bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of the Fatigue Resistance of Sealants to Movement at Intersections of Sealed Joints and Improvements in the Joint Design Method
Authors: Miyauchi H , Tanaka K
Published: April 2008

The paper investigates the fatigue resistance of sealants to movement at the intersections of sealed joints and proposes improvements to the method of joint design. As a first step, the fatigue resistance of sealed joint intersections to shear movement caused by the sliding motion of curtain wall panels was studied experimentally. Three types of building sealants were evaluated. Shear movement consistently deformed both the intersectional and linear sectional areas of joint specimens. Cracks formed within the intersectional area earlier than in the linear sections of the joints. As a second step, the fatigue resistance of sealed joint intersections to the rocking motion of curtain wall panels was studied experimentally. Two rocking motion types were evaluated. A rocking fatigue apparatus for the intersectional joint specimens was developed, and the number of cycles until crack formation was determined for given movements. We successfully obtained data on fatigue resistance of sealants using the new apparatus. Fatigue resistance of sealed joints is lower in the intersectional area than in the linear sections of the joints and is particularly lowest with simultaneous movements occurring in longitudinal and horizontal joints. Finally, the effect of curvature radii of curtain wall panel corners on fatigue resistance was studied at intersections of sealed joints. The fatigue test was carried out employing specimens with curvature radii varying from 0–8 mm. Shear movement consistently deformed the intersectional area of the joint specimens. A relation was found between curvature radius and the number of cycles to crack formation, i.e., the larger the curvature radius was, the higher the observed fatigue resistance was to joint movement.
Sealant Longevity for Residential Ducts
Authors: Walker IS , Sherman MH
Published: April 2008

Duct leakage is a major source of energy loss in residential buildings. Most duct leakage occurs at the connections to registers, plenums, or branches in the duct system. At each of these connections, a method of sealing the duct system is required. Typical sealing methods include tapes or mastics applied around the joints in the system. Field examinations of duct systems have shown that taped seals tend to fail over extended periods of time. The Lawrence Berkeley National Laboratory (LBNL) has been testing sealant longevity for several years. The accelerated test method developed by LBNL is being used as a basis for an ASTM standard under sub-committee E6.41. LBNL tests found that typical duct tape (i.e., fabric backed tapes with rubber adhesives) fails more rapidly than all other duct sealants. LBNL has also tested advanced tape products being developed by major manufacturers. The results of these tests showed that the major weaknesses of the tapes that fail are the use of natural rubber adhesives and the mechanical properties of the backing.
Issues Related to the Mechanical Property Characterization of Sealants
Authors: White CC , Hunston DL
Published: April 2008

Quantification of the mechanical properties of cured sealant is complicated by the presence of the Mullins effect. This paper examines the Mullins effect using five different sealants encompassing the range of properties and formulations found in commercial sealants. Three main observations include: the Mullins effect was observed in all sealant formulations studied, the Mullins effect was observed in both tension and compression strains, and there was a recovery of the Mullins effect after sufficient periods of time between repeated loading cycles. Simple rules were formulated to describe the Mullins effect. Moreover, the tests show that understanding the Mullins effect is crucial in characterizing the mechanical properties of a sealant.
Developing a Performance-Based Joint Sealant Specification for Airport PCC Pavements
Authors: Lacasse MA , Masson JF
Published: April 2008

Despite recent progress to develop a performance-based specification for bituminous sealants applied to asphalt concrete (AC) roadways and runways, a performance-based specification for cold-applied joint sealants for Portland cement concrete (PCC) aprons, taxiways, and parking areas has yet to be mapped and developed. Unique in-service conditions exist on these PCC pavements, where sealants are not only exposed to climatic effects and heavy traffic loads, but also to jet fuel and de-icing fluids. Installation and maintenance conditions are also unique in that it is often necessary to install or replace joint sealants at night or in a very short time so that aircraft traffic disruption is avoided. Hence, special consideration must be provided to ascertain that joint sealants are effective and durable. Recent studies on joint and crack sealants used on airport pavements that experience cold climates indicate that current specifications do not necessarily allow for the selection of durable sealants, and therefore sealant failure can be rapid. To address the issue of premature failure and to extend joint sealant service life, the elements of a performance-based specification for cold-applied joint sealants for PCC airport pavements is reviewed. The benefits of such a specification include the selection of joint sealants for specific local needs, reduced airport pavement maintenance costs, and extended airport PCC pavement service life.
Development of Compression Design Allowables for Composite Bolted Joints Using ASTM Standard D 6742
Authors: Sawicki AJ
Published: April 2008

Compression design allowables for carbon/epoxy laminates could be increased by taking advantage of hole-filling effects, if reliable design data were available. Previous research had demonstrated that filled hole compression strengths range between 5% to 35% higher than open hole strengths, due to variability in fastener-hole clearance and clamp-up torque. The importance of measuring these parameters for proper data interpretation resulted in the development of ASTM Practice for Filled Hole Tension and Compression Testing of Polymer Matrix Composite Materials (D 6742/D 6742M). Specific instructions regarding measurement, recording, and calculation of critical parameters for filled hole specimens are provided. The standard was implemented at Boeing- Philadelphia in the development of compression allowables for high-temperature materials used on the RAH-66 airframe. Enhanced compression strengths were demonstrated for several material systems tested in a variety of environments. A semi-empirical analysis technique permitted strain allowables to be generated using fewer laminate configurations and specimens than in previous programs.
Minimum Retention Settings: Examining Prediction Methods
Authors: Scher IS , Mote CD
Published: April 2008

By comparing the forces at the bindings required to ski normally to the forces recommended by the current setting standards, we evaluated the currently used method for selecting the ski-binding release forces for an individual. For 32 subjects (including beginning skiers through members of professional racing teams; 48 to 103 kg; 16 to 60 years of age), the lateral force at the toe binding and the vertical force at the heel binding were measured during skiing experiments. For each subject, the maximum lateral toe force and vertical heel force were measured in runs without falls and without binding releases.

For 20 of the 32 subjects, the current setting standards allow forces at the bindings that far exceed the forces required to ski in at least one release mode. Fifteen of the subjects generated maximum lateral toe forces during normal skiing that were less than 65% of the magnitude recommended in the current standards. For another 15 subjects, the maximum vertical heel force needed for normal skiing was less than 50% of the force recommended by the setting standards.

In order to improve the accuracy of the setting standards for the individual, we examined the relationships between the required settings and the variables used in the current standards (weight, height, age, and skier type) to select the settings. Multiple linear models that used skier weight, height, age, and skill level could not predict accurately the optimal settings for an individual (multiple R correlation coefficients were 0.57 and 0.73 for toe and heel settings). Furthermore, weight was found to be a poor predictor of the required settings, with all linear and quadratic correlation coefficients less than 0.46.

Nonanthropometric variables were considered for use in a predictive model for the best settings. Slope steepness and grooming were examined for a relationship with the forces generated during skiing, but no statistically significant relationships were found. Skier attitude, confidence, and skiing style appear to be related to the required settings. Measurements of the forces during low-velocity maneuvers before a day of skiing, which were found to generate high forces more often than downhill skiing and which incorporate skier confidence and style, could provide a better method of determining the settings for the individual skier.
Development and Validation of an Apparatus for Determining Snowboard Boot Stiffness
Authors: Torres K , Crisco JJ , Greenwald RM
Published: April 2008

An apparatus for measuring the mechanical properties of snowboard boot/binding systems in bending was designed and constructed. The apparatus was designed so that the direction of loading could be specified for a full 360° about the tibial axis of a prosthetic lower limb. Moment about the ankle joint was measured as a function of ankle rotation. Testing was conducted on two different boot/binding systems to evaluate device sensitivity. Two ankle joint configurations (articulating and rigid) and several boot strap tightness levels were also evaluated. Bending stiffness was calculated as the slope of the moment-rotation curve. Stiffness values were found to be a function of loading direction, boot/binding type, and surrogate leg and ankle design. Stiffness values varied with loading direction (e.g., forward lean, backward lean, medial bending, and lateral bending), ranging from 0.64 Nm/deg to 3.02 Nm/deg for the articulating ankle joint and with values as high as 10.38 Nm/deg for the rigid ankle in backward lean. Testing standards have not yet been developed for snowboard boot and binding designs, nor are there standardized methods for determining the physical properties of boots and bindings. The type of apparatus designed in this experiment can be used to quantify mechanical properties of the boot/binding system. These data may be useful in developing standardized tests and in better understanding the performance of these systems in the field.
Injuries in Alpine Skiing, Telemarking, and Snowboarding
Authors: Ekeland A , Rødven A
Published: April 2008

A central ski patrol-based registration of skiing and snowboarding injuries was performed by the Norwegian Ski Lift Association during the winter seasons 1996/1997 and 1997/1998.

At total of 3915 injuries and 32.894 million lift transports were recorded during the two seasons, giving an injury rate of 1.2 injuries per 1000 skier days or per 10 000 lift transports. Most of the injuries occurred during alpine skiing (57%) and snowboarding (34%), whereas telemark skiing accounted for 9% of the injuries. Many injured snowboarders suffered wrist injuries (29%), compared to only 4% for alpine and 3% for telemark skiers. Knee injuries were more common among injured alpine skiers (26%) than among telemarkers (13%) and snowboarders (6%), but the percentage of knee injuries was double as high for females as for males in all three disciplines. The injured telemark skiers suffered three times as many ankle injuries (13%) as alpine skiers (4%) and snowboarders (4%).

Injured snowboarders suffered more fractures (33%) than alpine (22%) and telemark (20%) skiers. Lower leg fractures were recorded for only 3.6% of the injured alpine skiers 20 years and older, whereas this injury accounted for 20% of the injuries among alpine skiers 12 years and younger. Injured alpine beginners suffered more knee injuries than experts. Almost half of the injured snowboarder beginners (44%) suffered wrist injuries compared to only 14% of the experts, but injured experts suffered more head, shoulder, and ankle injuries than beginners.

In conclusion, injured alpine skiers are most prone to knee injuries. Lower leg fractures have become uncommon among adult skiers but are still a common injury in children. Injured snowboarders are prone to wrist injuries and injured telemark skiers to ankle injuries. The percentage of knee injuries among females is twice that of males in all three disciplines.
A Two-Year Study of Skiboards
Authors: Shealy JE , Ettlinger CF , Johnson RJ
Published: April 2008

The purpose of this study is to determine the lower leg injury rate for skiboard users in comparison to the injury rate for users of traditional alpine ski equipment. Data were collected from ski areas representing approximately 1000 skiboard rental units. Injury rates for users of these units were compared to injury rates involving conventional alpine rental equipment at the same ski areas. A total of 75 ski areas were polled in the study. Sixteen areas submitted complete data with two of the areas reporting for two seasons. In all, 34 475 alpine units and 960 skiboard units were involved in the study. Alpine equipment accounted for approximately 860 000 skier visits with skiboards accounting for approximately 20 000 skier visits. For the all injury group, mean rentals between injuries (MRBI) was 321 for alpine and 147 for skiboards (risk ratio 2.2:1). For the lower leg Injury Group, MRBI was 2221 for alpine and 575 for skiboards (risk ratio 3.9:1).
Rates and Modalities of Death in the U.S.: Snowboarding and Skiing Differences—1991/92 through 1998/99
Authors: Shealy JE , Ettlinger CF , Johnson RJ
Published: April 2008

This study looks at trauma-related death rates and modalities of death between snowboarding and skiing. The snowboarding population is younger and has a higher percentage of males. Thus, based on the demographics of risk taking, one would expect the snowboarding fatality rate to be higher if the objective risk of death was the same between the two activities. This study spans the time period from 1991/92 to 1998/99 in the United States utilizing data generated by NSAA for both deaths and skier visit counts. The study specifically includes deaths occurring to recreational skiers and snowboarders who suffered an immediate traumatic death within the bounds of the patrolled ski area. Specifically excluded are deaths to employees, medical emergency deaths (i.e., cardiac arrest, etc.), and back country skiers. During this time there were a total of 426.4 million participant visits (MPV) and 285 fatalities to patrons of ski areas in the United States. Snowboarders accounted for 28 of the deaths (9.8%), and 257 were to skiers (90.2%). Snowboarders generated 61.5 MPV (14.4%), and skiers generated 365.9 MPV. The overall rate of snowboarding deaths (0.46 per MSV) is 35% lower than for alpine skiing (0.70 per MSV); conversely, the alpine skiing fatality rate is 54% higher than for snowboarding. The percent of deaths due to impact is higher for skiing than snowboarding, while the death rate for jumping and tree-well related deaths is higher for snowboarding than skiing.
Injuries and Risk Taking in Alpine Skiing
Authors: Goulet C , Régnier G , Valois P , Ouellet G
Published: April 2008

The purpose of this study was to investigate the relation between motivation toward alpine skiing, attitude toward risk-taking behavior, risk-taking behavior, and injury incidence. Participants were skiers over eleven years of age. They completed a questionnaire that investigated skill level, sources of motivation toward alpine skiing, attitude toward risktaking behavior, and risk-taking behavior. A MANOVA was performed to compare three groups of skiers: (1) 163 skiers caught on the slope while performing a voluntary thrill-seeking behavior that could directly or indirectly lead to a sequence of events frequently associated to injuries (RISK TAKING); (2) 190 injured skiers (INJURED); and (3) 219 randomly selected skiers (UNINJURED). Significant differences were found between the three groups on age and skill level (p < 0.001). Skiers from the RISK TAKING group were younger (19.9 years old) than those from the INJURED group (24.7 years old) who were in turn younger than the UNINJURED group (30.7 years old). Skiers from the INJURED group were the least skilled, while those from the RISK TAKING group were the most skilled (p < 0.001). No differences were found between the INJURED and the UNINJURED groups on their source of motivation for skiing and their attitude toward risk taking. However, skiers from the RISK TAKING group were significantly different than the other two groups on those cognitive variables. They perceived the risky behaviors presented in vignettes as being less dangerous than skiers from the UNINJURED and the INJURED groups. These results suggest that in future prevention programs, the emphasis should be placed on the development of skiing technique among the lowskilled skiers. It also questions the strategy of targeting risk takers in prevention campaigns.
Laboratory Simulation of Biomechanical Knee Behavior under Skiing and Falling Loads
Authors: Freudiger S
Published: April 2008

In order to provide a deeper insight into the relationship between critical load cases when skiing and the load build up in knee ligaments, a knee simulator has been developed. This mechanical knee simulator duplicates closely realistic knee response to skiing and falling loads. A computerized data acquisition and analysis surveys the exceedance of knee ligament injury thresholds. The close-to-realistic knee stiffness properties are assured by pneumatic cylinders, which are furthermore adjustable to consider the age dependency of the soft tissue characteristics. This knee simulator offers the following degrees of freedom of the tibia in respect to the femur, estimated to be relevant for that purpose: internal/external rotation, varus/valgus rotation, and flexion rotation in addition to anterior translation. The device has an open architecture, and upcoming newly developed knowledge about knee ligament properties, e.g., at typical high speeds of falling loads, can be implemented easily. The initial properties of the simulator are derived mainly from available literature data. This knee simulator is in particular suitable for ski safety binding designers. With a ski installed on the device's sole, it will behave similar to a real knee. The securing state of the binding during skiing loads as well as the releasing state of the binding during falling loads can be investigated on a comprehensive basis. The author is confident that the use of this simulator may help to understand the persistence of the still-important number of knee ligament injuries in skiing with today's ski safety bindings. An early result of a ski safety binding test is presented.
Critical Load Cases for Knee Ligaments at Skiing—An Engineering Approach
Authors: Freudiger S , Friederich NF
Published: April 2008

The number of ligament injuries at skiing remains very high. Despite improvements in ski safety equipment made in recent years, research and development is needed to work toward an effective breakthrough in preventing injuries. Knee surgeons together with biomechanical engineers have to research and to establish comprehensive specifications about the so-called “critical load cases,” with which future ski safety equipment will have to comply. We reviewed the current literature and analyzed the published injury mechanisms in order to check their plausibility regarding the related skiing maneuvers described. Derived from literature analysis and our own studies, we describe a new critical load case, the so-called “transition maneuver.” The sliding upper body undergoes a transition from the uphill side over the ski tails to the downhill side, leading to a geometrically enforced anterior tibial translation. We discuss published video sequences of injured skiers in respect to the probable maneuvers and the derived potential injury mechanism. We differentiate further between two main maneuvers where a ski rotates against the skier's inertia and where a skier rotates against his skis held in their track. An attempt is made to group the various maneuvers systematically into load cases, which can be considered critical for the knee ligaments. The four basic groups (flexion, external rotation, internal rotation, and extension) are split into a total number of 17 subgroups (i.e., load cases), with each of them comprising one or more distinctive (skiing) maneuvers. An overview of these “critical load cases” is presented in a table, which may be used as a check list for future classification of knee ligament injuries at skiing.
Arthroscopically Assisted Operative Treatment of the Tibia Plateau Fractures from Downhill Skiing
Authors: Yamagishi T , Fujii K , Tsuji M , Kurosaka D
Published: April 2008

Twenty-two skiers suffered fractures of the tibial plateau and eminence of the tibia from downhill skiing between 1993 and 1998. Sixteen cases of the 22 tibial plateau fractures were treated with an arthroscopic reduction and internal fixation of the articular surface without a formal arthrotomy or detachment of the anterior horn of the lateral meniscus. The average age of the patients at the time of surgery was 40 years (ranging from 24 to 55 years). Fourteen patients were male and eight patients were female. Twelve of these plateau fractures were classified according to Schayzker [15]. The distribution was as follows: one case Type I; three cases Type II; four cases Type III; two cases Type IV; zero case Type V; and two cases Type VI; ten cases of intercondylar eminence of the tibia were classified according to Meyers [13]; six cases of Type I; one case of Type II; three cases of Type III.

The Type II and III, according to Schayzker's fractures [15], required elevation of the depressed fragments from below through a bony window, bone grafting the resultant metaphyseal defect, and rigid internal fixation using an L-buttress plate. The principles for arthroscopic reduction and internal fixation of tibial plateau fractures are essentially the same as those of conventional open reduction and internal fixation. The split depression and joint depression fracture types were suited for arthroscopic reduction and internal fixation. The treatment goals are restoration of joint congruity, restoration of normal alignment, joint stabilization, and, ultimately, prevention of degenerative arthritis. There were no valgus malunions and no non-unions: radiographic findings of early degenerative changes were not seen in 14 of 22 patients at an average of twelve months follow-up (range from 6 months to 60 months).
Monitoring Deformations on the Church of the Transfiguration
Authors: Vahrameeva TI , Lubimov V , Tsvetkov VJ
Published: April 2008

The Church of the Transfiguration or Tserkva Preobrazhenskaya, located on Kizhi Island, Karelia, Russia, is a unique monument of the 18th century that has no analogs in world architecture. It is included on the UNESCO list of the most significant monuments constituting the World Cultural Heritage. The Kizhi Pogost includes three structures: the Tserkva Preobrazhenskaya (the summer church), the Tserkva Pokrovskaya (the winter church), and the Bell Tower. The Church of the Transfiguation is the focal point of the ensemble and is constructed of a system of log octagons that rise to a height of 34 meters (111.5 ft).

Typically, wooden buildings in Northern Russia last no longer than 250–300 years. The Church of the Transfiguration reached this critical age in the last quarter of the 20th century. This fact highlights the importance of restoration work and the monitoring of the general condition of the building.

A precise description of the wood log structure of which the church is composed is given. The monitoring of seasonal movement of the building is given starting from the erection of a steel frame inside the building in 1981 to 1983. Monitoring of building deformations have been monitored to analyze the interaction of the log structure and the steel frame.

Measurements conducted and discussed in the paper reveal interesting data regarding the seasonal movement of the structure as a whole and the behavior of the elements of which the structure is composed. Based on the systematic monitoring of the building it can be concluded that, apart from the seasonal movement, the building is stable. The observations did not reveal interaction between the steel framework and the wood structure.
Inspection and Evaluation of Decay in Log Structures
Authors: Mattsson J
Published: April 2008

The decay of wood materials in buildings due to fungal attack and the activity of wood boring insects is not uncommon. Such decay normally causes restricted areas of damage, but in some cases, the damage can be extensive and pose a serious problem. for this reason maintenance and repair are a natural part of a building's life cycle. The best way to restrict damage is to discover problem areas as soon as possible. However, all preventive work against damage and rehabilitation of damaged areas must be based on a fundamental knowledge and understanding of biological mechanisms. Otherwise there is a great risk of taking incorrect measures. Such mistaken efforts not only cause needless expense, but in cases of listed or protected buildings incorrect treatment can also cause damages that are not repairable — damages that may be more ruinous than the original decay that the repairs were designed to address.

Wood decaying fungi and wood boring insects occur everywhere where wood is used as a building material and can cause damage in most parts of those structures. The activity of these biological organisms vary due to microclimatic factors such as moisture content in the wood and temperature. The result is that damage that appears identical from building to building may actually develop very differently due to climatic factors. For this reason it is of primary importance to carry out a careful and thorough examination of all damage.
Strategies for the Preservation of Historic Wooden Structures
Authors: Lewandoski JL
Published: April 2008

The preservation of historic wooden structures usually involves choices concerning preservation of the artifact, preservation of design, original, current and future use, availability of materials, and accommodation of modern engineering standards. There is no one correct choice but rather a variety of strategies, one of which will be most appropriate to a particular project. The strategies are numerous and range from preservation of fabric by removal from service, to in-kind restoration, to partial or full replacement of structure with modern elements.
The Treatment of Fungal Growth in Heritage Structures in Denmark
Authors: Munck O , Fode J
Published: April 2008

Wood has always been a constituent and natural part of buildings. In ancient Danish buildings, wood was utilized for timber frames, floor beams, roof rafters, partitions, windows, and doors. Thoughtfully applied, wood is practically imperishable. However, even structural timber that is protected within the building envelope can become worn due to hundreds of years of use, or rotten due to the lack or improper maintenance of the roof and the facades.

This article deals with some of the construction principles that apply to heritage buildings in Denmark and with the problems connected with restoration of listed buildings after a wood-decay fungi attack. In relation to this we will describe some new remedial treatments, which are applicable especially when preservation of original structural timber is an absolute necessity.
A Computational Fracture Mechanics Approach for the Analysis of Facesheet-from-Core Disbond of Honeycomb Core Sandwich Panels
Authors: TerMaath SC , Ingraffea AR , Wawrzynek PA
Published: April 2008

The modified crack closure method is combined with finite element analysis to study the damage mode of facesheet-from-core disbond of honeycomb core sandwich structure. Explicit panel models containing an initial disbond region are analyzed to better understand this type of failure. Calculation of energy release rates is used to determine loading conditions that will cause disbond propa- gation. The edge peel-off case is used as an example, and parameter studies are performed to determine the importance of key properties with regard to damage tolerance of the panels.
Crack Wake Influence Theory and Elastic Crack Closure Measurement
Authors: Donald JK , Connelly GM , Paris PC , Tada H
Published: April 2008

Experimental and analytical evidence indicates that “closure” or interference of crack faces does not entirely isolate the crack tip from damaging strains. To account for the contribution of the cyclic crack tip strain below the opening load, a new analysis technique has been developed for estimating ΔKeff. This technique is based on crack wake influence theory (the relationship between the effect of crack wake interference on a displacement or strain measurement location and the corresponding effect at the crack tip). Solving the distribution and position functions provides a method of equating remote compliance measurements to reduction in crack tip elastic strain. The experimental method involves determining the ratio of the compliance of the shielded crack to that of the fully open crack (CR). This relationship remains elusive until it is recognized that 1 — CR is directly related to the influence of the closure mechanism on both the measurement location and the crack tip. The verification of this method includes experimental measurements of a large center crack panel with multiple displacement and strain gage measurement locations. The standard crack has been replaced with a milled slot, allowing precision blocks to be inserted at specific positions to simulate crack wake interference. Finite element analysis and theory of elasticity are linked to the experiment to better understand the measurement requirements for crack tip closure. The estimation of ΔKeff using the ratio of influences from the theory of elasticity can be directly compared with other approximation techniques such as the adjusted compliance ratio or opening load.
A Combined Experimental and Finite Element Study of Crack Closure Effects in Modified 1070 Steel
Authors: Dougherty JD , Srivatsan TS , Padovan J
Published: April 2008

The significance and even the existence of crack closure is being questioned by several researchers. The objective of this study was to determine if crack closure occurs and to quantify its significance. An approach combining experimental measurement techniques with finite element analysis techniques was utilized. For two values of compact tension specimen thickness, a series of tests were conducted to determine the effect of maximum stress intensity, load ratio, constraint, and single tensile overload on the crack closure and fatigue crack growth behavior of a modified 1070 steel. Test results indicated that constraint has a significant influence on crack closure and crack growth rate behavior. Thin specimens exhibited consistently lower crack growth rates and higher crack closure levels than the thick specimens, except for tests conducted at a high load ratio, where crack closure did not occur. The thin specimens also exhibited a more significant overload effect. A new finite element modeling technique, which uses substructuring techniques to model the load cycling and crack propagation of an entire compact tension specimen, was developed. Comparison of stationary crack and propagating crack finite element models revealed that plasticity-induced crack closure produces a significant amount of crack tip shielding, which effectively reduces the strain range and mean strain experienced at the crack tip.
Stress and Fracture Analyses of Semi-Elliptical Surface Cracks
Authors: Newman JC , Reuter WG , Aveline CR
Published: April 2008

The present paper concentrates on both elastic and elastic-plastic finite-element stress analyses of the surface crack in a plate subjected to tension and bending loads. Stress-intensity factor (K) equations that cover a wider range of crack-length-to-width ratios, than those previously developed by Newman and Raju, for various crack-depth-to-crack-length ratios and crack-depth-to-plate-thickness ratios have been developed and are presented. These equations are used in the subsequent fracture analyses of surface crack specimens subjected to tension and bending loads. From elastic-plastic finite-element analyses, the variations of a hyper-local constraint parameter (αh) along the surface-crack front were studied to identify the region of maximum constraint and the critical fracture location. (The hyper-local constraint parameter is based on the average normal stresses acting over the plastic-zone region on a line in the crack plane perpendicular to the crack front.) The application of linear-elastic fracture mechanics to fracture of surface-crack specimens made of a high-strength D6AC steel are presented for both tension and bending loads. Two methods were used to characterize fracture: the K2-integral around the crack front and K at a critical fracture location (ϕc). The critical fracture location was the location of the maximum of the product of K times αh. These two methods were used to evaluate the fracture toughness for both the crack-initiation loads and at the maximum failure load conditions. For tension and bending loads, the K2-integral method correlated 90% of the fracture data within ±25% in terms of load, whereas K at the critical fracture location correlated the data within ±20%.
Effect of Geometry and Load History on Fatigue Crack Growth in Ti-62222
Authors: Liknes HO , Stephens RR
Published: April 2008

Fatigue crack growth behavior of Ti-62222 mill-annealed material in sheet form was examined as a function of specimen geometry. The geometries investigated were the eccentrically loaded single edge-notch tension (ESE(T)), the compact tension (C(T)), and the middle tension (M(T)). Tests were conducted at room temperature at two load ratios (R=0.1 and 0.7) and covered a broad range of crack growth rates ranging from 10-7 to 10-2 mm/cycle. The same precracking and threshold test procedures were used for all geometries as each threshold test was started at the same crack length and continuous load shedding was applied at a K-gradient of C=-0.08 mm-1. As a result, the same stress intensity-crack length (K-a) history was maintained throughout all of the threshold tests. Experimental results showed differences in fatigue crack growth behavior at the lowest crack growth rates while higher crack growth rates were similar. Surface roughness differences at lower crack growth rates were observed at the same nominal ΔK for the three geometries, suggesting differing crack growth mechanisms. Discrepancies observed in specimen behavior are assessed in terms of the crack tip stress field distribution which include both y-direction and T-stresses. In addition, supplemental fatigue crack growth tests showed a dependence on crack length and load reduction procedure.
Increases in Fatigue Crack Growth Rate and Reductions in Fatigue Strength due to Periodic Overstrains in Biaxial Fatigue Loading
Authors: Varvani-Farahani A , Topper TH
Published: April 2008

Fatigue crack growth under biaxial constant amplitude straining (CAS) and a strain history having periodic compressive overstrains (PCO) were investigated.

A comparison of the growth of fatigue cracks under constant amplitude straining and under strain histories having periodic compressive overstrains revealed that the morphology of the fracture surface near the crack tip and the crack growth rate changed dramatically with the application of the compressive overstrains. When the magnitude of the compressive overstrains was increased, the height of the fracture surface irregularities was reduced as the increasing overstrain progressively flattened fracture surface asperities near the crack tip. The reduced asperity height was accompanied by drastic increases in crack growth rate and decreases in fatigue strength.

Crack opening stress measurements for biaxial fatigue cracks made using confocal scanning laser microscopy (CSLM) image processing of the crack profile, showed that the biaxial cracks were fully open at zero internal pressure for block strain histories containing in-phase periodic compressive overstrains of yield point magnitude. Therefore, for the shear strained samples there was no crack face interference and the strain intensity range was fully effective. For PCO tests with biaxial strain ratios of -0.625, and +1, effective strain intensity data were obtained from tests with positive stress ratios for which cracks did not close. The strain intensity factor ranges derived from popular fatigue life parameters were used to correlate fatigue crack growth rates for the various strain ratios investigated. These parameters all involved the shear strain range, and the normal strain range acting on the maximum shear strain plane. For various biaxiality ratios, the ratios of the effective strain intensity factor range to the constant amplitude strain intensity factor range at the threshold were found to be close to the ratios of the closure free fatigue limit obtained from effective strain-life to the constant amplitude fatigue limit.
Analysis of Fatigue Crack Closure During Simulated Threshold Testing
Authors: McClung RC
Published: April 2008

Load shedding procedures during fatigue crack growth threshold testing can, under some conditions, induce significant changes in fatigue crack closure levels, which can in turn artificially influence the apparent threshold level. In this paper, mechanics analyses of growing fatigue cracks that account for plasticity-induced closure are used to study load shed effects on crack opening levels during simulated threshold testing. Both finite element and FASTRAN strip yield models are employed, and the two approaches are compared. The current ASTM standard test method for determining thresholds is evaluated. Analyses explore the effects of initial stress, initial stress intensity factor, specimen size, material flow strength, and load shed rates on crack closure.
Mean Stress and Environmental Effects on Near-Threshold Fatigue Crack Propagation on a Ti6246 Alloy at Room Temperature and 500°C
Authors: Sarrazin-Baudoux C , Chabanne Y , Petit J
Published: April 2008

The cracking behavior of a Ti6246 alloy under cyclic loading superimposed to different levels of mean stress is studied, with special attention to the near-threshold fatigue crack propagation regime, and to possible coupled effects of corrosion and creep. Tests were conducted at room temperature and 500°C in selected environmental conditions (high vacuum, controlled atmospheric leak low pressure, controlled partial pressure of water vapor in pure argon) and at different frequencies. The near-threshold crack propagation at low Kmax (i.e. low R ratio) is shown to be highly sensitive to the environment, and a predominant detrimental influence of water vapor is observed, even under very low partial pressure. Conditions for the occurrence of an abnormal behavior consisting in the disappearance of the threshold for sufficiently high Kmax level, are discussed from tests performed at various constant Kmax levels in ambient air, high vacuum and humidified argon. This effect is observed in air and in vacuum for Kmax higher than 52 MPa√m, and is related to an intrinsic creep damage process which appears more efficient at room temperature than at 500°C and more accentuated in air than in vacuum. The origin of this abnormal near-threshold behavior is discussed in comparison with a similar behavior described in the literature at room temperature on another type of Ti6246 alloy and at 120°C on an IMI834. Additional experiments conducted at 500°C in humidified argon have shown a critical Kmax level reduced to 22 MPa√m. This behavior is suspected to be related to a contribution of stress corrosion cracking induced by water vapor when some conditions favoring a localization of the deformation and the attainment of a critical embrittlement are fulfilled.
Component Design: The Interface Between Threshold and Endurance Limit
Authors: Taylor D , Wang G
Published: April 2008

This paper discusses the use of methods derived from fracture-mechanics for the assessment of stress concentrations in components. It is known that some sharp notches can be modelled as cracks, their fatigue limits corresponding to the threshold value for a crack of the same length. Using this methodology for the assessment of components gives rise to two problems. The first problem concerns geometry: real stress concentrations have complex shape and cannot be modelled as notches of simple profile. The second problem concerns notch size: can short notches be modelled in the same way as short cracks? An approach has been developed which is an extension of the well-known critical-distance concept. It can be applied to both cracks and notches and takes into account the size effect. This has been tested using data from specimens containing short cracks and circular notches of various sizes; it has also been successfully applied to the analysis of a component in service.
The Big Question: When Should One Recommend Taking a Transformer Out of Service?
Authors: Grisaru M , Friedman H
Published: April 2008

This paper examines the goals and difficulties of dissolved gas analysis (DGA) implementation to evaluate the condition of transformers. Although the technique is quite old and well-known in many utilities throughout the world, diagnosis is still complicated and lies in the domain of the state of the art. The published guides indicating the limits for concentration values, or correlating gas ratio and failures, are too broad to be applicable in practice. Gas ratio guides refer to a single failure only, while in practice faults build up one on top of the other until the critical failure appears. This paper reviews some parameters liable to affect normal concentration values. The authors offer a different approach: to develop a database including all failures and unusual cases versus the gases developed at each stage. From the case histories, which took place at the Israel Electric Corporation, we have drawn some recommendations which help to find the right time for scheduled outage of the transformers. (Note: Israel Electrical Corporation acquires transformers on the free market. Therefore, the “gassing” transformers are different manufacturers.)
Comparative Tracking Index of Flame-Retardant Nylon and PBT
Authors: Markezich RL
Published: April 2008

Flame-retardant nylons and PBT have been used in the electrical and electronic industry for many years. To flame retard these materials, halogens can be used with different synergists. The choice of synergist and also the halogen flame retardant has a great effect on one of the electrical properties, the comparative tracking index (CTI). The choice of resin, PBT, nylon 6 or nylon 66 also has an effect on the CTI.
Modern, Low Fire Hazard, Thin Wall Insulated Wire—A Complex Balance of Properties
Authors: Gardner D , Whiteley RH
Published: April 2008

The complexity of electrical systems required for modern mass transport systems have been increasing over recent years. The size and weight of wire and cable installations are now important issues. The technical solution to these issues has been to move from thick and medium wall insulations to thin wall insulations. In addition, increased safety levels with respect to fire hazard properties are now demanded by the industry. Ignition resistance and reaction to fire are now considered to be of critical importance, especially for underground transit systems. The production of smoke, acid/corrosive gases and toxic fire products must all be minimized.

The functional properties of the wire, however, must not be compromised by these additional requirements of thin wall insulation and low fire hazard properties. A typical specification for such a wire therefore reflects a complex balance of properties.

This paper describes the elements of such specifications and reviews some of the test methods used to define the properties of the wire.
Fire Testing of Electrical Materials
Authors: Hirschler MM
Published: April 2008

In recent years electrical wire or cable insulation has been, once more, identified by NFPA statistics as a major material first ignited in residential fires (representing 7.6% of fires and 3.9% of fire fatalities in 1991–95) and the cause of 13% of catastrophic fires (1993–96). This highlights the need for renewed emphasis on fire testing of wires, cables and electrical materials. Cable fire tests can be subdivided into 5 categories: (a) Old fashioned small scale tests, which generally address only ignitability or flame spread, but the results of which are rarely meaningful in terms of real fire performance; (b) Vertical cable tray tests, of which there are a large variety, ranging in heat input from 20 kW up to 154 kW (in the case of riser cables), which address flame spread, and sometimes also smoke and heat release; (c) The Steiner tunnel NFPA 262 (UL 910) test, which determines wind aided horizontal flame spread, and smoke release, under a very high heat input (ca. 90 kW), with a relatively small mass load of cables; and (d) Small scale cable tests, often originally designed for materials, directed at measuring fundamental fire properties, such as heat release or critical fluxes for ignition or flame spread and thermal heating properties. (e) Tests for other cable fire properties, mainly smoke (obscuration, toxicity, corrosivity) and circuit integrity.
Effect of Gripping Technique on Tensile, Tensile Creep and Tensile Creep-Rupture Results for a High Tenacity Polyester Yarn
Authors: Thornton JS , Allen SR , Arnett SL
Published: April 2008

In order to facilitate a discussion of gripping technology, the effect of three types of grips on the results of rapid loading as well as long-term creep loading tension tests is assessed. As background, a review of combined stresses and friction effects is presented. Monitoring the effective gage length of the specimen under test shows how movement of the specimen in the grips can influence the apparent stress-strain behavior, and how initial use of some extensometry may serve to establish active gage lengths for repetitive testing. Creep-rupture results are affected by both stress concentrations and excessive specimen movement in the grips. There is evidence that a stick-slip resonance phenomenon in the grip can influence creep strain and creep rupture results, particularly data scatter. If the grips used to produce the creep-rupture results are not the same as the grips used to establish the ultimate tensile strength (UTS) then it may be invalid to express the creep-rupture results as a percentage of UTS. In this case, there are three distortions that can arise with two of them leading to overly optimistic estimates of the long term creep-rupture strength.
Wide-Width Geotextile Testing with Video Extensometry
Authors: Jones D
Published: April 2008

This paper demonstrates the difference between the results of using a conventional direct contact LVDT extensometer versus a non-contacting Video Extensometer where load at specific strains, ultimate load and elongation were measured. Previously, video extensometry has not been used for geotextile testing. Comparisons are made determining their measurement capability and ease of use. Direct contact systems displace yarns and rupture filaments in the fabric sample, which alter both the elongation and ultimate load of the sample. By measuring strain without placing a load on the yarns perpendicular to the loading direction, yarn slippage is eliminated. This principle allows for maximum tensile strength without pseudo failures due to yarn damage. Comparisons are also determined for length of time to calibrate, sample preparation before data acquisition, marking techniques and general observations made from using both systems.