bluuebunny/crossref_metadata_2025 huggingface dataset:
Prediction of human pharmacokinetics —gastrointestinal absorption
Authors: Fagerholm Urban
Published: July 2007

Permeability (Pe) and solubility/dissolution are two major determinants of gastrointestinal (GI) drug absorption. Good prediction of these is crucial for predicting doses, exposures and potential interactions, and for selecting appropriate candidate drugs. The main objective was to evaluate screening methods for prediction of GI Pe, solubility/dissolution and fraction absorbed (fa) in humans. The most accurate Pe models for prediction of fa of passively transported and highly soluble compounds appear to be the 2/4/A1 rat small intestinal cell model (in-vitro and in-silico), a newly developed artificial-membrane method, and a semi-empirical approach based on in-vitro membrane affinity to immobilized lipid bilayers, effective molecular weight and physiological GI variables. The predictability of in-vitro Caco-2, in-situ perfusion and other artificial membrane methods seems comparably low. The Pe and fa in humans for compounds that undergo mainly active transport were predicted poorly by all models investigated. However, the rat in-situ perfusion model appears useful for prediction of active uptake potential (complete active uptake is generally well predicted), and Caco-2 cells are useful for studying bidirectional active transport, respectively. Human intestinal in-vitro Pe, which correlates well with fa for passively transported compounds, could possibly also have potential to improve/enable predictions of fa for actively transported substances. Molecular descriptor data could give an indication of the passive absorption potential. The ‘maximum absorbable dose’ and ‘dose number’ approaches, and solubility/dissolution data obtained in aqueous media, appear to underestimate in-vivo dissolution to a considerable extent. Predictions of in-vivo dissolution should preferably be done from in-vitro dissolution data obtained using either real or validated simulated GI fluids.
Physical characteristics and aerosolization performance of insulin dry powders for inhalation prepared by a spray drying method
Authors: You Yu , Zhao Min , Liu Guangli , Tang Xing
Published: July 2007

The objective of this study was to investigate the influence of formulation excipients on the physical characteristics and aerosolization performance of insulin dry powders for inhalation. Insulin dry powders were prepared by a spray drying technique using excipients such as sugars (trehalose, lactose and dextran), mannitol and amino acids (L-leucine, glycine and threonine). High performance liquid chromatography and the mouse blood glucose method were used for determination of the insulin content. The powder properties were determined and compared by scanning electron microscopy, thermo-gravimetric analysis and size distribution analysis by a time-of-flight technique. The in-vitro aerosolization behaviour of the powders was assessed with an Aerolizer inhaler using a twin-stage impinger. Powder yield and moisture absorption were also determined. Results showed that there was no noticeable change in insulin content in any of the formulations by both assay methods. All powders were highly wrinkled, with median aerodynamic diameters of 2–4 μm, and consequently suitable for pulmonary administration. The tapped density was reduced dramatically when glycine was added. The powders containing mannitol, with or without L-Ieucine, were less sensitive to moisture. The highest respirable fraction of 67.3 ± 1.3% was obtained with the formulation containing L-leucine, in contrast to formulations containing glycine and threonine, which had a respirable fraction of 11.2 ± 3.9% and 23.5 ± 2.5%, respectively. In addition, powders with good physical properties were achieved by the combination of insulin and trehalose. This study suggests that L-leucine could be used to enhance the aerosolization behaviour of the insulin dry powders for inhalation, and trehalose could potentially be used as an excipient in the formulations.
Inhibition of P-glycoprotein function by tannic acid and pentagalloylglucose
Authors: Kitagawa Shuji , Nabekura Tomohiro , Nakamura Yutaka , Takahashi Tomoharu , Kashiwada Yoshiki
Published: July 2007

We studied the effects of tannic acid and 1(β),2,3,4,6-penta-O-galloyl-D-glucose (pentagalloylglucose), one of the components of tannic acid, on the P-glycoprotein (P-gp) function in multidrug-resistant P-gp over-expressing KB-C2 cells. Both tannic acid and pentagalloylglucose markedly elevated the accumulation of P-gp substrates, rhodamine 123 and daunorubicin, by inhibiting their efflux. A 19-fold increase in cellular rhodamine 123 was observed for tannic acid at 60 μM (85 μg mL−1) and a 21-fold increase was observed for pentagalloylglucose at 100 μM (94 μg mL−1). The increasing effects of these compounds in the accumulation were much larger than that of (-)epigallocatechin-3-O-gallate (EGCG), which has been revealed to have a prominent inhibitory effect on P-gp compared with other flavonoids. Analysis of verapamil-stimulated ATPase activity in membrane vesicles expressing human P-gp suggested that inhibition of P-gp function by tannic acid and pentagalloylglucose was at least partly due to ATPase inhibition of P-gp. The findings also suggested that the presence of a large number of galloyl groups in polyphenols strengthens the interaction with regulatory regions in P-gp.
In-vitro and in-vivo correlation for two gliclazide extended-release tablets
Authors: Mandal U , Ray K K , Gowda Veeran , Ghosh A , Pal T K
Published: July 2007

The aim of this study was to perform an in-vitro-in-vivo correlation (IVIVC) for two 60-mg gliclazide extended-release formulations (Fast and Slow release) given once a day and to compare their plasma concentrations over time. In-vitro release rate data were obtained for each formulation using the USP apparatus II, paddle stirrer at 50 and 100 rev min−1 in 0.1 M HCl and pH 7.4 phosphate buffer. The similarity factor (f2) was used to analyse the dissolution data. Eighteen healthy subjects participated in the study, conducted according to a completely randomized, two-way crossover design. The formulations were compared using area under the plasma concentration-time curve, AUC0-∞′, time to reach peak plasma concentration, Tmax', and peak plasma concentration Cmax', while correlation was determined between in-vitro release and in-vivo absorption. A linear correlation model was developed using percent absorbed data versus percent dissolved data from the two formulations. Predicted gliclazide concentrations were obtained by use of a curve fitting equation. Prediction errors were estimated for Cmax and area under the curve AUC0-∞ to determine the validity of the correlation. 0.1 M HCl at 50 rev min−1 was found to be the most discriminating dissolution method. Linear regression analysis of the mean percentage of dose absorbed versus the mean percentage of in-vitro release resulted in a significant correlation (r2 > 0.98) for the two formulations. An average percent prediction error for Cmax was 4.15% for Fast release and 3.99% for Slow release formulation whereas for AUC0-∞ it was 6.36% and 4.66% for Fast release and Slow release formulation, respectively.
Creep crack growth from a semi-circular surface crack in a creep-ductile material
Authors: Hyde T H , Smith S D
Published: July 2007

Creep crack growth results are presented for five lead alloy beams, of depth 40 mm and width 80 mm, subjected to pure bending. The beams each contained semi-circular, crack-like, surface defects, of radius 5 mm, centrally positioned, in mode I opening. The deformation and crack growth from this defect are presented along with the uniaxial properties of the material. The creep crack growth correlates with previous results for plane specimens on the basis of the C∗ parameter. The ‘cracks’ where found to bifurcate under creep conditions and they grew in a direction suggesting equivalent stress-controlled damage of the material.
Stress analysis of cemented orthotropic lap joints
Authors: Suzuki Shin-Ichi
Published: July 2007

The stress analysis is carried out for the orthotropic plate subjected to arbitrarily distributed loads along the edges. The functional form of one stress acting in a plate is assumed and the fundamental equations governing the plate are introduced using the principle of complementary energy. A lap joint is analysed using the present method. From the results of the theoretical analysis, it becomes evident that the effect of the mechanical properties of the orthotropic plate on tearing stress is remarkably large.
Finite element simulation of the deformation of corrugated food cans during sterilization
Authors: Yuan K-Y , Liang C-C
Published: July 2007

During the sterilization process of a typical food can, the geometric non-linear and elastic-plastic state is confronted. A derived procedure of updated lagrangian incremental formulation is proposed to simulate the deformation behaviour of the food can. The process is illustrated with a real example. Some interesting results can be noted wherein.
Effect of hydrostatic pressure on strand behaviour
Authors: Raoof M
Published: July 2007

High density, supposedly impermeable, polythene sheaths have been offered by cable manufacturers for corrosion protection of large diameter spiral strands used in deep water floating production systems.

Using previously reported orthotropic sheet theory, an insight is given into the effect of high external pressure on various sheathed cable characteristics, which include:

1 axial stiffness and hysteresis; 2 torsional stiffness and hysteresis; 3 free bending fatigue behaviour in the vicinity of end terminations.

It is shown that such high pressures can significantly alter the pattern of interwire/interlayer contact forces. Recent published research has clearly demonstrated the central role such interwire contact pressures play as regards cables’ fatigue life under various modes of loading. The present theory shows that increases in contact forces in deep water sheathed cable applications lead to significant reductions in cable fatigue life.

Moreover, such high external forces are shown to affect cables’ axial and torsional characteristics by suppressing the relative slippage of wires in the strand and increasing frictional forces between them. A higher cable stiffness will then follow. This then leads to significant variations in strands’ axial and/or torsional hysteresis which may have a considerable bearing on the overall dynamics of, for example, a guyed tower platform using sheathed strands.

The significant influence of high external pressures on various cable characteristics have been demonstrated by numerical examples on a realistic 39 mm outside diameter (OD) multi-layered structural strand. Results are also presented for the case of zero external pressure relevant to unsealed mooring cables in deep water applications, in which case the absence of the sheath will permit water migration inside the strand and the cable behaviour is independent of the level of water depth.
An improved strain gauge method for measuring KID for a propagating crack
Authors: Sanford R J , Dally J W , Berger J R
Published: July 2007

An improved strain gauge method for measuring the dynamic stress intensity factor, KID, of a running crack is described. By orienting the gauge relative to the crack propagation path the gauge response is optimized for the analysis. Higher order terms in the dynamic strain field representation are demonstrated to be important in the analysis. An application of the method is illustrated in the measurement of KID for a very hard alloy steel, 4340, with a crack propagating at 656 m/s.
Application of moiré interferometry to a contact problem
Authors: Fang J
Published: July 2007

Moiré interferometry of high sensitivity is applied in the present paper to solve the load distribution on the boundary of a semi-infinite plane. A hybrid method combining experimental data with numerical calculation is proposed. The displacement components normal to the edge are obtained from moiré fringes and the experimental results are substituted into linear algebraic equations to solve directly the contact stresses.
Tension and bending stress concentration factors in ‘U’, ‘V’, and opposed ‘U’–‘V’ notches
Authors: Kosmatka J B , Fries R H , Reinholtz C F
Published: July 2007

An analytical and experimental study has been performed to determine the tension and bending stress concentration factors as a function of notch depth for ‘U'—‘V’, and opposed ‘U'—‘V’ notches. Accurate results are produced using quadrilateral finite elements where the edge-lengths in the notch region are less than 10 percent of the notch radius, and using strain gauges where the active gauge length is less than 1/3 the notch radius. Results are presented for single ‘U’ and ‘V’ notches that are outside the range of previously published studies. A detailed stress analysis of a single notched specimen revealed the presence of a tension stress concentration factor ( Kt > 1) and a bending stress reduction factor ( Kb < 1) on the un-notched side of the bar directly opposite the notch. An approximate method of determining stress concentration factors for opposed ‘U'—‘V’ notch geometries is presented.
An experimental study of the elastic-plastic deformation of double ‘V’ butt welds
Authors: Lee M M K , Luxmoore A R
Published: July 2007

The elastic-plastic fracture behaviour of undermatched double ‘V’ weldments with defects was investigated experimentally. Undermatching occurs when the yield stress of the weld is lower than that of the parent plate. Five notched specimens subjected to tension and four-point bending were tested, and deformation and strains were measured using the moiré fringe technique. Results of the study indicated that the COD in weldments with a large undermatch remained constant for a temporary period, giving a ‘flattening’ effect of the COD curve. This effect arose from the weld being shielded from further deformation by the gradual strain build-up and subsequent yielding of the parent metal.
A mechanical electrical device for measuring the three–dimensional deformation of steel columns
Authors: Gibbons C , Kirby P A , Nethercot D A
Published: July 2007

As part of an extensive experimental study into the influence of semi-rigid connections on the behaviour of steel columns, a measurement device has been developed which permits the six individual components of three-dimensional deformation to be monitored. The theory used to process the measured deformations and the subsequent testing of a prototype device is described. A comparison between the deformations measured using the device, and those predicted using a column sub-assemblage finite element model is also presented.
The experimental assessment of the force components within structural steel ‘h’ sections
Authors: Gibbons C , Kirby P A , Nethercot D A
Published: July 2007

A technique is described for manipulating strain gauge data obtained from tests on structural steel ‘H’ sections such that individual force components may be identified. The technique recognises the different structural actions present when open sections deform in a full three-dimensional fashion (compression, major and minor axis bending, and warping) covering both elastic and elastic–plastic behaviour. The results obtained from experimental tests on beam columns exhibited excellent agreement with the corresponding predictions of a sophisticated non-linear finite element analysis.
Estimates of regions of stress concentrations in ‘t’ butt weld geometries
Authors: Etemad M R
Published: July 2007

Values of the surface and the die away distance to unity of stress concentration factor have been found on typical geometries of ‘T’ butt and cruciform joints using finite elements. Results show that within the range of geometric variables studies and within the uncertainties of the secondary variables (e.g., mesh pattern) the term that dominates both value and extent of stress concentration for tensile loading is the ratio of weld leg length to the size of the continuous member. It is also argued that simplified estimation schemes, such as linearization of the peak local stress bounded at unity, need not be conservative with large margins on both the peak value and the extent over which it operates.
Effective stress factors for piping branch junctions due to internal pressure and external moment loads
Authors: Moffat D G , Mwenifumbo J A M , Xu S H , Mistry J
Published: July 2007

Finite element data have been combined with experimental data to produce design curves and an associated equation, which will allow the calculation of the effective stress factors (ESF) for a wide range of piping branch junctions for both internal pressure and all six external moment load categories. The data suggest that modifications are required in design procedures for some geometries for internal pressure loading. For branch out-of-plane loading the present data agree reasonably well with ASME III design rules, but extend these to cover the full range of diameter ratios up to d/D = 1.0.
Estimating the creep-fracture mechanics parameter C [t] from uniaxial creep strain and rupture data
Authors: Smith D J
Published: July 2007

The methods of estimating the creep-fracture mechanics parameter C[ t] proposed by Riedel, Webster, Ainsworth, and their respective co-workers have been reviewed and extended. Quantitative estimates for C[ t] have been obtained for the infinite centre cracked plate (CCP) and compact tension (CT) specimens using uniaxial creep strain and rupture data for 1 CrMoV steel at 565°C. It has been shown that the estimates substantially differ for each method and on the assumed state of stress.

The creep material parameters for 1CrMoV at 565°C are shown to be different for stresses above and below 200 MPa. In selecting the appropriate material parameters for estimating C[ t] the reference stress technique is used. At high stresses the greatest estimate of C[ t] is obtained from Webster's method, the lowest obtained from Ainsworth's approach and an intermediate estimate obtained using methods proposed by Riedel. At low stresses, where stress redistribution from an initial elastic condition dominates, it has shown that Ainsworth's method is the largest estimate.

For industrial components, containing small cracks and subjected to predominantly tension loading, simple estimates of C[ t] can be obtained from the results given in this paper.
Methods for analysing large spiral strands
Authors: Raoof M
Published: July 2007

Simplified routines are presented for obtaining useful information on the macroscopic level as regards the magnitude of interwire/interlayer deformations. Axial hysteresis is shown to vary considerably with the type of strand construction: parametric studies on various constructions covering a wide range of cable (and wire) diameters and lay angle have been used to obtain a simple method of estimating maximum hysteresis and the associated load range/mean ratio at which it occurs. A method has also been presented for obtaining the full-slip stiffness matrix as regards coupled extensional-torsional characteristics. In particular, it is found that unlike certain previously available theories, the present model predicts a (very nearly) symmetrical stiffness matrix which is in agreement with published experimental observations. Numerical examples are presented to facilitate the use of the present paper to forecast various aspects of the behaviour of other spiral strands. Practical implications of including the no-slip modulus as regards coupled extensional-torsional wave propagation in pre-tensioned straight cables have been briefly discussed.
Nodular iron joint welded with nickel-iron electrodes: Hybrid/mixed finite element analysis
Authors: Ping Hu , Xiaoying Zhang , Zhenfeng Zhou
Published: July 2007

Nickel-iron type cast iron electrodes are widely used in welding QT600–3 nodular iron. In order to obtain the total field displacement, strain, and stress distribution of these welded joints under the critical fracture condition, a highly accurate elasto-plastic hybrid/mixed finite element method has been presented in this paper. Also, the corresponding plane stress element model has been given. In addition, this paper describes macro-imitation of the brittle structure in the welded joints. The calculated displacement results are in good agreement with the experimental measurement by using the Moiré fringe method. The reasons of fracture under the lower tensile stress are also discussed.
An expert system for the determination of creep constitutive equations based on continuum damage mechanics
Authors: Dunne F. P. E. , Hayhurst D. R.
Published: July 2007

Methods have been developed for the determination of a suitable stress range over which uniaxial creep tests should be carried out in order to find the best constitutive equations for the material. The method is based on a proposed empirical relation and Ashby deformation mechanism maps.

An automatic data logging system has been developed for the capture of uniaxial creep test data and a robust and reliable optimization scheme has been devised for the determination of the creep constitutive equations for a material.

The above methods have been combined in an expert system that enables the user without specialist knowledge to carry out uniaxial creep tests to determine the best creep constitutive equations for a material. The system is stored on two floppy disks and is run from any IBM compatible microcomputer.

The expert system has been used to determine the creep constitutive equations for copper.
The application of an anisotropic yield function of the sixth degree to orthotropic material
Authors: Takeda T
Published: July 2007

By combining Drucker's yield function with Hill's quadratic yield function, an anisotropic yield function of the sixth degree is proposed. The effects of the third deviatoric stress invariant and initial anisotropy are also included. Experimental evaluation is made on 1050 aluminium tubes under multiaxial stress states. The tubes in the as-received condition are subjected to progressive reductions in the hot extruding and cold drawing processes. They are annealed by heating at 200 °C for 1 h. By applying proportionally combined loadings of axial load, internal pressure, and torsion to the specimens, a change of yield stress with a rotation of the principal stress axes and a difference between the directions of the principal stress and principal strain increment are examined. In the tension-internal pressure stress field, it is found that this aluminum tube exhibits orthotropic anisotropy of high strength in the tangential direction. The yield surface in the tension-torsion stress field lies outside von Mises’ yield surface. The torsional yield stress deviates considerably from von Mises criterion. Such behavioural characteristics can be expressed precisely by the proposed yield function. In addition, it is experimentally verified that the normality rule is obeyed in strain behaviour.
Stress intensity determination by an experimental-numerical hybrid technique
Authors: Feng Z , Rowlands R E , Sanford R J
Published: July 2007

Stress intensity factors are obtained from displacement-prescribed boundary conditions on a subregion containing the crack. The subregion, whose boundary can be any arbitrary contour within the physical structure, is analysed numerically using structural finite elements. Nodal boundary displacements of this subregion are obtained photomechanically using a smoothing finite element representation. The technique requires little experimental information and is unaffected by rigid body motions. It is numerically stable and accurate - even in the presence of significant experimental scatter - and the measured data need not come from the immediate vicinity of the crack. The method's practicality is demonstrated by determining the stress intensity factors in a compact tension specimen from moiré-measured displacements at locations away from the crack tip.
Design equation for stress concentration factors of notched strips and grooved shafts
Authors: Kato A
Published: July 2007

A new design equation for stress concentration factors is presented in this paper. This equation is an empirical equation and has been derived based on theoretical results of semi-infinite plates with a notch under tension and also numerical results of strips and shafts with finite notches under tension or bending. It gives stress concentration factors of notched strips and grooved shafts under tension or bending with one expression. This equation can be applied to various shapes of notches and loading conditions and is very convenient for a practical use. Values calculated by this equation are found to be closer to the numerical results recently published than those calculated by Neuber's formula.
The significance of damage and defects and their detection in composite materials: A review
Authors: Cantwell W J , Morton J
Published: July 2007

In this paper the various failure modes which occur in long fibre composites are described and discussed. The significance of each of these fracture mechanisms, in terms of their energy-dissipating capacity as well as their effect on the residual load-bearing properties, is considered. A brief review of both the destructive and non-destructive techniques used for detecting and characterizing defects and damage is presented. The ability of each technique to identify the various fracture mechanisms involved in the failure of long fibre reinforced composites is discussed and their overall suitability for damage detection evaluated.
True bounds on Poisson's ratios for transversely isotropic solids
Authors: Theocaris P S , Philippidis T P
Published: July 2007

The basic principle of positive strain energy density of an anisotropic linear or non-linear elastic solid imposes bounds on the values of the stiffness and compliance tensor components. Although rational mathematical structuring of valid intervals for these components is possible and relatively simple, there are mathematical procedures less strictly followed by previous authors, which led to an overestimation of the bounds and misinterpretation of experimental results.
Application of moiré shearing interferometry to slope measurement of shallow shells
Authors: Wang L L , Yun D Z
Published: July 2007

A moiré shearing interferometry, used to analyse the interference effect in a particular optical set-up by the Fourier series method, is proposed in this paper. The slope fringe patterns of different shallow shells with eccentric holes are also given by this method.
An evaluation of mechanical strength test specimens for brittle materials
Authors: Stanley P , Karroum C
Published: July 2007

Several alternative test specimens for the determination of the fracture strength of a brittle material have been studied. These include a ring-supported ball-loaded thin circular disc, a disc symmetrically supported on three equispaced balls and loaded at the centre through a fourth ball, a cylinder under axial compressive point-loading, and a ‘pure shear’ beam specimen. The stress distributions in these specimens have been determined photoelastically and the stress data used to interpret fracture test data for batches of each specimen made from reactor-grade graphite. The stochastic nature of the fracture data has also been considered.
The linear elastic in-plane bending of curved hollow profiles having a thin-walled rectangular section
Authors: De Melo F J M Q , Vaz M A P
Published: July 2007

This paper presents a simple solution for the flexibility calculation of curved profiles having a rectangular thin-walled cross-section. Some assumptions related to geometric details about the shape of the deformed structure are included in the present analysis, aiming at an economic and accurate solution. Results concerning the distortion of the transverse section are compared with the corresponding data from the solution with a thin shell finite element analysis. A flexibility factor for the structure analysed here is presented as a graphical result.
Deformation and strength of stepped-lap joints bonded with adhesive resin
Authors: Mori K , Sugibayashi T
Published: July 2007

Deformation and strength of stepped-lap bonded joints under static tensile loading are investigated both analytically and experimentally. The joints used in this study consist of the same metal adherends of carbon steel and an adhesive of epoxy resin. The effects of the overlap length and number of steps on the joint strength are studied. The joint strength is predicted by applying the strength criteria on the adherends, the adhesive and their interfaces in the joint. The predicted results agree fairly well with the experimental initial cracking strengths. The experimental final fracture strengths of the joints increase with the overlap length and with the number of steps.
Modelling of the performance of leather in a uni-axial shoe-last simulator
Authors: Lin J , Hayhurst D R , Howard I C , Reedman D C
Published: July 2007

Previously developed constitutive equations are presented and discussed for shoe upper leather which undergoes large deformation. An energy potential function has been established using total Lagrangian strains for computer modelling of finite deformation of leather in shoe lasting. A practical last simulator, composed of a cylindrical last and uni-axial leather strip, has been developed to model a one-dimensional simulation of the lasting process. Experiments have been carried out to study the effects of different friction characteristics at the leather-last interface. The experimental results for the variation of the lasting force with the last displacement are presented and shown to be closely predicted by the computer models based on the multi-axial constitutive equations.
Spatial-carrier phase shifting method of fringe analysis for moiré interferometry
Authors: Poon C Y , Kujawinska M , Ruiz C
Published: July 2007

The theory of an automated fringe pattern analysis using the spatial-carrier phase shifting method for moiré interferometry is presented. The automated method is shown to provide a fast and accurate strain measurement over the whole field. Measurements on a brass specimen and a tapered laminated composite specimen are shown to highlight the efficiency and the capability of this technique for moiré interferometry. The filtering technique used to remove noise from the required displacement function is also presented.
A coupled thermo-elastic-plastic model with a modified direct iteration method in a cold extrusion process
Authors: Lin Z C , Pan W C
Published: July 2007

A thermo-elastic-plastic model in conjunction with an experimental flow stress-strain curve, is applied to a cold extrusion process. The flow stress is considered as a function of strain, strain rate, and temperature to simulate a more realistic situation. A modified iteration method is proposed to a linear piecewise continuous model to increase the accuracy and avoid divergence. The strain is calculated by Taylor's series expansion and is associated with its corresponding convergence criteria; an available scheme for the calculation of the strain rate is thus involved. In addition, a least squared method is proposed to check loading or unloading situations. An extrusion experiment is then made and the simulated loading force compared with the experimental loading force is very satisfactory.
The standard ridged uniaxial testpiece: Computed accuracy of creep strain
Authors: Lin J , Hayhurst D R , Dyson B F
Published: July 2007

The creep rupture behaviour and the accuracy of the measured strains for the uniaxial tensile testpiece with extensomenter ridges have been studied by use of the Continuum Damage Mechanics (CDM)-based creep finite element solver, DAMAGE XX. Multi-axial creep constitutive equations with multi-damage state variables were used in the computer modelling process. The procedure models the development of failed regions of the testpiece due to the stress concentration in the transition regions from the parallel portion to the extensometer ridges. The accuracy of the creep strain measurement for the testpiece was investigated with the variation of time, gauge length, and stress levels. The computer modelling results show that although the error of the creep strain measurement is a fuction of time, it is dependent upon the stress sensitivity of the material law. For power-law material the maximum error is invariant of the normalized stress, but dependent upon the value of n; and for the sinh-based material law the maximum error is dependent upon the magnitude of the applied stress.
Surface flaw stress intensity factor computation with quarter-point elements
Authors: Carpinteri Andrea
Published: July 2007

The stress intensity factor along the front of a semi-elliptical surface flaw subjected to tension or bending loading is calculated by means of a finite element analysis carried out with twenty node isoparametric three-dimensional elements. The stress and strain singular behaviour in the vicinity of the defect is modelled by moving the finite element midside nodes near the crack front to quarter-point positions. An extensive analysis is carried out by assuming different values of the flaw aspect ratio (0.2., 0.4, 0.6, 0.8, and 1.0), while the relative depth of the crack's deepest point is varied from 0.1 to 0.4. As regards the crack configurations previously tackled in the literature, the agreement between the results of the present study and those obtained by other authors is quite satisfactory, especially for small relative crack depths.
Mixed-mode stress intensity factors for inclined cracks in round bars
Authors: Hyde T H , Warrior N A
Published: July 2007

The frozen-stress photoelastic stress analysis technique is used to obtain the mode I and mode II stress-intensity factors for cracks in round bars. The bars, which are subjected to bending, contain cracks inclined to the transverse planes of the bars. Results for inclinations of 45, 60, 75, and 90 degress are obtained. Crack depths of 0.3 ×, 0.5 ×, and 0.7 × the diameter are investigated. The results are normalized so that they can be applied to similar shaped cracks in bars of any diameter and material subjected to bending. The agreement with previously published results (for the pure mode I case) is very good, i.e., within 3 percent. The choice of normalizing parameters makes the normalized mode I and mode II stress-intensity factor relatively insensitive to the crack inclination. The mode II stress-intensity factors are practically constant along the crack fronts whereas the mode I stress intensity factors fall sharply near the ends of the crack, i.e., where they break the surface of the bar.
A destructive procedure to determine the residual stresses in thick-walled cylindrical pressure vessels
Authors: Stark H L , Bau J , Kelly D W
Published: July 2007

The aim of this work is to develop a procedure for determining the three-dimensional residual stress fields in forged cylindrical pressure vessels. The procedure involves the destructive machining of the cylinder. Strain gauges record the strain variation on the outer surface of the cylinder as the inner surface is machined. A finite element model is then constructed, reversing the machining sequence, matching the increments in measured strain, and thus cumulatively arriving at the original distribution of residual stress. Examples include a numerical simulation for a thick disk and a practical application to thick-walled forged cylinders.
Investigation of residual stress distribution in a rail head
Authors: Zochowski M , Tracz M
Published: July 2007

This paper presents a destructive procedure for the determination of longitudinal residual stress distribution in a thin layer in the vicinity of the running surface of a rail head and the neighbouring area of rail cross-section. Wheel passages on the track produce plastic deformation in the running surface layer and thereby create a strong compression with a sharp stress gradient in the layer. This longitudinal stress distribution is a very important component of the stress pattern and strongly influences crack propagation in the rail head.
Constitutive equations for creep
Authors: White P S , Goodman A M
Published: July 2007

Creep constitutive equations are discussed in their role as material descriptions forming one of the governing conditions of an inelastic stress analysis. The view taken is that they must not only give an adequate picture of the material behaviour itself, but must also be suitable from the numerical point of view. Furthermore, in practical engineering contexts, constitutive equations must be principally aimed at giving information for structural assessment under realistic loading conditions and subject to various uncertainties. The choice of model is, therefore, not aimed at an exact material description, and the practial choice may be problem-dependent for a given material.

Both the classical formulation and the more recent unified formulation are outlined, with discussion of advantages and disadvantages. Some unified formulations are regarded as practically useful but great use is still to be expected of classical forms in which creep and plasticity are regarded as separate. In the latter class descriptions are given of the widely-employed time- and strain-hardening descriptions, of back-stress models, and of certain tertiary creep models including damage variables. The difficulties of anisotropy are also noted.

Finally the paper discusses the process of fitting material data to the classical time- and strain-hardening models, and some hints are given for the analyst who may be faced with performing this task for materials of interest.
Numerical analysis of creep in components
Authors: Becker A A , Hyde T H , Xia L
Published: July 2007

The application of numerical methods, particularly the Finite Element (FE) method, is widespread in the analysis and design of components operating at elevated temperatures. A brief overview of the FE method and the Boundary Element (BE) method is presented. To demonstrate the versatility and accuracy of FE solutions in modelling practical engineering problems, several examples are presented. The examples include indentation creep involving the reference stress approach, the use of damage mechanics, and creep crack propagation simulation. The FE solutions are shown to be in good agreement with analytical and experimental results.
Creep life assessment methods
Authors: Cane B J , Aplin P F
Published: July 2007

Over the past ten years significant progress has been made towards reliable methods for creep life assessment. Through development and application, methods are now at a stage at which their technical viability is established and the cost benefits are proven at the plant operation, maintenance, and strategic planning levels. This paper reviews creep life assessment methods with particular reference to those based on component strain measurement. It is concluded that, through validation, standardization, and data/knowledge banking, consolidation of the substantial amount of information now available must be an objective for the next 5–10 years, whilst not curtailing innovative development.
A three-dimensional graphical method for shear strain analysis
Authors: Taher S E-D , Almusallam A A
Published: July 2007

The efficiency of graphical methods for strain analysis depends merely on its simplicity and accuracy. For most strain definitions, the Mohr circle has proved to be the most powerful graphical technique. Unfortunately, its three-dimensional form has limitations concerning the determination of the shearing strain components on a general oblique plane. In this paper, the various deformation quantifiers and the existing extensions to Mohr's method which account for its drawbacks are briefly reviewed. A novel proposal to be appended to Mohr's original construction, allowing its complete generality, is given. It has the form of a simplified complementary triangular construction. A mathematical formulation of the suggested graphical techniques on the basis of Cauchy's formula and vector analysis is carried out.
Mechanisms-based creep constitutive equations for an aluminium alloy
Authors: Kowalewski Z L , Hayhurst D R , Dyson B F
Published: July 2007

A number of mechanisms-based constitutive equations were assessed in an effort to describe the creep behaviour of an aluminium alloy at 150°C. It was found that a sinh function of stress, rather than the usually used power law, is best able to describe the strain rate and rupture behaviour over the narrow stress range analysed. A single state variable theory which represents a dominant damage mechanism is not capable of predicting the shape of the tertiary curve; however, a two state variable theory which represents two mechanisms provides a good description. The two relevant mechanisms identified are creep-constrained cavitation and ageing of the particulate microstructure.

The non-linear equations which describe both these physical mechanisms are complex and strongly coupled. This makes it difficult to determine the constants in the constitutive equations from experimental data. The paper reports the development of automated numerical optimization techniques which overcome these difficulties.
An account of plasticity in the hole-drilling method of residual stress measurement
Authors: Beghini M , Bertini L , Raffaelli P
Published: July 2007

The elastic-plastic stress-strain field produced in a thin plate under equibiaxial loading during the operation of drilling a through-thickness hole was analysed. The plane stress condition and Tresca yield criterion were assumed for an elastic-perfectly plastic material. These hypotheses allowed the problem to be formulated by means of ordinary differential equations which were analytically solved. Within these particular conditions, the results gave indications of the effect produced by plasticity on the widely used hole-drilling method for residual stress measurement. In particular, the equality of final results with those obtained for a plate with a pre-existing hole loaded in an elastic-plastic regime gives useful indications for the experimental analysis of the effect of plasticity on residual stress measurement.
Shakedown of a CT specimen with St52 steel—experimental, analytical and numerical investigations
Authors: Huang Y J , Stein E
Published: July 2007

The paper deals with the shakedown behaviour of a CT (compact tension) specimen consisting of St52 steel under cyclical loading. Experiments have been carried out for determining the shakedown limit load. For comparison, the analytical and numerical methods are used to study the same problem. Satisfactory agreement has been achieved between the results from these different methods.
Three-dimensional photoelastic analysis of pile caps
Authors: Krishna Iyer P , Sam C
Published: July 2007

This paper presents a three-dimensional photoelastic investigation of two- and four-pile caps for different depth—pile spacing ratios. For the analysis, the pile caps were idealized as rectangular blocks subjected to patches of loading at the column and pile locations. The individual stress components, their maximum values and locations were determined. Graphs showing the variations of important normal and shear stress components across depth, non-dimensionalized with the applied column stress, were given. On the basis of the results obtained it is concluded that the factors which are not hitherto considered in the design of pile caps have a significant bearing on the stress distribution.
Elastoplastic stress and strain predictions for axisymmetric pressure vessel bodies under transient thermal loads
Authors: Adinarayana N , Alwar R S
Published: July 2007

Evaluation of localized peak strains at stress concentration zones under transient thermal loading is essential for the determination of low cycle fatigue life of a number of pressure vessels like steam turbine components and reactor vessels. Finite element analysis is a powerful technique but there are some difficulties in using the method for inelastic analysis of large-sized components. Several investigators have proposed approximate methods to determine inelastic strains at notches and other stress concentration zones from elastically calculated stress distributions. The accuracy of three of these methods, namely the Neuber rule, the Molski-Glinka rule and GLOSS analysis under thermal loading for axisymmetric pressure vessel bodies was investigated. A parametric study with geometry and material parameters as variables was carried out for three sizes of spheres with nozzles for the determination of peak strains and stresses under transient thermal loading using thermoelastoplastic finite element analyses and also by approximate methods. The same analyses have also been carried out for a steam turbine valve body for the same thermal loading, which is normally encountered by the valve body under start-up conditions. It has been found that GLOSS analysis is more accurate and the use of approximate methods has been recommended, especially for preliminary analyses in the development of new components.
Modelling creep failure in welded plates under uniaxial loading
Authors: Craine R E , Newman M G
Published: July 2007

Understanding more fully the behaviour of weldments is important since they can reduce the lifetime of structures at high temperatures, but performance factors are omitted from most existing design codes (with the exception of the high temperature fast reactor codes). Simple mathematical models which produce approximate solutions quickly are useful since they allow the design engineer to carry out rapid simulations. In this paper the ideas of continuum damage mechanics are incorporated into a model, based on the Cosserat theory of plates and a multi-axial version of Norton's creep law, which has been used recently to calculate the steady state creep strain rates in a weldment. Failure results are calculated numerically for a ferritic plate of constant thickness subject to uniaxial loading, the plate containing parent and weld metals, type IV material and a high-temperature heat-affected zone (HAZ). Results obtained for various material parameters and weldment configurations show that rupture times depend strongly on the choice of generalized stress in the damage evolution equation. The results also reveal that changes to the material strength of a region cannot be made in isolation if physically realistic results are to be obtained and, further, that early failures can occur if there are large differences in strength between the various parts of the weldment.
Three-dimensional design optimization using the boundary integral equation method
Authors: Erman Z , Fenner R T
Published: July 2007

Three-dimensional shape design optimization is demonstrated using the boundary integral equation method. Design sensitivities are obtained directly by differentiating the boundary integral equations with respect to normals to the surfaces at the design variable points. Coon's patches are employed in order to represent continuously changing design surfaces. The Broyden-Fletcher-Goldfarb-Shanno (BFGS) method which requires first-order derivative information has been adopted for the optimization part of the problems. Two examples, a perforated plate under biaxial stresses and a cantilever beam with end shear loading, are demonstrated for the smoothing of stress peaks and stress levelling.
The state of stress induced by a conical indenter
Authors: Truman C E , Sackfield A , Hills D A
Published: July 2007

Explicit equations are given for the state of stress arising in an elastic solid when a frictionless conical indenter is pressed into the surface.