bluuebunny/crossref_metadata_2025 huggingface dataset:
Further proposals for the application of liquid crystals to photoelastic instrumentation
Authors: Hearn E. J. , Walker N. , Cigari H. Shadrokh
Published: October 2008

Liquid crystal displays (L.C.D's) are well known for their application to electronic watches, calculators, games and digital thermometers, the technology involved being derived from electro‐optic effects observed in liquid crystals since about 1968. A previous technical note1 introduced proposals for the application of one type of liquid crystal cell (45°twisted nematic) to rapid conversion from plane to circular polarisation states by means of electrical switching of the cells from ‘off’ to ‘on’ states. This was shown to be particularly attractive for automatic control purposes.
Applications of thermoelastic stress analysis
Authors: Harwood N. , Cummings W. M.
Published: October 2008

Recent advances in infra‐red technology have permitted SIRA Ltd to develop a highly sensitive instrument for full field experimental stress analysis. The calibration and performance of this instrument (SPATE) is being evaluated on a wide range of structural materials and engineering components at NEL, and techniques have been developed to extend the instrument to wide band random loading applications. SPATE has proved to be a very successful and convenient instrument for performing non‐contacting experimental stress analysis on full scale engineering structures, and its extension to random loading conditions using specially developed signal processing software has produced a completely unique facility at NEL.
Photographic evaluation techniques in photoelasticity—Part 1
Authors: Meyer M. L. , Mehrotra C. L.
Published: October 2008

Sharp boundaries or thin lines seen on high contrast or Agfacontour photographs of optical fringes are interpreted as equidensity lines and calibrated for fractional order or isoclinic angle. Systematic variation of exposure determinants changes their positions and parameters so that the entire photographed field can be evaluated from sets of photographs either taken directly or copied from one or a few low contrast negatives. Photogrammetry resolves spatial detail down to 0002mm spot size and relates photoelastic results to model outlines and deformation measured on the same films.

The practical aspects of photography, exposure variations and evaluation are treated in this overview published in two parts. Part 1 covers photographic methods and application to isochromatics, Part 2 evaluation and calibration for fractional orders with examples, application to isoclinics and a summary of main features.
Mohr's circle in measurement of residual strains by through hole drilling technique: Effect of transverse sensitivity
Authors: Kabiri Majid
Published: October 2008

The construction of Mohr's circle for measurement of residual strains in thin plates by the Hole Drilling Method is described. The relative errors in determining the location of the centre and the radius of Mohr's circle due to ignoring the effect of transverse sensitivity are calculated. For normal gauges with low cross sensitivity, these errors are shown to be negligible (less than 1%).
The calibration of CERL‐Planer capacitance strain gauges
Authors: Fidler R.
Published: October 2008

CEGB‐Planer capacitance strain gauges are used extensively for monitoring the deformation of components operating in the creep range. However, there are significant differences between the way the gauges are installed for use and the way they are installed for calibration. This paper describes the various types of calibrations that have been carried out to identify the errors associated with these differences and the results show that, providing the manufacturers' recommendations are adhered to, the errors are acceptably small.
A selective diffraction order based lens plane grating shearing interferometer for the study of bent plates
Authors: Subramanian G. , Akella Prasad N.
Published: October 2008

A simple, elegant and flexible technique for the determination of partial slope, curvature and twist contours of bent plates is proposed. A single frequency cross‐grating (SFCG) placed just ahead of the field lens collects the light reflected by the smooth plate model. From the resultant diffraction pattern formed at the Fourier transform (FT) plane, based on the desired contours, only a few orders are permitted selectively to pass through to the recording plane. This manner of real time in‐situ filtering of the diffraction orders is new. While slope contours require double exposures, curvature and twist contours are obtained from single exposures.
Simultaneous X‐ray measurements in‐situ of tri‐axial stresses, Poisson's ratio and the stress free lattice spacing
Authors: Peiter A. , Wern H.
Published: October 2008

The tri‐axial X‐ray stress analysis allows, together with boundary conditions and fitting curves, a control of measurements and calculations for the determination in‐situ of Poisson's ratio and stress free lattice spacing. A complete internal stress field analysis is discussed in terms of the ‘X‐ray integral method’ on rolled steel discs of 100 Cr‐6 (ASTM: A 295, BS: 970/2).
Wire tensions and bending moments in axially loaded seven wire strand
Authors: Utting W. S. , Jones N.
Published: October 2008

Carefully instrumented tensile tests were performed on a straight single steel strand of seven‐wire construction having core and helical wire diameters of 3–66 mm and 3–33 mm, respectively, and a lay angle of 14‐6d̀. Strain gauges in groups of three with their grid axes parallel and having a common backing were attached to all six helical wires at the mid‐strand position. For loading within the linear range of the load‐extension response (all tests) and load‐rotation response (in tests with free and partial torsional restraint of the ends) the outputs from these strain gauges were used to compute wire tensions and bending moments. Strand extension, rotation and torque generated under axial load (fixed‐end and partial torsional restraint) were also recorded.

Test results showed that the share of the total strand load taken by the helical wires decreased as the torsional restraint on the strand was reduced. The mean tension in the helical wires was found to be 27‐5% smaller in the free‐end tests than in fixed‐end tests for a given strand load. Theoretical predictions underestimate this reduction in tension by up to 80%. Bending moments in the wires were found to be about 8% less than predicted in the fixed‐end condition and over 20% smaller in the free‐end condition.

As expected, the slope of the linear regions of the load‐extension and load‐rotation plots decreased as the torsional restraint was reduced. However, the rate of decrease in the case of load‐extension plots was found to be less than predicted theoretically and the rotation measured was generally less than predicted theoretically. This is consistent with the helical wire tensions being smaller than the predicted values since the tangential components of these reduced tensions would have less effect in their unwrapping action on the strand under increasing axial load.
An instrument for detecting arbitrary peaks and troughs of a fluctuating stress signal
Authors: Wastling M. A. , Smith J. W.
Published: October 2008

An instrument has been developed to detect arbitrary peaks and troughs of a fluctuating stress signal. This information is used to perform a fatigue life prediction. The instrument uses an analogue method of detecting peaks and troughs. This is considered to be cheaper and faster than the digital alternative. A microprocessor was employed to read peak/trough values from seven such channels and perform a ‘rainflow’ cycle count of the stress histories. The equipment has been tested on the Humber Suspension Bridge and has been shown to work satisfactorily.
Application guidelines for the parting out step in a through thickness residual stress measurement procedure
Authors: Shadley J. R. , Rybicki E. F. , Shealy W. S.
Published: October 2008

The first step in an often used destructive procedure for determining through thickness residual stresses in pipes and plates is a parting out step in which a coupon is removed from the parent material while strain gauges monitor the coupon's deformations. The changes in stress that occur at the gauged surfaces when the coupon is parted out, together with information about the stresses in the parted out coupon are used in a back computation method to estimate the stress distributions in the coupon before it was parted out. Either of two back computation methods can be used. One method assumes that the through thickness stress distribution changes that occur when the coupon is parted out lie on a straight line. This method is computationally quick and easy to use, but can be inaccurate if the lateral dimensions of the coupon are too small. The other method uses influence coefficients and greatly extends the range of coupon dimensions for which accurate results can be obtained; but, it is more elaborate than the straight line model and involves two rather time consuming steps. This paper presents guidelines for determining when the more elaborate influence coefficient method must be used in place of the straight line model in terms of the error that the simpler model would produce in the estimated residual stress distribution. This paper also simplifies the application of the influence coefficient method by tabulating the results of the two time consuming steps over the range of coupon dimensions for which this method is typically required. Example problems using the two back computation methods are presented.
Self‐compensated high plastic resistance strain gauges for use up to 300°C
Authors: You‐liang Zhu , Yang‐xi Zhang
Published: October 2008

The development of a high plastic strain gauge for use up to 300d̀C is presented. This kind of gauge can measure strain up to 8% and possesses good self compensation on carbon steel. Basic analysis, gauge wire, adhesive material, gauge structure and examples of application are also described.
Alongwind dynamic effects on bluff bodies
Authors: Royles Rodney , Kanda Jun
Published: October 2008

The dynamic alongwind coefficient has been evaluated by means of a single‐degree‐of‐freedom rectangular cylindrical model in a partial boundary layer wind tunnel. Experimental results show a tendency that the ratio of dynamic alongwind force coefficient to the static one is considerably greater than unity in a low reduced velocity range and increases when the reduced velocity decreases, while it converges to a fairly constant value less than unity when the reduced velocity increases. This tendency can be explained by pressure correlation effects. Although the turbulence intensity and scale were found to have a significant effect on the static coefficient value the ratio of dynamic to static coefficient appears to be insensitive to those turbulence parameters.
An assessment of a frictional strain gauge probe for dynamic strain measurement
Authors: Harwood N.
Published: October 2008

A probe for the measurement of surface strains on dynamically loaded structures has recently been tested at the National Engineering Laboratory (NEL). The procedure for estimating the amplitude of the conditioned signals from the frictional strain gauge attached to the probe is described and the usefulness of the technique is discussed. Calibration data are presented from comparative tests of the performance of the frictional gauge and bonded gauges on an axially loaded testpiece subjected to sinusoidal and random loading conditions.
Some reflections on characteristic angle, light intensity and their correlation to wavelength in three dimensional photoelastic media
Authors: Aben H.
Published: October 2008

Some optical phenomena in three dimensional photoelastic media are analysed. Suggestions made in Ref. 1 relative to the experimental technique of integrated photoelasticity are analysed and some misleading statements of the latter paper are indicated.
The derivation of the stresses in a pressurised pipe or cylindrical vessel with initial geometric imperfections
Authors: Tooth Alwyn S. , Lin‐Seng Ong
Published: October 2008

Several analytical methods are outlined to deal with the title problem when the vessel is free of external constraints. In essence these correspond to the Haigh equation, which provides a nonlinear relationship between the induced circumferential stress and the applied internal pressure. To make use of these analyses a survey of the cross sectional profile is required. The approach using an internal swinging arm has been found most useful. The extent to which an improved Haigh equation is valid is examined with reference to the pneumatic loading of a twin saddle supported horizontal vessel which contains imperfections and restraints at the supports.
Automated photoelastic analysis
Authors: Patterson E. A.
Published: October 2008

Photoelastic stress analysis can be a long and tedious process. However recent and current developments in the field of automated and computer aided photoelastic analysis mean that it is becoming possible to do more complex analysis and to perform it more quickly. This paper provides a survey of these developments and the advances in polariscope design.
A simplified method for predicting the stress concentration in notches from experimental stress data
Authors: Dhillon S. S. , Thompson J. C. , Negus K. J.
Published: October 2008

This paper describes a simple procedure to obtain very reliable estimates of the stress concentration at the root of a notch using only data from points beneath the notch root along its axis of symmetry. The advantages of the method are (i) data from only a few points are needed, (ii) the necessary computations require only a hand held calculator, (iii) inaccurate data becomes quite apparent to the analyst, and (iv) random experimental errors are largely compensated.
Strain gauge readings on a programmable pocket calculator
Authors: Taylor D. A. W.
Published: October 2008

Programs and command instructions are described for three readily available and established programmable pocket calculators which are an aid to the reduction of readings for rosette strain gauges both into principal strains and stresses, and also to the corresponding maximum shear stresses.
Early days with strain gauges ‐ a personal account
Authors: Maslen K R
Published: October 2008

A pre‐Congress ‐ IMEKO (Houston)/SEM (Portland Or) 1938 to 1988 Strain Gauge Jubilee Celebration ‐ publication by special arrangement with P K Stein co‐ordinator.
Errors in dynamic force measurement
Authors: Dixon M.
Published: October 2008

Loadcells for materials testing machines are calibrated statically by comparison with a transfer standard, traceable to the National Physical Laboratory. There is evidence to suggest that, under certain conditions, this static calibration may be insufficient for dynamic testing. The possibility of an error being generated by the inertia of the mass between the loadcell and the specimen is discussed and the results of experiments to measure this error are presented. For the case chosen it is shown that the inertia error may be predicted by calculation. Errors may also arise from the method of dynamic force measurement. The conventional DVM and the analogue peak hold voltmeter are widely used but are subject to errors in a practical machine situation due to their method of operation. Bandwidth limitations are also illustrated for a number of instruments with different sampling rates. A better, although more expensive and complicated solution is to digitise the signal and to use some form of spectral analysis such as the Fast Fourier Transform or the Cross Correlation Integral. The theory for the latter is presented and its merits discussed.
Pressure Vessel Proof Tests and BS 5500
Authors: Procter E
Published: October 2008

A recent BSSM meeting organised by the Pressure Systems Technical Group discussed proof testing of pressure vessels, with particular reference to nozzles etc which fall outside the normal design route and require stress analysis testing. The references in BS 5500 to brittle lacquer, strain gauges and competent persons were of particular concern, as were the interpretation of pressure/strain plots.

The BS 5500 design route is based on a shakedown approach. The paper attempts to describe shakedown and relate it to pressure/strain observations during proof testing. In this way the reader should be more able to make judgments.
Analysis of strain averaged data from finite length gauges and predictions of peak strain for planar notch and fillet problems
Authors: Thompson J C , Brodland G Wayne
Published: October 2008

From a previously derived modal (i.e., series) representation of the stress and strain fields in stress concentration regions, exact analytical expressions are obtained for the averaging effects of finite length gauges located on the boundary of a notch fillet. A simple method of analysing such data is described. It is then applied to two problems to show i) how easily poor or faulty data can be detected and ii) how a very reliable estimate can be made of the magnitude and location of the peak stress (or strain), even when using data from gauges beyond the very highly stressed (strained) region.
Residual stress measurements in a cruciform welded joint using hole drilling and strain gauges
Authors: Pang H.L. , Pukas S.R.
Published: October 2008

Residual stress measurements were made close to the toe of each fillet weld on a load carrying cruciform welded specimen by the hole drilling technique. A standard milling guide with high speed air turbine was used in conjunction with bonded resistance strain gauge rosettes. Experimental calibrations of the method were conducted under known uniform uniaxial tension loads.

A simple incremental drilling technique was used to determine the stress gradient with hole depth. Measurements were also made both at zero load and known tensile loads in order to study the interaction between residual stresses and the applied loads.
TERSA—A new technique for assessing residual stress
Authors: Mountain D.S. , Cooper G. P.
Published: October 2008

This paper outlines a completely new technique which could provide the basis of an instrument for the non‐contacting and non‐destructive determination of static and residual stresses in engineering components, assemblies and structures. The method has been given the acronym of TERSA, standing for Thermal Evaluation for Residual Stress Analysis and would be applicable to a range of metals, both ferrous and non‐ferrous and also to plastics. Some experimental work is described and results are presented which confirm the principle of the proposal.
Measuring the load eccentricity in helical compression springs
Authors: Dragoni E , Stroui A
Published: October 2008

An experimental device able to detect the load eccentricity in helical compression springs is described. The theory underlying the resolution of measured bending strains of the apparatus into effective load eccentricity is discussed. Laboratory results are offered for heavy duty springs and compared to theoretical estimates retrieved from the literature.
The early days of the Saunders‐Roe foil strain gauge
Authors: Jackson Peter G Scott
Published: October 2008

Peter Stein wrote to me in 1987 enclosing advance information on his proposed celebrations to mark the 50th anniversary of the resistance strain gauge in Portland, Oregon, and inviting WSM to become a ‘sponsor’ which was a way of raising funds to pay for the key pioneers and personalities to attend. For a modest sum one could sponsor an individual, and it suddenly occurred to me that one man who ought to be at the ‘party’ was Peter Jackson, who invented the foil strain gauge at Saunders‐Roe in the early 1950's.

I joined Saunders‐Roe shortly after he left, and have spent most of my working life involved in the design, development, manufacture, selling or application of foil strain gauges. I had never met Peter, and I wasn't even sure if he was still ‘with us’.

I had heard that he had relatives still on the Isle of Wight and after some discreet enquiries I found that he was living in California.

I promptly sent off the sponsors fee to Peter Stein and told him I was sponsoring the inventor of the foil strain gauge who was resident in California, and he tracked down Peter Jackson and invited him to the conference, although I didn't know he would be there.

It was quite a moving moment when someone tapped me on the shoulder in Portland and said “are you Les Window? I'm Peter Jackson”….
Energy efficiency ensured through surface temperature and heat flow studies
Authors: Klmber T
Published: October 2008

Surface temperature and heat flow measurement is a highly desirable but difficult thing to accomplish. Unlike applications where transducers in protective tubes are immersed in fluids under controlled or known circumstances, surface measurements require sensors to be outside vessels where environmental conditions may affect results. In addition, surface contours and thermal as well as electrical paths between the sensors and the objects of measurement influence output signal integrity. Selection of sensors and mounting techniques both influence measurement system performance.
Experimental method for determining through thickness residual hoop stresses in thin walled pipes and tubes without inside access
Authors: Jr. J R Sorem , Shadley J R , Rybicki E F
Published: October 2008

The determination of through thickness residual stresses in pipes and pressure vessels is of growing interest because of emphasis placed on life prediction, design, and failure analysis of piping systems. Most of the through thickness residual stress measurement techniques require the placement of gauges on the outside and inside of the pipe. These methods are severely hampered when gauges cannot be placed on the inside of the pipe. This constraint could arise for small diameter pipes, long pipes or for pipes that have been used in a service condition causing corrosion or fouling of the inner surface.

This paper focuses on the first step of a three step procedure for determining residual hoop stresses in thin walled pipes and tubes. The method described is designed for cases where it is impossible to place gauges on the inside of the pipe. The method yses biaxial strain gauges on the outside of the pipe and involves a through thickness axial cut of the pipe. Based on the change in strain on the outside of the pipe, changes in the hoop residual stress distribution due to the axial cut are obtained with the method presented here. The method provides a means to evaluate changes in stresses on both the outside surface and the inside surface of the pipe as well as an evaluation of the change in through thickness hoop stress distribution at any location in the pipe cross section. This paper further demonstrates that the problem of shortening long pipes to enable placement of gauges on the inside of the pipe can result in the loss of significant residual stress information.
Strain gauge reinforcement of plastics
Authors: Little E G , Tocher D. , O'Donnell P.
Published: October 2008

A major disadvantage in strain gauge work on plastics is the effect of strain gauge reinforcement, which induces signifcant errors in the quantitative evaluation of strain derived from the plastic. The parameters influencing reinforcement are well documented and procedures have been developed that permit the identification and correction of this effect in certain situations. The principal causes, effects and corrective procedures are reviewed and where appropriate compared with results obtained by the authors of this article.
On the bending of a stretched wire ‐ case study of a tension measuring device
Authors: Parameswaran M A , Narasimhan S. , Srinivasan V.
Published: October 2008

The case of a stretched wire bent successively over a system of three pulleys has been analysed with specific reference to a commonly used wire tension measuring device. With the help of the simple theory of elastic bending, expressions for the tension variation, angles of wrap, deflections etc., at the pulley have been obtained. A brief parametric study leads to some useful design guidelines. The analysis can be usefully applied to other systems also where wirelwire rope is bent over multiple pulleys.
The Kelvin Hall fairground accident
Authors: Pook L P
Published: October 2008

‘The spread of information about failures within the technical community is essential and it is a sad refection on society that legal and political constraints are doing so much to prevent this spread’, Max S M Saltsman1. Details of such a failure are described here.
Prediction of stress and displacement fields in stress concentration regions by least squares asymptotic analysis of displacement data
Authors: Dhillon S S , Thompson J C
Published: October 2008

This paper demonstrates that highly accurate predictions of the stress fields, including the peak stress of a stress concentration region, can be obtained easily by a least squares asymptotic analysis (LSAA) of even a relatively sparse set of displacement data from points in this zone lying sufficiently far from the boundary to avoid ‘edge effects’.
Quality assurance in dynamic testing
Authors: Harwood N.
Published: October 2008

An agency concerned with the quality assurance of dynamic testing has recently been established. The following paper describes the nature and structure of this agency which is known as the DTA (Dynamic Testing Agency). The aims and philosophy of the DTA are discussed and the importance of the use of reliable experimental data in structural assessment and for the verification of theoretical predictions is emphasised.
The measurement of deformation of a bridge by moiré photography and photogrammetry
Authors: Forno C , Brown S , Hunt R A , Kearney A M , Oldfield S
Published: October 2008

Optical techniques offer advantages over mechanical methods for displacement measurement. A comparative study has been made between photogrammetry and moiré photography during a destructive test applied to a bridge. The first provided accurate values for point displacements whereas the second revealed the whole field movements and indicated the region of eventual failure.
Errors in strain measurement at high frequency
Authors: Dixon M
Published: October 2008

Two possible sources of error in strain measurement at high frequency were considered. The performance of the strain gauge itself was measured by comparison with a reference transducer. Several installations were shown to he satisfactory at up to 100 Hz hut another showed a progressive attenuation with frequency. Attempts to reproduce the fault with another installation were unsuccessful. The sources of error within the instrumentation were also considered and measurements made on the dynamic performance of several voltmeters.
A solution for the problem of load introduction in biaxial fatigue tests
Authors: de Jong G. J.
Published: October 2008

The concept of introduction of biaxial loads in a specimen made of sheet material using soft clamps of unidirectional aramid composite sheet is presented. Using this concept it is possible to generate realistic biaxial tensile stress states in specimens made of sheet materials without the introduction of unwanted fatigue critical areas.
A linear algebra approach to stress and strain at a point and theories of yield
Authors: Milner P. R.
Published: October 2008

A straightforward method is described whereby the magnitudes and directions of the principal stresses and strains in two or three dimensions may be derived using the matrix methods of elementary linear ulgebra. The ideas are extended to simplify the classical derivation of the extreme values of shear stress and of the octahedral stresses. After a description of several visual aids, the work concludes with a definition of the von Mises yield surface consistent with the foregoing procedures.
Non‐uniform residual stress measurements by the hole drilling method
Authors: Schajer G S
Published: October 2008

A recent paper by H L Pang and S R Pukas1 touched on some important aspects of non‐uniform residual stress measurement by the hole drilling method. This note discusses three significant issues raised in that paper, and presents a dissenting viewpoint. The three issues concern: the reliability of calibration constants derived from finite element calculations, the choice of basic stress calculation formulations, and methods used to compute the residual stress variation with depth from the specimen surface.
Strain gauge measurements within the school laboratory practice
Authors: Ficker T.
Published: October 2008

A simple technical device has been proposed suitable for exercising strain gauge measurements in introductory courses in tensometry. Its conception has followed from a theoretical strain analysis of the circular thin steel plate loaded by a concentrated central force. The analysis has taken into account a non linearity of the studied strain field and has used a strain tensor for original expression of Poisson's ratio and Young's modulus of the material of the plate. The derivation of analytic expressions of both these constants enabled one to estimate their values by means of the strain gauge measurements. In this way the proposed device demonstrates further application possibilities of the strain gauge method.
Sensitivity calibration of post‐yield strain gauges under cyclic plastic straining
Authors: Rees D. W. A.
Published: October 2008

A plastic sensitivity calibration procedure is outlined for strain gauges under cyclic, four point bending. Tests show that the gauge resistance changes in an approximately linear manner with longitudinal strain for the first quarter cycle of loading. Calibration curves for subsequent reversals to the direction of deformation display zero‐shift and non‐linearity. Under balanced strain cycling, there is evidence of a cyclically‐stable, sensitivity calibration loop. Theoretical considerations are given in which it is proposed that separate sensitivity factors apply to the elastic and plastic components of strain. It is shown that the plastic sensitivity factor is a function of (i) plastic strain induced hardening and softening in the gauge foil and (ii) any apparent change to the gauge resistivity due to imperfect bonding. The elastic component sensitivity factor equals the manufacturer's value only in the absence of hardening. The two sensitivities may be combined to give a total sensitivity factor when a post‐yield strain gauge suffers elastic‐plastic straining.
A numerical and experimental study of the yield surfaces in cross shaped aluminium plates
Authors: Olivito R. S. , Stumpo P. , Surace L.
Published: October 2008

The behaviour of metals can be described through knowledge of its yield surfaces and constitutive relationships. Starting from this point, numerical and experimental analyses were developed about the yield surface evolution in aluminium cross shaped sheets subjected to incremental hardening. The results of using both the Szczepinski & Miastkowski experimental technique and an F.E.M. code for solving non‐linear stress and strain problems, which uses a macro‐programming language, were compared. The influence of the chosen offset and of the loading path on the shape and evolution of the yield surfaces were analysed. The determination of such surfaces and their evolution with the increase in plastic deformation is still of great importance.
Transducer interconnection with a standard fieldbus
Authors: Jordan J.R.
Published: October 2008

This paper discusses fieldbus systems and introduces MIL‐STD‐1553B, IEC International Fieldbus, Arcnet, Bitbus and The Local Operating Network as examples of the world‐wide fieldbus activity. The main features of fieldbus instrumentation are introduced and communication protocols, safety and condition monitoring applications, and smart instrumentation are discussed.
The multi‐load method of determining discrete system parameters in a loaded three dimensional photoelastic model
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 loaded three dimensional photoelastic model is discussed in this paper. It is well known that once the geometry of the loaded member and the geometry of loading on the member are fixed, the secondary principal stress directions at any particular point along any line of consideration remain constant. The secondary principal stress values will get multiplied by the factor through which the loading on the component is increased. This has been made use of in the present method and from the characteristic parameters obtained at the end of any light path for different loadings on the three dimensional model, the secondary principal stress difference and their orientations are obtained. The method proposed is a fully non‐destructive method of testing and involves measurements only on a transmission polariscope.
The laser strain gauge: micro machining of diffraction gratings using an Excimer laser
Authors: Wileman P. , Coupland J.M. , Creasey C.D. , Rowley D.M. , Halliwell N.A.
Published: October 2008

The laser strain gauge is a recently developed instrument for the single point measurement of surface strain to a resolution of 1 μm. It measures the deformation of a diffraction grating adhered to or etched into the surface of various substrates. In comparison with a conventional electrical resistance strain gauge the new gauge offers greater thermal stability and avoids the inconvenience of electrical connections. When gratings are etched directly into the surface of a component absolute strain measurements over its lifetime are possible.

High frequency (1000 lines/mm) diffraction gratings can be etched into the surface of various substrates including carbon steels, polymers and ceramics using an Excimer laser. This paper describes the optical beam delivery system necessary for this application and demonstrates the feasibility of this exciting new technique.
An assessment of simple photoelastic models in aircraft design
Authors: Albiol R.
Published: October 2008

Polyurethane sheet material has excellent properties for the manufacture of quick, cost effective design stress models. It is easy to model using very sharp instruments such as a scalpel with water lubrication. Because of its low stiffness, loading rigs can be constructed from engineering ply‐wood and other similar materials with the load being applied by means of dead weights or screw devices. The principle of the ‘self calibrating model’ developed by the ESA Group at Filton makes the results to be fully quantifiable. It is very rare that the opportunity arises in aircraft design and manufacture when the results of the simplified stress model can be validated against the behaviour of the real component. This paper reports on such an occasion when very good correlation was demonstrated. The correlation of the results, which was not known before, was established to be good. The conclusion is that the method for the type of problem analysed is cost effective and reliable.
Alternative calibration techniques for quantitative thermoelastic stress analysis
Authors: Dulieu‐Smith J.M.
Published: October 2008

In recent years thermoelastic stress analysis has been established as an important experimental technique. The SPATE (Stress Pattern Analysis by Thermal Emissions) system, marketed by Ometron Ltd., is the standard equipment for thermoelastic stress analysis. The signal obtained from the SPATE equipment is directly proportional to the sum of the principal stress on the surface of the structure under evaluation. For quantitative stress analysis accurate calibration constants must be obtained; these are dependent on the radiometric properties of the SPATE system detector and the material properties and condition of the surface in question. This paper describes a number of calibration techniques commonly in use. The factors which affect the accuracy of each technique are discussed in detail. An experimental calibration study of a “steel” is also included.
Polycarbonate for frozen stress photoelasticity
Authors: Pappalettre Carmine , Galietti Umberto
Published: October 2008

The possibility of using polycarbonate in the frozen stress photoelastic technique is investigated. The results obtained from strip specimens made of laminated and extruded polycarbonate and from plates confirm this possibility.
Automatic ordering of isochromatic fringes ‐ a new methodology
Authors: Ramesh K. , Kelkar Asish A.
Published: October 2008

The intensity variations in the isochromatic fringe field are significant and even minute variations can be recorded using the modern day CCD cameras. The sodium vapour source (589. 3 nm) used in general has upto 4% of another wavelength of 589. 6 nm. In view of this, the minimum intensity forming a fringe is affected and is significant at high density fringe zones. This aspect is used to identify sources and sinks in the fringe field and a new methodology for fringe ordering is proposed. It requires only one image to be processed and hence is equally applicable for static and dynamic problems.
Finite strain analysis by image processing: smoothing techniques
Authors: Amodio D. , Broggiato G.B. , Salvini P.
Published: October 2008

This paper is concerned with a methodology for measuring large strain fields based on digital image processing and numerical computations. The facility, already described in a previous paper by the authors, is based on a stereoscopic‐procedure, which returns the locations of a dot grid, previously etched on the surface of the work piece, in a three dimensional space. The markers are acquired by two CCD cameras from two different viewpoints. The data are then processed by a procedure based on shape function analysis. Tlie strain field is described by a plane Lagrangian referential co‐ordinate system, so that it is possible to take into account large displacements and finite rotations. Thus, the definition of a strain tensor on a 3‐D surface is widely discussed. The present paper faces the question of the noise propagation through the post‐processing algorithm. The method proposed is able to supply the confidence limits of the returned measurements.

The strain analysis procedure was tested by a numerical input. A set of data were simulated, as returned by the acquisition system, for a specific strain problem. In this way the statistical parameters of the data can be easily controlled to explore a wide surrounding of cases. The complete post‐processing procedure was then applied to an experimental case concerning a high strain tensile test.
TV‐shearography for measuring 3D‐strains
Authors: Steinchen W. , Yang L.X. , Schuth M.
Published: October 2008

The shearographic interferometry is employed as a nondestructive full field, optical testing and measuring method without contact. Fringes of constant strain (so called isotase, tasis (Greek)=strain) can he observed in real time on the surface of the investigated machine parts and structures of any material and are represented by the shearogram. Using shearography two states of “deformation are recorded by doubly exposing a Holotesl film in an ordinary camera or stored by an electronic image processing system. In the lens of the camera a shearing element inside or outside the focus is integrated or the lateral Michelson shearing interferometer is used. Rigid body motions of the object are not recorded. Local deformation irregularities caused by a defect under or on the surface of the specimen create, strain concentrations; the homogeneous surrounding is poorly superimposed by an interference pattern. The shearogram shows dark and bright fringes which are the functions of the displacement derivative. The holographic interferometry measures the out of plane deformations directly. Terms of the out of plane strain can be determined by the shearographic method as well as the in plane strain fringes which are described in the following.
A technique for smoothing interior thermoelastic data and enhancing boundary information
Authors: Barone S.
Published: October 2008

This paper presents a technique by which it is possible to smooth thermoelastically measured interior information and to enhance edge data from non‐boundary measured values. The methodology is based on the compatibility equation and an iterative procedure. The technique has been successfully applied to correctly quantify the stress concentration around a hole in an araldite plate.
Contact stresses for a footing on an orthotropic elastic medium
Authors: Antony S.J. , Chandrashekhara K.
Published: October 2008

This paper deals with the contact stress analysis for a strip footing interacting with (i) a homogeneous orthotropic halfplane and (ii) multilayered orthotropic halfplane. The contact stresses have been obtained using a combined approach(finite element method‐analytical)in which the stiffness matrix for the footing has been obtained using the finite element method(F.E.M) while for the different cases of orthotropic medium(halfplane) considered here, suitable analytical solutions have been used. The halfplane needs to be discretised only along the contact length. Hence the solution can be obtained with a minimum input data and also the solution scheme is computationally efficient. Results have been presented for the contact stress distribution, displacement profile and bending stress distribution in the footing.
Factors affecting the intensity distribution in high stress gradient zones in digital photoelasticity
Authors: Mangal S. K. , Ramesh K.
Published: October 2008

In digital photoelastic analysis it is observed that in high stress gradient zones the fringes become brighter. It leads to erroneous results, if not accounted for, in those techniques which use quantitative values of intensity to evaluate the experimental parameters. In this note, the reasons for the above phenomenon is investigated and suitable recommendations are given.
Introduction to thermoelastic stress analysis
Authors: Dulieu‐Barton J. M.
Published: October 2008

The theory of thermoelastic stress analysis is reviewed and the assumptions in developing the theory are assessed. The equipment for thermoelastic stress analysis is based on infrared detection systems. The commercially available systems are described and appraised. Techniques for calibrating the output from the detectors are also provided.
Thermoelasticity for the analysis of crack tip stress fields — a review
Authors: Tomlinson R. A. , Olden E. J.
Published: October 2008

A comprehensive review is given of methods to determine the stress intensity factor at crack tips using thermoelastic stress analysis. In order to obtain accurate results a number of areas of experimental procedure need to be considered and these are discussed in detail. The paper concludes with a discussion on the future potential of the use of thermoelasticity for the analysis of cracks.
The development of simultaneous thermo‐ and photo‐elasticity for principal stress analyses
Authors: Barone S. , Patterson E. A.
Published: October 2008

A technique is developed for determining the individual principal stresses by measuring experimentally the sum and the difference of the principal stresses over a surface of an engineering component. This application, which results from previous research on the thermoelastic response of polycarbonate coatings typically used in reflection photoelasticity, is based upon the simultaneous use of thermoelastic stress analysis and automated photoelasticity. Full field patterns of the individual principal stresses can be evaluated, even over complex geometric surfaces, by properly processing the data obtained by the independent experimental techniques.
Design for prestressing tendons layout in stiffening walls via an experimental technique
Authors: Paloto J.C. , Ortega N.F.
Published: October 2008

The present paper describes the implementation of an experimental technique that allows one to optimise the efficiency of layout design for ropes, tendons, etc in prestressed structures. An application with a certain grade of complexity has been developed, i.e. a stiffening partition wall in hollow sections, with a central opening. This structural typology is normally used in bridges.
Monitoring Downforce
Authors: Cross A. , Gough S.
Published: October 2008

Abstract: How the engineers at The Strain Gauging Co. Ltd. convert existing vehicle components into valuable aids for racecar engineers and designers.
In‐Fibre Grating Techniques for Strain Sensing
Authors: Bennion I. , Zhang L. , Everall LA.
Published: October 2008

Abstract:The principles of fibre optic strain sensing based on the use of in‐fibre Bragg gratings are presented with emphasis on advances in the grating inscription technology. Multiplexed array techniques for structural health monitoring are described with reference to modern industrial applications. Recently established techniques for improving the multiplex density, for extreme strain monitoring, and for high sensitivity measurements using long period gratings are addressed.
The Development of a Hybrid Technique Employing the Boundary Element Method for Thermoelastic Stress Separation
Authors: Barone S. , Pitarresi G.
Published: October 2008

Abstract: This paper presents a development of a hybrid technique employing a boundary element method for determining individual stress components in two‐dimensional arbitrarily shaped domains from experimental isopachics only. The procedure consists of a numerical solution of two Poisson equations representing equilibrium for two‐dimensional plane‐stressed solids with zero body forces. An existing technique is employed for smoothing interior thermoelastic data and enhancing boundary information. The algorithm of stress separation has been implemented with the help of commercial codes. The whole procedure has been tested through a complete post‐processing example of thermoelastic stress analysis data.
Residual Stress Measurement at Corus, Swinden Technology Centre
Authors: Middleton J. C.
Published: October 2008

Abstract: The hole‐drilling and x‐ray residual stress measurement techniques used by Corus, Research, Development & Technology for product integrity and development have been reviewed. Calibration of the x‐ray technique can be undertaken although comparative measurements are often adequate. The application of the x‐ray residual stress measurement method to heat‐treated surfaces, stainless steel and bar straightening is described.
Neutron and Synchrotron X‐ray Strain Scanning
Authors: Withers P. J. , Webster P. J.
Published: October 2008

Abstract: Neutron and synchrotron X‐ray strain scanning provide the opportunity for mapping residual strain distributions within polycrystalline materials non‐destructively. The neutron method is now reasonably mature, industrial standards for measurement are being defined and new dedicated neutron strain scanners are being built at ISIS in the UK and at the ILL, France, as well as in the United States. Synchrotron strain scanning on the other hand is relatively new and is much less well developed but, with penetrations typically hundreds of times greater than most laboratory X‐rays and intensities millions of times greater, it can provide maps of near‐ and sub‐surface strain of unparalleled detail and strain resolution. The capabilities and complementarity of the two methods are reviewed and contrasted in this paper through a series of case studies.
Multi‐step Load Impression Creep Tests for a 1/2Cr1/2Mo1/4V Steel at 565°C
Authors: Hyde T. H. , Sun W.
Published: October 2008

Abstract: Impression creep tests under multi‐step load conditions were performed for a service‐aged 1/2Cr1/2Mo1/4V steel at 565°C, corresponding to uniaxial stresses in the range of 100–150 MPa. Results of the tests have shown that the minimum creep strain rate data of the material, produced from the creep curves obtained under different load histories, are in good agreement. The results obtained indicate that the results from a multi‐step load test of an impression creep specimen, which is particularly useful when the test material is very limited, can be used to obtain the secondary creep properties for a material from a very small test sample.