bluuebunny/crossref_metadata_2025 huggingface dataset:
On the In-vitro Antimicrobial Activity of Oleuropein and Hydroxytyrosol
Authors: Bisignano Giuseppe , Tomaino Antonio , Cascio Rossella Lo , Crisafi Giuseppe , Uccella Nicola , Saija Antonella
Published: October 2002

Secoiridoides (oleuropein and derivatives), one of the major classes of polyphenol contained in olives and olive oil, have recently been shown to inhibit or delay the rate of growth of a range of bacteria and microfungi but there are no data in the literature concerning the possible employment of these secoiridoides as antimicrobial agents against pathogenic bacteria in man.

In this study five ATCC standard bacterial strains (Haemophilus influenzae ATCC 9006, Moraxella catarrhalis ATCC 8176, Salmonella typhi ATCC 6539, Vibrio parahaemolyticus ATCC 17802 and Staphylococcus aureus ATCC 25923) and 44 fresh clinical isolates (Haemophilus influenzae, eight strains, Moraxella catarrhalis, six strains, Salmonella species, 15 strains, Vibrio cholerae, one strain, Vibrio alginolyticus, two strains, Vibrio parahaemolyticus, one strain, Staphylococcus aureus, five penicillin-susceptible strains and six penicillin-resistant strains), causal agents of intestinal or respiratory tract infections in man, were tested for in-vitro susceptibility to two olive (Olea europaea) secoiridoides, oleuropein (the bitter principle of olives) and hydroxytyrosol (derived from oleuropein by enzymatic hydrolysis and responsible for the high stability of olive oil). The minimum inhibitory concentrations (MICs) calculated in our study are evidence of the broad antimicrobial activity of hydroxytyrosol against these bacterial strains (MIC values between 0.24 and 7.85 μg mL−1 for ATCC strains and between 0.97 and 31.25 μg mL−1 for clinically isolated strains). Furthermore oleuropein also inhibited (although to a much lesser extent) the growth of several bacterial strains (MIC values between 62.5 and 500 μg mL−1 for ATCC strains and between 31.25 and 250 μg mL−1 for clinical isolates); oleuropein was ineffective against Haemophilus influenzae and Moraxella catarrhalis.

These data indicate that in addition to the potential employment of its active principles as food additives or in integrated pest-management programs, Olea europaea can be considered a potential source of promising antimicrobial agents for treatment of intestinal or respiratory tract infections in man.
Piping elbows with cracks Part 2: Global finite element and experimental plastic loads under opening bending
Authors: Yahiaoui K , Moffat D G , Moreton D N
Published: October 2002

Experimental and finite element (FE) plastic load results of cracked piping elbows under opening in-plane bending are presented and compared with data from similar defect-free components. The elbows used were short-radius components with an outside diameter of 88.9 mm and thickness 5.49 mm. Axial (at the crown) and circumferential (at the intrados) blunt crack-like defects were produced using electric discharge machining (EDM) procedures. Both short (0 = 21° axial or 2β = 46° circumferential) and long (0 = 75° axial or 2β = 120° circumferential) defects were investigated with three depth-thickness ratios a/t = 0.5, 0.75 and 1.0. The FE simulations employed the measured true stress-strain properties for the elbow material and included geometric non-linear behaviour.

The results obtained show that piping elbows under opening bending can tolerate substantial defects, with reductions in plastic loads compared with the defect-free component of the order of 15 per cent or less in most cases, except when the defect is through-wall and circumferential and covers an angle 2β = 120° or more, in which case the reduction in plastic load can be as high as 40 per cent.
Twisted impregnated yarns: Elastic properties
Authors: Naik N K , Madhavan V
Published: October 2002

Twisted yarns are normally used for increasing the lateral cohesion of filaments and also for ease of handling. By twisting yarns, the microdamage can be localized, leading to possible increase in the failure strength of the yarns. In this paper, an analytical method is presented for predicting the elastic properties of twisted impregnated yarns made of long unbroken filaments. In the analysis, various degrees of twist in filaments at different radii of the yarn and possible migration and microbuckling are considered. The effects of the twist angle and the extent of migration and microbuckling on the elastic properties and the pre-straining of the yarn are presented.
Non-linear bending of shear deformable laminated plates under lateral pressure and thermal loading and resting on elastic foundations
Authors: Shen Hui-Shen
Published: October 2002

A non-linear bending analysis is presented for a simply supported shear deformable composite laminated plate subjected to a combined uniform lateral pressure and thermal loading and resting on a two-parameter (Pasternak-type) elastic foundation. The formulations are based on Reddy's higher-order shear deformation plate theory, including the plate-foundation interaction and thermal effects. The analysis uses a mixed Galerkin-perturbation technique to determine the load-deflection curves and load-bending moment curves. Numerical examples are presented that relate to the performances of antisymmetric angleply and symmetric cross-ply laminated plates subjected to thermomechanical loading and resting on two-parameter elastic foundations from which results for Winkler elastic foundations are obtained as a limiting case. The influences due to a number of effects e.g. foundation stiffness, plate aspect ratio, total number of plies, fibre orientation and initial thermal bending stress, are studied. Typical results are presented in a dimensionless graphical form.
Analytical expressions of the influence functions for accuracy and versatility improvement in the hole-drilling method
Authors: Beghini M , Bertini L
Published: October 2002

Analytical expressions of the influence functions suitable for obtaining variable through-thickness residual stresses by the hole-drilling method are proposed. They were determined by interpolating the results of accurate finite element simulations of the experimental arrangement as prescribed by the ASTM standard. The effects of the geometrical parameters and material properties were included. The influence functions allow the relaxed strain measured by the strain gauge rosette to be directly calculated for a general residual stress distribution. With no interpolation of tabular values, they can be employed to evaluate the coefficients required for the application of the integral method. It is also shown how the influence functions can be used to obtain residual stress distribution on the basis of a fully general series expansion.
Stress concentrations at an oblique hole in a thick plate
Authors: Stanley P , Starr A G
Published: October 2002

An empirical equation has been obtained for the elastic stress concentration factor at an isolated oblique circular-cylindrical hole in a thick flat plate subjected to a uniform, arbitrarily oriented uniaxial tension. The equation is presented and its development is outlined in this note.
A shrink-fit peg in a hole subjected to bending: Unloading, reloading and frictional shakedown
Authors: Urriolagoitia-Sosa G , Hills D. A
Published: October 2002

The problem studied is that of a peg, shrink-fitted into a recess within an elastically similar block of material. In this paper, earlier results for the slip and separation states induced by the application of a monotonically increasing remote transverse force are extended to the cases of unloading and reloading. The steady state slip pattern present is also inferred. Knowing the shakedown condition will reveal the way that the component behaves when the load is cycled, determining the periods of major and minor damage. The interference contact pressure needed for prevention of steady state slip at all points in the steady state are deduced, and it is shown that this is less stringent than the pressure needed to avoid all slip in the first loading cycle.
Deformations and stresses in pin-loaded tubes under axial tension
Authors: Ahmad I , Stanley P
Published: October 2002

The results of an experimental study of the deformations and stresses developed in a series of pin-loaded cylindrical tubes subjected to an axial tensile load are presented and discussed. The effects of variations in the pin/tube diameter ratio and the position of the pin axis relative to the tube end are established for a particular tube thickness/diameter ratio (0.08), and the effects of variations in this ratio are described for two particular pin-tube configurations. The work also includes an assessment of the effects of lubrication at the pin-tube interfaces, pin clearance in the pin-holes, pin stiffness and restraint of radial deformations in the tube.
Solution of axisymmetric crack problems using distributed dislocation ring dipoles
Authors: Korsunsky A. M , Hills D. A
Published: October 2002

A solution procedure for the calculation of crack tip stress intensity factors arising at the edges of an arbitrarily shaped crack lying on a surface of revolution is described. The cracks are subject to an arbitrary axisymmetric stress field, devoid of torsion, and may be present in either an infinite space or two elastically dissimilar bonded half-spaces, of which one may, as a special case, have vanishing elastic constants. The technique employed is a one-dimensional integral equation approach, in which the kernel is formed from rings of dislocation pairs, arranged to form ring ‘dipoles’. The equation is hypersingular but may readily be inverted using powerful numerical quadratures, providing a computationally efficient solution. Examples of the use of the technique are then described.
Predicting rupture and low strain times for a 225Cr-1Mo steel using a six-ϑ projection technique
Authors: Evans M
Published: October 2002

The ϑ projection method of creep analysis is known to produce the poorest predictions of creep properties at low strains. This paper applies a recently suggested modification of the ϑ concept to 2.25Cr-1Mo steel where long term data exist to enable an assessment of this modification to be made. The modification takes the form of two additional ϑ terms that allow the initial stages of any creep curve to be modelled more accurately. The paper shows that the resulting six-ϑ approach produces predictions of long-term failure times that are marginally better than those obtained using the traditional four-ϑ approach. However, the six-ϑ approach is shown to be much more capable of accurately predicting times to low strains (1 per cent strain) at stress levels as low as 40 MPa at 838 K and 80 MPa at 813 K (well below the lowest stresses used in the ϑ analysis). Finally, weighting each ϑij in the six-ϑ approach is not recommended as it is shown to have a detrimental impact on the longer-term predictions obtained. This reflects inherent numerical difficulties associated with the six-ϑ approach.
Effects of geometry on the deformation of asphaltic plug joints subjected to surface tractions
Authors: Qian Z. Q , Akisanya A. R , Imbabi M. S
Published: October 2002

Asphaltic plug joints are widely used for accommodating structural movement in motorway bridges. In spite of their simplicity and low cost, these joints suffer premature failure, of which debonding at the asphaltic plug/pavement interface is an important mode. In this paper, fundamental studies of the debonding are carried out by means of detailed stress analysis. The asphaltic plug is assumed to be viscoelastic while the pavement is assumed to be linear elastic. Stress solutions are obtained using the finite element method for a range of joint angles between the asphaltic plug and the pavement. The traffic loads are simulated using surface tractions applied in the vicinity of an interface corner on the wearing surface. The results show that the interface may experience stress reversal as the surface traction moves from one side of the interface corner to the other. Further, the magnitudes of the interfacial stresses decrease as the joint angle is increased from the current value of 0° to about 45°, thereby reducing the likelihood of debonding.
Comparative measurements on autofrettaged cylinders with large Bauschinger reverse yielding zones
Authors: Venter A. M , de Swardt R R , Kyriacou S
Published: October 2002

A comparative study to map the residual strain/stress states through the walls of autofrettaged thick-walled steel cylinders has been conducted with neutron diffraction, Sachs boring and the compliance methods. Test samples with different wall thickness ratios were prepared to have significant amounts of reverse yielding due to the Bauschinger effect. All three methods indicate that the autofrettage action primarily influenced the hoop stresses, which varied rapidly close to the bores from compressive to tensile within the first half of the wall thickness. Quantitatively, results from the neutron diffraction and Sachs boring techniques compare favourably across large regions of the cylinder walls, while the compliance results showed different features. The existence of reverse yielding close to the cylinder bores has been sensed to different magnitudes and distances from the bores. Plastically yielded material regions identified from the neutron diffraction results correlated well with theoretical modelling.
Investigation of shape optimization for the design of life extension options for an F/A-18 airframe FS 470 bulkhead
Authors: Kaye R , Heller M
Published: October 2002

Shape reworking and bonded reinforcement are two procedures available to extend the fatigue life of cracked metallic aircraft components already in service. Typically for realistic applications, the design of reworks has been undertaken through trial-and-error finite element analyses, guided by simplified analytical formulations, the aim being to achieve reduced stresses while generally restricting the shape boundaries to circular and straight segments. In the present work, an automated sensitivity-based shape optimization procedure has been developed for the optimal design of free-form reworks and bonded reinforcements and demonstrated through application to a realistic practical problem, the F/A-18 FS 470 bulkhead. Here, a least-squares objective function written in terms of selected stress quantities is used, together with multiple basis shape vectors to specify allowable shape changes. For the rework option, a unique optimal solution has been determined, which achieves a region of constant boundary hoop stress which is 27 per cent less than for the nominal initial uncracked geometry, even though material removal at the critical location is accounted for. Subsequently, for the bonded reinforcement analyses, two distinct optimal designs were determined, corresponding to the case where either shear or peel stresses in the adhesive layer are minimized. Both the shape of the adhesive layer and the reinforcement are allowed to vary, and significant improvements over a conventional reinforcement design are obtained, as assessed by the reduction in peak stresses. These results indicate that the numerical shape optimization procedures presented can provide designs of reworks and bonded reinforcements, which offer significant improvements over standard designs.
The elastic compensation method for limit and shakedown analysis: A review
Authors: Mackenzie D , Boyle J T , Hamilton R
Published: October 2002

A comprehensive review of the elastic compensation method for calculating limit and shakedown load bounds for complex structures is presented. The origins of the method in pressure vessel design by analysis is described and related methods for load and shakedown analysis considered, in particular Marriott's reduced modulus method, Seshadri's GLOSS r-node method and Ponter's modified elastic modulus method. The paper concludes with a recommendation for future work: development of an element level formulation of the method.
Numerical modelling of hydrogen embrittlement of cylindrical bars with residual stress fields
Authors: Toribio J
Published: October 2002

A diffusion-based numerical model was developed to predict the life of cylindrical structural elements suffering hydrogen embrittlement in the presence of residual stress fields. The formulation of the model is based on stress-assisted hydrogen diffusion from the external environment into the metallic material and on a fracture criterion including both the stress level and a critical hydrogen concentration at the fracture point. The model is able to elucidate the effect on hydrogen embrittlement of residual stress fields which are frequently introduced into the engineering components during the manufacturing process.
Non-contacting residual stress decay detecting using alternating current stress measurement
Authors: Chen K , Brennan F. P , Dover W. D
Published: October 2002

Recent work conducted at the Non-Destructive Evaluation Centre of University College London on the residual stress decay detection using the new alternating current stress measurement (ACSM) technology is presented. Flat bar mild steel specimens were used in the experimental study. An equal biaxial compressive residual stress field was introduced into the specimen surfaces by shot peening. The specimens were then subjected to a constant-amplitude cyclic load on a fatigue-testing machine. Under this loading situation, hole-drilling tests indicated that only the residual stress component in the cyclic loading direction had significantly relaxed. Test results showed that this relaxation could be detected by using the existing ACSM system. Further theoretical and experimental efforts are needed to make this technology available for a wide range of practical applications.
Neutron diffraction analysis of the residual stress distribution in a bent bar
Authors: Ezeilo A. N , Webster G. A
Published: October 2002

A well-characterized residual stress distribution resulting from four-point bending has been analysed using the neutron diffraction technique. Residual stresses were obtained from the strains measured at discrete positions through the bent bar on the (111) and (311) crystal planes of a nickel-based alloy using the appropriate diffraction elastic constants. In addition a profile refinement method was used to determine the residual stresses from average strains from all the diffraction peaks in the spectrum. The measured residual stress profiles have also been compared with strain gauge data and with analytical and finite element predictions. It has been established that the profile refinement approach gives stresses which most closely match those obtained by the non-diffraction techniques.
Grid pattern for in-plane strain measurements by digital image processing
Authors: Barone S , Berghini M , Bertini L
Published: October 2002

This paper presents a non-contact and non-destructive method for full-field in-plane strain measurements. Digital image processing is employed for monitoring the deformations of grid lines marked on a planar surface of a component or a specimen. Full-field in-plane strain distributions are obtained by processing the geometrical characteristics of the grid with computer graphics algorithms. The strain field determined in the necking zone of a tensile specimen has demonstrated the benefit of the method.
Synchrotron X-ray residual strain scanning of a friction stir weld
Authors: Webster P J , Oosterkamp L Djapic , Browne P. A , Hughes D. J , Kang W. P , Withers P. J , Vaughan G. B. M
Published: October 2002

Synchrotron X-ray strain scanning has been used to determine the residual stress distribution over the cross-sectional area of a friction stir weld across an I-section made of extruded aluminium alloy type AA 7108 in the T79 condition. Measurements were made using the 311 reflection and a wavelength of about 0.35 A. The dominant longitudinal residual stress field is tensile within and to just outside the friction band where the field drops steeply. Further out there are regions of balancing compression falling to near zero at the outer edges of the sample. The longitudinal residual stresses vary within the range from -60 to 140 MPa. The transverse residual stresses are generally weaker but show a more marked through-thickness variation below the friction band. The residual stress maps show detailed features which are related to the heat flow from crown to root faces and differences between the advancing and retreating sides. The results demonstrate that synchrotron strain scanning is a practicable technique for determining non-destructively internal and through-surface residual strains in light element components. The synchrotron technique complements and extends the range at present covered by neutron and X-ray diffraction methods and is capable of substantial development.
Wire failures in ropes and their influence on local wire strain behaviour in tension-tension fatigue
Authors: Evans J. J , Ridge I. M. L , Chaplin C. R
Published: October 2002

Experimental work using multiple strain gauges has investigated the take-up of load by a wire at either side of a break and how this is affected by fatigue cycling. In addition the effect of a wire break on other wires at the same cross-section has been investigated. The results indicate that a significant amount of slippage can occur for up to 20000 cycles after a wire has broken, causing the load transfer length to change from two strand lay lengths to around three. The transfer length was found to be much lower for Lang's lay rope than ordinary lay and this was attributed to the greater interlayer forces in Lang's lay ropes. With respect to the effect of wire breaks on other wires at the same cross-section it was found that the primary increase is in the strains in wires in the same strand, although wire strains in adjacent strands also increase to some extent. Wires on the opposite side of the rope construction were found to show a decrease in surface strain after the break which may be attributed to local bending effects.
New forming limit diagram of laser tailored blank
Authors: Ghoo B. Y , Park S. W , Keum Y. T
Published: October 2002

The new forming limit diagram (FLD) of a laser tailored blank, which includes independent forming limit curves (FLCs) of a welded zone and constituent base metals, is introduced. To obtain the forming limits of a welded zone, hemispherical dome tests are performed with various widths of symmetric and asymmetric specimens. Together with the know-how to find specific strain conditions for the FLC of a welded zone, the experimental experience is discussed. The dome height at the fracture associated with various specimen widths in the same and different thickness combinations is also investigated in order to examine the formability of a laser tailored blank. In order to see the reliability and applications for the new FLD, the measured strains of a squared cup drawing and the simulated strains of a door inner panel stamping are compared with their FLDs. The successful prediction of the fracture with a new FLD reveals that the forming limits of a welded zone and constituent base metals should be found separately for the accurate evaluation of the formability and workability of the laser tailored blank.
Mechanical behaviour prediction in plain weave composites
Authors: Guagliano M , Riva E
Published: October 2002

The correct application of woven fabric composites requires an accurate knowledge of their mechanical behaviour, in terms of both global stiffness and strength. The aim of this paper is the development of a finite element (FE) approach to the description of the mechanical response starting from the actual mesostructure of the material. Experimental observations identified the unit cell on the basis of symmetry considerations. Different stacking configurations of the unit cell were considered. A global-local procedure was used to reduce the computational effort without losing computational accuracy. A damage model of the material under tensile load was defined and implemented in the FE code. A comparison with experimental stress-strain curves validates the approach proposed.
Slip initiation and progression in helical armouring layers of unbonded flexible pipes and its effect on pipe bending behaviour
Authors: Kraincanic I , Kebadze E
Published: October 2002

Comparatively straightforward analytical formulations are given for determining the bending moment-curvature relationship for a helical layer in unbonded flexible pipes. The approach takes into account the non-linearity of the layer caused by sliding of individual helical elements between the surrounding layers. Bending stiffness of a helical layer is found to be a function of bending curvature, interlayer friction coefficients and interlayer contact pressures. The analysis presented here is based on the Coulomb friction model and is derived using the principle of virtual work. Theoretical results for a typical unbonded flexible pipe using the non-linear formulation for helical layers are compared with experimental data.
Three-dimensional effects for through-thickness cylindrical inclusions in an elastic plate
Authors: Chang T , Guo W , Dong H. R
Published: October 2002

A quasi-three-dimensional theoretical closed-form solution for a cylindrical inclusion embedded in an isotropic elastic plate of finite thickness is obtained using the Kane-Mindlin theory. The present solution gives an insight into the transition from plane stress to plane strain. It is shown that strong three-dimensional effects exist near the inclusion even in very thin plates. Moreover, it is shown that two-dimensional plane stress and plane strain solutions are not always the two limits for a three-dimensional problem. The effects of plate thickness and inclusion radius, material constants of the inclusion and the matrix, as well as interference fitting on the stress concentration factor are discussed. The three-dimensional affected zone around the inclusion can be determined from the present solution. The variation of the lateral contraction and shear stresses is discussed. The comparison between the finite element results and the present results shows good agreement.
Finite element investigation into the torsion test in the range of large strains and deformations
Authors: Peng X , Qin Y , Balendra R
Published: October 2002

Torsion tests with thin-walled tubular, solid cylindrical and Lindholm-type tubular specimens were simulated using the finite element code ABAQUS, in the range of large strains and deformations. The results showed that for thin-walled tubular and solid cylindrical specimens the radii of the specimens almost remained straight during torsion; for Lindholm-type tubular specimens the twist angle of the cross-section at the two ends of the gauge section did not stay constant, due to the change of the specimen geometry (i.e. the end effect). A correction which considers the end effect should therefore be introduced when the stress-strain relationship is characterized. Compared with the stress-strain relationship obtained previously from experiment, a distinct difference was noted when conventional formulae were used to convert the torque and twist angle into the shear stress and shear strain. Further, the influence of axial constraint conditions at the two ends of the specimen was examined; the results showed that axial strains and stresses had no significant influence on the definition of the shear stress-shear strain relation, and hence these can be neglected when the stress-strain relationship is characterized.
Fuzzy logic methods in fatigue and creep
Authors: Harris J
Published: October 2002

Fatigue and creep laboratory data for metals normally exhibit scatter, which implies an element of uncertainty or vagueness in the results. Such data are usually treated by empirical correlations or by mathematical models with some theoretical basis. Confidence limits are sometimes given based upon an assumed probability distribution. On a fine scale, fracture mechanics studies consider the mechanism of crack growth, assuming a uniformly smooth continuum. The treatments aim to provide design working stresses and also the reliability basis for the formulation of inspection and maintenance schedules. Further uncertainty in the interpretation of laboratory test data in terms of in-service material characteristics arises from a few other sources, even if the material types are nominally the same.

Fuzzy logic is a natural means of expressing vague categories of information by means of fuzzy sets and also provides the means of performing logic operations on them. In this work, consideration is given to the application to some aspects of fatigue and creep. Some examples, including fuzzy boundaries between safe and unsafe states, are given to illustrate the methodology, the conclusions are also initially in the form of fuzzy sets. Compared with other methodologies, richer meaning is found in the results.
Designing the cross-section of curved beams for equal magnitude of peak bending stresses
Authors: Dragoni E
Published: October 2002

The paper discusses the problem of designing the cross-section of curved beams to achieve any desired ratio of the stress arising at the inner radius to that arising at the outer radius. A general design equation is developed which identifies the cross-sectional profiles enforcing that condition when the beam undergoes flexural and axial loads. Based on Winkler's theory for circumferential stresses, the equation shows the extent to which trapezoidal and triangular cross-sections can develop equal peak stresses for an assortment of loading conditions. Several three-dimensional finite element analyses of reference configurations are performed that confirm the theoretical findings.
Analysis of residual stresses generated by progressive induction hardening of steel cylinders
Authors: Pacheco P M C L , Savi M. A , Camarão A. F
Published: October 2002

The internal stresses generated during quenching can produce warping and even cracking of a steel body and, therefore, the prediction of such stresses is an important task. Phenomenological aspects of quenching involve couplings between different physical processes occurring in the phenomena. The present contribution is concerned with modelling and simulation of quenching, presenting an anisothermal model formulated within the framework of continuum mechanics and the thermodynamics of irreversible processes. A numerical procedure is developed based on an operator split technique associated with an iterative numerical scheme in order to deal with non-linearities in the formulation. With this assumption, the coupled governing equations are solved involving four uncoupled problems: thermal, phase transformation, thermoelastic and elastoplastic behaviours. The proposed general formulation is applied to analyse progressive induction hardening of steel cylinders. Numerical results suggest that the proposed model is capable of capturing the main behaviour observed in experimental data.
A force field superposition approach to plane elastic stress and strain analysis
Authors: Fenner R. T
Published: October 2002

The force field superposition method for linear elastic problems of stress and strain analysis involves representing the stress and displacement fields in a given solution domain as a superposition of fields generated by a number of point forces. These forces are located outside the solution domain, and in the case of two-dimensional, singly connected finite domain problems can be uniformly distributed around the perimeter of a circle enclosing the physical domain. Doubly connected and infinite domain problems can also be treated. The results of some simple test problems show that remarkable accuracy can be achieved with very little computational effort relative to other numerical methods. More complex problems require the solution domain to be divided into several subdomains, each of which may be subjected to superposition analysis.
A parametric study of inclusion interaction in particulate- and fibre-reinforced materials using the boundary element technique
Authors: Knight M. G , de Lacerda L. A , Henshall J. L , Wrobel L. C
Published: October 2002

The purpose of the present work is to analyse the effect of inclusion interaction within a composite material using the boundary element (BE) technique. The stress distributions have been examined as a function of the inter-fibre/particle separation distance, interfacial conditions and the relative moduli and size of neighbouring inclusions. In particular, the relative size of interacting inclusions detrimentally affects the localized stress concentrations (fully bonded), and in certain circumstances can result in a complete loss of contact within 'shielded’ inclusions (non-bonded). Furthermore, the analysis of inclusions with differing Young's moduli shows that, if one of them has a modulus greater than that of the matrix, and the other a modulus lower than that of the matrix, then there is a significant reduction in the local stress concentrations. Hence, microcracks, which often nucleate in and around second-phase materials, would have a lower probability of initiation, which in turn could lead to an improvement in the fracture strength of the bulk material. For verification, the results have been found to correlate well with the present authors' finite element (FE) simulations and, where possible, comparison of the results with analytical models shows good agreement.
Identification of the sources of non-adiabatic behaviour for practical thermoelastic stress analysis
Authors: Quinn S , Dulieu-Barton J. M
Published: October 2002

In this paper the sources of non-adiabatic behaviour in standard thermoelastic stress analysis are identified. Previous work on non-adiabatic effects is critically reviewed in the context of the practitioner of thermoelastic stress analysis, and from this a hierarchical relationship between stress gradients, material and loading frequencies is developed. These three effects are studied in turn, and the use of paint coatings is identified as the major cause of non-adiabatic behaviour.
Shakedown and plastic modelling of a two-tube problem
Authors: Peridas G , Hills D. A
Published: October 2002

The problem studied is that of two elastic-ideally plastic thin-walled tubes, connected end to end. Their outer ends are fastened to rigid walls, and the interface between them is subjected to a combination of axial force and torque. As the geometry is simple, it is possible to obtain closed-form solutions to the plastic flow rules, even though each member supports a complex stress state. The elastic, shakedown and limit states are found in closed form, together with the internal stress and displacement history.
Analysis of a thermally induced phase transformation strain state for the TiNi shape memory alloy under a complex stress state
Authors: Socha G , Dietrich L
Published: October 2002

In the paper an analysis of isostatic testing results for the Ti-51.0 at. % Ni shape memory alloy are presented. Tests were performed in a complex stress state, the tubular specimen being loaded by a combination of axial load and torque. After achieving a specified level of the load under complex and various stress states, a thermal cycle was started. During the test, the temperature-induced phase transformations were observed as variations in the transformation strain tensor components. These strain components were measured with the use of resistive strain gauges, digitally recorded and processed to extract pure phase transformation strains. For selected complex stress states, the transformation strain tensor components, principal transformation strains and characteristic temperatures of the phase transformations were found. On the basis of the experimental data, basic relations between characteristic parameters of an imposed stress state and the temperature-induced phase transformation strain state were determined.
Inclined edge cracks in compressive stress fields: Determination of mode II stress intensity factors
Authors: Porter M. I , Hills D. A
Published: October 2002

The problem of finding the crack tip stress intensity for an inclined edge crack in an elastic half-plane, subjected to a bulk compressive field, is solved. The technique is capable of finding solutions for very shallow cracks with friction present on the crack faces with accuracy, and in a computationally efficient manner.
The thermomechanical stress-strain response of intumescent mat materials through experiments and strain decomposition
Authors: Kim H. J , Kim J. S , Walter M. E , Lee J. K
Published: October 2002

Intumescent mat materials in catalytic converters undergo chemical reactions that lead to material property changes and volume expansion during heating processes. Dead weight (load control) and displacement control compression experiments have been performed to explore static and transient stress-strain responses. The apparatus and methods for both experiments are described. The experimental results together with a strain decomposition procedure yield a master curve that can be employed for constitutive modelling.
Boundary element analysis of cracked panels with mechanically fastened repair patches
Authors: Wen P. H , Aliabadi M H , Young A
Published: October 2002

In this paper, lap joints and mechanically attached repairs containing cracks are analysed by the boundary element method. A coupled boundary integral formulation of shear deformable plate and two-dimensional plane stress elasticity is utilized to allow the modelling of bending and membrane forces. Stress intensity factors, three for the bending problem and two for the membrane problem, are evaluated from crack-opening displacements. Several examples are presented to demonstrate the accuracy and robustness of the proposed method. The stress intensity factor solutions are shown to be dominated by the bending effect.
The torsional buckling behaviour of shafts with transverse holes
Authors: Robotham W. S , Hyde T. H , Williams E. J , Taylor J. W
Published: October 2002

The paper presents the results of a parametric finite element study of the failure behaviour of shafts with a single row of transverse holes, subjected to torsional loading. The introduction of the holes reduces the peak torque at failure compared with the equivalent plain shaft and the reduction increases with increasing D/t (shaft diameter-wall thickness) ratio and d/D (hole diameter-shaft diameter) ratio and with the number of holes. Depending on the geometry used, either plastic collapse or elastic-plastic buckling failure modes can occur. For given values of n (number of holes) and D/t and d/D ratios, the failure torque varies by less than 5 per cent for L/D (shaft length-diameter) ratios in the range 0.6 to 4. The greatest reduction in the failure torque occurs when the D/t ratio is such that the number of circumferential lobes in the elastic buckling mode for the equivalent plain shaft is the same as the number of holes in the shaft.
Limit loads for knuckle-encroaching nozzles in torispherical heads: Experimental verification of finite element predictions
Authors: Hsieh M. F , Moreton D N , Mistry J , Moffat D. G
Published: October 2002

The manufacturing and testing procedures for two experimental pressure vessels with large nozzles encroaching into the knuckle region of the vessel head are described. Experimental linear elastic stress levels and plastic loads for pressure and combined axial and in-plane bending nozzle loads are compared with predicted values determined using non-linear finite element analysis. The quality of the results are considered to justify the procedures developed by the authors to conduct a parametric study of the individual limit loads and their interaction for these complex structures.
Solution of the boundary value problem for a kinking crack in a bulk compression field
Authors: Porter M , Hills D. A
Published: October 2002

The solution of the boundary value problem for a macroscopic crack with a small wing crack, in a linear elastic brittle material, due to a bulk compressive stress field is considered. The crack, initially subject to pure mode II loading, propagates by kinking at its end and extending along a new trajectory, in the classical opening mode. The innovations of this paper are, firstly, the introduction of a free surface into an infinite plane solution, so that the original crack is an edge crack in a half-plane, and, secondly, the ability to consider rapidly varying stress gradients on both segments of the kinked crack. Solutions are presented for (a) an inclined crack in a uniform compressive field and (b) cracks subject to contact loading from a rigid punch loading the half-plane via a linear elastic interlayer.
Analysis of the buckling of long cylindrical shells embedded in an elastic medium using the energy method
Authors: Fok S. L
Published: October 2002

Buckling of a long cylindrical shell, embedded in an elastic material and loaded by a far-field hydrostatic pressure, is reanalysed using the energy method together with a Rayleigh-Ritz trial function. For simplicity, linear elasticity theory is employed and inextensional buckling is assumed. An expression is derived relating the pressure load to the buckling mode number, from which the critical load can be determined. The solution is similar to that given by Forrestal and Hermann using a more elaborate approach. However, the present solution predicts lower buckling load if Poisson's ratio of the surrounding medium is less than 0.5 and hence seems to provide better agreement with experiments.
Shakedown analysis for complex loading using superposition
Authors: Muscat M , Hamilton R , Boyle J. T
Published: October 2002

Bounding techniques for calculating shakedown loads are of great importance as design criteria since these eliminate the need for performing full cyclic loading programs either numerically or experimentally. The classical Melan theorem provides a way to recognize whether or not elastic shakedown occurs under a specified loading. Polizzotto extended Melan's theorem to the case where a combination of steady and cyclic loads are acting on the structure. The purpose of this paper is to present a finite element method, based on Polizzotto's theorem, to estimate elastic shakedown for a structure subjected to loads resulting from a combination of steady and cyclic mechanical loads. This method, called non-linear superposition, is then applied to investigate the shakedown behaviour of a biaxially loaded square plate with a central hole. Results obtained for the plate with a hole problem are compared with those available in the literature and are verified by means of cyclic elastoplastic finite element analysis.
Deformation behaviour of the cross-section of a heat-sealed area in plastic film used for liquid package bags
Authors: Umezaki E , Futase K
Published: October 2002

Displacements on a cross-section of a heat-sealed area in laminated plastic film used for liquid package bags are measured by a digital image correlation. All the specimens used for obtaining the images necessary to measure the displacements are cut into the required shape from heat-sealed package bags. The images are recorded by an 8mm video camera via a microscope, and digitized by an image-processing device. Twenty-six images are used for obtaining the displacements between the no-load condition and failure of the specimens. As a result, a characteristic displacement is found in the heat-sealed area.
The measurement of prior plastic deformation in metallic alloys using the neutron diffraction technique
Authors: Smith D J , Webster G A
Published: October 2002

The neutron diffraction technique has been used to determine the extent of prior plastic deformation in an aluminium alloy weld and preloaded cracked steel beams. The change in peak width has been shown to be a function of the prior plastic deformation, and is found to be insensitive to the direction of prior straining, material and the orientation of the diffraction vector. Prior plastic deformation has also been shown to influence the reference peak angle. The distributions of prior plastic strain in the steel cracked beam subjected to an overload were found to be in good agreement with results from finite element analyses.
Orientation and formability of orthotropic sheet metals
Authors: Ress D W A , Power R K
Published: October 2002

This paper examines the formability of automotive sheet metals: CR steels and 6000 series aluminium-magnesium alloys. Necking strains are used to determine the forming limits; i.e. a diffuse instability condition is reached under in-plane biaxial stressing. The theory admits material anisotropy, work-hardening and sheet orientation under any ratio of applied principal stresses. It has been programmed to accept orientations between the principal stress axes and the sheets' rolling direction in 15° increments between 0° and 90°. The ratio between the principal stresses may vary between 0 and ± 1. The input data required are the width-thickness strain ratios ( r values) in directions 0°, 45° and 90° to the roll and the Hollomon hardening exponent ( n value). The output is presented in four diagrams: the critical subtangent-stress ratio and plots between three combinations of the limiting principal engineering strains: (a) two in-plane strains, (b) major in-plane strain versus thickness strain and (c) minor in-plane strain versus thickness strain. Each diagram shows the influence of rotating the principal stress axes in increments of 15° to the roll. The forming limit diagram of type (a) gives the traditional presentation of a forming limit diagram (FLD). This FLD may be established experimentally from the strain in a surface grid lying around splits. In practice, a few production panels may be gridded for die-tryout and to examine a change in material. The alternative FLDs, types (b) and (c), are proposed to provide quality control with the increasing use of ultrasonics to monitor thickness of pressed panels. An example of type (b) is determined experimentally for CR1 steel.
Stress singularities at the free surface of an axisymmetric two-material creep test specimen
Authors: Hyde T H , Sun W
Published: October 2002

The nature of the stress singularity that occurs at the surface of an axisymmetric, two-material creep test specimen has been investigated. Steady state finite element analyses were obtained for this purpose, using Norton's power law creep equations having the same stress exponent for each material. The strength of the singularity was found to be strongly dependent upon the relative creep strengths of the two materials, but was surprisingly insensitive to the relative dimensions of the two materials. The implications of the results for practical situations are discussed.
End reinforcement of composite cylinders for biaxial testing
Authors: Mistry J , Dong L
Published: October 2002

A detailed theoretical investigation has been carried out into factors affecting external end reinforcement of GRP (glass-reinforced plastic) cylindrical specimens for biaxial tests using axisymmetric solid finite elements. The reinforcement method is intended as a general solution to a wide range of applied axial and hoop stresses in the third quadrant of the stress field. Among the parameters considered were the ratio of hoop-to-axial stress, material employed for reinforcement, thickness, length and taper angles of the reinforcement layers. The assessment of the effective control of high discontinuity stresses at the fixed ends by the end reinforcement was made with the help of the Tsai-Wu strain index distribution and decay length of the bending stresses. The paper also describes the preliminary experimental work to show the effectiveness of an external composite reinforcement method in controlling the strain distribution of GRP cylinders closed by rigid end flanges.
Stresses in a flat plate due to a loose pin pressing against a cracked hole
Authors: Lin S , Hills D A , Nowell D
Published: October 2002

The elastic contact stress field caused by a radially loaded pin in a nearly conforming hole is studied. The elastic limit of the configuration is found, together with crack tip stress intensity factors for radial cracks emanating from the bolt hole, the latter using the distributed dislocation approach. A closed-form solution is therefore generated to enable an elastic design philosophy to be followed for both perfect and flawed configurations, providing that there are no nearby boundaries.