIP cycle, subsequent to sintering, provided an increase in both mechanical properties and corrosion resistance. The improvement in corrosion resistance was attributed to a further reduction in elemental segregation, in comparison with the as-sintered condition.
Metallurgical Relationships of Porous-Coated ASTM F75 Alloys
Authors: Levine DJ
Published: December 2008

Discontinuous carbide formation along the grain boundaries was found to be a desirable condition for obtaining ASTM-recommended strength and ductility levels in a sintered alloy containing 0.3% carbon by weight and meeting the requirements of the ASTM Specification for Cast Cobalt-Chromium-Molybdenum Alloy for Surgical Implant Applications (F 75–82). Excessive carbides in the grain boundaries of this alloy caused a severe reduction in ductility, while relatively carbide-free grain boundaries produced acceptable ductility but a marked reduction in the ultimate and 0.2% yield strengths. This behavior was also true for an ASTM F75 alloy with a lower carbon level (0.24% by weight). However, the latter alloy failed to meet the strength levels specified in ASTM Specification F 75–82. Subsequent aging of similar specimens led to carbide precipitation within the grains and dissolution of grain boundary particles, which caused an immediate loss of ductility. In addition, there was evidence for the precipitation of intermetallic, topologically close-packed (TCP) phases, which have been shown to have deleterious effects on the room-temperature ductilities of cobalt-base alloys. This phenomenon occurs in alloys with both high (0.3%) and low (0.24%) carbon contents. The precipitate population and the severity of ductility loss were time and temperature dependent.
Morphological Characterization of Porous Coatings
Authors: Smith TS
Published: December 2008

The morphological characteristics of porous coatings used on orthopedic joint replacement devices may have significant effects on their long-term performance. A method is presented for accurately quantifying coating morphologies. Ten coatings, six commercially available, were investigated. The characteristics measured were the average volume porosity, volume porosity gradient, average pore size, average pore size gradient, and pore size distribution. Computerized image analysis equipment is used to collect data from metallographically prepared sections through the coatings. The data, from which the morphological parameters are determined, are then corrected for sectioning effects.
Anodic Polarization of Porous-Coated Vitallium Alloy—Effect of Passivation
Authors: Edwards BJ , Higham P
Published: December 2008

Passivation has the same effect on porous-coated Vitallium as it has on the smooth alloy. It decreased the current during anodic polarization by as much as two orders of magnitude. A potential scan reversal at + 700 mV for all specimens resulted in a hysteresis for passivated specimens (both smooth and porous) but not for nonpassivated specimens. The protection potential was + 296 ± 68 and + 345 ± 69 mV versus the saturated calomel electrode (SCE) for porous and smooth passivated specimens, respectively.

There were two objectives of this work. The first was to see if a simple anodic polarization test could detect any basic difference in corrosion behavior between porous and smooth Vitallium. The second was to see if a standard passivation treatment affected these two geometries differently, again as detected by anodic polarization. The authors found that this porous configuration responds to polarization in a manner similar to the smooth surface in either the passivated or nonpassivated condition. There is an increase in current associated with the increased surface area. However, the increase in current appeared to be less than one would predict, assuming a linear proportionality between the current and surface area.

All tests were performed on Vitallium in the form of modified patella buttons. The specimens were manufactured by Howmedica, Inc. The porous surface was identical to the P.C.A. configuration. All specimens, both smooth and porous-coated, underwent the same production heat cycle.
Characterization of the Corrosion Behavior of Porous Biomaterials by A-C Impedance Techniques
Authors: Bundy KJ , Luedemann RE
Published: December 2008

In this research, the corrosion behavior of Ti-6Al-4V extralow interstitial (ELI) and Co-Cr-Mo alloys with polished, grit-blasted, and porous-coated surfaces has been investigated. The A–C impedance technique and a variety of D–C methods were used for this purpose. Both highly stressed and nonstressed specimens were tested. Stress-enhanced release of corrosion products was demonstrated to occur in some cases. The A–C impedance method, which is capable of measuring both corrosion current and true surface area, showed that this effect was mainly due to an area increase caused by plastic deformation. The advantages and characteristics of the A–C impedance method for corrosion measurements of implant materials are also described.
Biological Significance of Metal Ion Release
Authors: Brown SA , Merritt K , Farnsworth LJ , Crowe TD
Published: December 2008

The issue of the biologic significance of metal ion release is addressed by reviewing the answers to five questions: what is released, how much is released, where do the ions go, what can they do, and what have they done? Data are presented to demonstrate that ions are released but not necessarily in proportion to the alloy composition. Nickel and cobalt bind to serum albumin, whereas chromium is released with a valence of +6 and binds to red blood cells. Tissue levels of chromium and titanium are often very high, indicating that these elements may form stable complexes that remain in local tissues. The results of chemical analysis of urine from animals exposed to metal ions from injection of salts or in vivo corrosion demonstrate a rapid excretion of nickel and cobalt; excretion of chromium is slow and represents a small percentage of the total to which the animal is exposed. The biological reactions of toxicity, metal sensitivity, and oncogenicity are discussed from the point of view of what they have been shown to do in laboratory and animal experiments. The limited number of clinical reports of these reactions are also reviewed. These issues are discussed in light of the need for future research and for the development of standard test methods for characterization of porous implant materials and the biological reactions to these materials.
Histological Comparison of Biological Fixation and Bone Modeling with Canine and Human Porous-Coated Hip Prostheses
Authors: Bobyn JD , Engh CA , Pilliar RM
Published: December 2008

Undecalcified hard-section histology was performed on twelve canine and eleven human porous-coated femoral hip prostheses implanted without bone cement. The period of implantation varied from four weeks to seven years. All of the canine and nine of the eleven human implants showed regions of substantial bone ingrowth along the porous-coated stem region. Areas of the two human implants ingrown with fibrous tissue were characterized radiographically by a radiopaque line surrounding, but separated from, the implant surface. Resorptive bone modeling was observed with both implant types, particularly proximally. New bone formation and hypertrophy typically occur at regions of proximity to or contact with the endosteal cortex and, in the case of proximally porous coated implants, at the junction of the porous and smooth implant surfaces. The smooth-surfaced distal region of proximally coated implants is typically surrounded by a thin shell of bone that is separated from the implant surface. Overall, resorptive and formative bony change appears more exaggerated in the canine, but the radiographic and histologic pictures of canine and human implants bear resemblances.
Radiographic Criteria for the Clinical Performance of Uncemented Total Joint Replacements
Authors: Gruen TA
Published: December 2008

Enthusiasm, concern, and controversy exist around the clinical application of porous materials for skeletal fixation of uncemented total joint replacements. The clinical and radiographic evaluations of such prosthetic components involve numerous measurements, which are necessary to communicate quantitative information on the patient's response, as well as the implant's performance. Just as communication requires a commonly accepted language for efficiency and effectiveness, clinical and radiographic analyses require commonly accepted criteria and terminology. The importance of radiography, the radiological factors influencing its interpretation, its evaluation methodology, and proposed criteria for sequential evaluation of the implant/bone interface and bone remodeling responses by using a zonal approach have been described to establish objectivity in the performance assessment of uncemented total joint replacements.
Strain Analysis of the Proximal Femur After Total Hip Replacement
Authors: Wuh HCK , Jones LC , Hungerford DS
Published: December 2008

Strain analysis of human cadaver femora after cemented total hip arthroplasty (THA) has demonstrated a reduction in stress transfer along the proximal femur. The principal objective of this study was to determine the effect of the cementless application of a pressfit, porous-coated prosthesis on the strain experienced by the proximal femur. Using the photoelastic coating technique (PECT), five human cadaver specimens were subjected to strain analysis before and after cementless arthroplasty with a PCA total hip prosthesis. After total hip replacement, the strain magnitudes were reduced for all points along the medial border when the femur was subjected to loading conditions. A reduction of the level of strain experienced by the calcar ranged from 34.7 to 43.7% under loads ranging from 750 to 2000 N—a considerably smaller reduction than that reported by previous investigators. The region of the greater trochanter was the only area of the lateral surface to demonstrate an increase in strain magnitude after THA; the other, more distal points laterally experienced a reduced level of strain. Increases in strain magnitude, although not statistically significant, were detected along the anterior aspect of the femora. Significant decreases in strain were observed at the two more distal points posteriorly, with no significant change proximally. As this investigation is an evaluation only of the immediate effect of the design of the prosthesis in achieving a press fit, and the specimens are without the benefit of bony ingrowth, additional studies are necessary to determine the effect of biologic ingrowth on the distribution of strain within the proximal femur.
A Biomechanical and Histological Examination of Different Surface Treatments of Titanium Implants for Total Joint Replacement
Authors: Saha S , Albright JA , Keating ME , Misra RP
Published: December 2008

The objective of this study was to evaluate biomechanically and histologically the effectiveness of different surfaces—specifically, smooth, textured, and plasma-sprayed porous surfaces—on titanium implants in achieving stable fixation for total joint replacements.

Hollow cylindrical metal plugs (5 to 6 mm in diameter) with different surfaces were implanted in the femora of two dogs. After five months of implantation, pull-out tests were carried out on these cylinders. The ultimate shear strengths were 11.54 ± 2.96, 3.17 ± 0.81, and 1.04 ± 0.32 N/m2 for the plasma-sprayed, textured, and smooth surfaces, respectively. As expected, the smooth cylinders showed the minimum pull-out strengths and the porous-coated ones the maximum. Histological examination showed maximum bony ingrowth in the plasma-sprayed group and moderate growth in the textured group. Our results suggest that a textured surface or a porous coating (plasma spray) on titanium implants could significantly improve the long-term stability of uncemented total joint replacements.
Quantitation of Bone Ingrowth into Porous Implants Submitted to Pulsed Electromagnetic Fields
Authors: Dallant P , Meunier A , Christel P , Guillemin G , Sedel L
Published: December 2008

This study has been conducted to evaluate the effect of electromagnetic fields of low frequency and low amplitude on bone growth into porous implants in order to consider a potential clinical application—that is, improvement of the anchorage in articular prostheses intended to be implanted without cement. The experiment has been conducted in vivo on sheep, using porous implants made of Ti-6Al-4V alloy implanted in the cortical bone. The electromagnetic stimulation was provided by external generators connected to Helmholtz coils placed on each side of the stimulated limb.

The results of this stimulation have been quantified by measuring the shear properties of the bone/implant interface and the bone regrowth around and into the porous implants in control and stimulated animals. These results were measured in a total of 16 animals sacrificed at three and five weeks after implantation. No improvement was shown in the mechanical properties of the bone/implant interface. On the other hand, the depth of bone tissue ingrowth and the ratio of bony ingrowth within the implant to the total new bone formation increased at five weeks (13 and 20%, respectively) when electromagnetic fields were used. However, this increase is not statistically significant.
Resorbable Porous Aluminum-Calcium-Phosphorus Oxide (ALCAP) Ceramics
Authors: Bajpai PK , Graves GA , Mattie DR , McFall FB
Published: December 2008

A porous aluminum-calcium-phosphorus oxide (ALCAP) ceramic has been developed for potential use in correcting bone defects. The material is at least partly resorbed and appears to have acceptable biocompatibility and toxicity characteristics for its intended applications. ALCAP ceramics are fabricated by calcining mixtures of aluminum, calcium, and phosphorus oxide powders and sintering the compressed blocks from calcined particles of the desired size. By varying the dimensions of the die, particle size, sintering time, and temperature, ALCAP ceramics have been fabricated that may be useful for repairing a wide variety of bone defects. The fate of ALCAP ceramics in both in vitro and in vivo environments has been studied by means of chemical analysis of tissues, chemical and enzyme analysis of implants, radiography, radioactive isotope uptake, scanning electron microscopy, energy-dispersive X-ray analysis, and histology. ALCAP ceramics were implanted in experimentally induced defects in long bones of rats and mandibles of rabbits. Results of these studies suggest that the ALCAP ceramics resorb and allow ingrowth of new bone.
Remote Videography of Small Mammals Under Conditions of Dim Illumination or Darkness
Authors: Frantz SC
Published: December 2008

A method is described for high-resolution videography of crepuscular and nocturnal mammals under field or laboratory conditions. The closed-circuit television camera provides a usable image in daylight as well as dusk/dawn applications. Infrared or red light illuminators must be used for darker conditions. A monitor interfaces with a motion detector and time-lapse video cassette recorder to allow fully automatic recording of activity. The onsite camera can be located more than 60 m from the controls for pan/tilt positioning and lens adjustment. Although the components are not particularly small or lightweight, the system is reasonably portable and functions in a wide range of temperature/humidity conditions. Detailed, remote monitoring and recording of small mammal (or other animal) behavior are possible under conditions not conducive to the presence of, or perhaps intolerable to, human observers.
Status of Laboratory Accreditation and Related Practices in Standards
Authors: Schock HE
Published: December 2008

This paper reviews rapidly growing specific standards for laboratory assessment and accreditation with applications in processes, products, and services. Identified are new standards for management, test methods, and commercial applications. The paper stresses recent achievements and standards with opportunities for growth. Industrial managers and writers of standards are directed to new references to improving productivity through preparing standards for test methods, quality systems, commercial requirements, and laboratory accreditation.
Accrediting Component and Materials Suppliers Laboratories
Authors: Locke JW
Published: December 2008

Just-in-time manufacturing principles require that quality assurance of components and materials supplied to the manufacturers be performed by the suppliers. This paper describes the evolution of a program developed by the American Association for Laboratory Accreditation (A2LA) to accredit these supplier laboratories in such a way that their test results will be recognized by a number of different manufacturers using the just-in-time manufacturing philosophy.
Operator Errors in the Measurement of Microindentation Hardness
Authors: Vander Voort GF
Published: December 2008

An interlaboratory test program (“round-robin”) was conducted by ASTM Committee E-4 on Metallography to develop information for a Precision and Bias section for ASTM Test Method for Microhardness of Materials (E 384). Knoop and Vickers indents were made by one person using seven specimens of varying hardness and six test loads: 25, 50, 100, 200, 500, and 1000 gf (five indents of each type at each load on each specimen). These indents were measured by personnel at 24 laboratories. The results demonstrate substantial variability in hardness which increased with decreasing test load and increasing specimen hardness, that is, with decreasing diagonal length.
Laboratory Accreditation in Canada: Update
Authors: Hysert GC , Archambault M
Published: December 2008

In 1970 the Standards Council of Canada (SCC) established the National Standards System (NSS) as a framework for managing standards work in Canada. The accreditation program for testing organizations is a critical component of the NSS. This paper reviews current SCC accreditation criteria and requirements for testing laboratories and—since 1984—calibration laboratories. It emphasizes the importance of the cooperation between the Department of National Defence, the National Research Council of Canada, and SCC and concludes with a review of the benefits resulting from a recently created network for accredited calibration laboratories.
Determination of Crack Propagation Directions in Graphite/Epoxy Structures
Authors: Smith BW , Grove RA
Published: December 2008

This paper presents the results of an investigation into the fracture surface characteristics of delaminations in graphite/epoxy composite materials. Relationships between fracture surface features and imposed singular failure conditions are illustrated for tension (Mode 1) and shear (Mode 2) loading. Interlaminar tension fractures were generated utilizing a double cantilever beam geometry. Interlaminar shear fractures were generated utilizing an end-notch flexural geometry. In both cases controlled crack initiation and progression were produced between various cross-ply orientations. Interlaminar tension fracture features are illustrated showing a relatively flat surface morphology and river markings resulting from microplane coalescence. The direction of coalescence is shown to correspond to the direction of propagation. Fractures produced by interlaminar shear exhibit numerous epoxy platelets (hackles) oriented perpendicular to the direction of resolved tension at the crack tip. These platelets were found to occur predominantly on one fracture surface, where the direction of applied shear coincided with the direction of propagation. The overall relationship of each of these features with fiber orientation is reviewed and its value in postfailure identification of crack directions and load states presented.
Microstructural Aspects of Crack Propagation in Filled Polymers
Authors: Newaz GM
Published: December 2008

A study was undertaken to evaluate the fracture behavior of sand and clay-filled polyester composites. A two-pronged effort was made (1) to characterize the fracture toughness of sand-polyester and sand-clay-polyester composites and (2) to identify the mechanisms which account for fracture resistance in these composites.

Separate laminates of sand-resin and sand-clay-resin were made using a polyester resin, sand (300-μm mesh), and clay (0.5- to 3-μm mesh) particulates. The volume fraction of the constituents were 30/70 and 23/7/70 in the laminates, respectively. Three-point bend notch tests were conducted to record the load-deflection response of the composites. Fracture energy was calculated based on linear elastic fracture mechanics. Results show that the fracture energy of the sand-polyester composite was about 25% greater than that of the sand-clay-polyester composite. Fractographic study was undertaken using a scanning electron microscope to determine the mechanisms which contribute to fracture resistance in the two composites. This evaluation was considered critical to evaluate the role of the sand and clay fillers on the overall fracture behavior.

In the sand-filled specimens, fracture steps were observed behind the particles, which are characteristic of the pinning mechanisms. These features arise from the crack front breaking away from the pinning position, that is, from the rigid sand particles. The toughening mechanism in this composite is essentially attributed to the crack-pining phenomenon and subsequent interaction of various crack fronts. In this case, the particles act as obstacles to the moving crack front, and additional energy is required to break away from the pinned positions, contributing to higher fracture energy. This increase in line energy of the crack front is analogous to the line-tension effect due to dislocation pinning in metals. However, in the sand-clay-polyester composite, the pinning mechanism appears to be absent. Rather, the fracture surface is rough and is reminiscent of quasicleavage-type damage. Fracture energy in this case may be related to the size and density of cavities. The toughening mechanism in this type of hybrid particulate-filled composite is not well understood and requires further investigation.
Fractographic Feature Identification and Characterization by Digital Imaging Analysis
Authors: Gould RW , McSwain RH
Published: December 2008

Fracture surface analysis has been relegated to the fractographer, who has developed skills in visual interpretation of unique fracture features. This process is based on correlation of features obtained from laboratory-created fractures with known failure modes to specific fracture surface features. The result has been considerable subjectivity, with conflicting opinions sometimes being rendered by different fractographers. Recent approaches to expand objectivity in the process have been related to quantitative microscopy procedures and to digital imaging analysis, with both indicating that nonsubjective fractographic analysis can be extremely beneficial. This study has taken the approach of digital analysis of scanning electron fractographs through Fourier transform analysis of spatial frequency content. The most common fracture features—fatigue striations, dimples, intergranular facets, and cleavage facets—have been uniquely defined in terms of frequency components. The result has been a significant advance in objectivity for fracture feature identification and characterization.
A Fractographic Investigation of Fatigue Damage in Carburized Steel
Authors: Newaz GM
Published: December 2008

A fatigue study was conducted to determine the performance of unnotched and notched carburized American Iron and Steel Institute (AISI) 8620H steel specimens and to evaluate the corresponding fatigue damage. Completely reversed, constant amplitude, load-controlled tests were conducted using cylindrical carburized steel specimens with stress concentrations of 1.00, 1.46, and 2.22. All tests were conducted at a frequency of 2 Hz under an ambient laboratory environment. Fatigue data plotted as stress amplitude versus mean fatigue life show that, at long life, both sets of notched specimens have similar performance. At shorter lives, the specimens with stress concentration of 1.46 exhibit superior performance compared with the specimens having a stress concentration of 2.22, as expected. The performance of smooth specimens is significantly better compared with the notched specimens at all lives.

Fractographic investigation conducted using scanning electron microscopy revealed the nature of initiation and the subsequent propagation of fatigue cracks in these specimens. At shorter lives, the crack initiation in smooth specimens was found to be surface-initiated at one or more sites on the surface, which then circumferentially converged and propagated through the carburized case into the core. The fracture surface of the case was smooth and flat, while in the core it was nonuniform and coarse. At higher lives, crack initiation in the smooth specimen originated at inclusions within the core. The subsurface crack initiation site showed convergence of radial lines toward a focal point, the site of a nonmetallic inclusion. Fractographs of notched specimens which failed at shorter lives show damage similar to that in smooth specimens. At longer lives, clear evidence of separation between the case and the core was found, with some evidence of subsurface initiation from nonmetallic silicon oxide inclusions having dimensions of 20 to 50 μm.
Fractographic Studies of the Ductile-to-Brittle Transition in Austenitic Stainless Steels
Authors: Place TA , Sudarshan TS , Waters CK , Louthan MR
Published: December 2008

Austenitic stainless steels are not generally thought to undergo ductile-to-brittle transitions as the temperature is lowered to 77 K or to be susceptible to hydrogen embrittlement. However, some austenitic steels do undergo a classic ductile-to-brittle transition, and are susceptible to hydrogen embrittlement even at the high strain rates used in an impact test. In this study the fracture behavior of Tenelon, 21-6-9, and 304L was investigated by testing hydrogen charged and uncharged Charpy specimens at temperatures ranging from 77 to 298 K. The fracture mode was determined with the aid of optical and scanning electron microscopy and X-ray analysis. Fracture initiation in the 21-6-9 and 304L was generally by ordinary dimple zone formation, though the Tenelon developed a brittle initiation mode at low temperatures. All of the steels showed a change from single to multiple crack initiation as the temperature was reduced. Propagation was by microvoid coalescence at higher temperatures, with a strong orientation effect in evidence where inclusions provided weak interfaces. A ductile-to-brittle transition was observed in both the Tenelon and the 21-6-9 steels. In the case of Tenelon, this transition resulted from {111} plane separation, and the reduction in toughness in 304L and 21-6-9 was associated with strain localization and formation of large microvoids. The presence of hydrogen did not introduce any new fracture modes but did enhance the embrittlement mechanisms which were promoted by low temperatures.
Fractography in the Failure Analysis of Corroded Fracture Surfaces
Authors: Ibidunni AO
Published: December 2008

Fractographic information retrieval from oxidized or corroded fracture surfaces is very important in failure analysis. In order to determine the mode of failure, the surface oxides must be removed without destroying the original surface morphology of the fracture. Over the years, several methods have been utilized in the removal of surface oxides. However, chemical dissolution of the oxides coupled with ultrasonic cleaning has been the most effective. The effectiveness of two commercially available proprietary products and of orthophosphoric acid in the removal of surface oxides without destroying the fracture surfaces is discussed. Three case histories, in which each of the chemicals has been utilized, are presented. The fractographic information obtained in each case was supported by metallography. Orthophosphoric acid, when coupled with ultrasonic cleaning, is very effective in the removal of oxides from fracture surfaces.
Fractographic Analysis of Hydrogen-Assisted Cracking in Alpha-Beta Titanium Alloys
Authors: Meyn DA , Bayles RA
Published: December 2008

The role of hydrogen in the subcritical crack growth of titanium alloys is a subject of intense interest to those who use these alloys for structural applications. The most widely accepted theories are based on the absorption of hydrogen (in the case of environmental hydrogen-assisted cracking), its diffusion to regions of high tensile stress, and the initiation of microcracks at hydrides precipitated in such regions. One of the difficulties with such a mechanism is the paucity of observations of titanium hydrides on fracture surfaces, such as those caused by stress corrosion cracking or inert-environment sustained load cracking caused by residual hydrogen impurity. Another difficulty has been the identity in microstructural crack paths between stress corrosion cracking in hydrogen-containing (saltwater, etc.) and hydrogen-free (carbon tetrachloride) environments.

Studies reported in this paper suggest that hydrogen is not unique in its ability to cause alpha cleavage, but may be a primary cause of alpha-beta interface cracking. Alpha cleavage also occurs in sustained load cracking, but is not, in the present studies, influenced by hydrogen content. Cracking in environmental hydrogen gas is primarily distinguished by alpha-beta interface cracking. The detailed fractographic character of such interface cracking appears to show that the microstructural locus of interface cracking is at the boundary between the alpha phase and the interface phase. The existence of this phase in bulk materials has recently been called into question, and it will be one purpose of this paper to discuss the role of hydrogen content on its formation and the effects of this phase on fracture mechanisms.
In-Reactor Creep Rupture Behavior of the D19 and 316 Alloys
Authors: Puigh RJ , Hamilton ML
Published: December 2008

In-reactor creep rupture data on one heat and two cold work levels of the D9-type alloy and on two heats of cold worked 316 stainless steel have been obtained from the Materials Open Test Assembly (MOTA) experiment in the Fast Flux Test Facility (FFTF). The on-line detection of creep ruptures using a tag gas technique has provided in-reactor creep rupture data for irradiation temperatures of 575, 605, 670, and 750°C to a peak fluence of 9 × 1022 n/cm2 (E > 0.1 MeV). Similar thermal creep rupture data have been accumulated for exposure temperatures of 650, 704, and 760°C to exposure times of 10 000 h. In general, the in-reactor rupture times are comparable to or less than those exhibited by the thermal testing. The 10% cold worked condition of D9 exhibits slightly better creep rupture resistance when compared to the 20% cold worked condition. The inreactor failure strains are less than those of the thermal controls for a given temperature.