bluuebunny/crossref_metadata_2025 huggingface dataset:
A Clinical Review of the Hyperlaxity of Joints with Particular Reference to Osteoarthrosis
Authors: Bird H A
Published: February 2007

The range of observed movement at a given joint varies with a gaussian distribution throughout the population. Individuals whose joints display an unusually high degree of laxity are susceptible to a variety of rheumatic and orthopaedic symptoms. The impression that such individuals develop premature osteoarthrosis is a strong one, but hard to prove. In addition, certain individuals with inherited abnormalities of connective tissue are undoubtedly at risk of accelerated osteoarthrosis.

The observed range of movement at a joint is determined by a variety of factors. The main ones are the muscular tone, the laxity of the collagen that contributes to the joint capsule and surrounding structures, and the shape of the articulating bony surfaces. The first of these is probably neurologically mediated, the latter two are usually genetically determined. In a majority of cases it is probably the mechanical joint instability that produces the articular damage, though the alternative hypothesis is that the osteoarthrosis is initiated by genetic aberrations in the collagen that coincidentally cause lax joints. Clinical and family studies using the Leeds Hyperextensometer will help to clarify this and it remains a possibility that genetic markers may point to those individuals who will be at particular risk of osteoarthrosis should joint hyperlaxity develop.
Varus and Valgus Deformities of the Knee Joint: Disease Specific or Biomechanical?
Authors: Fawthrop Fiona , Cushnaghan Janet , Shue Lily , Dieppe Paul
Published: February 2007

160 patients (231 knees) with an angulation deformity of the knee have been examined. Varus deformity was uncommon except in patients with osteoarthritis. Osteoarthritis subsets, such as pyrophosphate arthropathy tend to cause a valgus deformity, as does rheumatoid disease. An analysis of 50 consecutive patients presenting with idiopathic knee osteoarthritis supports the impression that focal disease of the medial (common) or lateral (uncommon) compartment can occur. Different disease processes, with different associations, may be responsible. The biomechanics of the knee joint in relation to the development of angulation deformities is discussed.
Detection of Myocardial Scars in Neonatal Infants from Computerized Echocardiographic Texture Analysis
Authors: Kamath M V , Way R C , Ghista D N , Srinivasan T M , Wu C , Smeenk S , Manning C , Cannon J
Published: February 2007

It has been demonstrated that highly reflectile echoes (HREs) on standard echocardiograms may represent foci of myocardial fibrosis, calcification, or infiltration. A pilot study of the echocardiograms of premature infants by our group has indicated the presence of HREs in many stressed infants. We have subsequently shown that these HREs correspond to myocardial scarring or necrosis.

By studying normal two-dimensional echocardiograms and those with visually observed highly reflectile echoes (HREs), we have been able to develop echo-intensity ranges for normal neonatal myocardium and suspected foci of necrosis. An amplitude analysis of the intensity levels of these highly reflectile areas (HREs) in the echocardiogram has indicated that their mean intensity was significantly higher than the surrounding healthy myocardial areas. Significant correlation was found between these highly reflectile echo zones and calcified or necrotic tissue based on postmortem pathological examination.

An objective method of quantifying the ultrasonic reflection amplitude has thereby been developed by us, based on image analysis of the echograms available from the B-scan system. Algorithms have been developed for evaluating the greylevels (or echo intensities or reflection amplitudes) of the pixels, normalizing them with respect to the reflection amplitude of the pericardium, and then printing out the grey-level distribution over an image. Appropriate software has been developed to designate scarred myocardial segments, based on the mean and standard deviation of the selected region on the echo image in comparison with these values for the pericardium.
Syringe Pump Design
Authors: Wadham Paul
Published: February 2007

With the evolution of special care baby, intensive care, and coronary care units over the last decade, there has developed a need for greater accuracy in the control of increasingly potent infusions.

The design of bedside syringe pump infusers that administer the contents of a syringe to a patient at a constant and predetermined rate will be considered in terms of their ergonomics, control, and safety.

Syringe pump design has evolved over the past few years from simple mechanised forms of syringe driving to very sophisticated and precisely-controlled drive systems capable of high volumetric accuracy over a wide range of clinical conditions and sustained for long time periods. This has led to the development of new and critical forms of drug therapy.

In addition, important progress has been made in the safety and reliability aspects of syringe pump design. Modern syringe pumps are expected to have fail-safe electronics to protect the patient in the event of a fault occurring. With the advent of modern microprocessor techniques, future syringe pumps can be expected to incorporate further sophisticated operational and safety enhancements, whilst remaining simple to operate.

Typical safety enhancements could include the incorporation of a variable pressure sensor to protect against unwanted pressure build up in the IV line, the use of absolute linear encoding techniques for control and monitoring of the infusion, and the increasing use of self-tests and diagnostics to aid the user.

Operational enhancements could include the ability to support pharmacokinetic techniques, as well as closed loop drug therapy and remote computer control.

Whilst this suggests that infusion therapy might become too sophisticated for day to day use, comprehensive interactive instructions and diagnostic aids would contribute greatly to ease of use.

Good user training will be of increasing importance to maximize the benefits of the advances in syringe pump design.
Parenteral Nutrition and Infusion Technology
Authors: Wood Susanne R
Published: February 2007

Parenteral nutrition is used to support life during a period of intestinal failure when nutrients cannot be absorbed through the gastro-intestinal tract. Hypertonic solutions of amino-acids and glucose, with added vitamins, electrolytes, and trace elements, are administered, together with isotonic fat emulsions, directly into the superior vena cava or right atrium of the heart.

Access to the central venous circulation is obtained by the insertion of a soft, silicone rubber catheter into a neck or arm vein. Life threatening metabolic disturbance, infection, and catheter-associated complications may occur in the absence of attention to detail.

To prevent sudden changes in fluid and electrolyte status, and blood glucose levels, a method of flow control must be selected which remains accurate when infusing fluids of varying density or when the patient is mobile. It is important that the method selected does not allow high pressures to develop in the soft intravenous catheter and can be managed safely in the intensive care unit, the general ward, or by the patient in his own home.
Continuous Insulin Infusion
Authors: Pickup John C
Published: February 2007

A major new approach to the improvements of metabolic control in insulin-dependent diabetic patients is the replacement of insulin by delivery systems which simulate non-diabetic insulin secretory patterns. In the last ten years a number of open-loop, extracorporeal, portable infusion pumps have been used in research trials tasting from a few days to several years. Routine treatment by insulin pumps is now being considered. Most infusers are syringe-drivers, although peristaltic and reciprocating pumps have also been employed. All are based on a slow, basal delivery rate, supplemented by insulin boosts at meal-times. The most popular infusion route is via the subcutaneous tissue. Technological development is concentrating on miniaturisation, alarms (such as low battery state and motor over-run) and more flexible/programmable delivery rates.

Attempts are in progress to ‘close the loop’ using an implanted glucose sensor. Most electrodes are amperometric or potentiometric enzyme sensors employing immobilised glucose oxidase. Encouraging in vivo results are being obtained from a novel amperometric biosensor which uses ferrocene to mediate electron transfer. The most likely implantation site is the subcutaneous tissue.
The Development and Application of Portable Infusion Devices
Authors: Derlien M L
Published: February 2007

Portable infusion devices are designed for the controlled delivery of a drug solution into the body over an extended period of time. Two categories of pumps are described. Non-electric pumps, which include balloon-powered, vapour-pressure, and spring-powered pumps; and electric pumps, which include peristaltic, piston-and-valve, and syringe pumps. The drug may be delivered to a variety of sites (e.g., subcutaneous or intramuscular) through various channels. Current clinical applications include iron chelation, analgesics in terminal cancer, post-operative pain, Heparin administration, insulin for diabetes, cancer chemotherapy, and various hormone administrations. Infusion can be continuous or pulsatile depending on the application. It is predicted that there will be more widespread adoption of current techniques and that smaller and more intelligent pumps, which may include closed loop control, will be developed.
Curve and Surface Representation by Iterative B-Spline Fit to a Data Point Set
Authors: Lord Marilyn
Published: February 2007

The method of B-splines provides a very powerful way of representing curves and curved surfaces. The definition is ideally suited to applications in Computer Aided Design (CAD) where the designer is required to remodel the surface by reference to interactive graphics. This particular facility can be advantageous in CAD of body support surfaces, such as design of sockets of limb prostheses, shoe insoles, and custom seating. The B-spline surface is defined by a polygon of control points which in general do not lie on the surface, but which form a convex hull enclosing the surface. Each control point can be adjusted to remodel the surface locally. The resultant curves are well behaved. However, in these biomedical applications the original surface prior to modification is usually defined by a limited set of point measurements from the body segment in question. Thus there is a need initially to define a B-spline surface which interpolates this set of data points. In this paper, a computer-iterative method of fitting a B-spline surface to a given set of data points is outlined, and the technique is demonstrated for a curve. Extension to a surface is conceptually straightforward.
The Clinical Aspects of Heart Valve Replacement: An Overview
Authors: Taylor K M
Published: February 2007

Cardiac surgeons have to start from the basis that no perfect heart valve prosthesis presently exists. In the past few years a number of heart valve substitutes have been released for clinical implantation with little objective data to support their clinical acceptability. Uncertainty exists in the minds of many cardiac surgeons in interpreting results of in vitro and in vivo testing. Confusion has been increased by the tendency of many units to implant a small number of a variety of different heart valve substitutes, thus losing the opportunity for meaningful data. Further progress in the understanding and development of better heart valve substitutes will require a disciplined approach, both to in vitro and in vivo testing.
The Long-Term Clinical Assessment of Heart Valve Substitutes
Authors: Drury P J , Black M M , Lawford P V , Kay R
Published: February 2007

This paper describes the organization and routine management of the UK Multicentre Valve Trial. Details are given of the present data bank comprising information on 9859 artificial valve implants collected from 44 surgeons in 22 centres. The paper discusses various analyses of the long term performances of different valves. The validity of these analyses and this approach to valve performance assessment is discussed with reference to: (i) the limitations of the present statistical techniques, (ii) the inherent variability of data arising from differences in patient/prosthesis selection and surgical techniques amongst the various participating centres, and (iii) a new approach for the estimation of the failure rates of valve implants taking such inherent variability of the data into consideration.
Laboratory Assessment of the Design, Function, and Durability of Pericardial Bioprostheses
Authors: Fisher J , Reece I J , Jack G R , Cathcart L , Wheatley D J
Published: February 2007

The design, function, and durability of four pericardial bioprostheses have been studied in the laboratory. Variations in design and construction affected both the pressure difference across the valves and the leaflet dynamics. In the durability tests tissue failure was found in all valves, with tears at the edge of the leaflets caused by abrasion on the cloth-covered inner frames. In the Ionescu–Shiley standard valves, tears were also detected at the coaption sutures. These results have been compared with failure modes in explanted clinical valves.
The Causes of Femoral Head Roughening in Explanted Charnley Hip Prostheses
Authors: Isaac G H , Atkinson J R , Dowson D , Kennedy P D , Smith M R
Published: February 2007

The effect of particles of first, acrylic bone cement containing either barium sulphate or zirconium dioxide as X-ray contrast media, and secondly, particles of fresh cortical bone, on a surgical grade stainless steel surface against which polyethylene was rubbing, has been investigated. It was found that under physiological loads, particles of acrylic cement which have been embedded in the polyethylene bearing surface caused severe scratching of the stainless steel. Some scratches were found to have pronounced lips similar to those observed on the femoral heads of explanted Charnley hip prostheses. Cortical bone produced only slight damage to the stainless steel. In the case of the acrylic cements, the abrasive constituent was isolated and found to be clusters of particles of the X-ray contrast medium. Particles of acrylic cement are frequently observed embedded in the wear surfaces of explanated Charnley acetabular cups and these particles have also been found to contain clusters of X-ray contrast medium particles. It is therefore concluded that the damage to implanted stainless steel prostheses is predominantly caused by the X-ray contrast medium in the acrylic cement.
A Review of Some of the Rheumatological Problems and Engineering Capabilities
Authors: Bird H A
Published: February 2007

Up to 150 different diseases can affect the joints and musculoskeletal system. These range from musculoskeletal rheumatism, which is self-limiting and causes no demonstrable joint pathology, through metabolic and degenerative joint diseases to the chronic auto-immune disorders of inflammation of which rheumatoid arthritis is the most common in the United Kingdom, and the most severe.

Many of these conditions are characterised by inflammation which has the cardinal symptoms of heat, swelling, pain, erythema, and loss of function. Rheumatologists require accurate and objective methods of measuring all these parameters at a large number of joints, each of different anatomical structure, in order to adequately monitor the course of the disease and its response to treatment. Complementary information is required on the function of muscles, ligaments, tendons, and bone, as well as the joints. Although the individual analysis of each of these components is likely to provide the most information on disease pathogenesis, functional evaluation which integrates many of these variables simultaneously is likely to provide most information on the patient's progress. Both are needed.

In the realm of therapeutics, a wide range of prostheses, all of sound bioengineering design, are available. Greater problems arise in the matching of different prostheses to an individual patients needs and in their fixation in a patient whose disease is constantly altering the joint contour. The attention of bioengineers is now being directed towards the design of replacements for other parts of the joint and musculoskeletal system, for example, ligaments. Adequate methods of testing these under repetitive stress and of measuring the improvement they provide will be increasingly required.
An in Vitro Method for the Measurement of Sarcomere Length in Human Muscle
Authors: Cutts Alison
Published: February 2007

A possible means of quantifying the surface electromyographic (EMG) signal is to try to relate it to the sarcomere length of the muscle, which is a function of muscle tension. The present work deals with the measurement of sarcomere length in human muscles. Sarcomere length is measured by using a thin sheet of muscle as a diffraction grating and obtaining and photographing its diffraction pattern using a modified light microscope. Samples of human muscle are available only from cadavers in the anatomical position, so a procedure for prediction of sarcomere length at other positions is described. The limitations of working with cadavaric tissue are outlined and discussed, and, for the readers unfamiliar with the structure and physiology of striated muscle, a brief description of this is given.
Microwave Thermography in Rheumatic Disease
Authors: Fraser S M , Land D V , Sturrock R D
Published: February 2007

Microwave thermography is a technique measuring emitted microwave radiation from sites of inflammation. The wavelength used is of the order of 10 cm and is therefore able to penetrate to clinically useful depths. A microwave detector was applied to the study of the knees of normal individuals and patients with rheumatoid disease in conjunction with clinical assessments. There was a significant correlation with the clinical variables. The technique was found to be valid independent of environmental conditions and to have acceptable reproducibility in normal individuals over three months. Microwave thermography is currently being applied to studying the sacroiliac joints as a possible diagnostic aid in ankylosing spondylitis. Future work on the use of microwave thermography will include an assessment of the ability of the technique to measure the response of the patient with rheumatoid arthritis to therapy.
Pre- and Post-Operative Gait Analysis of Hip Osteoarthritic Patients Fitted with Ceramic Autophor Total Hip Replacement
Authors: Rigas C , Xenakis T
Published: February 2007

A number of gait parameters were recorded and analysed for two groups of patients. Group A consisted of hip osteoarthritic patients, examined just prior to operation. Group B consisted of patients fitted with a ceramic Autophor hip replacement, following hip osteoarthritis. The measuring system was a conductive walkway in conjunction with a dual light-beam/photocell sub-system. Analysis included comparisons of the gait parameters between the patients and the normals taken from the literature, between the two sides of each patient, and between the two groups. Values for group B, in general, showed an improvement, compared with those for group A, but they were still inferior to the corresponding values for normals.
Mechanical Properties of Trabecular Bone by a Non-Destructive Compression Testing Approach
Authors: Linde Frank , Gøosthgen Charlotte Buch , Hvid Ivan , Pongsoipetch Buntoeng , Bentzen Søosren
Published: February 2007

In order to optimize non-destructive mechanical testing of trabecular bone specimens, different techniques were analysed, and correlations were established between properties derived from such non-destructive testings and those derived from destructive testing. Non-destructive testing to a fixed percentage of predicted ultimate stress was hampered by inaccuracy of this prediction. Simulation of non-destructive testing conducted to the linear' part of the compression curve using a drop of the increase of the stiffness (slope of the compression curve) below a certain value as stop criterion revealed strong correlations ( r: 0.97–0.99) between the stiffness at the stop point and modulus of elasticity derived from destructive testing. However, trabecular damage will probably occur during such testing because high strain values were obtained. Testing to a fixed strain (0.6 per cent) also revealed strong correlation between the stiffness at the 0.6 per cent strain level and modulus of elasticity ( r = 0.96) derived from destructive testing. By this technique trabecular damage was avoided and standardized elastic and viscoelastic energies could be obtained. Prediction of modulus of elasticity by indirect methods such as modulus of elasticity of specimens from the opposite symmetric location ( r = 0.73), bone mineral concentration ( r = 0.72) derived from photon absorptiometry and the CT number ( r = 0.78) derived from quantitative computed tomography showed less strong correlations.
Design and Development of a Versatile Hip Joint Simulator and a Preliminary Assessment of Wear and Creep in Charnley Total Replacement Hip Joints
Authors: Dowson D , Jobbins B
Published: February 2007

This paper describes the design of a new 3-station hip joint simulator and briefly discusses early results.
Prosthetic Hip Failure: Preliminary Findings of Retrospective Radiograph Image Analysis
Authors: Jones P R , Taylor C J , Hukins D W L , Hardinge K , Porter M L
Published: February 2007

We present the results of a retrospective study based on radiographs of 75 successful total hip replacements, and 103 which involved failure of the femoral component of the prosthesis. The failures were selected to exclude cases in which infection was implicated. Success was defined as absence of adverse clinical or radiological symptoms for at least 12 years after surgery. A failure was either obvious, for example, stem fracture, or defined as one which showed progressive radiological and clinical degeneration resulting in the need for revision surgery. Measurements were made on radiographs which had been obtained immediately post-operatively, so that the features measured would depend on surgical procedure rather than on any subsequent biological response. Computer image analysis has been used to make precisely defined, reproducible measurements of 58 parameters characterising the insertion of the femoral component of a standard Charnley prosthesis. These parameters include geometry of insertion, distribution of cement, surrounding bone thickness, and so on. Clinical findings, including patient weight, were also recorded with the measurements on computer disc. Preliminary statistical comparisons indicate that several of the measured parameters are of predictive value for determining the long-term success or failure of total hip replacements.
Bearing Surface Design in Total Knee Replacement
Authors: Walker Peter S
Published: February 2007

Surfaces for condylar total knee replacement are designed using computergraphics techniques. An average anatomical femoral surface is represented mathematically. Mathematical equations are written to describe normal knee motion and normal laxity. Tibial surfaces are generated by placing the femur stepwise in multiple sequential positions, through a defined three-dimensional motion or laxity path. In addition, a flat tibial surface is defined, to represent the least amount of femoral-tibial conformity in currently-used knee replacements. Elasticity theory is used to calculate the maximum contact stresses at the femoral-tibial contact points. The least stresses are produced with a fixed axis cylindrical motion, while the highest are with a flat tibial surface. A surface based on laxity produces lower stresses than for normal knee motion, and is thought to be acceptable in terms of both freedom of motion and stability. Such a laxity surface is proposed as being suitable for total knee design.
A Methodology for Mechanical Measurements of Technical Constants of Trabecular Bone
Authors: Yahia L H , Drouin G , Duval P
Published: February 2007

Vertebral trabecular bone was tested by non-destructive uniaxial and triaxial loadings with the purpose of investigating the orthotropic properties of bone. A triaxial testing apparatus using hydrostatic pressure was developed and allowed to characterise the bony tissue in a three-dimensional stressed state. Thirty specimens, in the form of 10 mm cubes, were tested. The Young's moduli obtained in this study for the trabecular bone of human lumbar vertebrae are found to be in agreement with the values obtained by ultrasonic methods. Analyses of triaxial compressive tests provided, for the first time, the Poisson's ratios of vertebral trabecular bone. These values are found to satisfy thermodynamic restrictions established by Cowin and Van Buskirk (1986). Finally, no significant differences in the material properties were found for segment level (L3-L4).
Stress Concentration Factors under Dynamic Loading Conditions
Authors: Durelli A. J. , Dally J. W.
Published: February 2007

Dynamic photo-elasticity has been employed to determine the stress concentration factor at a central circular hole in a strut subjected to axial impact. The model was machined from a low modulus photo-elastic material (a urethane rubber compound known commercially as Hysol 8705), and the photographs of the dynamic fringe patterns were taken with a ‘Fastax’ camera or a microflash-camera combination.
Instability and Steady-State Coupled Motions in Vibration Isolating Suspensions
Authors: Henry R. F. , Tobias S. A.
Published: February 2007

When using non-linear spring systems for vibration isolating suspensions, motion initiated in one of the degrees of freedom may cause another degree of freedom to become unstable and commence to vibrate. Subsequently, the two motions become coupled.

The paper deals with instability and coupling phenomena observed with a six degree of freedom model suspension. This is done by reducing the system to equivalent two-degree of freedom non-linear systems, and subsequently discussing the various types of solution of these. The equations of motion discussed are of the form

It is shown that when the value of the coefficients n and r is n = r = 3·0 then the equations describe the instability and coupling phenomena relating to the vertical motion and the pitching motion of the mass. When n = r = 1·0 then the equations describe the conditions arising between the vertical motion and the yawing motion. The various solutions of these equations are discussed. It is shown that instability in a mode can arise only when the ratio of the linear natural frequencies of the mode initially at rest and the mode initially disturbed lies within certain limits. For n = r = 3·0 the mode with the lower natural frequency may, upon motion having been initiated in the higher mode, become unstable and commence to vibrate. On the other hand, the mode with the lower natural frequency can vibrate on its own since the higher mode remains stable at rest. For n = r = 1·0 the conditions are reversed. Thus, in both systems the coupling is non-symmetrical, but it can be reversed by changing the ratio of the natural frequencies in the appropriate way. The steady-state coupled solutions of the two types of systems are also different. For n = r = 3·0 the steady coupled solution involves a motion in which the degrees of freedom vibrate with equal or opposite phase. For n = r = 1·0 the coupled modes vibrate with a phase difference of ±90°. In both cases the amplitudes of the two degrees of freedom are related, their frequencies are equal and are determined by the amplitudes.
Propagation of Fatigue Cracks in Various Sheet Materials
Authors: Frost N. E.
Published: February 2007

Fatigue tests have been carried out on sheet specimens approximately 10 in. wide by 0·1 in. thick containing a small central slit, and measurements of the growth of the fatigue cracks initiated by the slit were made as the test proceeded. Nine common engineering sheet materials were tested, the applied nominal cyclic stresses being of a relatively low order, that is, between about ±1/2 and ±5 ton/in2; in each test a mean tensile stress was applied so that the loading was never compressive. The results were analysed in accordance with the geometrical similarity hypothesis suggested by Frost and Dugdale (1)†, that is, d l/d N = K l, where l is the crack length and N is the number of cycles. It was found that over the region of stable continuous fatigue crack growth the coefficient K was proportional to the cube of the alternating stress for all materials tested and the growth law could be represented by d l/d N = σ3 l/ Ns where Ns depended on nominal mean stress and material, and σ is the alternating stress.
Laminar Flow in the Open Thermosyphon, with Special Reference to Small Prandtl Numbers
Authors: Leslie F. M. , Martin B. W.
Published: February 2007

By use of approximate methods, the rates of heat transfer are predicted for laminar flow due to natural convection in heated vertical cylinders closed at the lower end and opening at the top into a reservoir of cool fluid. Most interest is shown in the flow found for small values of Prandtl number associated with mercury and liquid metals. The type of flow is found to depend upon the Prandtl number as well as the product of the Rayleigh number and radius/length ratio.
The Vibration of Rotating Shafts Supported in Flexible Bearings
Authors: Gladwell G. M. L. , Bishop R. E. D.
Published: February 2007

This paper deals with an axially symmetric system composed of a uniform or non-uniform flexible shaft rotating in flexible bearings. It is shown how natural frequencies and characteristic functions may be found, using data that have been presented previously. Systems having flexible bearings whose mass is negligible are shown to be simpler than those whose bearings are massive and a discussion of their free and forced motions is given. Free and forced motions of shafts supported in massive bearings are shown to demand special treatment and an analytical approach is explained for each.
Approximate Theory for the Thermal and Irradiation Creep Buckling of a Uranium Fuel Rod and Its Magnesium Can
Authors: Alexander J. M.
Published: February 2007

A simplified theory is developed for calculating the creep buckling of a fuel element, including both thermal and irradiation creep of the uranium, and thermal creep of the magnesium alloy can. This is made possible by introducing creep rate moduli for both uranium and can, analogous to Young's Moduli for simple elastic buckling. The relationship between these rate moduli and the fundamental creep equations is discussed in detail and justification given for the proposal that the rate modulus should be defined as the slope of the stress strain-rate curve at the mean stress. The theoretical inter-relation between the results of sagging bar tests and the fundamental creep equation is also discussed.

A typical calculation for a highly rated channel is included, and it is shown that the contribution of the can to resisting buckling is quite significant, more than doubling the buckling time for half the elements, and adding about half the buckling time for the remainder. Suggestions for further work are put forward.
Non-Newtonian Flow and the Oil Seal Problem
Authors: Tanner R. I.
Published: February 2007

It appears to be difficult to explain the action of oil seals if the fluid is regarded as Newtonian. A possible hypothesis is that the fluid, when subjected to extremely high shear rates, behaves in a non-Newtonian manner. Utilizing a fairly general stress-strain-rate relation, a simplified analysis of the seal problem is given. Comparison with the currently available experimental work shows that non-Newtonian effects are not likely to provide a complete explanation of the oil-seal problem.
Effect of Temperature Variations across the Lubricant Films in the Theory of Hydrodynamic Lubrication
Authors: Hunter W. B. , Zienkiewicz O. C.
Published: February 2007

The effects of temperature variations within the thickness of the oil film, and the ensuing viscosity variations which are thought to be responsible for the lift in parallel surface bearings, are studied with reference to the classical case of an infinitely wide inclined pad. A numerical solution for a typical bearing is obtained for different thermal boundary conditions and a comparison with results of the classical analysis is made. Very considerable differences from the classical analysis are obtained. Some results of the heat balance in bearings are presented.
Tensile Testing of Materials at Impact Rates of Strain
Authors: Harding J. , Wood E. O. , Campbell J. D.
Published: February 2007

A review is given of the techniques that have been used in the construction of dynamic tension-testing machines. The problems involved in obtaining reliable tensile stress-strain curves at high strain rates are discussed. A new apparatus, designed to give accurate stress-strain curves in tension at strain rates of the order of 1000 per second, is then described. The theoretical basis of the test method is indicated, and some experimental results obtained with the apparatus are presented, both for materials that exhibit a definite yield point and for those that do not.
Notch Effects and the Critical Alternating Stress Required to Propagate a Crack in an Aluminium Alloy Subject to Fatigue Loading
Authors: Frost N. E.
Published: February 2007

Fatigue tests at zero mean load have been carried out on aluminium alloy (BS.L65) specimens containing edge cracks of various lengths. It was found that the relationship between the crack length l (inches) and the critical alternating propagation stress σ (ton/in2) was given by σ3 l = 0·2. A similar type of relationship (i.e., σ3 l = 5·5) was obtained previously for mild steel (2).

Fatigue tests have also been carried out on notched specimens and the occurrence of non-propagating cracks discussed in terms of the above relationship.
Case Study in the Rolling of Steel Bars
Authors: Eilon S. , Avi-Itzhak B.
Published: February 2007

Some variables affecting the rolling operations of steel bars are discussed, including the effect of bar cross-section variations on length variations. The distribution of bar lengths is obtained from the ratio of billet (inlet) to bar (outlet) cross-sections and the effect of burning losses during the process is studied. It was found that the ratio of bar length to billet length is virtually independent of input length and that the distribution of these ratios is approximately normal. These results were compared with observations of lengths ratio in an experiment, which included various inputs. The lengths ratios distribution and its parameters facilitate process adjustment by an appropriate selection of billet size in order to obtain a desirable mean bar length. They also provide a basis for further analysis of scrap, which occurs when the bars have to be trimmed to specific lengths.
Optimizing the Shearing of Steel Bars
Authors: Eilon S.
Published: February 2007

The paper deals with problems of scrap and waste incurred in the shearing of steel bars and with the effect of bar length variability on the scrap function. These basic problems are characteristic of many industrial operations. The analysis in this paper attempts to present solutions to the following: when no more than one final bar (product) is to be obtained per standard bar of a given distribution, what length ought to be selected, and alternatively, for a given final product what mean for the bar distribution should be aimed at? What is the loss function when several identical bars are to be obtained per standard bar, and what is the effect of the distribution variance on this function? When several non-identical products are sheared, what shearing methods should be selected? Some of the solutions are illustrated by examples drawn from a case study in industry.
Upper-Bound Values for the Loads on a Rigid-Plastic Body in Plane Strain
Authors: Westwood D. , Wallace J. F.
Published: February 2007

A rigid-plastic body at the yield point is stressed by external forces due to normal pressure and Coulomb friction. By considering the process of tube ironing, it is shown that upper-bound values for the loads may be determined using the polygon of forces. This method is extended to sheet drawing, sheet extrusion, and the compression of a wide thin lamina, taking account of Coulomb friction on external boundaries.
Random Vibrations of Non-Linear Suspensions
Authors: Ariaratnam S. T.
Published: February 2007

The method of investigating the random vibrations of dynamical systems using the theory of the Markov random process and the associated Fokker-Planck equation is presented. Some exact solutions of the Fokker-Planck equation are obtained in the case of certain one-degree and two-degree-of-freedom non-linear suspensions of current practical interest and used in an approximate evaluation of the mean squared response to white-noise excitation.
Stress Analysis of Flanged Pipe Joints by the ‘Frozen Stress’ Photoelastic Method
Authors: Robertson G.
Published: February 2007

In the paper is described an investigation carried out to determine the elastic distribution of stress in rings and flanges using the frozen stress photoelastic method. Preliminary tests on rings and flanges showed linear load-residual deflection relationships over the main test ranges. A series of tests was performed on plain rings of different thicknesses loaded uniformly round the inner edge and round a diameter corresponding to the pitch circle. Three series of tests, namely to investigate the influence of flange thickness, number of bolt holes and length of hub, were performed on model flanges subjected to simulated bolt loading. A further series of tests was performed on flanges integral with a short length of pipe and subjected to internal pressure. The complete distributions of tangential and radial contour stresses were obtained over the whole free surface of the rings and over the free surface at both types of radial section of symmetry in the flanges. The axial deflections were also measured. The test results are compared with those computed from the various theoretical solutions.
The Theoretical Strength of Band-Reinforced Pressure Vessels
Authors: Higginson G. R.
Published: February 2007

In this paper a plastic work method is used to examine the strength of cylindrical pressure vessels with circumferential reinforcing bands. The theory is based on a rigid-plastic material. The results are expressed in terms of two dimensionless parameters, one representing the volume and quality of the reinforcing band material, and the other its distribution.
The Creep Buckling of Composite Members
Authors: Alexander J. M. , Webster G. A.
Published: February 2007

The simplified theory put forward in an earlier paper (***)‡ is extended and generalized to cover the case of the thermal creep buckling of prismatic two-member components such as reactor fuel elements, all phases of creep and elastic strains being considered. The tangent modulus approach is used and small deflections are assumed; it is shown that even with these assumptions a solution in closed form can be obtained only in the case of a single rod.

Approximate methods of solution are then discussed, in which primary and secondary creep phases only are considered, but with certain simplifying assumptions. Throughout most of the analysis a modified form of Andrade's creep equation is used, namely ε = α t1/3+β t+γ t3, where α, β, and γ are functions of stress and temperature, ε and t are creep strain and time.

Typical curves are presented, based on data for an aluminium alloy, illustrating the contribution to buckling deflection likely to be expected from primary creep, for the single rod.
On the Stability of a Gimbal Mounted Gyroscope
Authors: Prentis J. M.
Published: February 2007

The combination of large gimbal frame inertia with slackness in the main rotor bearings can result in a gyroscope executing self-excited oscillations. Such a gyroscope can be simulated by a model which reproduces the main features of this instability. As a first step towards a full analysis of this behaviour the paper establishes the stability criteria for the model.
Plastic Stress–Strain Relations and Yield Surfaces for Aluminium Alloys
Authors: Ivey H. J.
Published: February 2007

The theoretical study of the behaviour of materials in the ‘plastic’ state has progressed rapidly on the basis of a few assumptions, some of which are insufficiently well supported, and even occasionally contradicted, by available experimental evidence.

In the present work three types of experiment are carried out. In the first several different materials are ‘overstrained’ into the plastic region, either by tensile or by shear stresses, and then subjected to additional stresses, shear or tensile respectively, the modulus of resistance to the additional stresses being measured. Similar experiments have been carried out previously but the results are not wholly concordant. The present work indicates that for initially stress-free material the ‘incremental’ type of theory is well founded. An explanation for the behaviour of material in other conditions is suggested which does not involve the existence of ‘corners’ on the ‘yield surface‘overstrained’ into the plastic region, either by tensile or by shear stresses, and then subjected to additional stresses, shear or tensile respectively, the modulus of resistance to the additional stresses being measured. Similar experiments have been carried out previously but the results are not wholly concordant. The present work indicates that for initially stress-free material the ‘incremental’ type of theory is well founded. An explanation for the behaviour of material in other conditions is suggested which does not involve the existence of ‘corners’ on the ‘yield surface’.

In the second type of experiment one material is subjected to a complicated ‘stress history’, and the corresponding strains are measured. Certain improvements are made in relation to previous experimental techniques. The results indicate that the Reuss equations, used in conjunction with the Maxwell (or Mises-Hencky) flow function, give a very satisfactory prediction of the behaviour of this material.

In the third type of experiment, one material is subjected to varying ‘overstrains’ of a particular type and its subsequent ‘yield stress’ (or, more strictly, limit of proportionality) under different combinations of complex stress determined. The results indicate that in the case of this material the ‘subsequent yield surface’ to a first approximation translates in the direction of the overstrain, but is considerably modified in shape by strain-hardening and by the Bauschinger effect. It remains concave towards the inner (elastic) region but this region does not necessarily contain the stress-free origin.
Stress Distribution on the Boundary of a Circular Hole in a Large Plate during Passage of a Stress Pulse of Short Duration
Authors: Riley W. F. , Durelli A. J.
Published: February 2007

A solution to the problem of the stress distribution on the boundary of a circular hole in a large plate during passage of a stress pulse of short duration is presented. The solution was experimentally obtained by using a low-modulus urethane rubber model in a combined photoelasticity, moiré, and grid analysis. The stress pulse of short duration was generated by detonating a small charge of lead azide on an edge of the plate. The hole was placed at a location in the plate where both dilatational and distortional waves would be felt. It was also located in such a way that a symmetric point was available in the free field for making free-field stress determinations. The short-duration pulse at the free-field symmetric point had a length of approximately 25 hole diameters; the portion associated with the pulse front (rise from zero to peak) was approximately 5 hole diameters.

The results of the study indicate that the stress of greatest magnitude is a compressive stress which develops on the hole boundary as the front of the stress pulse passes the hole. The maximum tensile stress which develops much later is only about half as large. As the end of the stress pulse passes the hole, the tensile and compressive stresses on the hole boundary are essentially equal in magnitude. The isochromatic fringe pattern during this period indicates that the hole is located in a stress field of pure shear. The orientation of the pattern indicates that the stress pulse is primarily a distortional wave at this time. The maximum dynamic compressive stresses on the boundary of the hole can be computed to a first approximation by applying the Kirsch solution for a hole in an infinite plate, considering the biaxial stress field and assuming an average value of stress over the hole diameter. The free-field biaxial stresses as computed from photoelasticity and moiré data were used in making this check. The maximum dynamic tensile stresses on the hole boundary were always smaller than the values computed using the same procedure.
Low Endurance Fatigue of a Mild Steel and an Aluminium Alloy
Authors: Benham P. P. , Ford Hugh
Published: February 2007

Mild steel and an aluminium-zinc-magnesium alloy were tested axially under cycles of constant load range and constant total strain range at frequencies between 5 and 15 c/min for endurances from monotonic tension to 50 000 cycles. Mean loads or strains of zero and half the maximum in tension were studied. Hysteresis loops were recorded automatically at regular intervals throughout the life to failure. Two mechanisms of fracture were found for mild steel during load cycling, a necked-out type caused by cyclic ‘creep’, and conventional fatigue. The aluminium alloy did not exhibit this behaviour and could not in fact be broken in repeated tension at endurances below 600 cycles. For strain cycling a linear relationship was found to exist when the logarithm of the total or plastic strain range was plotted against the logarithm of the number of cycles, for each metal and mean strain. Load and strain cycling results cannot be compared on the basis of the setting-up cycle (that is, the conditions for the first cycle), but only in the steady cyclic condition after work hardening or softening has occurred. During a test each of the metals worked towards a steady cyclic condition. A smooth curve is obtained when the total energy to fracture is related to the endurance, for all cases of load and strain cycling studied.
Effect of Oil on the Pitting of Rollers
Authors: Martin J. B. , Cameron A.
Published: February 2007

The apparatus used in this investigation was an opposed double roller machine with rollers 70 mm diameter loaded against a 30 mm 3 per cent nickel steel shaft rotated at 3000 rev/min. The viscosities of the test oils which were of two types, naphthenic and paraffinic, were between 3 and 530 centistokes. Above about 20 cS the pitting endurance limit increased with the fourth root of the viscosity alone, and was not influenced by the type of oil. The effect of viscosity is thought to be due to the damping of the pressure wave in the crack. This index (1/4) and the critical viscosity (20 cS) are probably dependent on the speed of rolling.

The slope of the fatigue line, before the endurance limit, varies with the oil. This has an important bearing on the ‘time to pitting’ method of test.

The pitting cracks were shown to be of two sorts, shallow and deep. This is due to there being a band of work-hardened steel at approximately the Hertzian depth. Most cracks did not penetrate this band and gave rise to shallow pits 0·002-0·004 in. deep. Those which did get through it went down at an angle of about 40° to the surface and were 0·020-0·030 in. long, giving pits of greater depth.

In Appendix I the equation for the viscous pressure loss in a crack, due to the compressibility of the oil, is derived.