bluuebunny/crossref_metadata_2025 huggingface dataset:
Triaxial Relaxation Tests on a Soft Clay
Authors: Silvestri V , Soulié M , Touchan Z , Fay B
Published: February 2009

Results of consolidated undrained triaxial relaxation tests on a soft sensitive clay of eastern Canada are presented and discussed. The initial consolidation phases of the traxial tests are carried out under both isotropic and anisotropic stress conditions.

The results show that pore water pressures remain approximately constant during the relaxation phases of the tests. The phenomenological model developed by Prevost (Journal of the Geotechnical Engineering Division, ASCE, Vol. 102, No. GT12, 1976, pp. 1245–1259) describes the observed response quite well. In addition, because the clay possesses a well-defined volumetric yield curve, the position of this curve should be taken into account when analyzing the resuls. Finally, triaxial test procedure and equipment modifications used in the laboratory investigation are fully described.
Preparation of Reconstituted Sand Specimens
Authors: Vaid YP , Negussey D
Published: February 2009

Review and assessment of sand sample preparation techniques from both theoretical and experimental viewpoints are presented. Sample densities obtained by air pluviation are shown to be sensitive to rate of pouring and drop height. Terminal velocity is reached at a very small drop height, and homogeneous samples of the same initial density tend to be formed by pluviation of uniform sand in water. Uniformly dense samples obtained by vibration of loose pluviated samples show no detectable difference in behavior when compared to samples densified by control of drop height only. Effective confinement during densification by vibration appears to prevent formation of a loose top layer. A loose top layer in an otherwise dense sample leads to a marked decrease in liquefaction resistance. Preparation of triaxial sand samples by pluviation in water is recommended because it results in initially saturated specimens, and homogeneous samples of desired densities can be replicated without difficulty.
Compression and Shear Deformation of Soil Under Wide-Ranging Confining Pressure
Authors: Kitamura R , Haruyama M
Published: February 2009

The conventional triaxial drained compression test was conducted on specimens under wide-ranging confining pressure, 9.8 to 9.8 × 103 kN/m2 (0.1 to 100 kgf/cm2). Three kinds of soil were used for the test: clayey soil, Toyoura sand, and soft sedimentary rock (“Shirasu,” derived from pyroclastic flows in the southern part of Kyushu Island in Japan). Confining pressure higher than 9.8 × 102 kN/m2 (10 kgf/cm2) was generated by a nitrogen gas cylinder; confining pressure lower than 9.8 × 102 kN/m2 (10 kgf/cm2) was supplied by a common air compressor. The compression curves (the e-log p relation) under wide-ranging pressure are shown for three kinds of soil. Stress-strain relations and stress-dilatancy relations in the shear deformation process are also shown. It is concluded that the mechanical behaviors of clayey soil and sandy soil are similar under wide-ranging confining pressure although these materials are often treated as different.
Interpretation of Triaxial Compression Test Results on Partially Saturated Soils
Authors: Peterson RW
Published: February 2009

A laboratory investigation was conducted to assess the influence of density on the shear strength of unsaturated soil. To vary density, compacted specimens of an expansive clay soil were subjected to different stress histories prior to shear. Tests were performed at a constant water content. The Hvorslev “true friction-true cohesion” concept was used to normalize the effects of density differences on the shear strengths of both saturated and unsaturated specimens. It was determined that shear strengths of unsaturated soils were dependent on the stress state, density, and water content of specimens at failure. A modified Mohr-Coulomb failure model to predict the shear strength of unsaturated soils is proposed. The effect of suction is to increase the value of the cohesion intercept in this model. The actual measurement of soil suction is not required to apply the model.
Probabilistic Characterization of Shear Strength Parameters Using Triaxial Test Data
Authors: Kulatilake PHSW
Published: February 2009

The Mohr-Coulomb model is used as the strength criterion in this study to model shear strength. Thus, the procedure is applicable only for the soils and rocks whose deterministic strength follows the Mohr-Coulmob criterion. Available methods to obtain point estimates for the strength parameters from triaxial test data are discussed. Inaccuracy of the traditional method is pointed out. A method which requires weighted regression analysis and propagation of error technique is developed to obtain point estimates for the strength parameters. Chi-square tests for bivariate beta and bivariate normal distributions are performed on point estimates of strength parameters to check the applicability of the distributions in representing the distribution of the strength parameters. Both probability distributions seem to be useful in representing statistical distribution of strength parameters.
Interpretation of Triaxial Test Results of Cohesionless Soils: A New Model
Authors: Baladi GY , Wu TTH
Published: February 2009

The demand for more reliable methods of predicting the stress-strain relationship of large particle soils, and for more realistic assessment of the influence of grain characteristics on the shear behavior of cohesionless materials, makes it very important that the geotechnical profession develop a reliable modeling technique to accurately evaluate the effects of test and specimen variables. Large size particles in a soil matrix make it difficult to determine the strength parameters using conventional laboratory equipment. The relevant properties of the prototype materials (which contain large size particles) could be evaluated by using laboratory-reconstructed specimens with smaller particle sizes.

Traditionally, shear strengths of different types of cohesionless soils were compared using a constant relative density or void ratio. It was found that because of the differences in the range of limiting densities, soils with a constant relative density or void ratio but with different grain sizes would undergo different behavior during shear. At a constant void ratio or a constant relative density, some soils may experience volume increase; others may undergo a volume decrease; still others may experience no volume change during shear. Thus, comparing the shear strengths of different types of soils (that is, different grain size materials) based on the soils' relative densities or void ratios may led to inaccurate conclusions. The model should be based instead on the soils' response under the applied loads rather than their states of compaction.

This paper presents a new model (percent dilatation) whereby the shear strength of cohesionless soils, comprised of different particle sizes, can be compared and studied based on their behaviors during shear. The percent dilatation (PD) model was developed using data from 178 drained static triaxial tests, designed and conducted to study the effects of soil density, confining pressure, moisture content, and grain characteristics (size, gradation, shape, and particle angularity) on the shear strength of cohesionless soils.
Pore Pressure Response of an Undisturbed and Reconstituted Anglian Till in Undrained Triaxial Compression
Authors: Little JA
Published: February 2009

Laboratory tests designed to expose fundamental mechanical behavior of very stiff, heavily overconsolidated soils can be difficult to interpret. Parallel testing of soil reconstituted from the matrix of the undisturbed soil therefore enables the observed behavior during testing to be assessed in a comparative way, and such effects as previous stress history, sampling, and soil fabric to be examined.

Undrained 38-mm-diameter triaxial compression testing of an Anglian till sampled undisturbed was carried out in conjunction with a soil reconstituted from its matrix. Analysis of pore pressure data showed that the critical state parameter Ac.s gave good predictions of pore pressures generated in the normally and lightly overconsolidated specimens, but tended to overestimate pore pressure in the most heavily overconsolidated specimens. It is shown that this may be accounted for by the overconsolidated specimens not reaching ultimate failure at the critical state. Parry's (1958) method of presenting pore pressure data at failure is used to construct pore pressure paths for the tills during undrained compression.
Shear Band Formation in Triaxial and Plane Strain Tests
Authors: Peters JF , Lade PV , Bro A
Published: February 2009

This paper presents the results of a combined theoretical and laboratory study of the formation of shear bands in triaxial compression, triaxial extension, and plane strain compression. The principal finding is that shear bands are initiated more easily under plane strain than under axially symmetric conditions of the triaxial test. The triaxial compression test is most resistant to shear banding, although the theory tends to overestimate the stability of this test. The lack of agreement between the theory and experiment requires a reassessment of the suitability of isotropic hardening laws even for monotonic loading.
Influence of Specimen Preparation Techniques and Testing Procedures on Undrained Steady State Shear Strength
Authors: Dennis ND
Published: February 2009

Results are presented for four series of isotropically consolidated undrained triaxial shear tests conducted on recompacted specimens of Banding Sand. Specimen preparation procedures and the method of loading were varied to determine their effect on the undrained steady state strength of the sand and on the position of the steady state void ratio curve. Comparison of test results indicates that both sample preparation technique and method of loading affect the undrained steady-state strength.
Stress Path Considerations in Multistage Triaxial Testing
Authors: Schoenemann MR , Pyles MR
Published: February 2009

The particular sequence of axial load and confining-stress change employed in a multistage triaxial test can dramatically influence the stress paths imposed on triaxial specimens, as can isotropic and anisotropic consolidation. The cumulative radial strain in isotropically consolidated specimens can be as much as three times greater than that in anisotropically consolidated specimens at the end of the third stage of a test. Cumulative axial strain was about equal in isotropically and anisotropically consolidated specimens, even though the isotropically consolidated specimens apparently experienced less total compressive strain by the end of a test. While increased strain did not appear to influence the results from multistage triaxial tests on relatively insensitive residual soils, the influence on tests results for more sensitive soils may be significant.
State-of-the-Art Paper: Hollow Cylinder Torsional Devices: Their Advantages and Limitations
Authors: Saada AS
Published: February 2009

Hollow cylinder torisional devices have recently attracted the attention of both researchers and practitioners as tools of great promise to be used in the development of constitutive relations as well as in the determination of strength parameters of both isotropic and anisotropic soils. They are a natural extension of the standard triaxial devices and provide a much wider variety of stress paths to be investigated or to simulate. This state-of-the-art paper reviews the relevant literature, examines the advantages and limitations of these devices, and discusses some of the difficulties encountered in their use. Their versatility is pointed out, and the role they play in the development of constitutive relations is evaluated. Examples, drawn from both static and dynamic conditions, help illustrate the wide variety of stress paths these devices are capable of producing.
A True Triaxial Testing Cell
Authors: Silvestri V , Yong RN , Mohamed AMO
Published: February 2009

Results of both drained and undrained triaxial tests performed with a true triaxial cell on both natural and artificial clays are presented and discussed. The true triaxial apparatus, which has been used for about 20 years, is fully described. The apparatus has recently been modified to improve the measurement of lateral deformations. Tests were performed on both isotropic and anisotropic materials.
True Triaxial Test of Rock Under Stress and Strain Rate Control
Authors: Esaki T , Kimura T , Aoki K , Nishida T
Published: February 2009

The significance of true triaxial tests instead of conventional tests has been enhanced because of the need for generalized constitutive laws for geomaterials. To investigate the behavior of rock masses having restricted conditions for strains, tests of marble under strain rate control as well as stress rate control were performed using a specially designed true triaxial apparatus with rigid platens. As an example of a set of restricted conditions, the condition of the mean principal strain being constant was adopted when the octahedral shear strain was increased. The direction of stress paths obtained under these conditions is discussed, along with the elastic, dilatant, and contractile behavior of marble as clarified by stress controlled tests.
Development of Microstructure to Optimize Mechanical Performance of Power Generation Equipment
Authors: Marshall P
Published: February 2009

The factors responsible for the development of microstructure in CEGB construction ceramics and steels are assessed as a function of composition, thermomechanical treatment, thermal ageing, and environmental degradation. The relationships between microstructure and mechanical properties (tensile, toughness, creep, and fatigue) of relevance to structures operating in power generation equipment are then developed in quantitative terms.
Microstructural Stability and Control for Improved Irradiation Resistance and for High-Temperature Strength of Austenitic Stainless Steels
Authors: Maziasz PJ
Published: February 2009

Current advanced austenitic stainless steels were developed for irradiation resistance from research data accumulated for nearly 20 years on light water, fast breeder, or magnetic fusion reactor (LWR, FBR, and MFR, respectively) materials programs. The austenitic prime candidate alloy (PCA) is an example of an advanced alloy developed for irradiation resistance for the MFR program. The PCA composition has nickel and chromium modifications and titanium additions, relative to the more familiar Type 316 stainless steel, which provide better resistance to void swelling and helium embrittlement. Research on microstructural evolution, phase stability, and solute segregation in the last six to seven years has provided the additional insight to allow the design of newer and better austenitic alloys. These newer steels are based on the combined additions of Ti, V, Nb, C, and P aimed at controlling and improving the formation and stability characteristics of matrix and grain boundary precipitation. These additions promote the formation of fine MC and phosphide phase particles in the matrix which refine the helium bubble distribution and improve void swelling resistance. The additions also promote MC formation at grain boundaries to trap helium bubbles and provide embrittlement resistance. These newer advanced austenitics also show much better unirradiated high-temperature strength than Types 304, 316, or PCA stainless steels. Their strength and precipitation characteristics suggest that the newer advanced austenitics may have a direct spinoff to applications that require improved creep resistance at high temperatures.
The Role of Electron Microscopy in Gas Turbine Materials Development
Authors: Sprague RA , Smashey RW
Published: February 2009

Future gas turbine engines will require improved materials that cost less and overcome current design limitations without compromising product performance and reliability.

Advanced materials R&D emphasis has changed to address the challenges of new materials, including nonmetals, such as carbon/carbon, composites, and ceramics. Process redirection now focuses upon defect minimization and quicker reduction to practice (i.e. cost reduction and enhanced design property minimums. These objectives will also apply to 21st century power plants.

These changes require increased understanding of microstructural and property relationships which are being defined with the assistance of modern electron microscopy techniques. Examples of the application of some of these techniques to the development of new aircraft engine materials and processes are presented.
Microstructure-Property Relationships in Directionally Solidified Single-Crystal Nickel-Base Superalloys
Authors: MacKay RA , Nathal MV
Published: February 2009

This paper discusses some of the microstructural features which influence the creep properties of directionally solidified and single-crystal nickel-base superalloys. Gamma prime precipitate size and morphology, γ-γ' lattice mismatch, phase instability, alloy composition, and processing variations are among the factors considered. Recent experimental results are reviewed and related to the operative deformation mechanisms and to the corresponding mechanical properties. Special emphasis is placed on the creep behavior of single-crystal superalloys at high temperatures, where directional γ' coarsening is prominent, and at lower temperatures, where γ' coarsening rates are significantly reduced. It can be seen that very subtle changes in microstructural features can have profound effects on the subsequent properties of these materials.
Special Languages, Terminology Planning and Standardization
Authors: Galinski C , Nedobity W
Published: February 2009

Special languages are the common concern of several groupings of our society. Special languages play an important role in standardization because knowledge is conveyed primarily by linguistic means. Subject communication is greatly facilitated if standardized terminology is used. An overview of the various efforts of terminology planning and standardization is provided with special emphasis given to the international activities and standards of ISO/TC 37, “Terminology (Principles and Co-Ordination).” Also, some of the possible applications of standardized terminologies, such as knowledge-based systems, are discussed.
“The Wordtree”: An Add-On, Binomial Brancher of Process Words
Authors: Burger HG
Published: February 2009

Niels Bohr's complementarity principle requires that we measure radiation either as particle (= matter) or wave (= process), but not both as simultaneously. We must now broaden Bohr's discovery to the words that describe phenomena.

Most terminological words are structural. We report a missing link, “The Wordtree®.” It is a new kind of concept-pinpointer (ISBN 0-936312-00-9) that groups all words by their effect on the environment—by procedure (= transitive verb). It behavioristically, not mentalistically, divides each binarily into its subprocesses, such as TO JOCKEY = TO RIDE AND TO MANEUVER. The Hierarchy half of the book arranges the 24,600 transitives from simple to complex. The Index half alphabetizes them. Thus the user can trace any process back, phase by phase, toward its components (its causes) or forward toward its potential effects. There are a quarter million words, including all parts of speech. Thereby the reader can pinpoint any idea and then skip-branch (instead of plodding) to its causes or effects. It includes 90,000 words of instruction and theory.
Terms as Database Records
Authors: Strehlow RA
Published: February 2009

The standardized definitions of the American Society for Testing and Materials reflect a significant effort by many specialists working in numerous technical committees. The compiled set of ASTM terms and their definitions include attribution and source information as well as other important data associated with the definitions.

Enhanced awareness of terminology in recent years has led to an increase in the number of terms presented in the Compilation of ASTM Standard Definitions. This increase is associated with a larger number of multiply defined terms. Because of this and the several functions served by the Compilation, a need has become evident to attempt an enhancement of terminology management capability. With the recognition that definitions are amenable to being cast as database records, explorations have been conducted on structuring definitions of terms in this form.

The objective being developed by a working group of ASTM's Committee on Terminology is to convert the Compilation to a database structure. The desired goals include the need for simplicity and user transparency, economy of implementation, and, most importantly, usefulness to the technical committees and ASTM as a whole in the Society's terminology management effort.

A description is presented of a draft database record structure that is intended to address some of the important issues of this ongoing effort. Examples of applications are also discussed.
Management of Technical Terminology in Standards Organizations
Authors: Ellis WP
Published: February 2009

The pioneering work of Wuster carried on by Felber in Austria, together with the activities of the Vienna School of Terminology and its progeny INFOTERM, have established principles of terminology practice and management that are well accepted in worldwide terminology circles. It appears, however, that in the United States this work is little known or ignored in consensus standards organizations.

In 1982 the ASTM symposium Terminology: The Cornerstone of Global Communications Through Standards (later made into an STP entitled Standardization of Technical Terminology: Principles and Practices), sponsored by the ASTM Standing Committee on Terminology, brought to the attention of that standards organization the realization that terminology has become a recognized technology, if not a science. Therefore, ASTM ought to use the principles and practices of technical terminology to manage the development and maintenance of the special vocabularies specific to ASTM technical committees. This usage will result in coherent and efficient employment of term concepts and meanings to give authority, credibility, and improved user comprehension to the pertinent standards.

The purpose of this paper is: (1) to relate experiences of ASTM technical committees in the process of revising their separate terminology standards; and (2) to show how a uniform system of terminology management, tailored to the special requirements of those committees, can produce terminology standards that are useful and probably essential to the experts within the committees and to the larger group of users, who do not have specialized knowledge of the field.

These committee experiences within one standards organization indicate procedures that would lead to a uniform policy of terminology management by the ASTM Committee on Terminology, and more widely, to improved and uniform terminology development in U.S. standards bodies.
An Examination of Mixed-Mode Debonding in the Blister Test
Authors: Liechti KM , Hanson EC
Published: February 2009

Crack opening displacements normal to the plane of an interface crack in a blister specimen are measured using optical interferometry. The displacements are measured up to and including the onset of crack growth and are used to define limits of elastic and inelastic elastic behavior and examine mixed-mode fracture criteria. The extent of inelastic behavior increases with increasing shear component and dominates the onset of crack growth in a bimaterial combination of glass and epoxy.
Mechanical Behavior Assessment of Epoxy Adhesive in the Double-Lap Joint
Authors: Gilibert Y , Klein MLL , Rigolot A
Published: February 2009

In order to evaluate the mechanical behavior of joints in a double-lap adhesively bonded assemblage by means of strain gages located at the outer surfaces of adherends, this study takes into account the non-linear beavior of the bond. This behavior may be caused by joint unevenness, which produces some plastic adaptation at the onset of pulling, or by the opening of microcracks. Since the measurement profile along the sample keeps the same shape as the analytic solution, at least up to the threshold of flaw propagation, the model is based on the classical theory that the adherends are solicitated in traction and the adhesives comport in simple shear but with a sliding coefficient (ratio of shear modulus to joint thickness) that varies along the overlap. A quasi-linear approximation of the solution permits a numerical estimation of shear modulus, which allows an assessment of adhesive mechanical properties and double-lap joint quality.
Chevron-Notched Specimens for Measuring Adhesive Fracture Toughness
Authors: Spingarn J
Published: February 2009

The Mode I fracture toughness of a nylon-modified epoxy adhesive joint has been measured using a chevron-notched specimen. Special data reduction techniques were developed for this bonded specimen. The fracture toughness KIc, and corresponding fracture energy GIc, for the adhesive were extracted from the Kc measured for the joint, and the toughness calibration (K-to-G) was shown to be insensitive to adhesive thickness. The measured KIc values were found to be reproducible and reasonable when compared to values reported for other toughened epoxies. Using this technique, we found that the toughness increased slightly with mouth opening rate (or crack velocity), decreased with adhesive thickness over the range 50 to 375 µm and remained fairly constant with temperature until Tg (glass transition temperature) was approached.
Factors Influencing Elastic Stresses in Double Cantilever Beam Specimens
Authors: Crews JH , Shivakumar KN , Raju IS
Published: February 2009

An elastic stress analysis was conducted for a double cantilever beam (DCB) specimen using finite-element methods. The purpose of this study was to identify the important parameters that influence stresses ahead of the delamination front. The study focused on an aluminum DCB specimen, typical of adhesively-bonded joints, and on a graphite/epoxy specimen representing a co-cured composite. Opening mode σy stresses ahead of the crack tip were calculated and compared with those for a monolithic reference specimen. Beyond the singularity-dominated region very near the crack tip, the σy distribution was elevated compared to the monolithic case. Both the adhesive thickness and the adherend transverse (thickness-direction) stiffness were found to influence the elevation of σy. In contrast, the thickness of the adherend and its longitudinal stiffness had very little effect on this stress distribution. Estimates for adhesive yielding beyond the aluminum DCB crack tip showed that both the area and height of the plastic zone increased to a peak value for increasing adhesive thicknesses. Results from this study should provide insight for comparing data from different DCB specimens and for designing new DCB specimens.
A Comparison of Pure Mode I and Mixed Mode I–III Cracking of an Adhesive Containing an Open Knit Cloth Carrier
Authors: Ripling EJ , Crosley PB , Johnson WS
Published: February 2009

A modified TDCB specimen was used to compare crack resistance in pure mode I and mixed mode I–III loading. Static and fatigue tests were conducted on two commercial, modified epoxy film adhesives (FM 73 and FM 300K) having a wide open knit polyester carrier. The fatigue tests were conducted at 10 Hz in a low humidity and at 3 Hz in a high humidity.

The fracture toughness of both adhesive systems, in terms of Gtotal, was 1 ⅔ to 2 times higher for the mixed-mode specimens than for the pure mode I specimens. For the dry fatigue tests, ΔGT for a fixed crack growth rate was also much higher for mixed mode than for Mode I cracking. A fracture law based on these data would be quite different from one based on the large amount of mixed mode I–II data now available. These differences appear to be the result of differences in fracture behavior produced by different types of carrier cloths. For Mode I cracking in the present study, separation occurred between the adhesive and the carrier cloth, which lowered both the cyclic and static debond resistance to values less than those reported earlier for FM 300 with a tricot knit carrier. For the mixed-mode specimens, on the other hand, the carrier cloth, rather than separating from the adhesive, shredded, which increased the crack resistance above the mixed-mode values reported previously for FM 300. This behavior suggests that the carrier cloth in film adhesives has a greater influence on crack resistance than generally thought. Thus fracture laws for adhesive joints may also be more complex than previously thought.
Application of Fracture Mechanics and Acoustic Emission to the Characterization of Adhesively Bonded Joints Tested in Mode I Opening
Authors: Ziane E , Coddet C
Published: February 2009

Cleavage tests have been performed on double cantilever beam (DCB) specimens made from two types of galvanized steels bonded with an epoxy resin (Redux 609) after different surface treatments. During the test, acoustic emission was monitored in order to determine the microscopic initiation of the fracture. From the load-displacement curves, the fracture energy GIc is calculated according to Berry's method. Resistance curves are also described showing that for all systems there is always a noticeable resistance to fracture propagation. The analysis of the results is based on the variance analysis technique in order to determine the significance of the effect of each variable on the performance of the joint and to detect the possible interactions between the parameters.
Understanding Effects of Adhesive Ductility and Bondline Geometry on Tube-and-Socket Joint Performance
Authors: Miller JM , Hammill JL , Luyk KE
Published: February 2009

Tube-and-socket joints are commonly used in adhesively bonded structural assemblies. Three parameters which can affect the structural performance of bonded tube-and-socket joints are overlap length, bondline thickness, and adhesive properties. Adhesive shear behavior and the effects of overlap length and bondline thickness on tensile failures and stress distributions in a round tube-and-socket joint are evaluated. Bondline thickness is varied using finite element models to determine its effect on maximum radial and shear stresses and stress variations through the adhesive thickness. Measured tensile failure loads are compared with predictions from a fully plastic closed-form analytical model.

Results show the measured tensile failure loads of tube-and-socket joints to be dependent on bondline thickness and adhesive ductility. Joints with thin bondlines develop higher tensile failure loads than joints with thick bondlines. The combination of thick bondlines and the brittle adhesive resulted in the lowest tensile failure loads. Predicted stress distributions from finite element analyses show the magnitude of the maximum radial stresses in tube-and-socket joints to be strongly dependent on bondline thickness. Maximum radial stresses are higher in thick bondlines than in thin bondlines. The brittle adhesive is sensitive to the high radial stresses occurring in thick bondlines, as evidenced by tensile failure loads and predicted stress distributions. The ductile adhesive is not as sensitive to the magnitude of the radial stresses.
Measurement of Three-Dimensional Effects in Fracture Mechanics
Authors: Smith CW
Published: February 2009

After citing several experimental methods used for measuring three-dimensional effects in opaque and transparent cracked bodies, an integrated optical method is focused upon for obtaining two independent estimates of fracture parameters associated with linear elastic fracture mechanics (LEFM). Results of the use of these methods to study the effect of free surfaces upon the stress singularity of cracks intersecting them are presented and a means of interpreting the results within the framework of LEFM is suggested.
Three-Dimensional Elastic Surface Cracks
Authors: Cruse TA
Published: February 2009

This paper discusses a variety of issues associated with the elastic fracture mechanics modeling of surface cracks; both analytical and experimental issues are addressed. The primary analytical focus is on the use of the boundary integral equation method for elastic fracture mechanics analysis. An advanced code is highlighted. A new formulation for three-dimensional crack-surface integral equations is presented with some new analytical results associated with the free-surface singularity. Essential agreements with the results of Benthem are obtained. Fatigue crack growth results for surface cracks in tension and bending are compared with analytical solutions. It is shown that surface cracks in tension grow essentially in accord with an elastic fracture mechanics prediction, whereas surface cracks in bending do not conform to the elastic prediction, based on surface values of the elastic stress-intensity factor. Some thoughts for further research are given.
Three-Dimensional Effects Affecting the Precision of Lifetime Predictions
Authors: Kordisch H , Sommer E
Published: February 2009

A series of laboratory experiments on smooth and side-grooved compact specimens, as well as plates under tension with surface flaws, has been reevaluated by means of three-dimensional elastic-plastic finite-element analyses. Particular emphasis is laid on the calculation of the local crack-tip loading parameter, J, and of the local constraint factor, q. These parameters are correlated with experimental findings concerning initiation and stable crack propagation. A first-guess correlation between q and the slope of J(Δa) curves is established.
Computation of the Amplitude of Stress Singular Terms for Cracks and Reentrant Corners
Authors: Szabó BA , Babuška I
Published: February 2009

The theoretical basis and performance characteristics of two new methods for the computation of the coefficients of the terms of asymptotic expansions at reentrant corners from finite-element solutions are presented. The methods, called the contour integral method (CIM) and the cutoff function method (CFM), are very efficient: the coefficients converge to their true values as fast as the strain energy, or faster.

In order to make the presentation as simple as possible, we assume that the elastic body is homogeneous and isotropic, is loaded by boundary tractions only, and, in the neighborhood of the reentrant corner, has stress-free boundaries. The methods described herein can be adapted to cases without such restrictions.
Damage Tolerance of Stiffened-Skin Structures: Prediction and Experimental Verification
Authors: Vlieger H
Published: February 2009

Some consequences of application of current damage tolerance airworthiness requirements for transport aircraft are discussed in terms of designing stiffened-skin structures for safety under all operational load conditions. Compliance with these requirements can be shown by analysis supported by test evidence. To provide the designer with analytical tools to demonstrate that his design meets the required residual strength and crack propagation properties, a number of computer routines were developed by the National Aerospace Laboratory. The principles underlying the calculation procedures used in these computer programs are discussed. An approach incorporated in the computer programs to predict the residual strength of stiffened panels with a skin of a ductile material (such as 2024 alloy) is included. Applications of these programs to some practical stiffened-skin structures are presented together with analysis-test correlations.
Mechanical Durability Assurance in Automotive Structures
Authors: Landgraf RW
Published: February 2009

Approaches for assuring the mechanical durability of ground vehicle structures are reviewed in the context of continuing developments in computer-aided engineering tools. Examples involving service data acquisition, vehicle loads analysis, component stress analysis, damage analysis, and fatigue life prediction are presented to illustrate the impact of new technologies on vehicle design. Finally, some current problem areas and prospects for the development and implementation of improved design strategies are discussed.
Role of Damage Tolerance and Fatigue Crack Growth in the Power Generation Industry
Authors: Coffin LF
Published: February 2009

The problem of intergranular stress-corrosion cracking (IGSCC) in boiling water reactor (BWR) piping is discussed and the body of work undertaken in the author's laboratory to solve that problem is described. Particular attention is given to the development of electrical potential crack monitoring techniques and their application to surface crack growth, particularly under conditions approaching those found in service. The important role of water chemistry and its control is described in this context.

The concept and description of sensors to monitor in situ the degree of damage containment from intergranular stress-corrosion cracking is then described, with reference to use in piping components and other types of monitoring.

Finally, a concept for the life management of structures is described where damage processes are identified and monitored in situ using appropriate sensors to measure the damage rate continuously. In conjunction with damage monitoring, an applicable life prediction model is used to forecast the future damage state and to assist in the decision process for appropriate required actions to optimize plant operation.
Three-Dimensional Crack-Tip Deformation in a Plastically Deformed Three-Point Bending Specimen
Authors: Wu X-P , Chiang F-P
Published: February 2009

A new technique of holospeckle interferometry using twin-plate recording has been developed in which three-dimensional crack-tip deformation within an area of 1 mm2 can be mapped in detail. The resulting fringe has a sensitivity of 0 to 3 μm for out-of-plane displacement and 1.3 μm for in-plane displacement. The difficulty due to a difference in sensitivity between the hologram and specklegram techniques is eliminated by judiciously pairing the front (or back) plate of one holospecklegram with the back (or front) plate of another at different stages of loading. The technique was applied to a notched three-point-bending aluminum specimen under large-scale yielding. A three-dimensional crack-tip deformation field was obtained, and strain contours were plotted. This shows that the region directly above the crack experiences a relatively small amount of strain.
Application of the J Concept to Fatigue Crack Growth in Large-Scale Yielding
Authors: Lambert Y , Saillard P , Bathias C
Published: February 2009

Fatigue crack propagation tests were performed on compact tension specimens of AISI 316 steel, in the elastic-plastic and plastic regions. The parameter ΔJ was chosen to characterize propagation. Results show that there is a Paris law type correlation between propagation rate and ΔJ. An effect on propagation rate, which is attributed to the R = Pmin/Pmax ratio, has been noted.

A numerical verification of the applicability of the ΔJ concept was determined by use of a theoretical equation. These results were compared with experimental results.
Fracture Toughness of Stainless Steel Welds
Authors: Mills WJ
Published: February 2009

The effects of temperature, composition, and weld-process variations on the fracture toughness behavior for Types 308 and 16-8-2 stainless steel (SS) welds were examined using the multiple-specimen J-resistance-curve procedure. Fracture characteristics were found to be dependent on temperature and weld process, but not on filler material. Gas-tungstenarc (GTA) welds exhibited the highest fracture toughness, a shielded-metal-arc (SMA) weld exhibited an intermediate toughness, and submerged-arc (SA) welds yielded the lowest toughness. Minimum expected fracture properties were defined from lower bound fracture toughness and tearing modulus values generated here and in previous studies.

Fractographic examination revealed that microvoid coalescence was the operative fracture mechanism for all welds. Second-phase particles of manganese silicide were found to be detrimental to ductile fracture behavior because they separated from the matrix during the initial stages of plastic straining. In SA welds, the high density of inclusions resulting from silicon pickup from the flux promoted premature dimple rupture. The weld produced by the SMA process contained substantially less manganese silicide, while GTA welds contained no silicide inclusions. Delta ferrite particles, present in all welds, were substantially more resistant to local failure than the silicide phase. In welds containing little or no manganese silicide, delta ferrite particles initiated microvoid coalescence, but only after extensive plastic straining.
Fatigue Behavior of Axial and Pressure Cycled Butt and Girth Welds Containing Defects
Authors: Leis BN , Goetz DP , Scott PM , Hudson CM
Published: February 2009

This paper presents the results of a study directed at developing a data base for establishing fitness-for-purpose defect acceptance criteria for welds with defects. The study focused on A106 Grade B steel pipe. Data are presented for flat plate, wall segment, and vessel specimens and actual pipe sections containing either artificial or natural planar or volumetric defects. Defect acceptance criteria developed from the test data are discussed.
Effect of Temperature and Strain Rate on Upper Shelf Fracture Behavior of A533B Class 1 Pressure Vessel Steel
Authors: Jung YH , Murty KL
Published: February 2009

The effect of interstitial impurities on the upper shelf fracture characteristics of A533B Class 1 steel was examined using single specimen unloading compliance J-integral tests. Three-point bend tests were performed on fatigue precracked side-grooved Charpy-size specimens using a specially designed compression jig that minimized misalignments usually encountered in direct compression tests. Experimental results obtained as a function of the test temperature and strain rate revealed the effect of dynamic strain aging (DSA) as a drop in the critical crack initiation fracture toughness, Jq. As predicted from DSA models, the minimum in Jq shifted to higher temperatures at higher test speeds (strain rates). The kinetics of the toughness minima agreed with the diffusion of carbon or nitrogen, or both in steels. The effect of neutron irradiation was noted to result in a shift of the J-integral minimum to higher temperatures, resulting in an apparent increase in toughness at lower temperatures following neutron radiation exposure. The usual radiation embrittlement was noted at higher temperatures where DSA was absent.
Using Combined Experiments and Analysis to Generate Dynamic Critical Stress Intensity Data
Authors: Swenson DV , Ingraffea AR
Published: February 2009

In this paper the authors give a short description of a finite-element model of mixed-mode dynamic crack propagation. They then discuss the use of combined experiments and analysis procedures to generate critical stress-intensity data as a function of crack velocity. Because of the sensitivity of the analysis to the boundary conditions and specified crack velocity, it is difficult to generate reliable KID(v) data using this approach. This is due to uncertainties in both the analysis and the measured crack position. Suggestions are made for alternate test methods to reduce some of these uncertainties.
Ductile Crack Bifurcation and Arrest in Pressurized Pipe
Authors: Kobayashi AS , Emery AF , Love WJ , Chao Y-H , Johansson O
Published: February 2009

This paper presents selected results on ductile crack propagation, curving and branching, and crack arrest from ten dynamic pipe rupture tests. Strain gage results adjacent to the crack path showed that a Dugdale-Barenblatt strip yield zone, of the order of eight pipe diameters in length, preceded the propagating crack tip and that the maximum principal strain direction changed from the hoop to the axial direction approximately 6 to 8 pipe diameters downstream of the crack tip. This change in principal strain direction constitutes the sufficiency condition for crack curving or branching prior to crack arrest in the absence of a crack arrester. The necessary condition for crack arrest is the sudden and sufficient increase in fracture resistance due to either increased apparent fracture toughness or a pipe opening restraint in the crack path.
Determination of Dynamic Fracture Behavior in 4340 Steel Compact Crack Arrest Specimens Using Birefringent Coatings and Finite-Element Analysis
Authors: Khatri S , Barker DB
Published: February 2009

A split-birefringent coating technique, coupled with high-speed photography, was used to record the dynamic isochromatic fringe pattern associated with crack propagation and arrest in 4340 steel compact crack arrest fracture specimens. From the data contained in the isochromatic fringe patterns, the associated dynamic stress-intensity factor was calculated in two different ways. First, the dynamic stress-intensity factor was calculated from the isochromatic fringe information directly. Next, the isochromatic fringe patterns were used to obtain a crack position history which was used for input to a two-dimensional dynamic finite-element code used in the “generation mode.” These two dynamic stress-intensity factors were compared with each other and with the crack arrest toughness as calculated by the proposed ASTM method for estimating crack arrest toughness.
Approximate Methods for Analysis of Dynamic Crack Growth and Arrest
Authors: Nilsson F
Published: February 2009

Approximate methods that are less time-consuming than finite-element method (FEM) analysis are needed for dynamic crack propagation and arrest calculations. In this context the one-dimensional wave propagation models, where the cracked section is modeled by a flexibility matrix, may be a reasonable alternative. Such models are compared with fully dynamic two-dimensional FEM calculations of experimentally observed crack growth histories in an edge-cracked rectangular sheet. A fairly good agreement is obtained; the discrepancies could mainly be ascribed to differences in the end conditions. The author concludes that spring models are worth further examination in order to make them a practical tool for engineering design analysis.
Some Aspects of Performing Dynamic Measurements and Analyses on the Compact Crack Arrest Specimen for A533-B Steel
Authors: Brickstad B , Dahlberg L
Published: February 2009

The four countries of Sweden, Norway, Finland, and Denmark are participating in a joint project which includes performing instrumented crack arrest experiments on A533-B steel. The primary aim of this study is to determine the dynamic fracture properties during propagation and arrest. Dynamic finite-element methods calculations were used to analyze earlier reported experiments on the transverse wedge-loaded compact crack arrest (CCA) specimen, in order to obtain guidance for future experiments regarding measuring technique, material characterization, and the crack-tip model. The computations indicate that the dynamic effects on the stress-intensity factor are small for the CCA specimen. It is also shown that proper determination of the displacement controlled boundary conditions can be made by measuring displacements at the load line. Computations were also made with the material treated as elastic-viscoplastic. It was found that nonlinear material behavior is likely to be important for A533-B steel at least at room temperature and higher temperatures.