bluuebunny/crossref_metadata_2025 huggingface dataset:
Press load monitor
Authors: COULSON H.
Published: October 2008

The article describes the design and use of an instrument which displays the peak frame load during a single operating stroke of a press. It consists of a strain gauge link permanently bolted to the frame of each press to which a portable electronic unit is connected. The technique of using a strain gauge link eliminates the problems encountered when a load cell is used, or when a strain gauge system is bonded directly to the machine frame.
Electrical noise
Authors: BARNES S. G.
Published: October 2008

An important consideration in the measurement of high accuracy, low level, differential data signals is the effect of electrical interference or ‘noise’.

The various techniques which can be used to minimise these effects, or reduce them, are considered. Typical sources of noise encountered in instrumentation systems are discussed and the additional problems associated with transmission systems are described. An analysis of the fundamental noise problem, capacitive coupling, is presented and an outline of the design principles which are necessary for accurate, noise–free measurements is given.
Stress intensity factors for nozzle corner cracks
Authors: RUIZ C.
Published: October 2008

Stress intensity factors have been determined by means of the frozen stress photoelastic technique for nozzle corner cracks in pressure vessel models. The model geometry was chosen to represent a nuclear reactor vessel with a radial branch, and cracks of varying depth were introduced longitudinally. The results were compared to experimental data obtained from burst tests, thus extending their scope.
Urethane casting techniques
Authors: McNICHOLAS J. B. , DONALDSON M. W.
Published: October 2008

The preparation of a liquid rubber formulation for both cold and hot casting of photoelastic models is explained. Membranes and thin–walled structural models are amongst the examples considered qualitatively. Suggestions are made for the development of approximate but rapid methods of analysis. Of necessity the applications outlined are based on brief trials only and further development work is required.
Applications of operational amplifiers in strain gauge circuits
Authors: BROWN G. M.
Published: October 2008

Operational amplifiers, originally developed for analogue computation, are now widely used in analogue instrumentation, signal conditioning, servo controls, voltage and current regulators and an extensive range of other functions. In experimental mechanics, operational amplifiers are ideally suited to applications involving strain gauges. Both Wheatstone bridge and ballast (potentiometer) circuits are examined together with the limitations and constraints imposed by amplifier and external circuit considerations. These limitations are important, whether relatively simple operational amplifiers or the more complex instrumentation amplifiers are used. Many manufacturers provide a wide range of ‘off‐the‐shelf’ integrated circuit and discrete amplifiers, together with comprehensive specifications, permitting selection of a suitable device. Before discussing strain gauge applications, the properties of operational amplifiers will be reviewed briefly.
Some problems encountered in testing models in a large centrifuge
Authors: RIGDEN W. J. , ALLEN J. H.
Published: October 2008

Owing to the stress–dependent nature of soil properties, the use of models under increased gravity is the most satisfactory method of testing the very large structures encountered in civil engineering. This paper outlines some of the problems produced by a high ‘g’ environment in the measurement of strain, displacement and soil and water pressure.
The construction and stability of a surface mounted vibratingwire strain guage
Authors: PARROTT L. J.
Published: October 2008

The construction of a surface–mounted vibratingwire strain gauge for use in creep tests is described and some results on the stability of the gauge are presented. Novel features of the gauge construction include a pressed one–piece clamp for holding the wire and provision for a secondary strain measuring system. Relaxation of the vibrating wire caused relaxation of the gauge. There was no significant relaxation due to the clamping method. Cyclic straining of the gauge before use virtually eliminated zero displacement. The use of an unloaded control specimen, which is gauged at the same time and with the same wire tension as the creep specimen, is recommended. Alternatively, relaxation measurements on the wire can be used to correct measured strains. Either of these procedures will reduce the effect of gauge relaxation on creep strains to less than 3 μstrain.
Optimising strain gauge orientation for load measurement by means of rosette analysis
Authors: WHITE M. T.
Published: October 2008

When measuring load by means of strain gauges attached to a structure it is not always obvious that the gauge position may be more sensitive to extraneous load components than had been assumed. This note describes a method of defining the orientation of the strain gauge in order to respond to the required load component, with minimum crosscoupling, as the principal strain direction changes.
Moiré from high speed deformations
Authors: De CALUWÉ M.
Published: October 2008

A method is described for the photographic recording of moire “test gratings when deformations are changing with high speed. An ultra–short flash pulse is used to illuminate the grating. This is an important feature of the equipment and the necessary requirements for it are discussed in detail. The circuit diagram and constructional details are given.
Apparatus and instruments for the laboratory study of multi–anchored flexible retaining walls
Authors: KURDI I. I. , Jordan Amman , HANNA T. H.
Published: October 2008

Details are presented of the apparatus and instruments developed for the study of the behaviour of laboratory scale multi–anchored flexible retaining walls. The instruments enabled measurements to be made of the earth pressures on and the bending moments in very flexible walls. The shearing and thrust forces at wall base level and the individual anchor wire loads, as well as the movements of the wall and the retained sand, were also monitored throughout a simulated wall construction sequence.
Stress measurement by X–ray diffraction using film techniques
Authors: ANDREWS K. W. , GREGORY J. C. , BROOKSBANK D.
Published: October 2008

For some X–ray stress measurement applications the photographic film methods may be preferred to diffractometer methods. The principles applied to the former are reviewed and the accuracy and sources of error are examined. The main procedures include the standard ‘two exposure’ method (including the use of the sin2 method), and the use of a relationship depending on the asymmetry of rings at oblique incidence. A number of apparent errors in the literature are explained and resolved. The simplest formula for the second method takes the form s̀=k.δR.

In the most favourable cases the accuracy of stress measurement is of the order of ±30 MN/m2 or ±2 ton f/in2. Larger errors arise for hardened surfaces with microstresses, and are likely to be larger for the second method. Both methods obviously give the most favourable results when sharp diffraction rings are obtained. However with proper care and appreciation of the factors considered, practically usefulresults are obtained under most circumstances. The treatment is illustrated by particular reference to surface residual stress measurement on steels.
Etching moire test grids in steel
Authors: DE CALUWÉ M.
Published: October 2008

A description is presented of practical methods for etching moire test grids of 20 lines/mm (500 lines/ in) maximum, in steel. Good reproducibility and quality are assured and no sophisticated apparatus is required. The test plates are not specially prepared and the techniques allow the production of the grids on parts of full–scale structures and components.
Protection of vibrating wire surface strain gauges
Authors: BEALES C. , CULLINGTON D. W.
Published: October 2008

To protect vibrating wire gauges against damage from construction work and weather, a cover has been designed which permits access to the gauge for manual and automatic readings and which does not interfere with gauge performance. The protected gauges have been used to measure strains on steel plates and stiffeners forming the diaphragm, webs and flanges of the box girder of the Milford Haven Bridge. 94 of the 100 gauges installed were still operating satisfactorily after 16 months use in very adverse conditions.
Measurement of strains in plain and perforated epoxy models by means of embedded strain gauges
Authors: EPELLE O. B.
Published: October 2008

In the embedded strain gauge technique, the use of miniature gauges with very thin copper leads minimises reinforcing effect on the model. The technique. in this form, was applied to the investigation of three–dimensional strain distributions. Suitability of the method was assessed by determining the mechanical properties of epoxy resin from strains measured in cylindrical and rectangular models subjected to uniaxial tension and in a rectangular beam model subjected to pure bending. The central portion of the beam was subsequently perforated with a triangular array of holes to simulate the geometry of a heat exchanger tube plate. Strains in the ligaments were then measured for various ligament efficiencies, with the model under bending and under tension.
Brush coating of resists for normal and high frequency moiré techniques
Authors: DE CALUWÉ M.
Published: October 2008

A limitation on the use of normal moiré technique may be the practical difficulties which can be encountered on coating the resist layers for the production of etched gratings. A description is given of a simple coating method which can be applied to any testpiece and which requires only a brush and some skill on the part of the operator.

The method can also be used to coat resist layers suitable for the production of high frequency gratings of more than 1 000 lines/mm (25400 lines/in).
Practical aspects of transducer application
Authors: WALLACE R. H.
Published: October 2008

In selecting transducers to use in a given application, it is not enough merely to consult the catalogues and choose one having the right range—‐even when this is known initially. It is important to have regard to the parameter to be read and the method of connecting the transducer (in as far as its place of sensing is concerned) and to consider how the interface with the read–out equipment is to be effected. This choice may also be affected by the method chosen for display and/or recording. Such is the field covered by this article, which does not deal with the design of transducers—‐except where this conditions their suitability for the particular measurements—‐nor is their manufacture or calibration a subject of comment. Because the writer has been mainly concerned with development testing, particularly of aeroengines, the article will deal primarily with such measurements as represent transient, pulsating or vibratory effects and less with steady state checks. Many of the precautions—‐but not all—‐that are mentioned, are relevant also to the latter cases. Measurements at frequencies over 5 Hz are thus implied, unless otherwise stated.
Tests on ring–stiffened cylindrical shells with external pressure
Authors: MONTAGUE P.
Published: October 2008

External pressure tests were conducted on thin multi–bay cylindrical shells to investigate the significance of out‐of‐roundness in relation to elastic and collapse behaviour.

Conclusions are drawn about the developing elastic deflection profiles of the shells during loading and suggestions are proposed for the prediction of the collapse mode and the collapse pressure.
Measurement of residual stresses in a Noryl telecommunications co–ordinate selector switch
Authors: Golsby R. J.
Published: October 2008

The moulding residual stress level in a miniature non–metallic (Noryl) telecommunications switch was measured using strain gauge and photoelastic techniques. Strain gauge results were obtained using a modified Waisman and Phillips1 layer removal technique, which indicated maximum residual stresses of the order of 650 lbf/in2 (4.5 MN/m2) and a considerable stress gradient in the cross section of the component. Photoelastic measurements were made on slices from components in polycarbonate which has the same mould shrinkage value as Noryl. The results showed a maximum surface residual stress of 240 lbf/in2 (1.7 MN/m2). Interpretation of the exceptionally high fringe orders observed, was very difficult and the validity of this application of photoelasticity is questioned.
The modulus of rigidity of overstrained torsion bars
Authors: Swift W. A. C.
Published: October 2008

The production of Bauschinger Charts for six spring steels has been described in an earlier paper. The present paper shows that for four of these steels a common Bauschinger Chart can be produced. This chart is then used to predict the effective modulus of rigidity for an overstrained bar subjected to torsion in the overstraining direction. Comparisons are made between the results of practical tests, an empirical law derived from the experimental results and the theoretical predictions.
The study of simulated gravity stresses using an image de‐rotation technique
Authors: KARMIS M. , WADDELL P.
Published: October 2008

A non‐stroboscopic system for ‘freezing’ rotational motion, based on an image de‐rotation principle, has been adapted to allow the study of simulated gravity stresses induced in small‐scale models under centrifugal loading. The resulting system proved to be efficient and inexpensive; it performed equally well in reflection or transmission and was thus perfectly suited for photoelastic or moiré fringe investigations in ‘real time’, i.e. by direct observation.
The effects of age and moisture regime on the response of briquetted acoustic gauges
Authors: POTTER M. M. A. , SWAMY R. N.
Published: October 2008

In‐situ measurement of concrete strains with acoustic gauges often requires that the gauges are encapsulated or ‘briquetted’ for protection. The effects of age and moisture regime on the response of the briquetted gauge are, however, unknown. Studies extending up to 700 days on these two effects are presented and gauge response is compared to that of the unbriquetted gauge. It is shown that both age and the moisture condition of the briquetted gauge influence its response. By choosing a datum, relevant to their environment and related to some time after the peak of hydration temperature is reached, the response of the briquetted gauge can be made to be close to that of the unbriquetted gauge. Tests show that if this is done the stability and dependability of the briquetted acoustic gauge can be relied upon.
Accurate measurement of residual stress on any steel using the centre hole method
Authors: BEANEY E. M.
Published: October 2008

The centre hole method has been shown to be a simple and reasonably accurate method of measuring residual stress. With a 1.6 mm diameter hole, the method can be applied on operational plant and the equipment required is sufficiently portable for use on site. Its application has, however, been limited to use on low‐strength steels, due to problems associated with forming the hole.

This paper describes the development of an air‐abrasive technique for forming the hole, which allows the centre hole method to be used on any steel with a measurement accuracy of better than±8%.
Misuse of regression techniques in calibration
Authors: SMITH J. D.
Published: October 2008

The use of standard computer regression techniques in the calibration of transducers leads to incorrect deductions when hysteresis is present. The ‘best’ line obtained does not minimise errors and valid points may be rejected whilst invalid experimental points are retained. An alternative graphical technique is suggested and the problems associated with the zero point are discussed.
Visco‐elastoplastic stress concentration in a strip with a circular hole
Authors: NISHITANI T.
Published: October 2008

The visco‐elastoplastic stress concentration in a strip with a circular hole has been investigated for various rates of increase of stress by means of the photo‐rheological method, using specimens of celluloid at 65d̀C. The stress concentration factors at the stress raiser are considerably influenced by the stress rate. Such an effect cannot be analysed by ordinary photoplasticity in which the time effect is not taken into account.
Use of Mohr's circle to transform stretch components
Authors: BUITRAGO J. , DURELLI A. J.
Published: October 2008

Following previous work by Meyer it is shown how a general triangle in a homogeneous finite strain field can be transformed using Mohr's circle. Then as an application a general expression is given to determine principal components from rosettes in finite strain fields. The results obtained will be useful in the analysis of grid data.
The use and understanding of photoelastic coatings
Authors: BLUM A. E.
Published: October 2008

The important features of the photoelastic coating technique are described and the effects of shear lag and differential thermal expansion are outlined. Applications of the technique in the study of stresses in components of internal combustion engines are presented and the significant influence the work has exerted on the development and optimisation of these components is shown.
The biaxial tensile strain field from a conventional load‐splitting tree
Authors: TERRY G.
Published: October 2008

It is shown that satisfactory equi‐biaxial strain conditions can be attained in large panels using a conventional load‐splitting tree. Electrical resistance strain gauges show that the strain field is practically uniform and equi‐biaxial over the central 44% (approximately) of the area of a square panel.
Practical problems in calibration of torque tubes
Authors: SMITH J. D.
Published: October 2008

Static calibration of torque tubes transmitting 30 MW at 6,000 rpm was required to an accuracy of 0.1%. The technique used is described and the various sources of error are analysed and discussed.
A five‐component strain gauge wind tunnel dynamometer
Authors: MOLLAND A. F.
Published: October 2008

The design, construction and calibration of a five‐component dynamometer is described. The dynamometer was constructed primarily for the testing of ship control surfaces including, in particular, skeg rudders; it has facilities for the independent adjustment of angle of attack, and the derivation of the forces and moments, on both rudder and skeg.

An outline of the specialised design requirements is given. The basic design concept is described together with the reasons for the choice of shear flexures and their dimensions, strain gauges, circuits, bridge voltages and instrumentation. Following a brief description of the calibration rig and programme, the calibration results and origins of interactions are described and discussed.

It is concluded that the relatively small size of the interaction corrections and overall measuring accuracy of the dynamometer confirm the choice of the overall design concept and design details.
A new capacitive strain measuring circuit
Authors: HUDDART J.
Published: October 2008

A critical survey is made of capacitive measuring circuits used for strain gauges. A versatile new circuit is described which has distinct advantages over circuits in present use and a typical application with a capacitive ring strain gauge is described.
Determination of intensity factors at an arched crack tip by the method of caustics
Authors: ROSAKIS ARIS
Published: October 2008

Perpendicular sections of caustic surfaces reflected by the constrained zone around the tip of an arched crack in a perspex plate under plane tension, were measured and analysed. The experiments corroborated the theory, the Theocaris' method of Caustics and also show that the intensity factors are functions of the curvature of the crack and the subtended angle.
Behaviour of underwater enclosures of optimum design
Authors: ROYLES R. , SOFOLUWE A. B. , BAIG M. M. , CURRIE‡ A. J.
Published: October 2008

Experiments are described which support the application of the membrane theory of shell analysis in determining optimum shapes for underwater structures of constant strength. A relationship between marine life and such structures is considered and design procedures for shape selection are given. Proposals for the investigation of the behaviour of such structures under loadings other than the initial design forces are outlined both from an analytical! numerical and an experimental approach.
Effect of temperature on vibrating wire strain gauges
Authors: MARSHALL J. K. , HUNTER P.
Published: October 2008

Vibrating wire strain gauges attached to buried pipe can exhibit changes in strain readings when subjected to changes in ground temperature. It is essential that the correct interpretation is placed upon the readings. An analysis is given which, it is suggested, will give true pipe strain values from the indicated strain readings. Two solutions are outlined, a graphical analysis which tends to be intuitive and a theoretical analysis which derives a solution from first principles.

True strain in the pipe is influenced by thermal effects due to changes in ground temperature, and mechanical effects due to the constraint placed upon the pipe by the surrounding soil. Both analyses consider the thermal and mechanical components of true strain and the theoretical analysis enables these individual components to be determined from the indicated strain readings.
Stresses in a 60° perforated wedge
Authors: SARNA S. P. , ALI S. M. J.
Published: October 2008

This paper deals with the determination of stresses around a circular hole in a cantilevered wedge of uniform thickness subjected to end loading, using electrical resistance strain gauges. The authors have previously reported a similar investigation on a 45 wedge. The results obtained are compared with the theoretical analysis for an infinite perforated wedge given by Ling and Hsu. The stress concentration factors are calculated on the basis of nominal stress in the wedge at the hole boundary (using the theory for calculating stresses in a wedge without a hole). A maximum stress concentration factor of 3–2 was indicated for an end vertical load; and a maximum factor of 2 6 was indicated for an end horizontal load.
A note on curvature and twist measurements using the Ligtenberg‐Moiré method
Authors: FOSTER C. G.
Published: October 2008

In this note an alternative technique for measuring curvature and twist is discussed. The method relies on measuring the line spacing in a single exposure reflected pattern. Use of this technique appears to be preferable in many applications.
The torsional stiffness of prismatic beams of isosceles triangular cross section: a survey of methods for small included angles
Authors: ARMSTRONG G. , GILL P. A. T.
Published: October 2008

Six approximate methods of calculating the torsional stiffness of prismatic beams of isosceles triangular cross section are compared with the exact solution for the cross section in the form of a sector of a circle.
Steady state strains in power transmitting flat belts made of composite material
Authors: PALMER R. S. J. , JARVIS J. L.
Published: October 2008

Strain data for a simple two pulley belt drive was obtained using a photoelastic coating technique. The operating strains present were not constant along the driving and load sides but varied in an irregular manner. The average strain gradually increased on the driving side and decreased on the load side as the power transmitted was increased.
Photoelastic study of the elastic stress distribution around discontinuous fibres
Authors: HOLLAWAY L. C. , ALLISON I. M.
Published: October 2008

The mechanism by which load is transferred from a discontinuous fibre to surrounding unbroken fibres has been examined in some detail using two dimensional photoelastic models in which the applied load is aligned with the fibre axes. The gap in the broken fibre is assumed to have occurred during fabrication and is thus filled with the matrix material. Three different end gap configurations have been analysed and it is concluded that, for all practical purposes, the disturbance due to the broken fibre does not extend beyond the immediately adjacent fibres. Substantial shear stresses are developed in the matrix for some distance along the fibre from the discontinuity with a consequent early transfer of load. Paradoxically, this effect is not accompanied by the development of reduced maximum stresses at the broken fibre tip for any of the configurations included in these tests.
Two simple methods for deformation demonstration and measurement
Authors: SEVENHUIJSEN J.
Published: October 2008

A problem in the area of the investigation of structural behaviour is the elastic plastic deformation in the vicinity of disturbances like crack tips. Intrinsically the deformation can be measured by measuring the deformation of a grid on the surface in the vicinity of the disturbance. The paper describes a new simple grid system. The grid system consists of the picture layer of a selected photo printing paper. The picture layer is pealed off its carrier and is bonded on the polished specimen surface by means of a fresh cyanoacrylate cement. This system can sustain deformations up to 40% and has a very good contrast. A square grid is bonded on the local surface, the grid is photographed at several load values and later the negatives are magnified and read by means of an image analyser.

A relevant question arising in the investigation of the buckling of a metal sheet with Z‐section stringers is how the sheet and the stringers deform relative to each other. This is answered by bonding drinking straws perpendicular to the surface of the specimen at several locations. When the surface rotates out of plane the free ends of the straws show relatively large displacements which have been recorded by means of a 35 mm film camera. The free ends of the straws have been provided with small white disks with central black dots. Films are read by means of an image analyser. Very small differences in rotations between the stringer heads and the sheet can be detected before the specimen collapses.
Absolute calibration of accelerometers at high frequencies
Authors: ZHOIMG‐MIN YU , WEN‐LONG LI , XIAN‐QUAN DONG
Published: October 2008

This paper describes the calibration of commercial accelerometers with mass load by laser interferometry at frequencies ranging from 2 kHz to 10 kHz. It is shown by experiment that the effect of mass load on the frequency response of commercial accelerometers with inverted centre mounted compression design is negligible. The comparison method adopted by some foreign companies has been analysed and the relative motion between the top of the mass load and the upper surface of a commercial accelerometer has been measured, thus explaining the obvious errors in frequency response curves obtained by using the comparison method.
Birefringent effects in the cyclic loading for an elastic‐viscoplastic polymer
Authors: NISHITANI T. , KOIKE Y.
Published: October 2008

The general plastic deformation should be considered by the elastic‐viscoplastic theory, which contains the viscosity in addition to the elastic am plastic properties. In this paper, the birefringen effects are experimentally investigated by using celluloid as elastic‐viscoplastic polymer under cyclic loadings. The optical relations in the loading and the unloading processes are semi‐empirically deduced for the elastic‐viscoplastic solid. The deduced optical relations give good agreement with the actual observations under the cyclic loadings for various cyclic conditions.
On the determination of boundary stresses by the finite element method
Authors: ALLISON M. , SOH A. K.
Published: October 2008

The conventional finite element method has been modified to allow the elastic stresses along the free boundaries of a structure to be determined with improved accuracy. The results obtained by this ‘modified’ method are compared with both a photo‐elastic and some traditional finite element solutions.
Tests on a simply supported rhombic plate
Authors: SARNA S. P. , ALI S. M. J.
Published: October 2008

This paper deals with tests done on a simply supported isotropic rhombic plate subjected to certain conditions of lateral loading. The loading conditions used were (i) uniformly distributed load covering the whole plate, (ii) patch load at the centre of the plate, (Hi) uniformly distributed load over a quarter of the plate. Bending moments were obtained at certain important locations on the plate, using electrical resistance strain gauges. The central deflections were also recorded. The results obtained were compared with the available theoretical results. The correlation for the case of uniformly distributed load covering the whole plate was found to be good.
The effect of trimming on strain gauge accuracy
Authors: KERR J.
Published: October 2008

During a programme of fatigue testing welded tubular joints, similar to those in use in North Sea offshore structures, it was necessary to measure the strain as close to the weld toe as possible and also to detect crack initiation. To this end general purpose miniature foil strain gauges were used. The backings of these gauges were trimmed prior to installation to enable placing the measuring grid as close as possible to the weld toe. The investigation described was carried out to assess the accuracy of these strain gauge installations.
The behaviour of post yield strain gauges
Authors: REES D. W. A.
Published: October 2008

The calibration of post yield electrical resistance strain gauges in tension shows that their behaviour is strongly dependent upon gauge construction, bond strength, the presence of instability and the mechanism of plastic deformation. For medium tensile strains in the range 0‐5% the calibrations reveal that the gauge sensitivity factor consists of separate elastic and plastic components which are respectively identified with recoverable and irrecoverable strain components.
The prediction and measurement of axial forces, bending moments and accelerations in an engine connecting rod
Authors: TILBURY R. J.
Published: October 2008

An engine connecting rod was fitted with two accelerometers, an axial force bridge and a bending moment bridge. These transducers enabled the acceleration components (along the connecting rod axis and perpendicular to it), the axial force and the bending moment, to be measured at the transducer locations.

A theoretical method of analysis was carried out and a computer programme was developed, for use on a PET computer, to execute the repetitive calculations of the above mentioned quantities.

The connecting rod was fitted into a Ford two‐litre OHC automotive engine. A few components were manufactured to complete the test rig.

Three engine tests were conducted using combinations of engine load and cylinder gas pressure. The outputs from the transducers were recorded on photographic film from a galvanometer recorder. The traces were then analysed to reveal the variation of the dynamic properties with crankshaft angle.

The experimental and theoretical results of the three tests were compared. The experimental accelerations and axial force were in close agreement with the predicted results. However, the experimental and the predicted bending moment distribution, did not agree at all well.
Teaching energy methods in a final year course on mechanics of materials
Authors: RICHARDS T. H.
Published: October 2008

Now that computer power is so readily available, engineers may contemplate design models of far greater sophistication than previously. When a design analysis task involves stress and deformation analysis, the energy (or variational) principles of mechanics provide such a powerful methodology for the formulation of complex models that it is important for such topics to be introduced to undergraduates. In this paper, the structure and underlying philosophy of a one term package suitable for final year mechanical engineering students is discussed.
Measurement of surface strains in GRP products
Authors: Scowen G. D.
Published: October 2008

Current work on fibre composite materials required the measurement of surface strains on glass reinforced plastics (GRP) products subjected to static loading. A study undertaken to account for anomalous results obtained with electrical resistance strain gauges showed that strains measured at a given load, increased with decreasing gauge length and foil gauge resistance. Measurement of localised strains using gauges of length up to 25 mm are subject to considerable discrepancy when compared with gauge lengths of less than 13 mm.
Experimental comparison of solution methods for the axisymmetric photoelastic problem
Authors: Danyluk H. T. , Doyle J. F.
Published: October 2008

A method of component separation in axisymmetric photoelastic problems based on the use of the compatibility condition is experimentally tested against the more common methods of oblique incidence and subslicing. The results show the method to be comparable in accuracy, but to have the distinct advantage of not requiring additional measurements other than those in the meridional plane.
Passage of light through a general three dimensional model—equations linking characteristic parameters with system parameters
Authors: KESHAVAN S. Y.
Published: October 2008

The determination of the secondary principal stress difference and their orientations for a discrete slice of thickness dz along a particular light path in a three dimensional photoelastic model is discussed in this paper. These quantities are determined in terms of the characteristic parameters1 and their variations at discrete points distance z and z + dz along the light path. The variations of the characteristic parameters are obtained by deriving the equations linking the characteristic parameters for the light path and the system parameters of the discrete element. The validity of the equations so derived has also been checked by applying these equations to the solution of the problem of a uniformly twisted prismatic bar.
Strain field analysis with the X‐ray integration method
Authors: Peiter A. , Lode W.
Published: October 2008

The so‐called X‐ray sin2 method for measuring internal stresses is not always acceptable, because it postulates a constant orthogonal stress distribution in the layer passed by the beam. It is demonstrated that the often measured non‐linear distribution of deformations is numerically connected with stress distributions, which are variable and inclined against the surface. The calculation of the internal stresses and their parameters is based on the solution of trigonometric polynoms of the variable with integrals. The penetration depth of the X‐ray beam must be known. For general numeric solutions a computer program can be given. Solutions step by step can be carried out with a programmable pocket calculator. The ‘sin2 method’ is a special case of the integration method, which is still developing.
A simple graphical method to determine the action of a system of retarders
Authors: KESHAVAN S. Y.
Published: October 2008

Graphical methods for the study of the transformation of polarised light are essentially pictorial representations of the changes in the polarisation of light as it passes through a system of polarisers and retarders. The analysis is common in both photoelasticity and crystallography. These graphical methods are useful:

In finding the changes in the light ellipse parameters as the polarised light passes through various elements of the polariscope, without cumbersome calculations.

In finding the characteristic parameters of a particular light path in a three dimensional photoelastic model or for a series of linear retarders.

In estimating various errors in the elements of the polariscope.

In the proposed method, knowing the characteristic parameters along a particular light path, a simple graphical method for determining the linear retarders which cause the variation of polarisation of light along the light path is illustrated.

In a general loaded three dimensional photoelastic model, the characteristic parameters can be found at intervals along the light path. This graphical method makes use of the characteristic parameters and splits the light path into individual retarders which cause the combined effect for the light path.
Three methods to ascertain proper compensation in a general system of retarders
Authors: KESHAVAN S. Y.
Published: October 2008

One can regard a three dimensional photoelastic model as a general system of linear retarders. These linear retarders can he individually separated out using a compensator. In the general case, a compensator can he used to cancel the combined effect of the linear retarders up to a certain required point along the light path. The discrete linear retarders from the point of entry of light to the model to the point along the light path under consideration can be replaced by a resultant optically equivalent model which is characterised by three discrete quantities called the characteristic parameters.1 If the compensator cancels the characteristic retardation completely and is orientated along the axis of the linear retarder of the optically equivalent model for any general light path, such a configuration of the compensator would correspond to the ideal case of compensation. However there could exist, for any particular three dimensional model, particular values of characteristic parameters, which, along with the value of retardation introduced by the compensator would result in a resultant optically equivalent model having the same primary and secondary characteristic directions2 as in the ideal case of compensation. This can lead to a misinterpretation of the results.

In this paper three very simple methods have been described to ascertain the correct positioning of the compensator.
Least squares asymptotic analysis of photoelastic data from stress concentration regions in plane problems
Authors: Thompson J. C. , Negus K. J.
Published: October 2008

A complete separation of stresses throughout the entire stress concentration region near notches in plane, isotropic, linearly elastic plates is achieved using only conventional, easily obtained photoelastic (difference and directions of principal stresses) data. These data are analysed by a special least squares technique based on previously derived equations which describe the asymptotic character of the rapidly varying stress field near the root of the notch. The paper demonstrates the ability of the technique to predict stress concentrations as well as individual stresses accurately using only a small amount of data of typical experimental accuracy from arbitrary data points within the stress concentration zone.
A technique for conducting shakedown tests at elevated temperatures
Authors: Ng H. W. , Brookfield D. J. , Moreton D. N.
Published: October 2008

The necessity for reliable shakedown/ratchetting data for stainless steel type 316 arises from its widespread specification in nuclear power plant. In such applications this material is required to operate at temperatures of about 500d̀ C. This paper details an experimental technique which permits such shakedown/ratchetting tests to be undertaken at elevated temperatures.
Hole shape optimisation in circular discs with two neighbouring holes
Authors: Rajaiah K. , Naik N. K.
Published: October 2008

Using a two‐dimensional photoelastic technique, hole shapes have been optimised in diametrically loaded circular discs with two neighbouring holes leading to minimum s.c.f. Results are given for a range of disc diameter/hole diameter ratios (15.39 $ D/d $ 3.74). In comparison with circular holes, the s.c.f's have been reduced upto about 21 per cent at regions where peak stresses act. The results include the stress distribution around the holes, optimum geometries developed and the effect of tilting the load direction.
Minimum intensity seeking positions in polariscope set‐ups
Authors: Keshavan S. Y.
Published: October 2008

Conventional polariscope set‐ups like the plane polariscope or the dark or bright field set‐ups specify the positions of the various optical elements with respect to the polarising axes of the photoelastic model for determining the isoclinic and isochromatic parameters.

In this paper, it is shown that such specification is not necessary since, for any light path, the positions of the optical elements for an absolute minimum in intensity of the light emerging from the analyser are unique. To illustrate this, the case of a general retarder introducing a retardation 2δ at an azimuth θ with respect to the axis of the polariser is discussed and the conditions for the determination of the isoclinics and isochromatics are obtained.
The determination of post yield stresses from strains measured on strain hardening materials
Authors: Wright Douglas C. , Tooth Alwyn S.
Published: October 2008

The paper examines the computational techniques of Mendelson1 and that proposed by Moreton‐Moffat2 to derive post yield stresses from strain gauge readings and compares them with the fundamental Prandtl‐Reuss approach. Although the approach by Mendelson is extensively used in one form or another in elasto‐plastic analysis its application in the experimental stress analysis field is less common. Moreton‐Moffat highlighted this application and modified Mendelson's method claiming that it was unnecessary to use the post yield constitutive law. In this latter respect their approach is shown in general to be inadequate. The technique based on the Mendelson approach1 is found to be an accurate and useful solution especially when modified to incorporate the slope of the constitutive law at the mean stress of any particular finite step. Although the method is an approximate strain analogue of the Prandtl‐Reuss equations the approximation is excellent for practical step sizes.
A modern data collection system
Authors: SCOTT R. H. , GILL P. A. T.
Published: October 2008

A data collection system is described which utilizes the products of separate manufacturers to give a cheaper and more flexible system than could be achieved by buying a single ‘all in’ package.

A description of the software requirements of such a system is given along with a description of its use in a typical logging application.
Vector representation of Moiré fringes
Authors: Asundi Anand
Published: October 2008

Moiré fringes are represented as vectors and their characteristics established using vector algebra. It is shown that the Moiré fringe vector of deformation is the vector sum of those due to extension and rotation.>
Extension to the blind hole drilling technique for residual stress determination with airabrasive hole forming
Authors: Owens Alan
Published: October 2008

For an austenitic clad ferritic steel plate it was necessary to determine the residual stress state between the austenitic surface and a region below the austenitic/ferritic interface.

The thickness of claddings was 6 mm and to determine the stress variation between the surface and 8 mm an incremental analysis is required. Any material removal en masse in conjunction with small hole residual stress measurements would have resulted in a stress redistribution and hence a distortion in the stress field being measured. In conjunction with strain change measurements on the other face the sensitivity would not have been sufficient. These two options assume that a thin layer of material over relatively large areas can be removed by a non‐stress inducing technique.

A blind hole residual stress measurement using a 13 mm diameter hole 13 mm deep will facilitate accurate incremental analysis to a depth of 8 mm.

The end mill method of hole forming cannot be used with stainless steels because of the random damage effect which is induced in the readings. The airabrasive method which induces no damage effect was used.

The standard airabrasive method of hole forming produces a 2 mm diameter and a 2 mm deep hole.

The modification of the standard airabrasive system is discussed which enables 13 mm diameter and 13 mm deep holes to be formed.

A deviation from the standard hole/gauge layout geometry has been investigated due to non‐availability of suitable standard rosettes, and a significant increase in sensitivity has been obtained.

The incremental stress results for the austenitic layer and the austenitic/ferritic interface are discussed using the results from 1.6 mm, 3.2 mm and 13 mm diameter/deep holes.
An experimental investigation of a method to obtain isoclinic data from isochromatic data
Authors: Doyle J. F. , Keen K. , Clift G.
Published: October 2008

If the photoelastic model has a line of symmetry and is made from a stress frozen sheet, then it is shown how the isoclinics can be obtained from isochromatic measurements only. The accuracy is investigated with experimental examples. The method should have applications in transient problems and where the sandwich method is used.
Setting the scene—the national quality campaign*
Authors: Spickernell D. G.
Published: October 2008

The paper outlines the role of the British Standards Institution in the national campaign to improve the product quality of British industry.
X‐ray strain field atlas
Authors: Peiter A. , Lode W.
Published: October 2008

Considering one‐axial strain fields in the penetration depth of X‐rays, the corresponding measurement distribution of e versus sin2 ψ are calculated for 24 different one‐axial strains. The parameter is the measurement direction. The deformations of neighbouring points are calculated with Taylor series and described with linear expressions. There are five different types of curves, which can be combined linearly. The calculations are only applicable for plane surfaces.
Creep stress concentration during loading and unloading processes in a strip with semi circular notches
Authors: Nishitani T. , Ikeda K.
Published: October 2008

The stress concentration during the loading and unloading processes of transient creep is investigated for a strip with semi circular notches by means of the photo‐viscoplasticity, using specimens of celluloid at 65d̀C. The relations between the stress concentration factor, the geometries of strips, and time during the loading and unloading processes are derived from the time dependent variations of isochromatic fringe orders. Such trends cannot be analysed by the ordinary photoplasticity in which the time effect is not taken into account.
On the determination of interfacial stresses in a composite material
Authors: Soh A. K.
Published: October 2008

The conventional finite element method has been modified to allow the elastic stresses along the fibre matrix interfaces of a composite to be determined with improved accuracy. The results obtained by this ‘modified’ method are compared with both a photoelastic and some traditional finite element solutions.
A computer program for repetitive strain gauge rosette analysis
Authors: Nowell A. F.
Published: October 2008

A system is described with which the signals from a strain gauge rosette can be used to compute principal stresses and their orientation, the results being plotted on a VDU screen and updated continuously.
Development of temperature compensated high elongation resistance strain gauges for use up to 250°C
Authors: You‐liang Zhu , Yang‐xi Zhang
Published: October 2008

The paper describes the development and evaluation of temperature compensated high elongation resistance strain gauges for use from room temperature to 250°C. These gauges could be temperature‐compensated on steels with coefficient of thermal expansion α = 11 ppm/°C. Thermal output within 250°C was about 1 μm/m/°C and maximum standard deviation of 5 gauges was 34 μm/m. Strain limit was > 4% at room temperature and at 250°C. Gauge factors of different strain ranges at R.T. and at 250°C are tabulated. Some applications are stated.