bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Powder Morphology and Sintering Atmosphere on the Structure-Property Relationships in PM Processed Co-Cr-Mo Alloys Intended for Surgical Implants
Authors: Becker BS , Bolton JD
Published: March 2009

This study analysed the possibility of producing biocompatible, porous functionally graded metallic acetabular cups using powder metallurgy techniques, where a porous surface provided a substrate for incorporating a polymeric compliant layer which was supported by a rigid inner core. Two different Co-Cr-Mo powders were investigated, a water atomised powder and a novel bimodal powder; each had a different powder morphology leading to differences in compressibility and sintering behaviour. Suitable combinations of compaction pressure and sintering temperature were used to produce porous materials containing 5–33% total porosity. Moreover, sintering was conducted in three different atmospheres; under vacuum, in flowing argon and in a flowing molecular mixture of 75%H2/ 25% N2. The resulting alloys were subjected to mechanical tests including hardness, tensile strength and ductility. Variations in pore morphology led to differences in surface chromium, bulk nitrogen and carbon content which resulted in marked differences in properties, although the lower the bulk porosity the better the properties exhibited.
The Role of the FCC-HCP Phase Transformation During the Plastic Deformation of Co-Cr-Mo-C Alloys for Biomedical Applications
Authors: Salinas-Rodríguez A
Published: March 2009

The plastic deformation behavior of solution treated Co-27Cr-5Mo cast alloys with C contents up to 0.31 wt% were studied at 298 K by means of uniaxial tension and compression tests. In addition, the effect of initial grain size on the plastic flow behavior of annealed Co-27Cr-5Mo-0.05C wrought alloy was investigated. Optical and scanning electron microscopy and X-ray diffraction techniques were used to characterize the microstructures produced by plastic deformation.

Carbon contents greater than 0.05 wt% and furnace cooling after solution treatments at 1250 °C were found to inhibit the occurrence of strain-induced fcc(metastable)=>hcp phase transformation and lead to high strain hardening rate, high strength and low ductility. A similar behavior was found in annealed, 0.05 wt% C alloy for grain sizes smaller than 10 μm. In contrast, a fast cooling rate after the solution treatment and grain sizes in the range 100–2000 μm for this later alloy were found to promote phase transformation during deformation which lead to a rapid decrease of the rate of strain hardening. The yield strength and the strain hardening behavior of both cast-solution treated and wrought-annealed materials were found to depend on the type of loading during the tests.

The results allowed to conclude that the strain-induced fcc(metastable)=>hcp phase transformation plays an important role during large strain plastic deformation of low carbon Co-27Cr-5Mo implant alloys. However, when the carbon C in these alloys is larger than 0.05 wt%, the ductility and the fracture behavior are controlled by the size, morphology and distribution of secondary phase carbide particles in the microstructure.
Comparison of Two Cobalt-Based Alloys for Use in Metal-On-Metal Hip Prostheses: Evaluation of the Wear Properties in a Simulator
Authors: St. John KR , Poggie RA , Zardiackas LD , Afflitto RM
Published: March 2009

One of the areas of research for reducing the generation of wear debris from total joint replacements is the utilization of cobalt alloys that meet ASTM F 1537 for the production of metal on metal bearing pairs. The standard currently allows carbon contents to range between 0% and 0.35%. Some research on metal-on-metal hip bearings indicates that alloys with carbon content at the upper end of this range will yield bearing pairs with superior resistance to wear. The purpose of this study was to compare the wear resistance of components manufactured from high carbon (0.24%) and low carbon (0.06%) alloys when tested in a hip simulator.

Wear of the metal cups was measured by a gravimetric (weight loss) technique every 500 000 cycles to a total of 5 000 000 cycles. Wear of the metal heads was evaluated approximately every 1 500 000 cycles, to 5 000 000 cycles. Results of the study show a small difference in wear between the two alloys. After the initial wear-in period, the samples with the higher carbon content exhibited a significantly lower wear rate than those with the lower carbon content.
Effect of Metallic Counterpart Selection on the Tribological Properties of UHMWPE
Authors: Killar JA , Freese HL , Kennedy RL , LaBerge M
Published: March 2009

This study was aimed at evaluating the effect of counterpart selection on the wear rate, and the surface and subsurface properties of ultra high molecular weight polyethylene (UHMWPE). The frictional and wear properties of an implant grade UHMWPE in contact with ASTM F 1537 cobalt-based alloy and ASTM F 138 316L stainless steel were characterized. The average contact angle measurements obtained for the 316L SS surfaces were statistically higher (C.I.=95%) than those measured for the Co-Cr-Mo alloy samples. The surface roughness of the metallic counterparts was not significantly altered during wear testing. UHMWPE sub-surface changes as well as wear rate were more pronounced with 316L SS counterparts.
Metal-On-Metal Hip Replacements: Wear Performance and Cellular Response To Wear Particles
Authors: Campbell P , McKellop H , Alim R , Mirra J , Nutt S , Dorr L , Amstutz HC
Published: March 2009

This study examined the clinical wear performance of second-generation metal-on-metal (M-M) total hips and evaluated the cellular reaction to, and characteristics of, the wear particles. Twenty cobalt chrome (CoCr) M-M THRs were studied, including ten Metasul conventional total hips (THRs), and ten McMinn surface replacements (SRs). As in the first-generation M-M hips, wear ranged from undetectable to 32 μm in the SR femoral shells (ave 15.7 ± 14 μm) and from undetectable to 19 μm in the THR balls (ave 10.1 ± 7 μm). Self-polishing of third body scratches was evident. Two THRs exhibited clusters of micropits, which had been described on first-generation M-M hips but these did not appear to correlate with accelerated wear. CoCr particles were either dense or amorphous and were mostly in the nanometer size range. There were generally fewer macrophages in the tissues than seen with M-PE THRs, and there was a more inflammatory response to bone cement particles compared with metal particles. Nevertheless, the long-term response to these very small CoCr particles should be monitored.
Serum Protein Carriers of Chromium in Patients with Cobalt-Base Alloy Total Joint Replacement Components
Authors: Hallab NJ , Jacobs JJ , Skipor A , Black J , Mikecz K , Galante JO
Published: March 2009

The distribution of chromium (Cr) in fractionated serum was studied from peripheral blood of patients with and without Cr-containing Cobalt-base alloy total joint replacements: 1)10 patients with cobalt-chromium-base alloy prostheses; and 2) 10 age-matched controls without implants. Two molecular weight ranges were found to primarily bind Cr (at ≈70 kD and ≈140–180 kD) in patients with Cobalt-base alloy total joint replacements. This pattern of concentration-dependent metal-protein binding within molecular weight ranges that include immunoglobulins warrants further investigation.
Commissioning Major Pharmaceutical Manufacturing Facilities
Authors: Fay ST , Howard TP , Stevens WT
Published: March 2009

Commissioning is the planning, coordination, management, and execution of activities that form the bridge between the construction phase and the operation and maintenance phase of a facility life-cycle. Commissioning helps demonstrate the facility works properly and establishes systems for reliable operations and maintenance. Validation is a major part of the overall commissioning process. Substantial savings are possible in terms of costs and schedule through more effective coordination of commissioning activities. Benefits of a coordinated approach include: • Increased confidence that facility meets intended requirements (e.g., GMP, safety, environment, production capacity,) • Eliminating waste through duplication • Providing for consistent and efficient commissioning • Quicker achievement of successful initial operations
Standards and Practices for Computer Validation and System Definition
Authors: Stotz RW , Bluhm AR
Published: March 2009

In the validation of automated systems for the pharmaceutical and health care industries, assurance of compliance with applicable regulations is accomplished through a well designed validation program. The program must be designed to provide documented evidence that automated systems (hardware and software) have done, are doing, and/or will do, reliably, what they are supposed to do--the key word in this statement being “documented.” The documentation requirements for automated, particularly “paperless” systems, can be a formidable obstacle to validation; however, if a modular, or life-cycle, approach (qualification of the component parts followed by qualification of the integrated system) is used the task becomes manageable. One approach we have found in our experience to successfully generate, evaluate, and manage the documentation required for validation of automated systems is the use of a Quality Plan. This approach has also proved invaluable in defining the system, the first step in any life-cycle approach to validation of an automated system. The following discussion outlines the Quality Plan approach to validation of computer systems, and focuses on system definition because of its importance as the basis for both the design and testing of these systems and associated software. Although the discussion addresses systems used primarily in the pharmaceutical and health care industries, the Quality Plan concept is applicable to any system that must function reliably and with documented performance.
Validation Studies in the Regeneration of Ion-Exchange Celluloses
Authors: Levison PR , Streater M , Jones RMH , Pathirana ND
Published: March 2009

A clean-in-place procedure involving storage in 0.5M-NaOH for several hours has been found effective in the regeneration of process-scale columns (25 1) of Express-Ion ion-exchange celluloses following preparative loadings (2–9 kg) of a hen egg-white protein feedstock. These conditions have been demonstrated to provide simultaneous sanitization of the media following a gross microbial challenge, as indicated by decreased bioburden and endotoxin levels. We have developed an ion chromatography procedure for detecting and quantitating potential hydrolysis products originating from the functional groups bonded to anion and cation-exchange media. Using these techniques we demonstrate no detectable leakage of functional groups from the ion-exchange celluloses during the bed regeneration process. There was no significant loss of glucose from the matrix during this procedure.
Developing Procedures to Meet GMP Requirements
Authors: Malooley MJ
Published: March 2009

A comprehensive set of documented quality procedures is required by the Food and Drug Administration's Good Manufacturing Practices. In order to successfully develop a comprehensive set of procedures, the motivation must be to maintain quality and reduce variability. Quality system procedures should follow a logical structure. One such structure consists of tiered Quality Policies, Administrative Support Procedures, and Technical Procedures. Each procedure should be traceable to a requirement established in the Quality Policy Manual. Once an effective set of procedures is in place it must be actively managed. Procedure management includes mechanisms for keeping the documents current, ensuring accessibility to the procedure users, and training on the use of the procedures.
Process Development, Scale-Up and Validation of a Recombinant E. Coli-Based Fermentation Process
Authors: Sniff KS , Garcia LA , Hassler RA , Seely RJ , Young MD
Published: March 2009

The goal of validation of a fermentation process is to provide documented evidence that the production process performs as intended. The product from a validated fermentation process should have pre-determined characteristics which indicate the process is performing consistently. Changes in the fermentation process for production of recombinant human interleukin-1 receptor antagonist while in clinical trials included growth medium and extended time after induction. The goals of the development and scale-up activities were to develop a reproducible, scalable process yielding high quality material and to introduce the new process to the manufacturing facility in a timely fashion. In the course of development and scale-up, further modifications were required to maintain reproducibility and product quality. The start-up batches from both the pilot-scale and the production facility provided the data sets for validating the process, establishing the limits for operating variables and the control limits for performance parameters.
Staying in Control — Ongoing Calibration and Change Control Practices
Authors: Busfield JT
Published: March 2009

All regulated drug companies-pharmaceutical, medical device, and biopharmaceutical-dedicate considerable resources to the validation effort involved in starting a new facility or process. This effort is aimed at insuring that the process is under control. However, this state of control would be short-lived if not actively and rigorously maintained. Two programs essential to maintaining a process in a state of control are the Calibration and Change Control programs. A Calibration Program involves controlling the accuracy of the instruments that control the process. If the calibration of this equipment is not controlled, the process cannot be in control. A Change Control Program is the insurance that the effort spent in initially validating equipment and processes is not voided by an ill-conceived change to the equipment or process. The program provides that any change must be reviewed by appropriate personnel, its impact evaluated, the requirement to revalidate and/or the extent of revalidation examined, and the documentation of the changes maintained.
Fracture Analysis in the Ductile/Brittle Regime: A Predictive Tool Using Cell Models
Authors: Shih CF
Published: March 2009

The 29th Symposium Swedlow Lecture described the current state of the art of predicitve fracture mechanics tools. Both two-parameter and mechanism-based approaches were reviewed, with emphasis placed on the development of computational cell models. Within their respective regimes of applicability, both approaches are shown to correctly correlate constraint effects on fracture toughness levels.
Applicability of Sub-Charpy-Size Bend and Impact Specimens for Estimation of Fracture Toughness in the Transition Region
Authors: Planman T , Nevalainen M , Valo M , Wallin K
Published: March 2009

As part of a test program to introduce small specimen test techniques, fracture toughness tests have been performed with 20% side-grooved small (10∙10∙55 mm) and “ultra-small” (3∙4∙27, 5∙5∙27 and 5∙10∙55 mm) specimens. The objectives were to evaluate the measuring capacity of small specimens and to verify the applicability of the statistical cleavage fracture model of VTT for such test data. Two pressure vessel steels were used in the study. Most of the tests were performed in the transition range and ended at cleavage fracture, but some tests were also conducted in the temperature range of ductile tearing. According to the measured data, the 100 MPa√m reference temperatures (T0), determined even with 3∙4 mm specimens, are in good agreement with those of the larger specimens. The statistical specimen size correction only was applied in the analyses, i.e., without any consideration of specimen constraint. The measurements made in the ductile range indicate that practically similar fracture resistance curves can be obtained with the 5∙10 mm and larger specimens up to the J-level of 500 kN/m. Also, correlations have been developed, by applying a fracture mechanics approach, for estimating the Charpy transition temperatures of ferritic structural steels from small specimen test data. The correlations were verified by analyzing test data produced with Charpy (ISO-V) and KLST-type subsize specimens (3∙4∙27 mm). Two energy criterion combinations were applied for determining transition temperatures, i.e., the criteria based on the area of the specimen ligament, being in accordance with the master curve definition, and those derived from an empirical mean relationship found between the upper-shelf energies measured with ISO-V and KLST specimens for various steels. The results show that both of these criteria can be used to give a satisfactory correlation between the transition temperatures and that the standard deviations of the correlations are approximately equal, i.e., around 15°C. A method is proposed for estimating the Charpy upper-shelf energy from subsize specimen data.
Fracture Behavior of Surface Crack Tension Specimens in the Ductile-Brittle Transition Region
Authors: Joyce JA , Link RE
Published: March 2009

Surface cracked tension specimens of ASTM A533, Grade B steel plate were tested to failure in the ductile-to-brittle transition region. Two different specimen configurations were used: one configuration was loaded in tension except for the natural bending resulting from the presence of the surface crack, the second configuration had an offset test section and was pin-loaded to provide a strong bending component in addition to the tension load. For each configuration, at least seven repeat tests were conducted at each of two temperatures. All specimens failed by cleavage and the critical J-integral, Jc, was obtained using three-dimensional finite element analysis of the specimen. The FEM analysis was validated by comparison with experimental strain gage and displacement measurements taken during the tests. The results were compared with previous fracture toughness measurements on the same plate using 1.6T and 1T SE(B) specimens, 1T SC(T) specimens, 1T edge cracked SE(T) specimens, and precracked Charpy specimens. The present results exhibited the expected elevation in fracture toughness and downward shift in the transition temperature compared to the highly constrained, deeply cracked SE(B) specimens. The master curve approach was used to characterize the transition curves for each specimen geometry and the shift in the transition temperature was characterized by the associated reference temperature. The master curves from the pre-cracked Charpy specimen sets tested here do not accurately predict the full constraint master curve and are non-conservative even in comparison with the tension loaded surface crack specimens and short cracked SE(B) specimens.
Analyses of Buckling and Stable Tearing in Thin-Sheet Materials
Authors: Seshadri BR , Newman JC
Published: March 2009

The purpose of this paper was to verify the capability of the STAGS (general shell, geometric and material nonlinear) code and the critical crack-tip-opening angle (CTOA) fracture criterion to predict stable tearing in cracked panels that fail with severe out-of-plane buckling. Materials considered in the analyses ranged from brittle to ductile behavior. Experimental test data used in this study are reported elsewhere. The STAGS code was used to model stable tearing using a critical CTOA value that was determined from a cracked panel that was “restrained” from buckling. The STAGS code and the critical CTOA were then used to predict the influence of buckling on stable tearing and failure loads. Parameters like crack-length-to-specimen-width ratio, crack configuration, thickness, and material tensile properties had a significant influence on the buckling behavior of cracked thin-sheet materials. Experimental and predicted results showed a varied buckling response for different crack-length-to-sheet-thickness ratios because different buckling modes were activated. The effects of material tensile properties and fracture toughness on buckling response were presented and discussed. The STAGS code and the CTOA fracture criterion were able to predict the influence of buckling on stable tearing behavior and failure loads on a variety of materials and crack configurations.
Effect of Residual Stress on Brittle Fracture Testing
Authors: Hill MR , Panontin TL
Published: March 2009

Residual stress present in coupons used for fracture testing will influence the experimental determination of fracture toughness. Triaxial residual stress (e.g., due to welding) can alter both the driving force for fracture and the crack-tip constraint at a specified load, so that the apparent toughness of a coupon depends on the residual stress present. In this paper, we employ a micromechanical failure theory (the RKR model) to predict brittle fracture loads for three-point bend samples with and without triaxial residual stress. Finite element modeling is used in the study to introduce an idealized welding residual stress field, to simulate the crushing of the coupon by circular platens (referred to as homogenization or local compression), and to simulate three-point bend testing. Results show that the residual stress markedly changes load at fracture, which would be used to compute apparent fracture toughness. Furthermore, the method of superposition commonly used is not able to accurately predict this effect.
Fully Plastic J-Integrals for Through-Wall Axial Cracks in Pipes
Authors: Harris DO , Woytowitz PJ
Published: March 2009

The purpose of this paper is to present results for fully plastic J-integrals for through-wall axial cracks in pressurized pipes. Results are presented for power law hardening material for crack lengths ranging from zero to semi-infinite. The small crack results are based on previously available information for through cracks in infinite sheets. The semi-infinite results are obtained in closed form and are based on the differences in stored strain energy of an uncracked pipe and a pipe with a slit running its full length. Finite element computations are used to provide results for two intermediate crack lengths, which then allowed the interpolation between the small and semi-infinite results. The finite element calculations used three-dimensional elements with a singular element that appropriately modeled the crack tip. The results should be of use in the analysis of critical crack length in pipes pressurized to levels where plasticity should be considered, and in the analysis of creep/fatigue crack growth in high-temperature piping.
Elastoplastic Crack Growth in Pressure-Sensitive Materials
Authors: Shah KR
Published: March 2009

Analytical elastoplastic stress and deformation fields around a plane-strain crack tip for pressure-sensitive, dilatant materials such as rock, concrete, and ceramics are derived. Classical Prandtl field with an assembly of constant-stress and centered-fan sectors is valid for a stationary crack in a material following the Mohr-Coulomb yield condition. The dependence of the size of plastic zone and the crack-tip opening displacement on far-field loading through J-integral is evaluated and the role of internal friction angle (ϕ) for the pressure-dependent material is identified. An unloading elastic sector was found to be needed in the trailing zone of the crack-tip for growing conditions. The extent of this sector increases with the friction angle and is more than 90 degrees for ϕ = 30°. If near-tip crack opening displacement field can be assumed to be invariant during the crack propagation history, then the complete fracture resistance curve can be estimated. The J-resistance increases and approaches a steady state value similar to the experimental observations for concrete and different rocks. The validity of the analysis is performed by fitting the analytical resistance curve with the experimental data. The elastoplastic fields assume the crack faces to be traction-free and would be different for pressurized cracks such as fluid-driven fractures. The dependence of the fields and resistance curve on the crack pressure is also evaluated.
The Use of Local Approach to Fracture in Reactor Pressure Vessel Structural Integrity Assessment: Synthesis of a Cooperative Research Program Between EDF, CEA, Framatome and AEA Technology
Authors: Moinereau D , Frund JM , Brochar J , Valeta MP , Marini B , Joly P , Guichard D , Bhandari S , Sherry A , France C , Sanderson DJ
Published: March 2009

A cooperative research program on the field of the local approach to cleavage fracture applied to reactor pressure vessels is conducted between Electricité de France, CEA, Framatome and AEA Technology. The purpose of this program is to have a better knowledge of this kind of approach for reactor pressure vessels fracture mechanics integrity assessments regarding the risk of brittle fracture. This program includes both an experimental part on the A508 C13 steel and numerous 2D and 3D numerical computations.

The identification of m and σu parameters of Beremin model (local approach to cleavage fracture) is studied on the A508 C13 steel using mechanical tests on axisymmetrical notched tensile specimens AE2. The tests are performed at several temperatures (-100 °C, -130 °C and -170 °C) by three laboratories (EDF, CEA and AEA Technology). There are 120 specimens tested in total. The experimental results from different laboratories are compared and analyzed, the effect of temperature on m and σu parameters of Beremin model is discussed and a standard procedure to identify these parameters is proposed.

Within the framework of this program, numerous two-dimensional numerical calculations using the Beremin model have been performed by different partners on several cracked specimens (CT specimen, cladded vessels with flaws in cladding or in base metal under thermal loading…). Some comparisons between finite element programs (Aster, Castem 2000, Systus and Abaqus) are made on reference specimens in order to evaluate and validate finite element programs in the field of local approach to cleavage fracture. These comparisons show a rather good agreement on main parameters, notably on Weibull stress σw calculation for mechanical or thermal loading.

The “shallow flaw effect” is examined from these computations. The effect of the “a/W” ratio on the probability of cleavage failure is clearly underlined with the Beremin model using the “Weibull stress σw versus Stress intensity factor KJ” curves. Significant differences between cracked specimens are observed, related to the “a/W” ratio : for a given level of the stress intensity factor KJ, the probability of cleavage failure increases with increasing values of flaw depth. These results show that the Beremin model is able to predict an influence of crack tip constraint on fracture toughness.

Finally, first three-dimensional applications of the Beremin model are presented regarding the interpretation of large-scale tests performed on cladded specimens containing subclad flaws.
Evaluation of Fracture Toughness Results and Transferability to Fracture Assessment of Welded Joints
Authors: Minami F , Toyoda M
Published: March 2009

Fracture mechanics test results for welded joints are affected by the mechanical and metallurgical inhomogeneity in welds. The size of embrittled region encountered by the notch tip and the strength mismatch between the base and weld metals are major factors controlling the fracture resistance of welds. Larger sampling of embrittled region leads to lower fracture toughness of welds. Strength over-matching of the weld metal decreases the HAZ toughness, because the local stress in the HAZ is elevated by the constraint effect of the weld metal. This paper develops the procedure for fracture strength evaluation of welded joints based on the Local Approach. A key idea is the use of the Weibull stress, consisting of stress components in a specific region governing fracture initiation in welds. The concern of this paper is the transferability of toughness results to fracture performance evaluation of welded joints. It is demonstrated that the fracture performance of welded joints can be predicted successfully from 3-point bend test results using the Weibull stress concept. A new procedure for the derivation of fracture toughness requirements has been proposed. It is characterized by the equivalent CTOD, which provides a comparable Weibull stress of both toughness specimen and structural component. The equivalent CTOD concept enables the quantification of fracture toughness requirements to meet design solutions for welded components with mismatched welds.
Micromechanical Prediction of Fracture Toughness for Pressure Vessel Steel Using a Coupled Model
Authors: Goldthorpe MR , Wiesner CS
Published: March 2009

A method of analyzing the ductile to brittle transition region of a ferritic steel using a coupled micromechanical model of ductile damage, stable crack growth and cleavage fracture has been developed to improve the definition of upper shelf behavior for actual structures. Ductile damage is modelled using the Gurson model as modified by Tvergaard, along with a specially developed crack growth user element. The probability of cleavage fracture is predicted by post-processing the finite element results using the Beremin model of cleavage fracture. Predictions are made of ductile tearing and cleavage fracture in test specimen and wide plate configurations of A533B steel for a range of temperatures. The coupled model is capable of predicting transition toughness and transition temperature shifts for different levels of structural constraint. An analytically-based definition of the onset of upper shelf temperature (OUST) is the temperature at which the coupled ductile damage/cleavage fracture model predicts a probability of failure by cleavage fracture of 5%. Estimates of the shift in the OUST due to different levels of in-plane crack tip constraint are made using the elastic T-stress as a measure of constraint. There is potential for using the T-stress as a measure of structural constraint in order to determine shifts in transition temperature for materials with degraded toughness.
A Theoretical and Experimental Investigation of the Influence of Crack Tip Plasticity on Fatigue Crack Closure
Authors: Nowell D , Fellows LJ , Hills DA
Published: March 2009

A correlation is assumed to exist between the true crack tip stress intensity factor range existing at the crack tip, and the instantaneous crack growth increment. In order to find the true crack tip stress intensity range crack closure induced by local plasticity is modelled using a simplified model in which the yielding is confined to a line, and boundary elements, together with a quadratic programming procedure, are used to determine both the extent of plasticity and crack closure effects. A means of determining crack growth rate is then developed, which may use data obtained experimentally at a different R-ratio from that in the prototype. Confirmation of the general correctness of the hypothesis is obtained by conducting 4-point bend fatigue tests with varying degrees of load reversal, and moiré interferometric measurements of the crack tip displacement field. This enables correlations to be made between the measured values of the crack tip closure conditions and the values predicted by the model. Good agreement is found. The approach may be directly extended to cases where there are occasional under or overloads, or a complex loading regime is applied.
Prediction of Plasticity-Induced Closure in Surface Flaws Using a Modified Strip-Yield Model
Authors: Daniewicz SR
Published: March 2009

A slice synthesis methodology is developed and used to construct a modified strip-yield model for the semi-elliptical surface flaw, enabling prediction of plasticity-induced closure along the crack front and subsequent fatigue crack growth. A mathematical description of the model is presented. Slice synthesis methodologies have previously been limited to stress intensity factor and elastic crack displacement computation. Predictions of flaw shape evolution under cyclic loading are compared with experimental data for aluminum specimens under uniform constant amplitude loading. Model predictions are shown to correlate well with experimental data.
A Fatigue Crack Growth Theory Based on Energy Considerations: Further Developments on Small Crack Behavior and R Ratio Effect
Authors: Milella PP
Published: March 2009

The paper presents a further development of a fatigue crack growth theory based on an energy approach first published by the author in 1981 [1] and later revised in 1996 [2]. In an ideally elastic material containing a crack the only mechanism through which energy can be absorbed during a virtual crack extension is that associated to the creation of new free surface. It is an “in-out” situation in that a crack of a given length 2a under a stress state σ either becomes unstable or stays like it is. At variance, in a real elastic-plastic material the energy absorption rate R derives mainly from the energy stored ahead of the crack tip as plastic strain energy. The resistance R is no longer represented by a constant term, but becomes a rather complex function of crack length, increasing as the crack grows. The consequence is that even though a certain combination of crack size 2a and stress σ does not produce instability, yet there is sufficient energy in the system to drive the crack to a point where the driving force b is equal to the resistance R and the crack stops. Unloading the system and reloading it, the crack grows by fatigue indicating that the previous condition b = R is no longer satisfied. If this happens, it is because the volume that yields ahead of the crack tip is not capable during the reloading to absorb energy with the same rate as before. This forces the crack to grow further to regain the loss of energy absorption rate through the yielding of new material and to establish again the equilibrium between b and R. The author has related this lack of material capability to develop the same energy absorption rate in any of the following cycles to a shake-down effect that takes place in the plastic enclave. In each cycle, the loss of energy absorption rate is a fraction of the elastic one. The author has related this lack of material capability to develop the same energy absorption rate in any of the following cycles to a shake down effect that takes place in the plastic enclave. In each cycle, the loss of energy absorption rate is a fraction of the elastic one. Based on this hypothesis and on the assumption that the maximum fatigue crack growth can be inferred from the extension of the stretch-zone developed at the crack tip at the moment when the material starts to tear in a monotonic loading test, i.e., at JIc, a fatigue crack growth equation is obtained that relates the growth rate Δa not only to the stress intensity factor excursion ΔK, but also to the toughness KIc of the material, through an exponent n, ranging from 2 to 4, which depends on the shape of the material J-R curve. The theory and the equation also explain why short cracks shall grow faster than large ones and actually define what shall be considered as a real short crack. It is also explained why the fatigue crack growth rate depends on the ratio between the minimum and maximum applied stress and is practically the same in any material independently of its yield stress and toughness.
On the Crack-Tip Blunting Model for Fatigue Crack Propagation in Ductile Materials
Authors: Gu I , Ritchie RO
Published: March 2009

The conventional geometric crack-tip blunting model for fatigue crack growth based on the crack-tip opening displacement (CTOD) is examined numerically with the objective of modeling crack advance solely in terms of the effect of local plastic deformation, without introducing any specific failure criterion or presumed slip behavior. In the absence of an analytical solution for cyclic plastic deformation at the crack tip, computational solutions are used to check the validity of the description of fatigue crack growth rates as a nonlinear function of a linear stress intensity factor, K. A finite element analysis is performed in plane strain for a crack tip, blunted from an initial tip radius of submicron to micron size; the crack is considered for a wide range of lengths and is subjected to zero-to-tension cycling with both tension and bending loads. The calculated results are compared with experimental fatigue crack growth data on aluminum alloy 7075-T6, where it is found that with the tip radius of 0.5 μm, results are in reasonable agreement with experiment. By examining the crack-tip plastic deformation for the first and subsequent cycles, crack extension is seen to result from the dissimilarity in the loading and unloading deformation. Reverse yielding brings about a crack tip “shrink”, with a full recovery of cyclic CTOD and a partial recovery of crack advance. In the limit of a sharp crack, this model predicts that the maximum growth rate per cycle will be 0.35 of the cyclic CTOD. Such aspects are deemed critical in the future development of analytical solutions to this problem.
An Energy Based Critical Plane Approach to Multiaxial Fatigue Analysis
Authors: Rolović R , Tipton SM
Published: March 2009

A multiaxial fatigue damage criterion has been formulated based on observations that fatigue crack development is governed by stresses and strains acting on critical planes in materials. The damage parameter incorporates both Mode I and Mode II loading. Failure is defined as the development of an engineering size crack (approximately 1 mm in surface length). The proposed method can be applied to both proportional and nonproportional multiaxial loading as well as to uniaxial loading. Predictions based on the proposed method were compared to uniaxial and multiaxial in-phase and out-of-phase test data for three materials. The approach demonstrated improved life predictions relative to other methodologies.
Ultrasonic Pulse Transmit-Receiver Method for Detecting and Monitoring of Fatigue Damage
Authors: Mostafa I , Hailu S , Welsch GE , Hazony D , Halford GR
Published: March 2009

A dedicated ultrasound transmission method is used for in-situ detection and monitoring of fatigue cracks. For this purpose, piezoelectric transducers are embedded at the ends of hourglass-shaped specimens of HSLA steel. One transducer emits constant-amplitude time-limited pulses which travel as longitudinal and surface waves. The waves are received by the other transducer and their times-of-flight and amplitudes are readily monitored by a digitizing oscilloscope. During constant amplitude fatigue cycling at constant R, a decrease in surface wave amplitude indicates crack initiation while crack propagation is sensed by the change in the amplitude of both waves. During initial fatigue cycles, the transmitted wave amplitudes may decrease due to cyclic plastic strain and the accumulation of dislocations. In subsequent cycles, the lattice defects reach a saturation level giving rise to a steady state level of the transmitted wave amplitudes. Wave amplitudes monitored during saturation stage serve as a reference for subsequent measurements of amplitude decrease that indicates the growth of a fatigue crack. Changing the applied load in the early stage of fatigue cycling has a little effect on the saturation level. Such an effect diminishes with fatigue cycling and does not interfere with the ability of detecting crack initiation. The method is capable of monitoring the entire history of fatigue damage evolution from initial strain hardening, through strain saturation, crack nucleation, crack growth to failure.
Sustained Fatigue Crack Growth Oblique to an Applied Load Using Geometric Constraint
Authors: Magill MA , Zwerneman FJ
Published: March 2009

This paper presents the results of a research project on fatigue crack growth driven by sustained mode I and II loading. This project involved developing and analyzing a flat plate specimen capable of sustaining crack growth on a plane oblique to the direction of the applied load. Several of these specimens were built and fatigue loaded in the laboratory. Using geometric constraint, the crack was forced to grow in a direction other than perpendicular to the load. The resulting crack front stabilized into a curved or warped shape rather than straight and flat. Based on finite element analyses of these curved specimen cracks, it is concluded that the stress intensity factors (SIFs) were predominantly mode I, with the mode II and III SIFs being negligible. It was also determined that the oblique cracks grew perpendicular to the maximum principal stress.
Structural Loading and Fatigue Failure Analysis of Off-Road Bicycle Components
Authors: DeLorenzo DS , Hull ML
Published: March 2009

The research described herein accomplished the goals of off-road bicycle load quantification and fatigue life prediction. A fully-instrumented test bicycle was equipped with dynamometers at the pedals, handlebars, and hubs to measure all in-plane structural loads acting through points of contact between the bicycle and both the rider and the ground. A portable data acquisition system carried by the standing rider allowed, for the first time, this loading information to be collected during extended off-road testing. In all, seven experienced riders rode a downhill trail test section with the test bicycle in both front-suspension and full-suspension configurations.

The load histories were used to quantitatively describe the load components through the computation of means, standard deviations, amplitude probability density functions, and power spectral density functions. For the standing position, the coefficients of determination for the load components normal to the ground were greater than 1.35 for handlebar forces and 0.3 and 0.5-0.6 for the pedal and hub forces respectively. Thus the relative contribution of the dynamic loading was much greater than the static loading at the handlebars but less so at the pedals and hubs. As indicated by the rainflow count, high amplitude loading was developed approaching 3 and 5 times the weight of the test subjects at the front and rear wheels respectively. The power spectral densities showed that energy was concentrated in the band 0–50 Hz.

To illustrate the usefulness of the loading data, the load history at the pedal was used to determine the corresponding stresses at the pedal spindle hot-spot location. To predict the fatigue life, the resulting stress cycles were processed by use of a rainflow counting algorithm. Cumulative damage was quantified through Miner's linear damage rule used in conjunction with the nominal S-N method. The stress cycles were also used to develop a fatigue testing protocol for verifying analytical predictions of fatigue life.
Microstructure Evolution and Thermomechanical Fatigue Life of Solder Joints
Authors: Goldstein B , Jerina KL , Sastry SML
Published: March 2009

The thermomechanical fatigue properties of Sn-Pb eutectic based solders in a single lap shear configuration were investigated. The development of fatigue cracks through heterogeneously coarsened, Sn enriched, bands near the solder-intermetallic interface were observed in eutectic and solid solution strengthened alloys. Other authors had not previously reported the Sn enrichment of coarsened bands in eutectic solders. However, analysis of micrographs found in published literature found evidence of the development of Sn enriched regions in Sn-Pb eutectic solders with initially globular microstructures. Solder microstructures, which were initially lamellar eutectic, displayed no evidence of Sn enrichment in the coarsened bands. Dispersion strengthening was effective in inhibiting heterogeneous coarsening, and resulted in solders with the greatest themomechanical fatigue lifetimes.
Fatigue Life Predicition of Resistance Spot Welds Under Variable Amplitude Loads
Authors: Pan N , Sheppard SD , Widmann JM
Published: March 2009

The work presented here builds on the practical and effective spot weld fatigue life prediction method, the structural stress method (SSM), that was developed recently [1]. Constant amplitude loading tests for various spot weld joint configurations have been conducted and the SSM has been shown to accurately predict fatigue life [1].

In this paper, a variable amplitude fatigue life prediction method based on the SSM and Palmgren-Miner's rule is proposed. A test matrix was designed to study the fatigue behavior of spot welds under tensile shear loading conditions. Constant amplitude tests under various R-ratios were first performed to obtain necessary material constants. Variable amplitude tests were then performed. Experimental and finite element data are presented. The ability of the SSM to include load ratio effects and predict life for variable amplitude tests is illustrated.
Hydrogen Cracking During Service of High Strength Steel Cannon Components
Authors: Underwood JH , Troiano E , Vigilante GN , Kapusta AA , Tauscher S
Published: March 2009

An investigation of environmental cracking during service of high strength steel cannon components is described. Two cases of cracking occurred in similar prototypes of an advanced cannon over a two year period. The materials, component configurations, applied and residual stresses, environmental conditions, and the resulting cracking behaviors and SEM fracture surface characteristics are outlined. Laboratory hydrogen cracking tests of the cannon materials, finite element stress analysis, and stress intensity factor calculations were used to model the hydrogen cracking. The first cracking incident involved cracks up to 21 mm long near a pressure seal in a 1160 MPa yield strength ASTM A723 forged steel cannon tube, following five firing cycles. The second incident involved 50 mm long cracks that after thirty firing cycles had grown near the seal between two adjoining cannon components, one made from A723 and one from 1280 MPa yield strength PH 13-8 Mo stainless steel. The cause of cracking, given the presence of hydrogen laden propellant products and susceptible high strength steels, was the sustained tensile stresses arising from assembly preloads required to maintain pressure seals between cannon components. Recommended preventative measures include reducing the strength level of the existing martensitic steels, changing to austenitic nickel-iron base alloys, and redesign to lower the level of sustained tensile stress concentrations in areas subjected to propellant environments.
Outflow Methods for Evaluating the Soil Hydraulic Functional Relationships Between NAPL Pressure and Saturation in Porous Media
Authors: Bali KM , Grismer ME , Hopmans JW
Published: March 2009

Remediation and cleanup of petroleum product contaminated ground water often require modeling of fluid transport processes when immiscible liquid phases (e.g., water and oil) are present. Modeling of such multiphase transport systems requires knowledge of the functional relationships between fluid pressures, saturations, and permeabilities. We evaluated the applicability of the multistep outflow method used in soil science to determine these functions for two porous media (loam and sand) using Soltrol 130 and water as wetting fluids.

The analytical retention and permeability functions of van Genuchten (1980) and Mualem (1976) were used, with an inverse method that has been shown to be reliable in estimating water retention and unsaturated hydraulic conductivity in soils (Eching and Hopmans 1993), to estimate soil hydraulic function parameters for Soltrol 130 and water. The water and Soltrol 130 cumulative drainage as a function of time and the equilibrium saturations were used as input to a numerical model (MLSTPM) to optimize, through an inverse solution of the Richards equation, the parameters needed for the hydraulic functions.

Optimizations were carried out for saturation paths corresponding to monotonically decreasing wetting phase saturations only. The functional relationships between oil pressures, saturations, and permeabilities in Oso-Flaco fine sand were accurately predicted from the optimized water retention curve parameters based on scaling by the ratio of interfacial tensions. However, this scaling procedure was inadequate to predict oil hydraulic function parameters from those of water in Yolo loam.