bluuebunny/crossref_metadata_2025 huggingface dataset:
Case reports on the use of antimicrobial (silver impregnated) soft silicone foam dressing on infected diabetic foot ulcers
Authors: Tong Jasper WK
Published: August 2009

This article described four patients who had an episode of an infected foot ulcer, and subsequently treated with a novel antimicrobial soft silicone foam dressing together with standard off‐loading and antibiotic therapy. Qualitative description of the ulcer‐healing process was documented. All four ulcers showed positive wound contraction and reduction in size throughout the follow‐up period ranging from 3 to 16 weeks. In addition, clinical signs of infection were absent at the end of the follow‐up period. Moreover, surrounding skin maceration and trauma were absent in all wounds. Adequate moisture control was also achieved with the evidence of a healthy red granulating base, and a thin layer of clear light exudate in three out of the four cases. However, these reports had very little evidence to show the dressing's effectiveness in combating wound infection, but there might be some possible clinical efficacies of the dressing to control infection. Appropriate antibiotic therapy and off‐loading are still essential components when treating diabetic foot infection.
LOVely enzymes – towards engineering light‐controllable biocatalysts
Authors: Krauss Ulrich , Lee Jeeyeon , Benkovic Stephen J. , Jaeger Karl‐Erich
Published: August 2009

Light control over enzyme function represents a novel and exciting field of biocatalysis research. Blue‐light photoreceptors of the Light, Oxygen, Voltage (LOV) family have recently been investigated for their applicability as photoactive switches. We discuss here the primary photochemical events leading to light activation of LOV domains as well as the proposed signal propagation mechanism to the respective effector domain. Furthermore, we describe the construction of LOV fusions to different effector domains, namely a dihydrofolate reductase from Escherichia coli and a lipase from Bacillus subtilis. Both fusion partners retained functionality, and alteration of enzyme activity by light was also demonstrated. Hence, it appears that fusion of LOV photoreceptors to functional enzyme target sites via appropriate linker structures may represent a straightforward strategy to design light controllable biocatalysts.
Caries experience in individuals with cerebral palsy in relation to oromotor dysfunction and dietary consistency
Authors: Santos Maria Teresa Botti Rodrigues , Guare Renata Oliveira , Celiberti Paula , Siqueira Walter Luiz
Published: August 2009

The aim of this study was to investigate caries experience in individuals with cerebral palsy (CP) who have oromotor dysfunction and relate it to age and dietary consistency. Noninstitutionalized individuals with CP (n = 108) aged 4–19 years (mean: 10 years, 1 month ± SD 4 years, 5 months) were recruited for this study. Subjects who were severely impaired (35.2%) had orofacial motor dysfunction most frequently, followed by those who were slightly affected (27.7%), moderately affected (20.4%), and very slightly affected (16.7%). Age was a statistically significant factor for oromotor dysfunction (p= 0.007), with the youngest individuals having the most severe oromotor problems. Dietary consistency and oromotor function were statistically significant influence on the DMF index (p= 0.0352). The highest total DMF values were measured for individuals who were severely impaired and also the youngest, as well as for those receiving liquid diets. Early rehabilitation, intervention, and prevention are important for these individuals.
Eye shape and peripheral visual field recording in high myopia at approximately 54 years of age, as based on ultrasonography and Goldmann kinetic perimetry
Authors: Fledelius Hans C. , Goldschmidt Ernst
Published: August 2009

Purpose:  This study describes the posterior pole contour and visual field (VF) findings in an unselected series of adults (aged approximately 54 years) with high myopia.

Methods:  In 1962, 39 14‐year‐old teenagers with myopia of ≥ 6 D, in one or both eyes, were identified in a 1948 Copenhagen birth cohort (n = 9243). At a follow‐up in 2002, 61 eyes (52 with high myopia and nine fellow eyes; n = 31 subjects) were examined by ultrasound B‐scan, to allow: (a) measurement of the axial vitreous length supplementary to the customary axial A‐scan, and (b) assessment of the posterior pole contour of the eye. Further, the large‐object (V, 4e) kinetic Goldmann perimetry isoptre was recorded to outline the ambulatory VF.

Results:  An irregular posterior pole contour was observed in 15 eyes, unilaterally in 11 eyes and bilaterally in four (two subjects). Nasal fundus ectasia was suggested in six and other deviations from the sphere in seven subjects. Kinetic Goldmann perimetry showed marginal restriction in 14 eyes (12 subjects). Larger defects were found in four eyes (three subjects); the corresponding axial lengths exceeded 32 mm in the two subjects with unilateral defects, and symmetrical inferior binasal defects, probably unrelated to the myopia, were found in the bilateral subject.

Conclusions:  Unselected adult‐age high myopia mainly presented with a regular eye shape that was close to spherical. An irregular shape suggesting posterior staphyloma was seen in 13 of the 32 subjects under study, mainly unilaterally. No subjects were restricted in everyday activities by VF defects. Marginal Goldmann perimetry restrictions were described in 12 and significant defects in three subjects. Generally, longer eyes more often tended to show irregular posterior eye contours and/or VF defects.
Oxidative DNA damage in patients with cataract
Authors: Ates Orhan , Alp Hakan Hamit , Kocer Ibrahim , Baykal Orhan , Salman İlknur A.
Published: August 2009

Acta Ophthalmol. 2010: 88: 891–895

Purpose:  This study examines the levels of oxidative damage in patients with cataract.

Methods:  Blood samples were collected from 60 patients with cataract and 60 age‐ and gender‐matched healthy individuals to measure 8‐hydroxy 2‐deoxyguanosine (8‐OHdG) and malondialdehyde (MDA) levels.

Results:  A significant difference was observed in leukocyte 8‐OHdG levels in patients with cataract in comparison with healthy persons (p < 0.001). Similarly, a significant difference was observed in plasma MDA levels in patients with cataract in comparison with healthy persons (p < 0.001). In addition, a significant correlation was found between levels of 8‐OHdG in leukocyte DNA and plasma MDA (r = 0.859, p < 0.001).

Conclusion:  This study measured the oxidative DNA damage by measuring the 8‐OHdG in the leukocyte DNA in patients with cataract. In addition, the level of MDA – a marker for lipid peroxidation – was measured to determine lipid peroxidation.
Succinylcholine activation of human horizontal eye muscles
Authors: Lennerstrand Gunnar , Bolzani Roberto , Tian Suna , Benassi Mariagrazia , Fusari Maurizio , Campos Emilio , Schiavi Costantino
Published: August 2009

Acta Ophthalmol. 2010: 88: 872–876

Purpose:  Succinylcholine (Sch) can induce contracture in slow, multiply innervated muscle fibres of the extraocular muscles in animals of different species. Slow muscle fibres also exist in human eye muscle but their physiological properties have not been studied.

Methods:  Isometric tension development was recorded in the lateral and medial rectus muscles in 12 patients operated under general anaesthesia. A strain gauge probe was attached with 5−0 silk sutures to the muscle tendon. Recordings were made in 12 eye muscles with the tendon attached to the globe and in four muscles detached from the globe. Muscle activation was produced by i.v. injection of Sch at a dose of 0.2–0.3 mg/kg bodyweight.

Results:  A single injection of Sch induced slow contractures lasting for several minutes. In the muscles attached to the globe, mean maximal isometric tension was 12.2 g in the lateral rectus and 12.8 g in the medial rectus. Similar tension was shown in the muscles detached from the globe.

Conclusions:  The contracture of eye muscles in response to Sch showed characteristics typical of slow muscle fibre activation in amphibian and avian muscle and confirmed the participation of slow fibre systems in ocular motor control.
Clinical evaluation of simultaneous confocal scanning laser ophthalmoscopy imaging combined with high‐resolution, spectral‐domain optical coherence tomography
Authors: Helb Hans‐Martin , Issa Peter Charbel , Fleckenstein Monika , Schmitz‐Valckenberg Steffen , Scholl Hendrik P. N. , Meyer Carsten H. , Eter Nicole , Holz Frank G.
Published: August 2009

Acta Ophthalmol. 2010: 88: 842–849

Purpose:  To evaluate the clinical relevance of a new diagnostic modality, simultaneous confocal scanning laser ophthalmoscopy (cSLO) and high‐speed, high‐resolution, spectral‐domain optical coherence tomography (OCT), for the visualization of macular pathologies.

Methods:  OCT images and simultaneous recording of fluorescein angiography, indocyanine green (ICG) angiography, infrared, and blue reflectance (‘red‐free’) or fundus autofluorecence (FAF) images were obtained with a novel imaging device (Spectralis HRA + OCT; Heidelberg Engineering, Heidelberg, Germany). An optically pumped solid‐state laser generated the excitation wavelength (488 nm) required for blue reflectance, FAF and fluorescein angiography images. For ICG angiography and infrared imaging, diode laser sources at 790 and 815 nm were used. For OCT, 40 000 A‐scans per second were acquired with 7 μm axial and 14 μm lateral optical resolution. The B‐scans covering a transversal range of 30° had a scan width up to 1.536 A‐scans with a digital lateral resolution of 5 μm/pixel, a scan depth of 1.8 mm with 3.5 μm/pixel digital axial resolution and a scan rate of up to 48 B‐scans/second. In addition, volume scans could be obtained at 15, 20 and 30° fields of view. An integrated eye tracking allowed for live averaging of cSLO images as well as OCT B‐scans.

Results:  Early, neovascular and atrophic age‐related macular degeneration, macular telangiectasia, retinal arterial, branch vein occlusion and other pathologies were imaged, and cSLO and OCT frames correlated. Fluorescein and ICG angiographic phenomena recorded in cSLO images could be analysed accurately in corresponding OCT cross‐sections. Abnormal FAF signals were correlated to alterations at the outer retinal/retinal pigment epithelial cell layer in high‐resolution OCT scans. Three‐dimensional OCT enabled comprehensive retinal coverage. The imaging software tracked eye movements accurately. Averaging of live B‐scans enhanced image quality considerably.

Conclusion:  The combined cSLO/OCT system allowed for simultaneous recordings of topographic and tomographic images with accurate correlation between the confocal angiograms, FAF images as well as other imaging modes with the OCT scans. The instrument thus provides simultaneous multi‐modal imaging of retinal pathologies and disease.
Tremor‐related motor unit firing in Parkinson's disease: implications for tremor genesis
Authors: Christakos C. N. , Erimaki S. , Anagnostou E. , Anastasopoulos D.
Published: August 2009

Muscle tremors reflect rhythmical motor unit (MU) activities. Therefore, the MU firing patterns and synchrony determine the properties of the parkinsonian force tremor (FT) and the neurogenic components of associated limb tremors. They may also be indicative of the neural mechanisms of tremor genesis which to date remain uncertain. We examined these MU behaviours during isometric contractions of a finger muscle in 19 parkinsonian subjects. Our results reveal that the parkinsonian FT is abnormally large. Like the physiological FT, it is accompanied by in‐phase rhythms in all MU activities. However, there exist two important differences. Firstly, the synchrony during the parkinsonian FT is stronger than the normal one and therefore contributes to the FT enhancement. Secondly, the synchronous MU components partly represent rhythmical sequences of spike doublets and triplets whose incidences directly reflect the differences of the MU firing rates to the FT frequency. According to our analyses, the latter frequency coincides with the MU recruitment rate. Consequently, the numerous medium‐ and small‐sized active MUs contribute rhythmical twitch doublets and triplets, i.e. large force pulses, to the parkinsonian FT. The impact of this effect on the FT amplitude is found to predominate over the impact of the augmented synchrony. Importantly, apart from the rule governing the occurrence of doublets/triplets, the mean interspike intervals within such spike events are fairly fixed around 50 ms. Such regularities in MU activities may reflect properties of the neural input underlying the FT, and thus represent a basis for more focused studies of the generator(s) of parkinsonian tremors.
Learning to breathe: control of the inspiratory–expiratory phase transition shifts from sensory‐ to central‐dominated during postnatal development in rats
Authors: Dutschmann Mathias , Mörschel Michael , Rybak Ilya A. , Dick Thomas E.
Published: August 2009

The hallmark of the dynamic regulation of the transitions between inspiration and expiration is the timing of the inspiratory off‐switch (IOS) mechanisms. IOS is mediated by pulmonary vagal afferent feedback (Breuer–Hering reflex) and by central interactions involving the Kölliker–Fuse nuclei (KFn). We hypothesized that the balance between these two mechanisms controlling IOS may change during postnatal development. We tested this hypothesis by comparing neural responses to repetitive rhythmic vagal stimulation, at a stimulation frequency that paces baseline breathing, using in situ perfused brainstem preparations of rats at different postnatal ages. At ages < P15 (P, postnatal days), phrenic nerve activity (PNA) was immediately paced and entrained to the afferent input and this pattern remained unchanged by repetitive stimulations, indicating that vagal input stereotypically dominated the control of IOS. In contrast, PNA entrainment at > P15 was initially insignificant, but increased after repetitive vagal stimulation or lung inflation. This progressive adaption of PNA to the pattern of the sensory input was accompanied by the emergence of anticipatory centrally mediated IOS preceding the stimulus trains. The anticipatory IOS was blocked by bilateral microinjections of NMDA receptor antagonists into the KFn and PNA was immediately paced and entrained, as it was seen at ages < P15. We conclude that as postnatal maturation advances, synaptic mechanisms involving NMDA receptors in the KFn can override the vagally evoked IOS after ‘training’ using repetitive stimulation trials. The anticipatory IOS may imply a hitherto undescribed form of pattern learning and recall in convergent sensory and central synaptic pathways that mediate IOS.
The response of the tandem pore potassium channel TASK‐3 (K2P9.1) to voltage: gating at the cytoplasmic mouth
Authors: Ashmole I. , Vavoulis D. V. , Stansfeld P. J. , Mehta Puja R. , Feng J. F. , Sutcliffe M. J. , Stanfield P. R.
Published: August 2009

Although the tandem pore potassium channel TASK‐3 is thought to open and shut at its selectivity filter in response to changes of extracellular pH, it is currently unknown whether the channel also shows gating at its inner, cytoplasmic mouth through movements of membrane helices M2 and M4. We used two electrode voltage clamp and single channel recording to show that TASK‐3 responds to voltage in a way that reveals such gating. In wild‐type channels, Popen was very low at negative voltages, but increased with depolarisation. The effect of voltage was relatively weak and the gating charge small, ∼0.17. Mutants A237T (in M4) and N133A (in M2) increased Popen at a given voltage, increasing mean open time and the number of openings per burst. In addition, the relationship between Popen and voltage was shifted to less positive voltages. Mutation of putative hinge glycines (G117A, G231A), residues that are conserved throughout the tandem pore channel family, reduced Popen at a given voltage, shifting the relationship with voltage to a more positive potential range. None of these mutants substantially affected the response of the channel to extracellular acidification. We have used the results from single channel recording to develop a simple kinetic model to show how gating occurs through two classes of conformation change, with two routes out of the open state, as expected if gating occurs both at the selectivity filter and at its cytoplasmic mouth.
Limited ability to extend the digits of the human hand independently with extensor digitorum
Authors: Van Duinen Hiske , Yu Wei Shin , Gandevia Simon C.
Published: August 2009

While the human hand has an extraordinary capacity to manipulate objects, movement of its digits is usually not completely independent. These limits have been documented for extrinsic flexor muscles, although hand skills also require selectivity for extension movements. Hence, we measured the degree of independent control of the major extrinsic extensor (extensor digitorum, ED). Subjects grasped a cylinder, with the thumb perpendicular to the fingers. Load cells were connected to the proximal phalanges of the fingers and the thumb's distal phalanx. Intramuscular recordings using needle electrodes were made from the individual digital compartments of ED. Subjects were instructed to extend each digit isometrically in a voluntary ramp contraction to 50% maximal force. In total, the behaviour of 283 single motor units was analysed. More than half of the units associated with one ‘test’ finger were recruited inadvertently when another digit contracted to 50% maximum, with most units being recruited by extension of the adjacent digits. Usually, test motor units were recruited at higher forces by extension of fingers further from the test finger. Unexpectedly, extension of the thumb recruited many motor units acting on the little finger. Across tasks, at recruitment of the test motor units, the force produced by the test finger often differed between the voluntary and inadvertent contractions. Overall, the independent control of the output of ED is limited; this may reflect ‘spill‐over’ of motor commands to other digital extensor compartments. This level of control of the extrinsic extensor muscles is more independent than the control of the deep extrinsic flexor muscle but less independent than that of the superficial extrinsic flexor muscle.
On the Analysis of Short-Pulse Laser Heating of Metals Using the Dual Phase Lag Heat Conduction Model
Authors: Ramadan K. , Tyfour W. R. , Al-Nimr M. A.
Published: August 2009

Transient heat conduction in a thin metal film exposed to short-pulse laser heating is studied using the dual phase lag heat conduction model. The initial heat flux distribution in the film, resulting from the temporal distribution function of the laser pulse, together with the zero temperature gradients at the boundaries normally used in literature with the presumption that they are equivalent to negligible boundary heat losses is analyzed in detail in this paper. The analysis presented here shows that using zero temperature gradients at the boundaries within the framework of the dual phase lag heat conduction model does not guarantee negligible boundary heat losses unless the initial heat flux distribution is negligibly small. Depending on the value of the initial heat flux distribution, the presumed negligible heat losses from the boundaries can be even way larger than the heat flux at any location within the film during the picosecond laser heating process. Predictions of the reflectivity change of thin gold films due to a laser short heat pulse using the dual phase lag model with constant phase lags are found to deviate considerably from the experimental data. The dual phase lag model is found to overestimate the transient temperature in the thermalization stage of the laser heating process of metal films, although it is still superior to the parabolic and hyperbolic one-step models.
Analysis of a Hyperbolic Heat Conduction-Radiation Problem With Temperature Dependent Thermal Conductivity
Authors: Mishra Subhash C. , Kumar T. B. Pavan
Published: August 2009

This article deals with the analysis of a hyperbolic conduction and radiation heat transfer problem in a planar participating medium. Thermal conductivity of the medium is temperature dependent. Hyperbolic conduction is due to non-Fourier effect. The boundaries of the medium can be either at prescribed temperatures and/or fluxes. With both boundaries insulated, effects of a short pulse internal heat source in the medium are also considered. The problem is analyzed using the lattice Boltzmann method. The finite volume method is employed to compute the radiative information required. Transient temperature distributions in the medium are studied for the effects of various parameters.
Analytic Approximations for a Strongly Nonlinear Problem of Combined Convective and Radiative Cooling of a Spherical Body
Authors: El-Nahhas A.
Published: August 2009

In this paper, a nonlinear problem for combined convective and radiative cooling of a spherical body is considered. This problem represents a strong nonlinearity in both the governing equation and the boundary condition. Analytic approximations for the solution of this problem are obtained using the homotopy analysis method and via a polynomial exponential basis. Also, the effect of the radiation-conduction parameter Nrc and the Biot number Bi for the temperature on the surface of the spherical body is investigated and discussed.
Single-Phase Microscale Jet Stagnation Point Heat Transfer
Authors: Michna Gregory J. , Browne Eric A. , Peles Yoav , Jensen Michael K.
Published: August 2009

An investigation of the pressure drop and impingement zone heat transfer coefficient trends of a single-phase microscale impinging jet was undertaken. Microelectromechanical system (MEMS) processes were used to fabricate a device with a 67-μm orifice. The water jet impinged on an 80-μm square heater on a normal surface 200 μm from the orifice. Because of the extremely small heater area, the conjugate convection-conduction heat transfer process provided an unexpected path for heat losses. A numerical simulation was used to estimate the heat losses, which were quite large. Pressure loss coefficients were much higher in the range Red,o<500 than those predicted by available models for short orifice tubes; this behavior was likely due to the presence of the wall onto which the jet impinged. At higher Reynolds numbers, much better agreement was observed. Area-averaged heat transfer coefficients up to 80,000 W/m2 K were attained in the range 70<Red<1900. This corresponds to a 400 W/cm2 heat flux at a 50°C temperature difference. However, this impingement zone heat transfer coefficient is nearly an order-of-magnitude less than that predicted by correlations developed from macroscale jet data, and the dependence on the Reynolds number is much weaker than expected. Further investigation of microjet heat transfer is needed to explain the deviation from expected behavior.
Flow Maldistribution and Performance Deteriorations in Membrane-Based Heat and Mass Exchangers
Authors: Zhang Li-Zhi
Published: August 2009

Heat mass exchangers are crucial for the prevention of epidemic respiratory diseases such as H1N1 (swine flu). The flow maldistribution affects their performance seriously. The flow maldistribution and the consequent performance deteriorations in heat and mass exchangers are investigated. The focus is on moisture effectiveness deteriorations. As a first step, a computational fluid dynamics (CFD) code is used to calculate the flow distribution, by treating the plate-fin core as a porous medium. Then a coupled heat and moisture transfer model between the two air flows in the plate-fin channels is set up with slug flow assumption in the channels. Using the CFD predicted core face flow distribution data, the sensible heat and moisture exchange effectiveness and the performance deterioration factors are calculated with finite difference scheme. The results indicate that under current core to whole exchanger pressure drop ratio, when the channel pitch is below 2.0 mm, the flow distribution is quite homogeneous and the sensible and latent performance deteriorations due to flow maldistribution can be neglected. However, when the channel pitch is larger than 2 mm, the maldistribution is quite large and a 10–15% thermal deterioration factor and a 20–25% latent deterioration factor could be found. Mass transfer deteriorates much more than heat transfer does due to larger mass transfer resistance through membranes.
Constructal
Design of Particle Volume Fraction in
Nanofluids
Authors: Bai Chao , Wang Liqiu
Published: August 2009

We perform a constructal design of particle volume fraction of four types of nanofluids used for heat conduction in four systems: a circular disk, a sphere, a plane slab, and a circular annulus. The constructal volume fraction is obtained to minimize system overall temperature difference and overall thermal resistance. Also included are the features of the constructal volume fraction and the corresponding constructal thermal resistance, which is the minimal overall resistance to the heat flow. The constructal nanofluids that maximize the system performance are not necessarily the ones with uniformly dispersed particles in base fluids. Nanofluids research and development should thus focus on not only nanofluids but also systems that use them. The march toward micro- and nanoscales must also be with the sobering reminder that useful devices are always macroscopic, and that larger and larger numbers of small-scale components must be assembled and connected by flows that keep them alive.
Thermal Response of Supersonic Airflow to a Fin Protrusion Situated on a Curved Surface
Authors: Molki Majid , Fasig David W.
Published: August 2009

Aerodynamic heating of an airfoil with a short fin attached to its surface is computationally investigated. This research is motivated by the fact that the gap fillers inserted between the insulation tiles of the space shuttle thermal protection system may sometimes get loose and extend beyond the surface and cause an uneven aerodynamic heating of the surface. It is often difficult for engineers to determine whether the protruded gap filler would cause an undesirable effect in the boundary layer including early turbulence transition or shockwaves that could cause an unsafe increase in surface temperature. In this investigation, the supersonic flow over NACA 0012 airfoil on which a short fin is attached is studied using a computational approach. The method is validated by the experimental data available in published literature. The results indicate a significant increase in the surface temperature in the vicinity of the fin. This elevated temperature extends downstream beyond the location of the fin and covers a large portion of the airfoil downstream of the fin. The fin induces an oblique shockwave followed by an expansion wave.
Metallurgy and Behavior of Alloys for Reformer Furnaces
Authors: Jaske Carl E.
Published: August 2009

This paper reviews the metallurgy and behavior of centrifugally cast heat-resistant alloys for ammonia, methanol, and hydrogen reformer furnaces. The alloys include HK and HP, as well as proprietary versions of these materials produced by various foundries. Alloying and metallurgical factors that affect resistance to oxidation, carburization, and high temperature creep are discussed. Examples of the effects of environment and temperature on material behavior are provided. Finally, the use of material properties to predict the long-term performance of reformer furnace components is reviewed.
Temperature and Orientation Dependence of Creep Damage of Two Ni-Base Superalloys
Authors: Gordon Ali P. , Khan Sameer , Nicholson David W.
Published: August 2009

Both polycrystalline (PC) and directionally-solidified (DS) Ni-base superalloys are commonly applied as turbine materials to primarily withstand creep conditions manifested in either marine-, air- or land-based gas turbines components. The thrust for increased efficiency of these systems, however, translates into the need for these materials to exhibit considerable strength and temperature resistance. This is critical for engine parts that are subjected to high temperature and stress conditions sustained for long periods of time, such as blades, vanes, and combustion pieces. Accurate estimates of stress and deformation histories at notches, curves, and other critical locations of such components are crucial for life prediction and calculation of service intervals. In the current study, the classical Kachanov-Rabotnov model for tertiary creep damage is implemented in a general-purpose finite element analysis (FEA) software. Creep deformation and rupture experiments on samples from two representative Ni-base superalloys (PC and DS) tested at temperatures between 649 and 982°C and two orientations (longitudinally- and transversely-oriented for the DS case only) are applied to extend this damage formulation. The damage model coefficients corresponding to secondary and tertiary creep constants are characterized for temperature and orientation dependence. This updated formulation can be implemented for modeling full-scale parts containing temperature distributions.
A Comparison of Measurement and Modelling of Plastically Induced Residual Stresses in a 316H and a Weld 347 Stainless Steel
Authors: Turski M. , Wimpory R. C. , O’Dowd N. P. , Withers P. J. , Nikbin K. N.
Published: August 2009

Neutron diffraction measurements on two types of stainless steel have been carried out on Compact Tension (CT) specimens containing plastically induced residual stresses at the blunt notch root. The materials were a type 316H stainless steel parent material and a type 347 stainless steel weld material. The former exhibited a high creep ductility of ∼25% and the latter exhibited brittle behaviour under operating conditions with less than 10% creep ductility. The work is based in part on an ongoing collaborative effort by the Versailles Agreement on Materials and Standards, Technical Working Area, VAMAS TWA 31 Committee working on ‘Crack Growth of Components Containing Residual Stresses’. The objective of this paper is to examine how residual stresses and/or prior straining and subsequent relaxation at high temperature (550 °C for 316H and 650 °C for 347 weld) contribute to creep crack initiation and growth in the two steels. Elastic/plastic/creep finite-element results and neutron diffraction measurements are presented for the CT specimens before and after elevated temperature exposure. The results suggest that the mechanical induced normalised stresses and strains profiles ahead of the crack tip are insensitive to material, however the relaxation response of the materials appear to be dependent on the creep behaviour and ductility. Localised cracking in the plastically deformed material has been observed in both materials due to the redistribution of the residual stress field and associated creep deformation at elevated temperature.
Performance of Modern High Strength Steels (P91, P92) in High Temperature Plant
Authors: Shibli Ahmed
Published: August 2009

Steels such as P91 and P92 (9Cr martensitic steels) with higher creep strength were initially developed for use in the newer ultra supercritical power plants at temperatures above about 1050°F (570°C). However, soon these steels became popular materials as replacement components for conventional power plant and for HRSGs (Heat Recovery Steam Generators) operating at relatively lower temperatures. The main attraction was in terms of their lower weight per unit volume thus reducing construction, transportation and welding costs. Furthermore, due to privatization and restructuring of the electricity industry many of the existing power plants are now required to operate in cycling mode and this requires the use of materials with high resistance to thermal fatigue. Here high strength steels offer an additional benefit in that the lower section thickness reduces the level of through wall temperature gradients in thick section components. Because of this envisaged additional benefit a number of operators/owners of the existing plant have been replacing some of the ageing components in their plant with those made from these higher strength steels. For the HRSGs, there is a requirement to produce more compact units and here the higher strength steels are used to make smaller size components. This paper discusses these issues and the perceived benefits with the actual plant and more recent R&D experience. It further refers to the potential future techniques for damage detection and life estimation.
Fatigue-Creep Damage Evolution Model and Life Prediction Methods Under Stress Controlled Mode
Authors: Fan Zhichao , Chen Xuedong , Chen Ling , Jiang Jialing
Published: August 2009

Damage evolution of stress controlled fatigue-creep interaction actually is the ductility exhaustion process induced by cyclic creep and static creep. Based on the ductility dissipation theory and effective stress concept of the continuum damage mechanism (CDM), a new fatigue-creep interaction damage evolution model and life prediction method under stress control mode are proposed, in which mean strain is the damage parameter to define damage variable D, and mean strain rate at half life is the control factor related to fracture lives. As for 1.25Cr0.5Mo steel, stress-controlled fatigue-creep tests with different combination of stress amplitudes and mean stresses at 540°C were conducted to investigate fatigue-creep interaction. The results of damage descriptions indicate that, the damage model and mean strain parameter are applicable to describe damage evolution of cyclic creep-static creep interaction when ductility exhaustion is dominant. The life prediction results are found to be quite satisfactory relative to test data with a ±1.25 error factor, which is much better than that for the Frequency Separation method (FS) and Strain Energy Frequency Modified approach (SEFS). Further more, it is found that, when stress amplitudes are less than mean stresses, drastic interaction between cyclic creep and static creep will accelerate the material damage rate, so that the damage exponent reaches its peak value.
Life Prediction of the Tapered Pipe With High Temperature and High Pressure by Finite Element Methods
Authors: Bao Juntao , Gong Jianming , Tu Shantung , Li Yuesheng , Qiu Yanfei
Published: August 2009

Tapered pipe used in the main steam pipelines, which operated at high temperature and high pressure, including concentric tapered pipe and eccentric tapered pipe, they are sources of weakness in the piping system serviced in the power stations and the chemical plants, and creep is the significant reason that caused their failure. Creep damage analyses are carried out for these two kinds of tapered pipes by introducing user subroutine based on the modified Karchanov-Rabotnov constitutive equations into finite element program ABAQUS, then the effects of bending moments and internal pressure to the serviced life of the components are investigated by comparing four group of calculated results under different loads, the results indicated that eccentric tapered pipe is more inclinable to broken than concentric tapered pipe under the same conditions, so it is not recommended to use the eccentric tapered pipe in the piping system. The bending moments will accelerate the components’ failure, so it is necessary to take some advantages to reduce the bending moments near the tapered pipe, on the other hand, the life of the tapered pipe will decrease quickly with the internal pressure increasing, so the control of the operated pressure is important to ensure the serviced life of the pipelines.
Reference Stress Solutions for Idealized Branch Junctions
Authors: Kim Yun-Jae , Lee Kuk-Hee
Published: August 2009

The present work presents plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on detailed three-dimensional (3-D) FE limit analyses using elastic-perfectly plastic materials. The proposed solutions are valid to ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0. Comparison with FE results shows good agreement.
Critical Issues for Development of High-Cr Ferritic Steels for USC Power Plant at 650°C
Authors: Abe F.
Published: August 2009

Critical issues for the development of high-Cr ferritic steels for USC power plant at 650°C are described in terms of long-term creep strength and oxidation resistance. Creep tests were carried out for 9Cr-3W-3Co-VNb steel at 650°C for up to about 6 × 104 h. The addition of boron as high as 100ppm or more in combination with minimized nitrogen, which causes no formation of boron nitride (BN) during normalizing heat treatment, is essential for the improvement of long-term creep strength of base metal and welded joints. The addition of nitrogen causes the precipitation of fine MX carbonitrides, which significantly improves the creep strength. However, excess addition of nitrogen promotes not only the formation of BN during normalizing heat treatment and of Z phase during creep in base metal but also the formation of fine grained heat affected zone in welded joints. Therefore, the boron and nitrogen contents should be optimized for the improvement of long term creep strength of base metal and welded joints. On the other hand, the candidate steels for boiler at 650°C should exhibit oxidation resistance in steam at 650°C better than that of Gr.91 in steam at 600°C, because Gr.91 is being now used for long duration in power plants operating at 600°C. However, existing 9 to 12Cr steels, such as P92 and P122, cannot satisfy the criterion for oxidation resistance in steam at 650°C. The formation of Cr-rich oxide scale is achieved by pre-treatments such as pre-oxidation treatment and coating, which significantly improves oxidation resistance in steam at 650°C and satisfies the criterion for oxidation resistance. The assessment of resistance to exfoliation is a key issue for the Cr-rich oxide scale.
An Anisotropic Creep Damage Model for Anisotropic Weld Metal
Authors: Peravali S. , Hyde T. H. , Cliffe K. A. , Leen S. B.
Published: August 2009

Past studies from creep tests on uniaxial specimens and Bridgman notch specimens, for a P91 weld metal, showed that anisotropic behaviour (more specifically transverse isotropy) occurs in the weld metal, both in terms of creep (steady-state) strain rate behaviour and rupture times (viz. damage evolution). This paper describes the development of a finite element (FE) continuum damage mechanics methodology to deal with anisotropic creep and anisotropic damage for weld metal. The method employs a second order damage tensor following the work of Murakami and Ohno [1] along with a novel rupture stress approach to define the evolution of this tensor, taking advantage of the transverse isotropic nature of the weld metal, to achieve a reduction in the number of material constants required from test data (and hence tests) to define the damage evolution. Hill’s anisotropy potential theory is employed to model the secondary creep. The theoretical model is implemented in a material behaviour subroutine within the general-purpose, non-linear FE code ABAQUS [2]. The validation of the implementation against established isotropic continuum damage mechanics solutions for the isotropic case is described. A procedure for calibrating the multiaxial damage constants from notched bar test data is described for multiaxial implementations. Also described is a study on the effect of uniaxial specimen orientation on anisotropic damage evolution.
Partitioned Cyclic Fatigue Damage Evolution Model for PB-Free Solder Materials
Authors: Ladani Leila J. , Dasgupta A.
Published: August 2009

This study presents an approach to predict the degree of material degradation and the resulting changes in constitutive properties during cyclic loading in viscoplastic materials in micro-scale applications. The objective in the modeling approach is to address the initiation and growth of distributed micro-damage, in the form of micro-cracks and micro-voids, as a result of cyclic, plastic and creep deformations of material. This study extends an existing micromechanics-based approach, developed for unified viscoplastic models [Wen, et al, 2001], which uses dislocation mechanics to predict damage due to distributed micro-scale fatigue crack initiation [Mura and Nakasone, 1990]. In the present study, the approach is extended to a partitioned viscoplastic framework, because the micro-scale mechanisms of deformation and damage are different for plastic and creep deformation. In this approach, the model constants for estimating cyclic damage evolution are allowed to be different for creep and plastic deformations. A partitioned viscoplastic constitutive model is coupled with an energy partitioning (E-P) damage model [Oyan and Dasgupta, 1992] to assess fatigue damage evolution due to cyclic elastic, plastic and creep deformations. Wen’s damage evolution model is extended to include damage evolution due to both plastic and creep deformations. The resulting progressive degradation of elastic, plastic and creep constitutive properties are continuously assessed and updated. The approach is implemented on a viscoplastic Pb-free solder. Dominant deformation modes in this material are dislocation slip for plasticity and diffusion-assisted dislocation climb/glide for creep. The material’s behavior shows a good correlation with the proposed damage evolution model. Damage evolution constants for plastic and creep deformation were obtained for this Pb-free solder from load drop data collected from the mechanical cycling experiments at different temperatures. The amount of cyclic damage is evaluated and compared with experiment.
Microstructure and Creep Rupture Strength of Welded Joints in the Steel P91
Authors: Purmensky Jaroslav , Foldyna Vaclav , Sondel Martin , Schwarz Drahomir , Koukal Jaroslav
Published: August 2009

The aim of the paper is to explain the reason why the creep rupture on welded joints at high temperatures is often observed in the heat affected zone (HAZ), especially in the so called intercritical zone (IC-HAZ). The creep rupture strength (CRS) of cross-weld joints is usually about 20 to 30% lower than that of the base material in the case of the creep resistant modified chromium steel. Precipitation strengthening (PS) depends on the interparticle spacing (IPS) of secondary phases — M23C6 and nanoparticles of MX. With increasing IPS of secondary phases the proof stress and creep rupture strength decreases, while creep rate increases. To estimate the IPS in HAZ the modelling technique was used for estimation of the microstructure and properties. The microstructure of HAZ modelled regions was analysed by transmission electron microscopy. The Smitweld machine was used to reproduce the thermal cycles in HAZ. Real creep tests were carried out on specimens with HAZ modelled regions and also on the P91 real welded joints. It was found that interparticle spacing of secondary phases in the HAZ is much higher than that in the base material. Therefore the proof stress and hardness as well as creep rupture strength of HAZ is much lower than that of the base material. It was observed that CRS in the HAZ is about 20% lower than that of the base material.
Comparison of Creep Damage Appearances Among Low Alloy Steel Pipes
Authors: Mitsueda Toshiki , Fujii Kazuya , Ohnuki Somei
Published: August 2009

To establish a remaining life assessment standard for aged thermal power boilers, internal pressure creep tests of representative low alloy pipe steels were conducted. The tested materials were 2.25Cr-1Mo steel, 1Cr-0.5Mo steel, and 0.5Mo steel. Specimens with and without welded parts in their trunks were made of each material and were φ 70 mm-L400mm-t15mm in dimension. Creep test conditions were 570–620°C × 59MPa and internal pressures were applied by Argon gas or water vapor. Creep tests were interrupted at intervals to acquire data on the crept material as creeping progressed. The observations of replicas from the specimen surface showed the characteristic features of each and the following results were obtained from the comparison of them. (1) The specimens of 2.25Cr-1Mo steel and 1Cr-0.5Mo steel suddenly expanded at about 80% of creep life ratio, and that of 0.5Mo gradually expanded from 60%. They finally ruptured with 15–20% expansions in diameter. (2) Although 2.25Cr-1Mo steel witnessed few creep voids near the end of its creep life, 1 Cr-0.5Mo steel and 0.5Mo steel witnessed many voids such as microcracks from mid-creep life onward. (3) Deformation of ferrite grains contributed to the expansion of 2.25Cr-1Mo steel specimens. On the other hand, partial separations of grains seem to have been owed to the expansions of 1Cr-0.5Mo steel and 0.5Mo steel. In 2.25Cr-1Mo steel, the strength of grain boundary versus grain interior seems to be higher than those of 1Cr-0.5Mo steel and 0.5Mo steels. (4) The amount of creep voids in the HAZ of 1.5Cr-0.5Mo steel was roughly three times that of 2.25Cr-1Mo steel.
Creep-Fatigue Damage: An International Perspective
Authors: Gandy David W. , Parker Jonathan
Published: August 2009

Improved knowledge of creep and fatigue interactions is necessary today more than ever as power-generating plants are exposed to cyclic operation. Understanding factors that impact damage initiation and propagation, as well as technologies to predict accumulation of damage in systems and components are required. This paper summarizes the primary results of an International Expert Workshop on Creep-Fatigue Damage Interaction that was held in Amsterdam in July 2006. The purpose of the Expert Workshop was to bring together key industry experts from around the world to do the following: • Assess and document current creep-fatigue test methods; • Evaluate analytical methodologies with respect to crack initiation and growth; • Discuss life prediction methodologies for different applications; • Assess deficiencies that exist in the area of creep-fatigue damage; • Identify future research and development requirements. The International Expert Workshop resulted in 16 action items which are delineated in this paper. Updates will be provided on progress made to date toward addressing these 16 items.
A Unified Anisotropic Constitutive Model for a Ni Base Directionally Solidified Superalloy
Authors: Yaguchi Masatsugu , Yamamoto Masato , Ogata Takashi
Published: August 2009

Macroscopic deformation behavior of a Ni base directionally solidified (DS) superalloy was experimentally investigated and an anisotropic constitutive model for the material was developed. Monotonic and creep tests were performed on uniaxial test specimens machined from DS plates so that the angles between loading direction and the solidified grain direction varied between 0 to 90 degrees. Tension-torsion creep tests were also conducted to examine the anisotropic behavior under multiaxial stress conditions. The material exhibited remarkable anisotropy under elastic and viscous deformation conditions, while it showed isotropy under plastic deformation conditions of high strain rates. Then crystal plasticity analyses were carried out to identify slip systems under creep loading conditions and presume the anisotropic creep behavior of the DS material analytically. A unified constitutive model was proposed to express both the anisotropic elasticity-viscosity and the isotropic plasticity. The elastic constants were determined applying a self-consistent approach to the material, and viscous parameters were modeled on the basis of the crystal plasticity analyses. Calculation results obtained using the constitutive model were compared to the experimental data to evaluate validity of the model. It was demonstrated that the constitutive model could adequately describe the anisotropic behavior under uniaxial and multiaxial stress conditions with a set of material parameters.