bluuebunny/crossref_metadata_2025 huggingface dataset:
Corrosion Behavior of Duplex and Reference Cladding in NPP Grohnde
Authors: Besch OA , Yagnik SK , Woods KN , Eucken CM , Bradley ER
Published: March 2009

The Nuclear Fuel Industry Research (NFIR) Group undertook a lead test assembly (LTA) program in NPP Grohnde PWR in Germany to assess the corrosion performance of duplex and reference (i.e., non-duplex) cladding. Two identical 16 by 16 LTAs, each containing 32 peripheral test rods, completed four reactor cycles, reaching a peak rod burnup of 46 MWd/kgU. The results from poolside examinations performed at the end of each cycle, together with power histories and coolant chemistry, are reported.

Five different cladding materials [three types of duplex (D1-D3) and two types of reference (R1, R2)] were characterized during fabrication. The corrosion performance of the cladding materials was tracked in long-term tests (∼900 days) in high-pressure, high-temperature autoclaves. The relative ranking of corrosion behavior in such tests corresponded well with the inreactor corrosion performance. The extent and distribution of hydriding in duplex and reference specimens during the autoclave testing has been characterized.

The in-reactor corrosion data indicate that the low-tin (1.3% Sn) Zircaloy-4 reference cladding, R2, had an improved corrosion resistance compared to high-tin (1.5% Sn) Zircaloy-4 reference cladding, R1. Two types of duplex cladding, D1 (Zr-2.5% Nb) and D2 (Zr-0.4% Fe-0.5% Sn), showed an even further improvement in corrosion resistance compared to R2 cladding. The third duplex cladding, D3 (Zr-4 + 1.0% Nb), had significantly less corrosion resistance, which was inferior to R1. The in-reactor and out-reactor corrosion performances have been ranked.
Comparison of the Long-Time Corrosion Behavior of Certain Zr Alloys in PWR, BWR, and Laboratory Tests
Authors: Garzarolli F , Broy Y , Busch RA
Published: March 2009

Laboratory corrosion tests have always been an important tool for Zr alloy development and optimization. However, it must be known whether a test is representative for the application in-reactor. To shed more light on this question, coupons of several Zr alloys were exposed under isothermal conditions in all or most of the following environments: In-Reactor: (1) PWR core at 300 to 340°C up to six years. (2) BWR core with a low sensitivity to nodular corrosion up to four years. (3) BWR core with a high sensitivity to nodular corrosion up to two years.

Ex-Reactor (in Autoclave): (1) 350°C/pressurized water up to three years. (2) 400°C/100-bar steam up to two years. (3) 350°C/0.01 M LiOH water up to two years. (4) 500 to 515°C/high-pressure steam 16 to 24 h.

In addition, the material condition of several of the examined Zr alloys was varied over a wide range.

For evaluation of the in-PWR tests and for comparison of out-of-pile and in-pile tests, the different temperatures and times were normalized to a temperature-independent “normalized time” by assuming an activation temperature (Q/R) of 14 200 K. Comparison of in-PWR and out-of-pile corrosion behavior of Zircaloy shows that corrosion deviates to higher values in PWR if a weight gain of about 50 mg/dm2 is exceeded. In the case of the Zr2.5Nb alloy, a slight deviation of corrosion as compared to laboratory results starts in PWR only above a weight gain of 100 mg/dm2. In BWR, corrosion of Zircaloy is enhanced early in time if compared with out-of-pile. Zr2.5Nb exhibits higher corrosion results in BWR than Zircaloy-4.

Alloying chemistry and material condition affect corrosion of Zr alloys. However, several of the material parameters have shown a different ranking in the different environments. Nevertheless, several material parameters influencing in-reactor corrosion like the second phase particle (SPP) size or in-PWR behavior as the Sn and Fe content can be optimized by out-of-pile corrosion tests.
Development of Pressure Tubes with Service Life Greater Than 30 Years
Authors: Coleman CE , Cheadle BA , Cann CD , Theaker JR
Published: March 2009

The steps required for the development of a Zr-2.5Nb pressure tube with a 30-year service life are outlined. The life-limiting factors of fracture and deformation are described, and progress towards closing the gap between the properties required to meet the target lifetime and the behavior of current materials is summarized. Fracture is avoided by eliminating hydrides at reactor operating temperatures, by controlling the initial hydrogen concentration and minimizing deuterium ingress from corrosion, and maintaining high toughness. Tube elongation has been reduced by microstructural modification, but transverse deformation remains a challenge.
Biaxial Deformation Experiments Over Multiple Strain Regimes
Authors: Miller MP , McDowell DL
Published: March 2009

Dominant inelastic deformation processes of polycrystalline metals in the infinitesimal strain regime are different than those at larger strains. Within the infinitesimal strain regime, dislocation/dislocation interactions and the nucleation and evolution of small-scale dislocation structures such as dislocation cells dominate the strain-hardening character of a face-centered cubic (fcc) material. As the strain transcends the infinitesimal regime, the dominant dislocation substructures become larger macroscopically oriented structures such as dense dislocation walls and microbands. These structures have a profound effect on the mechanical response of the material. The nonrandom crystallographic textures that form at large strain also affect the stress-strain response. With this in mind, interesting and technically significant questions arise concerning the effects of multiaxial nonproportional loading at large strain as well as the effect of a large prestrain on subsequent small-strain multiaxial cyclic deformation behavior. In an attempt to address this question, a matrix of multiaxial large- and small-strain experiments were conducted on Type 304L stainless steel. The large-strain tests consisted of compression, torsion, compression followed by torsion, and torsion followed by tension experiments. A non-proportional small-strain axial-torsional cyclic history was then imposed on material in an annealed state as well as material subjected to an effective torsional plastic prestrain on the order of ¯εp= 100%. Experimental details as well as modeling implications are presented.
Crack Initiation Life Behavior Under Biaxial Loading Conditions: Experimental Behavior and Prediction
Authors: Nowack H , Hanschmann D , Ott W , Trautmann K-H , Maldfeld E
Published: March 2009

An experimental program with proportional and nonproportional loading histories was performed with cruciform aluminum specimens on a biaxial testing machine. FEMFAT, a crack initiation life prediction method as originally proposed by Ott, which includes an elastic-plastic stress-strain analysis based on the finite element method (FEM) in combination with a Mróz-type material model and an event independent continuous damage (EVICD) evaluation approach on the basis of incremental plastic work was applied to predict the crack initiation life behavior as observed in the experiments. The predictions were partially extremely conservative.

Two new fatigue evaluation approaches, EVICD-J1 and EVICD-N, were developed on the basis of the original EVICD approach to account for the effect of mean stresses. They led to significant improvements in the predictions.

The new approaches do not need cycle counting and are applicable to arbitrary multiaxial loading histories in the low-cycle fatigue (LCF) and in the high-cycle fatigue (HCF) range.
Characterization of Ceramic Matrix Composite Tubes Under Uniaxial/Biaxial Monotonic and Cyclic Loading
Authors: Liao K , George ER , Reifsnider KL
Published: March 2009

A method for testing ceramic matrix composite (Almax fiber-reinforced alumina matrix) tubes under monotonic and cyclic loads (tensile/compression, torsional, and biaxial) is described. A data interpretation method is developed to determine ply-level elastic properties from elastic response of the tube measured under monotonic loadings. Monotonic tests were carried out at room temperature to determine the tensile and torsional strengths. Fatigue behavior under tension-tension, torsion-torsion, and biaxial cyclic loads was studied. Damage and failure modes of the tubes under these test conditions are described in detail.
Instability and Failure of Corrugated Core Sandwich Cylinders Under Combined Stress
Authors: Patel P , Nordstrand T , Carlsson LA
Published: March 2009

Collapse of corrugated board cylinders loaded in axial compression and combined compression/torque has been examined experimentally and analytically. Prior to the experimental study of the cylinders, a design analysis of the loading fixture and corrugated board cylinder were performed using the finite element method. A manufacturing technique of the specimens was also developed. The cylinders were tested on a tension/compression/torque MTS-machine at room temperature and 20 to 25% relative humidity. Experimental compressive force and torque at failure and failure initiation were in good agreement with prediction using the finite element analysis in conjunction with the Tsai-Wu failure criterion. Local buckling of the outer facing, between the corrugation tips, was observed prior to failure of the corrugated board cylinder. However, the failure initiated in regions different from those where local buckles appeared and at much larger stresses than those at the onset of local buckling. Thus, local buckling did not significantly influence the collapse load of the cylinder.
Crack Propagation in Cruciform IMI 834 Specimens Under Variable Biaxial Loading
Authors: Trautmann K-H , Maldfeld E , Nowack H
Published: March 2009

In the present study, the crack propagation behavior of cruciform IMI 834 specimens under different types of in-phase biaxial block loading histories was investigated. The test temperature was 350°C. The phenomenological crack propagation behavior and the orientation of the cracks in the biaxial tests are described. This study shows that the mean stress and the amplitude of the minor cycles in the blocks had a significant effect.

Linear crack propagation predictions were performed and indications of crack closure influences and load sequence effects were observed.
Application of a J-Q Model for Fracture in the Ductile-Brittle Transition
Authors: Landes JD
Published: March 2009

A model to predict cleavage failure of precracked bodies in the transition region for steels was recently proposed by the author. It is based on the concept that the stress-controlled fracture of a weak link triggers the failure of the entire body. The stress that triggers fracture is predicted by a numerical crack-tip stress analysis. The model uses toughness measured at one condition as input to predict toughness at another. For example, toughness measured at one temperature can be used to predict toughness at another temperature, or toughness measured from one geometry can be used to predict toughness for another geometry.

In this paper the model is applied to predict transition toughness for some cases where the toughness is known so that the predictions from the model can be evaluated. The results show that the predictions have the same trends as many of the measured transition toughness results. The model is also applied to several component-type geometries to show that it can be used to transfer laboratory results to structural component models.
Constraint Effect in Brittle Fracture
Authors: Chao Y-J , Zhang XH
Published: March 2009

Variation of apparent fracture toughness under predominantly (elastic) brittle fracture is investigated. Williams' asymptotic series solutions, including higher order terms, are used to characterize the crack tip stress and strain fields for various specimen geometries. Using a fracturing stress or a strain as the material property, it is demonstrated that a fracture event can be quantified by two mechanics parameters, K and A3 for stress-controlled fracture or K and T for strain-controlled fracture. A set of test data that covers a wide range of T and A3 is used to demonstrate the proposed fracture assessment procedure. Constraint-related issues such as size, crack depth, and biaxial stress effect are investigated. The material's failure locus is discussed relative to the ASTM recommended specimen geometries. It is shown that the ASTM in-plane size requirements place a finite-size window on the complete material failure locus. Since real structures may possess constraint levels either higher or lower than the ASTM standard test specimens, structures may fracture at an applied K either higher or lower than KIC. It is demonstrated that KIC determined according to ASTM E 399 and based on a linear elastic solution is not conservative when used to predict the fracture of specimens with low-constraint geometries. This trend is opposite to the corresponding constraint effect in cleavage fracture when the crack tip deformation at fracture is characterized by large-scale yielding.
Application of Constraint Modelling to Evaluation of Crack Growth Experiments
Authors: Faleskog J , Nilsson F , Shehu S , Öberg H
Published: March 2009

A large number of fracture mechanics experiments were carried out using a variety of specimens in order to investigate the applicability of the J-Q approach to initiation and growth of cracks. The study was performed at different temperatures spanning the transition interval of a pressure vessel steel. A comparison of the cleavage initiation levels with the model by Ritchie et al. (RKR) was also conducted. The experiments did not show, although the scatter was large, any systematic geometry effects that could not be explained within the framework of the J-Q concept. This was also the case for surface-cracked plates subjected to nonproportional loading. The trends of the dependence of the initiation on constraint are in qualitative agreement with the RKR model, although this model seems to underestimate this dependence for the current material. The ductile initiation level seems to be fairly independent of constraint but showed a tendency of variation with temperature.
Effects of Mixed Mode I/II Loading and Grain Orientation on Crack Initiation and Stable Tearing in 2024-T3 Aluminum
Authors: Amstutz BE , Sutton MA , Dawicke DS , Boone ML
Published: March 2009

The effects of material grain orientation and Mixed Mode I/II loading on crack initiation and stable tearing in 2.3-mm-thick, unclad 2024-T3 aluminum is experimentally investigated. Mode I experiments were performed on center-cracked specimens with the crack being oriented at various angles relative to the rolling direction. Defining θ to be the angle between the normal to the initial crack plane and the loading direction, Mode I/II experiments were performed using an Arcan test fixture for 0° ≤ θ ≤ 90° [corresponding to 90° ≥ β ≥ 0°, where β = atan (KII/KI)] with the crack oriented either along the rolling direction (T-L) or perpendicular to the rolling direction (L-T).

Results indicate that: 1. The Mode I crack tip opening displacement (CTOD) is a strong function of the orientation of the crack relative to the rolling direction; CTOD for a T-L specimen is 0.84 mm, increasing linearly with orientation angle to 1.05 mm for an L-T case. 2. The Mode I/II CTOD increases rapidly during initial increments of crack growth and then decreases towards a constant value as crack growth continues. 3. For θ < 68° (β > 29°), all cracks kinked and the Mode I/II plastic zones are similar to rotated Mode I plastic zones throughout the crack growth process. 4. JII = 0 reasonably predicts the direction of tension-dominated crack growth, but does not predict the transition to shear crack growth which occurs for θ ≥ 75°. 5. KII ≥ KI for θ ≈ 58° (β = 45°) does not quantitatively predict the transition to shear crack growth for θ ≥ 75° (β ≤ 22°), but does provide an indication of changing conditions in the crack tip region.
Effects of Crack Surface Morphology on Fracture Behavior under Mixed Mode I/III Loading
Authors: Hsia KJ , Zhang T-L , Socie DF
Published: March 2009

Material toughening due to crack surface friction under mixed mode loading is studied. A mechanistic model is developed for a crack with an intergranular fracture surface under mixed Mode I/Mode III loading. The model takes into account several microstructural and material parameters such as grain shape and friction coefficient between grain boundaries. By employing a self-consistent, fracture mechanics approach, the governing integral equation with a singular kernel is obtained. A special numerical technique is used to solve the integral equation. The frictional stress distribution along the crack face is obtained for different grain shapes and frictional coefficients. The results show that, because of crack surface friction, the material toughens significantly. The toughening ratio increases rapidly with the relative magnitude of the Mode III component of the applied load. Moreover, two parameters, the oblique grain boundary angle and the friction coefficient, are identified as the controlling parameters for the toughening behavior. Using an energy-based crack tip fracture criterion, fracture loci in KI - KIII space are constructed to serve as a failure criterion for mixed mode fracture. The model predictions are also compared with experimental measurements. Good agreement is obtained. Potential applications of the model to surface crack growth under rolling contact loading in the presence of lubricating fluids are discussed.
An Analytical Investigation of the Effect of Crack Depth (a) and Crack Depth to Width (a/W) Ratio on the Fracture Toughness of A533-B Steel
Authors: Smith JA , Rolfe ST
Published: March 2009

The use of various crack depths (a) and crack-depth to specimen-width (a/W) ratios in laboratory tests to model flawed structural components has led to considerable interest in the role of both the crack depth (a) and the a/W ratio on fracture toughness. To investigate the separate roles of crack depth and the a/W ratio, three-dimensional elastic-plastic finite element analyses, (FEA) of square SE(B) specimens with a/W ratios ranging from 0.1 to 0.5 [crack depths ranging from 2.0 mm (0.08 in.) to 50.8 mm (2.0 in.)] have been conducted. The material properties used in this analysis were those for the material used in an experimental study conducted at the University of Kansas (KU) and Oak Ridge National Laboratory (ORNL). The specimen dimensions were chosen such that the results for specimens having a fixed crack depth and varying a/W ratios could be compared to the results for specimens with a fixed a/W ratio and varying crack depths.

The results of the experimental studies had indicated that both the crack depth and the a/W ratio each have a significant effect on the fracture toughness. Both the lower bound toughness and the transition temperature were affected. Three-dimensional elastic-plastic FEA were used to model each specimen geometry, and the predicted stresses, CTOD, and J-integral for the various crack depths and a/W ratios were compared. The results of the FEA support the findings of the previous experimental study. For a high-constraint geometry (a/W = 0.5), there is not a significant change in the near tip stresses for different size specimens. However, for low-constraint geometries (a/W = 0.1), the near tip stresses are significantly affected by the actual crack depth and specimen size. The findings of this study are significant in helping to understand the relative role of crack depth, a/W ratio, and specimen size on fracture toughness. Future studies are expected to extend the findings of this study to the behavior of actual structures with cracks.
Ductile Tearing of Welded Structural Details
Authors: Gentilcore ML , Dexter RJ
Published: March 2009

Experiments were conducted at room temperature on 16 full-scale welded structural members containing fatigue cracks. These I-section and box-section members were fabricated from HSLA-80 steel that exhibits upper-shelf behavior at room temperature. These members consistently reached at least the net-section collapse load and deformed to several times the yield-point displacement. The experiments were analyzed with a variety of ductilefracture models including the three levels in the British Standards Institute document PD 6493, a stable tearing analysis using finite-element analysis to calculate J, and a limit-load analysis. These models were studied in order to evaluate their usefulness and degree of conservatism relative to experimental results.
Fracture Analysis of Full-Thickness Clad Beam Specimens
Authors: Keeney JA , Bass BR , McAfee WJ
Published: March 2009

Finite-element analyses were performed on full-thickness clad beam specimens to quantify fracture toughness for shallow cracks in material for which metallurgical conditions are prototypic of those found in reactor pressure vessels (RPVs). The beam specimens are fabricated from a section of an RPV wall (removed from a canceled nuclear plant) that includes weld, plate, and clad material with metallurgical factors potentially influencing fracture toughness for shallow cracks. A summary of the testing program is provided and the analyses of the test data are discussed, including comparisons of measured displacements with finite-element analysis results, applications of toughness estimation techniques, and interpretations of constraint conditions implied by stress-based constraint methodologies. Fracture toughness estimates were obtained from displacement data using finite-element techniques and estimation schemes based on the η-factor method. The J-Q methodology was used to assess crack-tip stress triaxiality in the clad beam specimens. The shallow-crack clad beam specimens showed a significant loss of constraint similar to that of other shallow-crack single-edge notch bend specimens. The stress-based Dodds-Anderson scaling model was also utilized to analyze constraint conditions in the clad beam specimens and appears to be effective in adjusting the test data to account for loss of in-plane constraint for uniaxially tested beams.
The Effect of Cyclic Loading During Ductile Tearing on the Fracture Resistance of Nuclear Pipe Steels
Authors: Rudland DL , Brust F
Published: March 2009

As part of the First International Piping and Integrity Research Group (IPIRG-1) program, a series of 152.4-mm (6-in.)-diameter Schedule 120, A106 Grade B carbon steel and TP304 stainless steel cyclic through-wall crack (TWC) pipe tests were conducted at 288°C (550°F). The conclusion reached from these experiments was that fully reversed loading decreases the ductile tearing resistance of nuclear pipe steels. As part of the Second International Piping and Integrity Research Group (IPIRG-2) program, a series of cyclically loaded compact tension [C(T)] tests were conducted to determine if this effect is present in laboratory specimens and whether these small-scale results can be used to predict larger through-wall crack pipe behavior. The specimens were run in displacement control using several cyclic displacement increments and stress ratios. It was found that as the stress ratio was decreased, i.e., the amount of compressive plasticity is increased, the ductile tearing resistance of the material decreased. Fractographic analysis was performed on several C(T) specimens to determine the cyclic degradation mechanism. It was found that crack tip sharpening and void flattening were observed and could be the mechanisms that contributed to the cyclic degradation. In addition to the laboratory tests, finite element analyses were performed on a cyclic C(T) specimen to verify the ASTM E 1152 procedure used and to calculate the cyclic J-R curves.
Experimental Investigation of Mismatched Weld Joint Performance
Authors: Tregoning RL
Published: March 2009

A mismatched welded component exists when the strength of the weld material is different than the strength of the base material. This research examined the effect of weld joint geometry and the mismatch level on the strength and fracture performance of high-strength steel weld components. Eleven different welded systems were constructed with the mismatch ranging between -36% to +47% and various weld joint profiles to sculpt fusion zone widths between 2 and 13 mm at the crack tip. Instrumented tension tests were utilized to characterize weldment strength behavior, while single-edge bend J-R curve testing of short (a/W = 0.15) and deeply (a/W = 0.5) cracked specimens was conducted to measure both baseline weld metal toughness properties and to determine the fracture performance of mismatched systems. The results indicate that more contact strengthening occurs in beveled, structural undermatched weldments compared to straight-sided welds. Flawed undermatched performance is highly dependent on the fusion zone width as well, while the degree of mismatching is a secondary effect. As the zone width decreases, the apparent tearing resistance also decreases. The overall performance of undermatched systems, however, can still be better than overmatched systems hen the inherent toughness of the overmatching weld metal consumable is poor.
Fatigue Crack Growth Damage in Elastomeric Materials
Authors: Bathias C , LeGorju K , Lu C , Menabeuf L
Published: March 2009

Fatigue crack growth in natural rubber is studied using fracture mechanics concepts and an extension of Griffith's criterion. The effects of load ratio, temperature, and environment are examined. It appears that, for cycles without compression, a mean stress in tension improves the fatigue behavior by inducing crystallization, whereas a minimum stress in compression greatly damages the material. Tests under inert atmosphere show that, in addition to the mechanical damage, an important chemical damage due to oxygen is present. The fatigue cracking of natural rubber is also approached studying the influence of damage mechanisms in relation to microstructural aspects. In this way, SEM observations of fracture surfaces show a marked dependence on crack growth rate, load ratio, temperature, and environment. For high growth rates, we observe some fatigue striations, and we notice a microscopic mechanism for formation of tongue structure, which is highly dependent on gaseous oxygen and typical of natural rubbers.
Stress Intensity Factor Calibration of Edge-Notched Beam
Authors: Gerstle WH , Lenke LR , Heo G
Published: March 2009

Several solutions necessary to determine the mixed-mode stress intensity factors in edge-notched plane stress beams subject to a wide variety of loading conditions are given. These solutions include stress intensity factors in an edge-notched beam subject to: (1) pure moment, (2) pure shear, (3) a point load at the bottom of the beam in the vicinity of the crack, and (4) a point load at the top of the beam in the vicinity of the crack. The solutions have been obtained through use of the finite element and boundary force methods. The techniques necessary to obtain accurate stress intensity factors using both methods are described. The convergence characteristics and behavior of both the finite element and the boundary force methods are discussed. The solutions are provided in approximate functional form for ease of use. An example is presented to demonstrate the use of the solutions.
Elastic Analysis of the Interaction Between Two Surface Cracks
Authors: Sun LK , Zhang L , Qin H
Published: March 2009

In this paper, the interacting behavior of two surface cracks in a plate subject to remote tension load perpendicular to the crack fracture surface is investigated based on a combination of the quasi-compatibility element method and the improved front solver method. Stress intensity factors for the two surface cracks are provided in the form of boundary influence factors [normalized stress intensity factor (NSIF)] for a wide range of crack geometries and distances among the cracks. The crack aspect ratio (crack depth-to-length ratio a/c) varied from 1/3 to 1.0, the crack depth-to-plate thickness varied from 1/3 to 2/3, and the distance, 2s, between the two surface cracks varied from 2/3c to 4c. The crack interacting factor was introduced to consider the interacting behavior of three-dimensional (3D) cracks. The degrees of freedom used here were 2529. The use of quasi-compatibility elements combined with the front solver made it possible to conduct analyses of 3D multiple cracks with personal computers. Secondly, an evaluation method for multiple surface cracks is discussed based on the NSIF values from this study.
A Three-Dimensional Weight Function Method—Evaluation and Applications
Authors: Zhao W , Newman JC , Sutton MA
Published: March 2009

A three-dimensional weight function method is evaluated by comparisons with exact or finite element solutions available in the literature. Three typical crack configurations considered are embedded elliptical crack, semi-elliptical surface crack, and quarter elliptical corner crack. It is found that the assumptions made in the weight function method are appropriate for the crack configurations considered. The method is shown to have the capability of providing accurate results without using a reference solution in many cases. A few application examples are given.
Analysis of Fatigue Crack Growth in Pin-Loaded Lug Joints under Inelastic Deformations
Authors: Prakash RV , Raju KN , Satish Kumar K , Dattaguru B , Ramamurthy TS
Published: March 2009

Results of an experimental program on fatigue crack growth in an interference fit lug joint and numerical estimation of relevant fracture parameters to correlate the experimental data are presented in this paper. Fatigue crack growth rates of naturally initiating cracks were estimated fractographically as a function of crack length for lug joints fitted with different levels of interference. The fracture parameters to correlate the crack growth behavior were estimated using a two-dimensional materially nonlinear contact stress finite element analysis. A path-independent integral, Δ Tp* computed for incremental loads and summed up (I) during cyclic loading was used as an elasto-plastic fracture parameter. Correlation of the experimental crack growth data and the evaluated range of ΔT resulted in a power law similar to the Paris equation. Further, the fatigue crack growth (FCG) rate was evaluated using the relationship between low cycle fatigue (LCF) parameters and the fracture parameter, ΔT, as estimated. These are in good agreement with the experimental results.
An Efficient Method for Calculating Multiaxial Elasto-Plastic Notch Tip Strains and Stresses under Proportional Loading
Authors: Reinhardt W , Moftakhar A , Glinka G
Published: March 2009

A method for calculating elasto-plastic notch tip strains and stresses in bodies subjected to proportional multiaxial loading is presented. Notch tip strains and stresses are estimated using the generalized Neuber's rule and equivalent strain energy density method. These estimates form upper and lower bounds of the exact solution. All necessary relationships in the form of five simultaneous algebraic equations are derived for a general multiaxial stress state. An efficient solution method is proposed enabling fast calculation of numerical values and the choice of the appropriate solution. This method may be particularly useful for fatigue analysis of notched components.
Testing and Evaluation of Fire-Resistant Hydraulic Fluids Using the Stabilized Heat Release Spray Test
Authors: Holke K
Published: March 2009

Hydraulic fluids for use in coal mining applications must be fire-resistant. Fire-resistance is defined by the particular standardized testing methods being used. In Europe, the required fire-resistance testing procedures are specified in 7th Edition of The Luxembourg Report [1]. In this report, there are three acceptable spray testing procedures; 1.) the Community of Six spray test, 2.) the United Kingdom spray test and 3.) the “stabilized heat release spray test” (Buxton Test). Of these three tests, the Buxton Test offers the greatest and most reliable quantitative characterization of the fire-resistance properties of a hydraulic fluid. The results of investigations conducted to evaluate the experimental reproducibility of the Buxton Test are discussed in this report.
Adhesion Properties of Sealants in Resealed Joints
Authors: Pagliuca A , Hutchinson A
Published: March 2009

Resealing of joints in a typical building structure needs to take place a number of times within the life-time of the building. The resealing process is more difficult than sealing joints for the first time and among the most significant difficulties are the removal of old sealant, and the likely presence of residues left in the joint. This aspect of obtaining adhesion to sealant residues left on surfaces represents the main focus of this paper. Following a review of the fundamental concepts of adhesion, surface analytical techniques are used to predict favourably the adhesion performance of tensile adhesion joints prepared with sealants and contaminated substrate surfaces typical of those encountered in practice. It is shown that surface energy measurements can provide a good prediction of adhesion performance, whilst surface tension measurements of uncured resealing materials indicate potential wettability and therefore resealed joint performance. In general, traces of existing sealant will almost always lead to a reduction in joint extension and performance, in proportion to the nature, amount and surface energy of the residue present.
Creep Crack Growth Behavior of Aluminum Alloy 2519: Part I—Experimental Analysis
Authors: Hamilton BC , Hall DE , Saxena A , McDowell DL
Published: March 2009

The discipline of time-dependent fracture mechanics has traditionally focused on the creep crack growth behavior of high-temperature materials that display creep-ductile behavior, such as stainless steels and chromium-molybdenum steels. Elevated temperature aluminum alloys, however, have been developed that exhibit creep-brittle behavior; in this case, the creep crack growth rate correlates with the stress intensity factor, K. The fracture characteristics of aluminum alloy 2519-T87 were studied at 135°C, and the creep and creep crack growth behavior were characterized utilizing experimental and numerical methods.

The strain to failure for creep deformation specimens was limited to only 1.2 to 2.0%. Creep crack growth tests revealed a unique correlation between the creep crack growth rate and K, a result consistent with creep-brittle behavior. No experimental correlation was found between the creep crack growth rate and the Ct, parameter. Microscopy of fracture surfaces revealed distinct regions of intergranular and transgranular fracture, and the transition between the fracture regions was found to occur at a critical K-level. Experimental results also appeared to show that initiation of crack growth (incubation) is controlled by the accumulation of a critical amount of damage ahead of the crack tip and that a correlation exists between the incubation time and K. Total time to failure is viewed as a summation of the incubation period and the crack growth period, and the design importance of incubation time is discussed.
Application of Reference Stress and Probabilistic Methodologies to Assessing Creep Crack Growth
Authors: Chell GG , Kuhlman CJ , Millwater HR , Riha DS
Published: March 2009

This paper describes the application of the reference stress approach and probabilistic methods to the determination of creep crack growth based on the time-dependent fracture mechanics parameter, C(t), where t is time. This parameter is defined as the simple sum of a transient component, C(t → 0), which is applicable to short times and a steady-state component, C*. The reference stress approach enables a relatively simple expression for C* to be derived. A scheme is developed that optimizes the fit of the reference stress approach to published computed solutions for Jp, the fully plastic component of the J-integral. The optimization scheme involves the derivation of an engineering parameter, V. An expression for C* is readily derived from an expression for Jp by invoking the creep-plastic analogy. Values of V are derived from the analysis of 189 sets of computed solutions. These values are statistically analyzed and used to derive a distribution function describing the uncertainty in V. This function is used together with distribution functions for other random variables (such as the creep strain rate coefficient and crack growth law coefficient) in example probabilistic analyses of flaws in welded internally pressurized pipes operating in the creep regime. Probability sensitivity factors are generated as part of the probabilistic analyses.
Fatigue Crack Growth of Two Advanced Titanium Alloys at Room and Elevated Temperature
Authors: Albertson TP , Stephens RR , Bayha TD
Published: March 2009

This paper provides fatigue crack growth information at low crack growth rates for two sheet titanium alloys: β-21S, a β alloy, and Ti-62222, an α + β alloy. Room (25°C) and elevated temperature (175°C) fatigue crack growth tests at two different stress ratios, R = 0.1 and 0.5, were performed. Effects of temperature and stress ratio were evaluated in order to study the complex interaction between fatigue, environment, and loading conditions. Crack-opening load was measured throughout the test from automated compliance measurements and was used to adjust fatigue crack growth data for crack closure. For β-21S, fatigue crack growth rates were similar at 175 and 25°C at a stress ratio of 0.1, while crack growth rates were lower at 175 versus 25°C at a stress ratio of 0.5 for the same nominal ΔK. Concepts associated with crack closure accounted for this as crack growth rates were found to be higher at 175°C than 25°C for both stress ratios when plotted as a function of ΔKeff, showing a temperature dependency on crack growth rate. For Ti-62222, fatigue crack growth rates were comparable between 25 and 175°C for R = 0.5, but were different at R = 0.1 where crack closure was observed at 175°C. Fatigue crack growth behavior of these two titanium alloys was comparable for all loading and temperature conditions.
Thermo-Mechanical Fatigue of the Monocrystalline Nickel-Base Superalloy CMSX-6
Authors: Kraft SA , Mughrabi H
Published: March 2009

Total strain-controlled thermo-mechanical fatigue (TMF) tests were performed between 600 and 1100‡C on as-grown near to [001]-orientated specimens of the γ′ precipitate-strengthened monocrystalline nickel-base superalloy CMSX-6. The strain-temperature cycle (in-phase, out-of-phase, diamond) has a strong influence on the mechanical and microstructural events occurring during TMF. For given temperature intervals, the fatigue lives were shortest for out-of-phase tests and longest for in-phase tests, respectively. For all cycle shapes applied, the maximum tensile stress level was concluded to be the lifetime-limiting factor. The failure mode of the investigated alloy depends also on the conducted strain-temperature history. While strongly localized crystallographic shearing along {111} planes was dominant for in- and out-of-phase cycling, creep-induced damage occurred in diamond cycle tests. The evolution and coarsening of the microstructure were also studied. The latter is compared with the formation of stress-, strain- and diffusion-induced coarsened raft-like structures found in creep testing of similar materials.
Coating Effects on Crack Growth in a Single Crystal Nickel Based Alloy During Thermo-Hechanical Fatigue
Authors: Bressers J , Martinez-Esnaola JM , Martin-Meizoso A , Timm J , Arana-Antelo M
Published: March 2009

Single crystal specimens of the nickel based alloy SRR99 with [001] orientation are subjected to TMF cycling between 300‡C and 1050‡C, using a −135‡lag between temperature and mechanical strain, and various R ratios. The in-situ observation of the test specimen by means of a computer vision system during TMF testing enables the initiation of microcracks to be detected when cracks have reached lengths of approximately 30 μm at the surface. High densities of point initiated micro-cracks are generated during the early stages of the TMF life. Crack increment measurements reveal marked differences between the growth rates of individual micro-cracks. The presence of a nickel-aluminide coating consistently reduces the TMF life, due largely to higher growth rates of the main crack in the substrate. In order to estimate the influence of initial crack distribution and density on life, a two dimensional crack shielding model is incorporated in a computer programme which is used to simulate the growth of interacting, parallel surface cracks. The effect of various parameters, including the density and the initial distribution of the microcracks, on the life spent to grow a crack to a pre-defined length, are discussed and the model predictions are compared with the experimental observations.
Isothermal and Thermomechanical Fatigue of Type 316 Stainless Steel
Authors: Zamrik SY , Davis DC , Firth LC
Published: March 2009

Discussed is the thermomechanical fatigue (TMF) life of Type 316 stainless steel under in-phase and out-of-phase cycling and a comparison with the isothermal fatigue case. The TMF tests were conducted in air over a temperature range of 399‡C (750‡F) to 621‡C (1150‡F) at several mechanical strain ranges: δεm = 0.4% through 1.0%. The isothermal fatigue data were from total strain range (δεm = 0.35%, 0.5%, 0.68% and 1.0%) tests conducted at 621‡C (1150‡ F). The results show that in-phase TMF is the most damaging cycle for Type 316 stainless steel at the high strain range levels (δεm > 0.7%), followed by isothermal fatigue cycling at 621‡C (1150‡F) and then out-of-phase TMF cycling. The out-of-phase TMF life curve was observed to cross over the isothermal fatigue life curve at δεm ≅ 0.6%, and the trend of the data indicate that the out-of-phase TMF life curve will cross over the in-phase TMF life curve at δεm < 0.4%, and become the most damaging cycle type at the lower strain range levels.
Thermal Fatigue Behavior of a SUS304 Pipe Under Longitudinal Cyclic Movement of Axial Temperature Distribution
Authors: Yamauchi M , Ohtani T , Takahashi Y
Published: March 2009

In a structural thermal fatigue test which imposed an oscillating axial temperature distribution on a SUS 304 pipe specimen, different crack initiation lives were observed between the inner and the outer surfaces, although the values of the von-Mises equivalent strain range calculated by FEM inelastic analysis were almost the same for both surfaces. The outer surface condition was an in-phase thermal cycle and an almost uniaxial cyclic stress (low hydrostatic stress). The inner surface condition was an out-of-phase thermal cycle and an almost equibiaxial cyclic stress (high hydrostatic stress). A uniaxial thermal fatigue test was performed under the simulated conditions of the outer and inner surfaces of the pipe specimen. The in-phase uniaxial thermal fatigue test result was in good agreement with the test result of the pipe specimen for the outer surface. The out-of-phase uniaxial thermal fatigue test which simulated the inner surface condition, showed a longer life than the in-phase uniaxial test, and thus contradicted the result of the structural model test. However, the structural model test life for the inner surface agreed well with the uniaxial experimental measurement when the strain range of the inner surface was corrected by a triaxiality factor.
A Fully Associative, Nonisothermal, Nonlinear Kinematic, Unified Viscoplastic Model for Titanium Alloys
Authors: Arnold SM , Saleeb AF , Castelli MG
Published: March 2009

Specific forms for both the Gibb's and complementary dissipation potentials are chosen such that a complete (i.e., fully associative) potential based multiaxial, nonisothermal unified viscoplastic model is obtained. This model possess one tensorial internal state variable (that is, associated with dislocation substructure) and an evolutionary law that has nonlinear kinematic hardening and both thermal and strain induced recovery mechanisms. A unique aspect of the present model is the inclusion of nonlinear hardening through the use of a compliance operator, derived from the Gibb's potential, in the evolution law for the back stress. This nonlinear tensorial operator is significant in that it allows both the flow and evolutionary laws to be fully associative (and therefore easily integrated), greatly influences the multiaxial response under non-proportional loading paths, and in the case of nonisothermal histories, introduces an instantaneous thermal softening mechanism proportional to the rate of change in temperature. In addition to this nonlinear compliance operator, a new consistent, potential preserving, internal strain unloading criterion has been introduced to prevent abnormalities in the predicted stress-strain curves, which are present with nonlinear hardening formulations, during unloading and reversed loading of the external variables. The specific model proposed is characterized for a representative titanium alloy commonly used as the matrix material in SiC fiber reinforced composites, i.e., TIMETAL 21S. Verification of the proposed model is shown using ”specialized” non-standard isothermal and thermomechanical deformation tests.
Analysis of the Thermo-Mechanical Fatigue Response of Metal Matrix Composite Laminates with Interfacial Normal and Shear Failure
Authors: Robertson DD , Mall S
Published: March 2009

In this study, an analysis of the thermo-mechanical fatigue (TMF) behavior of titanium-based metal matrix composites (MMCs) is accomplished by employing a modified method of cells micromechanics model coupled with a fiber/matrix interfacial failure scheme and the Bodner-Partom unified constitutive theory. Interfacial failure is based on a probabilistic failure criterion which considers the equivalent interfacial compliance to be a function of the interfacial stress. In this approach, the effects of both normal and shear failure of the interface have been included. MMC laminates with angle-ply and quasi-isotropic layups are analyzed for monotonic, cyclic, and thermo-mechanical fatigue loads, and where it is appropriate, comparisons with experimental data are made.
The Modelling of Irradiation-Enhanced Phosphorus Segregation in Neutron Irradiated Reactor Pressure Vessel Submerged-Arc Welds
Authors: Druce SG , English CA , Foreman AJE , McElroy RJ , Vatter IA , Bolton CJ , Buswell JT , Jones RB
Published: March 2009

Recent results on neutron-irradiated RPV submerged-arc welds have revealed grain boundary segregation of phosphorus during irradiation, which may lead to intergranular fracture. However, the experimental database is insufficient to define the dependence of the process on variables such as dose, dose-rate and temperature. This paper describes work in which two existing models of phosphorus segregation, under thermal or irradiation conditions, have been developed to obtain predictions of these dependencies.

The critical parameters in the models have been adjusted to give consistency with the available reference data, and predictions have been made of the dependence of segregation on a number of variables.
Radiation Damage Studies Using Small-Angle Neutron Scattering
Authors: Albertini G , Carsughi F , Coppola R , Rustichelli F , Stefanon M
Published: March 2009

This contribution reviews a number of small-angle neutron scattering (SANS) studies of irradiated metals and steels of relevance to fission and fusion technology. Information obtainable by SANS measurements is recalled with special reference to the determination of the size distribution function of the microstructural inhomogeneities. The selected examples concern studies of the main kinds of radiation defects: voids, precipitates, He-bubbles. Some recent results obtained on structural materials for the “first-wall” of fusion reactors are also presented.