bluuebunny/crossref_metadata_2025 huggingface dataset:
Material Properties for Use in FEA Modeling: Sealant Behavior with Ambient Laboratory Climate Aging
Authors: Wolf AT , Cleland-Host HL
Published: April 2008

Stress relaxation uniaxial testing is used to define the behavior of elastomeric materials in their functional range. The stress-strain data obtained by this method are used in finite element analysis (FEA) to model the behavior of the material in a given application. The objective of this study is to determine the effect of aging on the uniaxial stress-strain properties of silicone sealants. This paper examines the material behavior changes that occur as these sealants continue to cure at ambient laboratory conditions. The study is intended as a first step toward developing simple working models that account for the effects of sealant aging in FEA modeling. Uniaxial stress relaxation testing was conducted on six commercially available silicone structural glazing, insulating glazing, and weatherproofing sealants in tension and in compression at temperatures of -20°C, 22°C, and 80°C. Testing was carried out immediately after cure, i.e., after three days for two-part and after 30 days for one-part sealants, and after an additional one-year storage period at ambient laboratory conditions. The test specimens were pre-loaded prior to testing in order to eliminate the Mullins effect. Testing was carried out over a strain range of-45–90%. The specimen was loaded to the desired strain level and then allowed to relax. The load at the end of the relaxation period was used to calculate the engineering stress. Coefficient of variance (CoV) was used to determine the significance of material property changes with continued sealant cure. No significant changes in engineering properties were observed for two sealants. For two further sealants, half or more of the test results were within CoV, and no clear trends in property drift could be derived. The changes in material properties of the final two sealants were well outside the CoV limit, and moderate to strong stiffening was observed.
Concepts for Development of a Service Life Prediction Methodology for Sealed Building and Construction Joints—Review and Roadmap for Future Research
Authors: Wolf AT
Published: April 2008

Despite extensive research on durability of building materials and components performed over the past two decades, no reliable quantitative method of service life prediction (SLP) has gained wide acceptance. Generic guidance is provided in documents published by ASTM, RILEM, EOTA and ISO. Although the methodology is logical and easy to understand, its application is not simple, since much judgement is required in the interpretation of the results. Recently, a more specific method of estimating the service life of sealed joints has been proposed. The paper discusses the key requirements relevant to any service-life-prediction methodology, critiques the preliminary method proposed in the literature, and proposes a possible extension of this method.
Installation of Adhesively Bonded Composites to Repair Carbon Steel Structure
Authors: Roach D , Rackow K , Dunn D
Published: April 2008

In the past decade, an advanced composite repair technology has made great strides in commercial aviation use. Extensive testing and analysis, through joint programs between the Sandia Labs FAA Airworthiness Assurance Center and the aviation industry, have proven that composite materials can be used to repair damaged aluminum structure. Successful pilot programs have produced flight performance history to establish the viability and durability of bonded composite patches as a permanent repair on commercial aircraft structures. With this foundation in place, efforts are underway to adapt bonded composite repair technology to civil structures. This paper presents a study in the application of composite patches on large trucks and hydraulic shovels typically used in mining operations. Extreme fatigue, temperature, erosive, and corrosive environments induce an array of equipment damage. The current weld repair techniques for these structures provide a fatigue life that is inferior to that of the original plate. Subsequent cracking must be revisited on a regular basis. It is believed that the use of composite doublers, which do not have brittle fracture problems such as those inherent in welds, will help extend the structure's fatigue life and reduce the equipment downtime. Two of the main issues for adapting aircraft composite repairs to civil applications are developing an installation technique for carbon steel structure and accommodating large repairs on extremely thick structures. This paper will focus on the first phase of this study which evaluated the performance of different mechanical and chemical surface preparation techniques. The factors influencing the durability of composite patches in severe field environments will be discussed along with related laminate design and installation issues.
IBOLT: A Composite Bolted Joint Static Strength Prediction Tool
Authors: Eisenmann JR , Rousseau CQ
Published: April 2008

The objective of this paper is to describe the bolted joint analysis method developed and used by LM Aeronautics (named IBOLT) including the theoretical basis, required input, and coupon-level strength-prediction validation. IBOLT performs a fracture-mechanics-based static strength prediction for a rectangular composite joint element subjected to any combination of biaxial membrane loads, shear loads, and an off- axis bolt load. Out-of-plane bending moments are also treated. Joint configuration effects (single- or double-shear) are modeled by a beam-on-elastic-foundation analysis to account for the thickness and stiffness of the joint members as well as the bolt bending and shear stiffness. Empirical equations are included to account for fastener head geometry, effects of filled versus open holes, fastener/hole clearance, and fastener torque. Required input, in addition to the usual geometry, loads, fastener, and substrate elastic properties, includes a variety of special laminate-level joint properties. Uni-axial notched, un-notched, and bolted-joint coupon tests are conducted to develop these properties. In addition to these uniaxial coupon tests, bearing/bypass tension and bearing/bypass compression tests have been performed to validate the accuracy of IBOLT strength predictions. An overview of these validation results is provided, along with a brief summary of IBOLT's strengths and weaknesses as a practical bolted joint stress analysis tool.
Damage and Failure Mechanisms in Composite Bolted Joints
Authors: Bau H
Published: April 2008

This study's overall goal is to develop methods to accurately predict the strength of notched composite laminates. Empirical analyses of notched composite test data led to an understanding of failure mechanisms. Trends in ultimate strength versus layup parameters were extracted from several DoD test programs. A test program with incrementally loaded, notched coupons was conducted to track sub-critical damage. Damage states at near-ultimate loads were correlated to the ultimate strength trends. These trends were then attributed to specific matrix damage types.

Detailed finite element analyses of composite bolted joint configurations were conducted using solid element models with nonlinear material properties. Sensitivity studies were conducted to determine the mesh refinement needed for converged peak stresses. At the loads corresponding to initial damage in the incremental notched tests, linear and nonlinear finite element analysis consistently predicted peak ply stresses which were significantly higher than ply strengths derived from unidirectional coupon tests.
On-Slope Evaluation of Release Bindings for World Cup Freestyle Skiers
Authors: Heir S , Dimmen S , Ekeland A
Published: April 2008

The setting values as indicated on the scale of the toe bindings of 54 World Cup freestyle mogul skiers participating in a World Cup mogul competition in Lillehammer, Norway, were 92% (range 18 to 175%) higher than the ISO (International Organisation of Standardisation) recommended setting values. The estimated torque at which the bindings actually released when tested on-slope with a testing machine was even 15% (range—23 to 143%) higher than the setting value indicated, decreasing to 7% (range—22 to 88%) after the first release. Only 4 of the 54 skiers suggested a setting value within a range of 10% of the ISO recommendations when asked what they believed was the ISO recommended setting value in their own case. The findings of this study suggest that the ISO recommendations play a minor role when adjusting the setting value for release of the toe bindings for World Cup mogul skiers. Moreover, when tested the toe piece of the bindings released not only outside the ISO limits, but also at a higher torque than indicated by the setting values on the visual scale of the toe bindings.
Evolution of ACL Ruptures in French Ski Resorts 1992–1999
Authors: Laporte J-D , Binet M-H , Constans D
Published: April 2008

This work done by 72 French doctors in the “Médecins de Montagne” skiing safety network studies the evolution of the rate of ACL ruptures since 1992. The study was done on 232 571 injuries including 21 303 ACL ruptures. Alpine skiing ACL ruptures, which have been increasing since 1992, represent 12.5% of accidents (3125 MDBI). A control group is analyzed each season through interviews at the bottom of the slopes in parking lots and random evaluations.

We have ascertained that ACL ruptures represent 9.2% of total injuries in men, in comparison with 20% in women, over 24 years old. The case-control study, women versus men, stratified by age group, shows a remarkable ODDS ratio for adults (over 16 years old) with an extremely reduced confidence interval at 95% (3.26 < 3.41 < 3.56).

The ISO adjustment charts do not currently take into account a major risk factor, the feminine sex.

Among the possible preventive measures that can be taken for ACL ruptures in women is to evoke the decrease in adjustment values.

There are no studies that prove the effectiveness of a decrease in adjustment values on the incidence of ACL ruptures, but there are corroborating arguments in favor of a positive action. The only risks of a decrease in the adjustment are extremely low, in particular that of inadvertent release. Different authors have demonstrated the possibility of a decrease in adjustment without inadvertent release.

We suggest, beside the education of the skiers, in the prevention of the phantom foot, a 15% decrease in binding adjustment values for women over 25 years old, and 30% for beginners with less than 7 days of skiing.
Update on Injury Trends in Alpine Skiing
Authors: Johnson RL , Ettlinger CF , Shealy JE
Published: April 2008

Over the past 26 years, the authors have given many reports at ASTM Conferences on injury trends in Alpine skiing. These reports have generally taken two forms: a cursory report on a broad range of injury groups or an in-depth look at a specific injury group or sub-group of the general population. In the current study, the authors provide an update on two large injury groups that have been the subject of many earlier reports, fractures and sprains of the lower leg and sprains of the anterior cruciate ligament of the knee. Examples of the lower leg injury common to Alpine skiing are tibia fractures, ankle sprains and fractures, tibia plateau fractures, heel cord injuries, and knee sprains.

Between December 1972 and April 1998 the authors evaluated prospectively 15 526 injuires reported to the injury clinic operated in the base lodge of a moderate size northern Vermont ski area. During that time approximately 5 298 600 skier-visits (days) occurred at the area. Over that period the overall injury rate decreased by 46%. However, the change for the two target groups can not be expressed in such simple terms. Historically, the authors have described injury trends in mean days between injury (MDBI), fitting each year's MDBI to an exponential curve by regression analysis. In this study the authors explain why this technique can no longer be used for these two groups and propose new methods, which could lead to a better understanding of the trends identified by this study.
On-Slope Helicopter Evacuations of Seriously Injured Alpine Skiers and Snowboarders
Authors: Cadman R
Published: April 2008

In Canada, the use of helicopters to extricate injured skiers directly from a ski area is an exception rather than a rule. For the vast majority of injured alpine skiers and snowboarders, the traditional ski patrol toboggan is the preferred method of transporting the victim off the slopes. This investigation will review 43 helicopter medical evacuations (medivacs) from one major Canadian ski area in British Columbia. This ski area had an annual incidence rate of injury of 2.74 per 1000 skier visits (SV) during the 1997–98 ski season (366 mean days between injury, MDBI). The incidence rate of medivacs was 0.041 per 1000 SV (24 279 MDBI). The mean age of the medivac patient was 28.9 years, the age range was 51 years (10 to 61), and 79% of the patients were male.

Medivacs at this ski area are dependent on helicopter availability, weather, and a rapid risk analysis performed on the ski field involving the attending ski patrollers and on-duty mountain physician. This paper will also explore training issues and other uses of a helicopter in a major ski center.
History of Timber Construction
Authors: Foliente GC
Published: April 2008

The history of timber construction is presented from prehistoric to modern times, from the simple hut to multi-purpose halls, from trial-and-error construction to one based on engineering design and analysis, from simple beams and posts to modern spatial systems. The development of common timber construction forms and methods are briefly discussed. Wood, our only basic renewable resource, has been an important part of man's built environment. For this to continue in the future, developments in timber engineering and related technologies should meet the needs and challenges demanded by building occupants and by society, in general.
Wood Condition in the Church of the Transfiguration at the Kizhi Museum
Authors: Kozlov VA , Krutov VI , Kisternaya MV , Vahrameeva TI
Published: April 2008

The wooden Church of the Transfiguration was built during 1714 and is unique for its architectural beauty and longevity. It has been exposed to severe climate and mechanical loading conditions during its life, which led to deterioration from weathering, insects, fungi, and human intervention. This paper provides a review of the history of repair and protective measures that have been implemented, and summarizes recent scientific research to document the wood condition in the church. A database was created to incorporate the results of previous studies with current investigations of the quality and condition of each element of the building. A systematic approach to environment and wood condition monitoring was established to assess the durability of the church and to help evaluate the effects of future restoration by providing base-line data.
Conservation of the Wooden Garner in Paezeriai, Lithuania
Authors: Vilconciene N , Drobeliene J
Published: April 2008

Wooden monuments make up a large part of the Lithuanian cultural heritage. Therefore the problem of preservation of wood structures is faced. An authentic timber garner or barn still remains in the boyhood home of Vincas Kudirka, the famous Lithuanian writer, critic, and author of the music and lyrics of the national anthem of the Republic of Lithuania.

The conservation of the garner was performed to prevent deterioration of authentic wood and to extend its durability. Causes for and extent of wood deterioration and decay were investigated. The investigation showed that the wood had been seriously damaged by insects; fungi had spread and penetrated deeply into the wood; and part of the wood had completely decayed. A project of wood conservation was designed on the basis of the results of the investigation and the project was implemented in the summer of 1992.

The conservation of the wooden garner consisted of replacement of decayed wood; preparation of the wood for conservation by cleaning away dirt, lichens, algae, fungi, and insect damage; conservation of the original wood; stabilization of the original wood; and microbiological monitoring of conserved wood.
The Role of Natural Conservation of Wood in Preservation of Wooden Architectural Monuments
Authors: Kudrjavtseva EI , Litvintseva AP
Published: April 2008

The rate of wood decay is an important factor to bear in mind when choosing a restoration strategy for wooden architectural monuments. Carrying out restoration hurriedly often leads to the destruction of an authentic monument because the restoration strategy fails to take into account the natural conservation of the wood caused by the biological equilibrium between wood-decomposing organisms established during the period of a monument's life. This quilbirium results in the minimizing of dangerous fungi activity and prevents the active growth and spread of the dangerous building rot fungi.

In this paper, we describe the case of natural wood conservation at the Ensemble of St. Nicholas' Church in Kovda village (Murmansk region, Northern Russia), dating from the 17th century. We suggest that one of the main reasons for equilibrium formation at this monument is its total contamination by a mold Trichoderma viride Pers. This fungus is known to be an active antagonist of many wood-destroying fungi; it could totally restrict growth of dangerous fungi Serpula lacrymans and Coniophora puteana that exist at the Kovda monument. The Kovda ensemble represents an example of the inappropriate use of the total restoration approach that has, due to the complete rebuilding of the Bell Tower, already lead to irreversible damage of the whole ensemble.
Conservation Investigation for Preservation of a Historic Timber Hut in Antarctica
Authors: Hughes JD
Published: April 2008

There is a common presumption that the ‘dry’ cold in Antarctica will preserve historic buildings, but this has proved not to be true. Identified conservation problems include high humidity, fungi, salt damage, surface erosion by windborne particles and corrosion of metals.

This paper reviews assumptions about the behavior of timber in extremely cold climates and the structural effects of snow accumulation and extreme wind loading. The professional collaboration required to properly investigate the unusual preservation problems of the hut is discussed with particular reference to the abandoned huts of the Australasian Antarctic Expedition, led by Douglas Mawson during 1911–14.

Investigations required include structural modeling; erosion measurements; documentation and preservation of historic information contained in the timber cladding of the buildings; and special requirements for the preservation of the scientific integrity of the magnetic laboratories. Conservation monitoring and treatments developed for Antarctic sites may be applicable for historic buildings in Arctic and alpine regions.
Technical Basis for the Master Curve Concept of Fracture Toughness Evaluations in the Transition Range
Authors: McCabe DE , Merkle JG , Wallin K
Published: April 2008

An American Society for Testing and Materials (ASTM) standard method (E 1921-97) has been developed that exclusively uses fracture mechanics test practices and advanced statistical methods to establish the ductile-to-brittle transition range of fracture toughness for structural steels. The development of suitably accurate analyses had been slowed in the past due to an incomplete understanding of the operational mechanisms that control the fracture toughness behavior of structural steels. New perspectives taken are (1) that dominant linear-elastic conditions need not be rigidly enforced in specimens and (2) that the effect of specimen size on fracture toughness performance is mostly controlled by a weakest-link mechanism instead of being completely controlled by crack tip constraint conditions. The weakest-link behavior is defined from local cleavage crack initiators such as precipitates, inclusions, and grain boundary embrittlement, namely, all microstructural features in steel. Statistical models can be built upon such mechanisms that result in defined fracture probability levels and, when coupled to a master curve concept, can more accurately define the true location of the ductile-to-brittle transition temperature.

An integral part of the ASTM test standard development work has been the production of a supporting technical basis document. This document presents substantial background data and supporting theoretical aspects that have been used to justify the method development. The paper will include some of the salient features presented.
A Unifying Principle for Evaluating Fracture Toughness in the Elastic and Plastic Regimes with Planar Fracture Specimens
Authors: Donoso JR , Landes JD
Published: April 2008

Recently, Donoso and Landes proposed the existence of a common format equation (CFE) for developing calibration functions for two-dimensional fracture specimens. In the CFE approach, the relation between load, plastic displacement, and uncracked ligament size is expressed as the product of three terms: (1) a constraint factor, (2) a geometry and crack length-dependent function (G), and (3) a hardening function (H). The history-dependent component of the calibration functions, namely H, has been explored by the same authors, using two different hardening functions: a power law and a three-parameter function, designated as the LMN function. For the geometry function G, on the other hand, a power-law dependence on normalized ligament length, i.e., G ∝ (b/W)m (where W is the specimen width), is used for all of the classical two-dimensional fracture specimens. This type of behavior for G has been derived from the GE EPRI Handbook equations and has also been observed experimentally. From such a relationship, a crack-length independent value of eta plastic, ηpl is obtained that is equal to the exponent m.

The application of a ductile fracture methodology requires, in addition to the calibration functions, the fracture toughness of the material, usually given by the J-R curve. The computation of J, according to standard procedures, needs both its elastic and plastic contributions. The elastic component is normally evaluated in terms of K, the stress-intensity factor for the geometry and test conditions. The plastic component of J, on the other hand, is equal to the area under the load-plastic displacement curve per unit net section area of specimen, multiplied by the plastic eta factor, ηpl. The purpose of this work is to extend the use of the CFE approach to the elastic region of the load-displacement curve of standard frac-ture specimens, focusing on both their elastic compliances and their elastic eta factors, ηel. The elastic compliances and the G functions of the predominantly bend-type geometries, i.e., SE(B), C(T), and SE(T) specimens, are compared, showing that the elastic and the plastic eta factors are practically equal. This allows one to evaluate J in these geometries in terms of total displacement. The same does not apply, however, to the tensile M(T) and DE(T) geometries. In addition, K factors will be derived for the bend-type geometries based on the dependence of the elastic compliance with ligament size.
Method for Predicting J-R Curves from Charpy Impact Energy
Authors: Gioielli PC , Landes JD , Paris PC , Tada H , Loushin L
Published: April 2008

In this paper a mechanistic rationale for the fracture process is applied to the CVN impact test so that the J-R curve fracture toughness could be estimated for materials that have only a CVN energy value as the fracture toughness characterization. The method assumes that the fit to the J-R curve can be given a standard form by assuming that the product of J and the tearing modulus, T, is a constant. Given this standard fitting form, the CVN energy is used to estimate a point on the J-R curve. Using this single point and the constant J × T product, the J-R curve is estimated with the two-parameter power law fit specified in ASTM standards. The procedure is applied to metals that undergo purely ductile fracture, that is, those that have CVN energy that would be characterized as “upper shelf” or 100% shear.

The method requires a calibration between impact energy, which has energy contributions from factors other than the fracture process, and the J-R curve point used in the fit. It is calibrated using three steel alloys where both CVN energy on the upper shelf and J-R curve fracture toughness data exist. The results show that a consistent calibration factor can be assumed that applies to all of the steels. Using that factor and the standard J-R curve fit, the prediction was good for all the steels examined. From these J-R curves, the initiation toughness value JIC can also be determined using the JIC construction from ASTM Standard Method E 1820. The resulting determination of JIC shows why the simple process of fitting data sets does not give a universal prediction of toughness. The material tensile strength plays a role in the determination of JIC.
Fracture Toughness Testing with Notched Round Bars
Authors: Wilson CD , Landes JD
Published: April 2008

A method to simplify fracture toughness testing and reduce testing costs is discussed. An alternative specimen geometry, the notched round bar (NRB), has been combined with a simpler testing methodology. A multispecimen technique using notched round bars with finite notch root radii ρ was applied to 2024-T351 and overaged 2024 aluminum alloy. No fatigue precracking was used. A graph of apparent fracture toughness Kρ versus the square root of notch root radius √ρ was extrapolated to ρ = 0, corresponding to a fatigue precracked configuration. The resulting fracture toughness values were the same as those obtained from ASTM E 399 tests. Apparent fracture toughness Jρ, determined from NRB J-R curves for overaged 2024, was graphed versus notch root radius ρ. The extrapolated value of fracture toughness was the same as that obtained from ASTM E 813 and E 1152 tests.
3-D Finite Element Modeling of Ductile Crack Growth in Thin Aluminum Materials
Authors: Gullerud AS , Dodds RH , Hampton RW , Dawicke DS
Published: April 2008

This work describes the development and verification of a 3-D model to predict stable, Mode I crack growth in thin, ductile aluminum alloys. The model extends the standard 2-D form of the crack tip opening angle (CTOA) methodology, which determines crack extension based on obtaining a critical angle at the crack tip. When the CTOA reaches the critical value, all the nodes along the current, 3-D crack front are released simultaneously, thereby growing the crack in a self-similar manner. Evaluation of the CTOA occurs at a specified distance behind the crack tip; this decouples CTOA evaluation from mesh refinement. The CTOA-based model also includes adaptive load control strategies to minimize the effects of discrete load increments on the growth response. To evaluate the effectiveness of the described approach, this work describes a validation study using load-crack extension data from 2.3-mm-thick Al 2024-T3 specimens tested at NASA-Langley. The test matrix includes C(T) and M(T) specimens, with varying widths (50 to 600 mm), a/W ratios, and levels of constraint to suppress out-of-plane bending. Comparisons of load-crack extension curves from experiments and analyses of a constrained 150-mm C(T) specimen provide a calibrated critical CTOA value of 5.1°. Analyses using the calibrated CTOA value for constrained and unconstrained specimens provide predictions of peak load in good agreement with the experimental values.
Fracture Mechanics Validity Limits and Physical Evidence of Constraint in Fracture
Authors: Lambert DM , Ernst HA
Published: April 2008

The consideration of fracture behavior should be a matter of vital concern in current design efforts. Many materials exhibit grossly different behavior when discontinuities are present in the structure. These may be inherent in the material or may stem from poor manufacturing, handling, and /or design practices. Inclusion of fracture behavior in the design models is the subject of fracture mechanics. Ultimately, a knowledge of fatigue and fracture becomes very important in avoiding disaster.

This paper is written with two primary purposes: to characterize the physical nature of fracture, and to dramatize the need to characterize the central flat fracture differently from the surface, shear fracture. To this end, the contents of the paper are organized as follows: (1) validity limits of fracture mechanics: this information was originally developed for the purpose of extracting similar fracture data and will be used here to help characterize bulk constraint effects and to establish the existence of the surface effect; (2) analysis of crack face displacements of planar specimens subjected to loads: this includes actual crack-, separation-, and stretch-profiles; and (3) consideration of three-dimensional fracture in light of the existence of two distinct fracture zones that exhibit different failure mechanisms; for this purpose, G and J as a function of depth below surface are discussed, as well as several constraint factors as a function of depth.
The Role of Cohesive Strength and Separation Energy for Modeling of Ductile Fracture
Authors: Siegmund T , Brocks W
Published: April 2008

Barenblatt's idea of modeling the crack process zone by means of a cohesive zone has attracted considerable attention for predicting ductile crack growth. The model allows separation of the energy necessary for material separation from global plastic work. This has been a key problem in ductile fracture when searching for reasons for the geometry dependence of crack growth resistance curves. When using cohesive zone models, the correct determination of the cohesive zone material parameters is of eminent importance. In the past these parameters—the cohesive strength and the separation energy—were assumed to be material constants. However, micromechanical considerations show that this assumption is only an approximation in the case of ductile fracture. Here, the underlying mechanisms of void nucleation, growth, and coalescence are dependent on the stress triaxiality. This effect is accounted for in the new constitutive equation for cohesive zone models as presented here. In this new “triaxiality-dependent cohesive zone model,” the cohesive material properties are taken to be dependent on the stress triaxiality in the solid element adjacent to the cohesive element. For low triaxiality, low values of cohesive strength and large values of the separation energy are observed; the opposite holds true for cases of high triaxiality. Ductile crack growth in a mild steel under quasistatic loading was investigated. The results from the use of the triaxiality-dependent cohesive zone model are compared to those of the Gurson-Tvergaard-Needleman (GTN) model as well as to the cohesive zone model with constant material parameters. The dissipation rate is shown to be a favorable measure for the characterization of the crack growth resistance. It allows the description of both the (global) plastic dissipation and the (local) work of fracture.
Fatigue Analysis of Multiple Site Damage in Lap Joint Specimens
Authors: Wang H-L , Grandt AF
Published: April 2008

This paper describes research to determine the influence of multiple-site damage on the fatigue life of lap joint specimens. Multiple-site damage is an important concern in aging aircraft and deals with determining failure conditions for multiple crack configurations. The goal of this paper is to determine the fatigue life for a mechanically fastened joint with multiple fatigue cracks located along one row of rivet holes. A predictive model for the fatigue life is evaluated with the results of several precracked specimens tested to failure under constant amplitude loading. Predictions for the growth and coalescence of individual cracks in specimens with various initial crack configurations and applied stress levels agree well with the experimental results.
Subsurface Fatigue Crack Initiation and Propagation Behavior of Induction-Hardened Shafts under the Effect of Residual and Applied Bending Stresses
Authors: Zhang H-Y , Stephens RI , Glinka G
Published: April 2008

The Society of Automotive Engineers Fatigue Design and Evaluation (SAEFDE) Committee has been conducting a long-term program aimed at the development of a predictive capability for fatigue life of SAE 1045 induction-hardened shafts. As a part of a larger-scale investigation provided by the SAEFDE committee, this research provided an analytical model capable of predicting the total fatigue life, both crack initiation and crack propagation, of an induction-hardened shaft under applied bending stress. The analysis procedure incorporated the effects of residual stresses. Total stress intensity factors were calculated and superimposed using applied bending stress intensity factors and residual stress intensity factors along the subsurface elliptical crack front. Fatigue tests were conducted using SAE 1045 induction-hardened shafts to verify the analytical models of subsurface fatigue crack growth. The total fatigue life calculations of subsurface failure showed a factor from 0.6 to 0.8 compared with the experimental results. The analytical model and experimental data confirmed that the majority of the total fatigue life is spent in the crack propagation phase.
Estimation Procedure for Determination of Fatigue Crack Propagation in Metal Alloys
Authors: Hertzberg RW
Published: April 2008

Estimation of closure-corrected fatigue crack propagation (FCP) data in monolithic metal alloys was reported recently by the author, using a simple computational method. The quantity E√b, where E = the modulus of elasticity, and b, the dislocation Burgers vector, is used to define a stress intensity factor, corresponding to an FCP rate of b/cyc. The remainder of the FCP curve at higher FCP rates (where da/dN > b) is found to follow a relation of the form: da/dN = (ΔK/E)3(1/√b). Good agreement is found between computed FCP data and recently reported experimental test results for various aluminum, titanium, and steel alloys. Such computations allow for a rapid and inexpensive way to estimate the FCP response of metals under both long and short crack growth conditions.
Safety in Ice Hockey: Third Volume
Authors: Ashare AB
Published: April 2008

Description

The latest volume in this series enhances our understanding of both the injuries incurred in the game of ice hockey and of the techniques used to decrease the risk of these injuries.

25 peer-reviewed papers cover:

• Injury Surveillance--discusses the injury surveillance system and the principles of ice hockey injury research.

• Protective Equipment--focuses on the certification of protective equipment for ice hockey in the U.S., and the designs and standards for various forms of ice hockey headgear.

• Spinal Injuries and Concussions--explores various aspects of these types of injuries, including care and transport of injured players and a three-decade perspective.

• Penalties, Injuries, and Pressures--examines psychosocial and psychological aspects of aggressive play, views and assessments of rule infractions and penalties, and liability issues facing the in-line skating industry.

This volume is a valuable resource for hockey equipment manufacturers, academic sports biomechanics, all hockey coaches and administrators, sports medicine physicians, and athletic trainers.
The Effect of Biaxial Strain Ratio and Periodic Compressive Overstrains on Fatigue Crack Growth Mode and Crack Growth Rate
Authors: Varvani-Farahani A , Topper TH
Published: April 2008

Biaxial fatigue tests were performed on thin-walled tubular 1045 steel specimens in a test fixture that applied internal and external pressure and axial load. There were two test series, one in which constant amplitude fully reversed strains were applied and another in which large periodic compressive strain cycles causing strains normal to the crack plane were inserted in a constant amplitude history of smaller strain cycles. Ratios of hoop strain to axial strain of λ = - 1 (pure shear), λ = -0.625, λ = - v (uniaxial straining), and λ = +1 (equibiaxial straining) were used in each test series. A confocal scanning laser microscopy (CSLM) image processing technique that gave a resolution of 0.25 μm was developed and used to obtain three-dimensional images of small cracks as they were opened under load. The information in the images was used to construct cross sections of cracks from which crack depth, shape and crack opening stress were obtained.

For pure shear straining tests (λ = -1) and for tests at a strain ratio of λ - 0.625 surface cracks rapidly initiated on planes of maximum shear in both constant amplitude and overstrain tests but did not increase significantly in length until near the end of the tests. Instead they grew into the specimen until they were semi-circular in shape. This phase occupied approximately 90% of the fatigue life. Then they began to grow in length as well as depth and linked up to cause failure.

In the uniaxial and equibiaxial straining tests, crack growth initiated on planes of maximum shear at 45° to the surface of the specimens (Stage I crack growth) before changing to Stage II growth perpendicular to the applied stress. The cracks once initiated grew continuously in both the length and depth direction until failure took place.

The magnitude and frequency of application of the periodic compressive overstrain cycles in the second test series was chosen to reduce the crack opening stress level below the minimum stress level of the constant amplitude cycles so that they experienced closure-free crack growth. The compressive overstrains significantly increased crack growth rates and decreased the threshold strain intensity for the smaller constant amplitude cycles. They also caused a large decrease in the small cycle fatigue resistance as measured by their equivalent strain-life curves.
Determination of Ct-Parameter Considering Effects of Accumulated Creep Deformation During Loading Period
Authors: Lee JH , Kim YJ , Yoon KB
Published: April 2008

Most of the assessment equations for Ct, which is a well-known fracture parameter characterizing creep and creep-fatigue crack growth rates, have limited applicability to constant load conditions. However, crack growth due to creep can also occur under varying load conditions when the load rate is slow enough such that accumulated creep deformation near the crack tip can't be neglected. An estimation equation of the Ct-parameter that can be applied to the case of slow load rising was derived by the authors and denoted as (Ct)r.

In this paper, correlation between (Ct)r at the end of the load-rising period and Ct at the beginning of the succeeding load hold period is shown. And a new Ct estimation equation that can be applied to the load hold period following a slow load rising period is derived using the relation between (Ct)r and Ct. Finite element analyses of several cases with various load-rising conditions were performed. The results support accuracy of the proposed Ct estimation scheme. General applicability of the equation is also discussed.
Fracture Mechanics: Forgotten German and Austrian Pioneers of the Turn of the 20th Century
Authors: Rossmanith HP
Published: April 2008

This contribution gives an overview of the early history of fracture mechanics and highlights the contributions of Karl Wieghardt and Alfons Leon to the development of the basic analytical equations of fracture mechanics. It is shown that the work of these pioneers anticipated many of the later developments by several decades. It will also be shown that particularly the work by Wieghardt was in fact directly related to a practical failure case and the neglect of his fundamental paper is unjustified.
Effects of Kmax on Fatigue Crack Growth Threshold in Aluminum Alloys
Authors: Newman JA , Riddell WT , Piascik RS
Published: April 2008

Effects of Kmax on closure-free, near-threshold fatigue crack growth are examined in ingot metallurgy aluminum alloys 2024 and 7050, and powder metallurgy aluminum alloy 8009. Significantly lower closure-free fatigue crack growth thresholds, as well as accelerated fatigue crack growth rates, were observed as Kmax increased. Results indicate that no single value of fatigue crack growth threshold exists, because near-threshold fatigue crack growth is dependent on both Kmax and ΔK. The near-threshold Kmax effect is linked to an increase in crack-tip void production. Experimental observations suggest that Kmax-accelerated, closure-free, near-threshold fatigue crack growth rates were caused by changes in crack-tip process zone damage mechanism(s) that are a result of increased crack-tip driving force.
Fatigue Crack Growth Threshold Concept and Test Results for Al- and Ti-Alloys
Authors: Marci G
Published: April 2008

The fact that fatigue crack propagation (FCP) rates approach zero asymptotically as the fracture mechanics loading parameter ΔK decreases toward certain limiting values is the reason for the scientific interest in these so-called ‘threshold’ values. In respect to the practical use of these ‘limiting values’, the author divides them into two groups, namely in ‘non-propagation conditions’ ΔKth and in a material property ‘FCP-threshold’ ΔKT. It is shown that ΔKT must be an integral part in the functional correlation between FCP-rates and the cyclic loading conditions expressed in ΔKeff. The experimental determination of ΔKth on six Al-alloys and four Ti-compressor disk alloys show that ΔKT exists for all the alloys investigated. The effect of temperature on ΔKT was investigated on one Ti 6Al 4V- and one Ti 8Al 1V 1Mo disk material at room temperature (RT) and 260°C and at RT, 260°C and 360°C, respectively. No temperature effect on ΔKT was found for the temperature range investigated.
Resistance Curves for the Threshold of Fatigue Crack Propagation in Particle Reinforced Aluminium Alloys
Authors: Tabernig B , Powell P , Pippan R
Published: April 2008

The threshold of stress intensity factor range ΔKth increases with increasing crack extension until it reaches the constant value of long cracks. Such curves can be interpreted as resistance curves for the threshold of fatigue crack propagation.

In the paper a very simple method to measure such R-curves is presented and a concept based on the R-curve is used to describe the propagation/non-propagation behavior of physically small cracks. The application of the R-curve technique results in the Kitagawa diagram where one can estimate the fatigue limit of components containing “small” flaws. R-curve tests and standard fatigue experiments at different stress ratios were performed on a 20 vol% SiC particle reinforced 359 T6 cast aluminum alloy which contains naturally small flaws up to 400 μm. Application of the R-curve concept is demonstrated and the estimations are compared with experimental results of the fatigue tests. Good agreement between the predicted and measured failure behavior was found.
Effect of an Overload on the Threshold Level of Ti-6-22-22
Authors: McEvily AJ , Ohashi M , Shover R , DeCarmine A
Published: April 2008

The effects of overloads on the fatigue crack growth behavior of the high trength α/β titanium alloy Ti-6-22-22 have been investigated. Fatigue cracks were grown at a baseline R level of 0.1, and single overloads, ranging in magnitude from 2–3 times the baseline level, were applied to determine the effect of the overloads on subsequent fatigue crack growth behavior. Because of the high yield strength of the alloy, 1225 MPa, the number of delay cycles following an overload was not as pronounced as in alloys of lesser strength. A principal effect of an overload in this titanium alloy was to increase the threshold for fatigue crack growth. An experimental procedure based upon the increase in threshold level was adopted to determine the maximum level of crack closure resulting from an overload.

The novel observation was made that following a sufficiently high overload the rocess of further crack growth involved the emergence of a surface crack ahead of the preexisting crack. It was also observed that the crack growth behavior at distances well beyond the overload plastic zone size could be sensitive to prior overload history.
Relation Between Endurance Limits and Thresholds in the Field of Gigacycle Fatigue
Authors: Bathias C
Published: April 2008

In order to predict fatigue crack propagation at very long life a piezoelectric fatigue machine was built in our laboratory. This device is able to fail specimen at 1010 cycles and to determine thresholds up to 109 mm/cycle. The originality of this machine resides in the possibility to apply simultaneously to a specimen a constant tension effect and longitudinal ultrasonic vibratory effort with adjustable amplitude. That is to say, the R ratio can be varied from -1 to 0.9.

It appears that the fatigue thresholds are about the same in conventional fatigue and in resonant fatigue if the computation of the stress intensity factor K is correct. But there is a very large difference between the endurance limits at 106 cycles and 109 cycles. It means about 10% for steels and 30% for aluminium and nickel-based alloys.

To improve the relation between thresholds and fatigue limits, the gigacycle fatigue is studied in a Ni alloy manufactured by powder metallurgy with two sizes of inclusions. The testing temperature is 450°C. The first conclusion is that there is not any infinite fatigue limit until 109 cycles. The second conclusion is a possible correlation between the fatigue limit and the threshold at R ratio = 0. This relation is much more improbable for R = -1 because an incubation phenomenon exists around an inclusion or a porosity loaded at low stress level.
A Size Effect on the Fatigue Crack Growth Rate Threshold of Alloy 718
Authors: Garr KR , Hresko GC
Published: April 2008

Fatigue crack growth rate (FCGR) tests were conducted on Nickel-based uperalloy 718 in the solution annealed and aged condition at room temperature. In each test, the FCGR threshold was measured using the K-decreasing constant R method. Initial testing was at two facilities, one of which used C(T) specimens with W = 127 mm. Previous data at the other facility had been obtained with specimens with W = 50.8 mm. A comparison of test results at R = 0.1 showed that the threshold for the 127 mm specimen was considerably higher than that of the 50.8 mm specimen. A check showed that this difference was not due to a heat-to-heat or lab-to-lab variation. Additional tests were conducted on specimens with W = 25.4 mm and at other R values. Data for the various specimens is presented along with parameters usually used to describe threshold behavior.
The Mechanics of Moderately Stressed Cracks
Authors: Riemelmoser FO , Pippan R
Published: April 2008

The intrinsic behaviour of fatigue cracks is discussed by a discrete dislocation model and by a BCS-type continuum mechanics approximation. The investigation of a homogeneous material shows that the near threshold regime and the existance of an intrinsic threshold itself can be ascribed to the dislocation nature of plasticity. By incorporating microstructural features in the analysis it is then shown that the intrinsic threshold value is determined only by the mechanism for the dislocation generation and does not depend on microstructural details like the grain size. However, in the near threshold regime and in the lower Paris regime the plastic deformation and the crack growth rates are severely influenced by microstructure. Therefore, a micromechanics approach should be used for the predictions of the plastic response of materials. Only in the upper Paris regime, where the cyclic plastic zone size exceeds several times the microstructural length scale usual continuum plasticity mechanics is appropriate to describe the events at the crack tip. Macroscopic quantities like the yield stress of materials cannot be used to describe moderately stressed fatigue cracks.