Showing papers in "Strain in 1993"

The dispersion of birefringence in photoelastic materials

Abstract: A spectral analyser was used to determine the variation with wavelength known as the dispersion of birefringence of the fringe constant f and the stress optic coefficient C for photoelastic materials. A disc was loaded diametrically and was subjected to the stress freezing thermal cycle. The intensity was measured along the diameter perpendicular to the load for wavelengths between 450 and 850 nm at 5 nm intervals. Using the theoretical solution to the stresses it was possible to calculate the stress optic coefficient for all wavelengths employed. A similar technique was used for an identical disc that was loaded at room temperature. It was found that the fringe constant was extremely linear with wavelength for both types of loading and for the materials CT200, CT1200 and MY750. The stress optic coefficient did not change much between sheets of the same material but was markedly different between materials. The dispersion of birefringence was found to be approximately constant but showed evidence of anomalous dispersion.

In-situ stress determination used in structural assessment of concrete structures

Abstract: Large span, post-tensioned bridges are now regularly subjected to spot checks. Bridge assessment requires a knowledge of the design pre-stress and of any losses that may have occurred since stressing. The assessing engineer is often faced with a lack of information, such as no detailed drawings, no confirmation that build was to design, and it is at this stage that on-site in-situ stress determination can be used to progress the investigation. The methods for in-situ stress determination are based upon the measurement of strain distribution due to local stress relief and the relationship of the strain redistribution to the in-situ stress state. The adaptation of the centre hole technique to the in-situ stress determination in reinforcement, stressing tendons and concrete and the necessary site requirements are explained.

A temperature calibration of a temperature/strain transducer based on two strain gauges

Abstract: The operation of a temperature/strain transducer, called “duplex gauge”, based on two electrical resistance strain gauges, that are temperature compensated for use on materials with different coefficients of linear expansion, was briefly recalled. Three steel specimens were equipped with “duplex gauges” and were subjected to temperature variations and no external loads were applied. The chosen experimental setup (i) to measure the outputs of the gauge temperature compensated for steel and titanium silicate and (ii) to impose known temperature, assured good accuracy and precision in evaluation of the temperature calibration curve. The obtained results showed that the strain differences could be considered, at least for the experimental arrangement examined, a linear function of temperature over the range of 20 to over 140°C. The prepared calibration chart, that allows the correction of temperature induced apparent strain, will be used in future research when generic temperature and strain fields are applied to specimens.

A new cheap pressure foil

Abstract: Fuyi pressurefilms are very popular for the measurement of pressures between flat surfaces. This method cannot however be adopted in an aqueous medium. The present paper offers a cheap solution based on the variation of transparency with pressure of a commercial packing film.

Holographic investigation into the mechanical behaviour of engineering ceramics

Abstract: The complex loading conditions to which a structural component is customarily subjected require a knowledge of the material responses to combined stresses, while almost all the data available for ceramic materials are obtained from uniaxial tests. It is necessary, therefore, to study the behaviour of engineering ceramics using specimens of proper shapes subjected to biaxial stresses and testing methods that enable high sensitivity monitoring and real time analysis of the surface strains. In this respect, an optical technique such as conjugate wave holographic interferometry gives satisfactory results. Characterisation tests are carried out on diametrically loaded discs in order to evaluate Young's modulus and Poisson's ratio of some classes of ceramic materials.

Transducer interconnection with a standard fieldbus

Abstract: 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.

Photoelastic stress analysis of reinforced polycarbonate orthodontic brackets

Abstract: A photoelastic investigation of the stresses in polycarbonate orthodontic brackets reinforced with stainless steel inserts is reported. Three inserts with different profiles are investigated. They are ranked with respect to the stresses generated at the interfaces of the metallic inserts and the polycarbonate material. Comparison of insert designs is quantified.

A numerical and experimental study of the yield surfaces in cross shaped aluminium plates

Abstract: 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.

Measurement of cab mounting point loads

Abstract: A transducer measuring three orthogonal force components has been incorporated in the flexible mountings of a lorry cab so that the dynamic response of the system is unchanged. The instrumentation used to monitor and record the mounting point forces, both during calibration of the transducers, and subsequent road trials has been described. Values of the Cartesian components measured at the front and rear cab mounting points during passage of the loaded vehicle over a simulated Australian road are presented, and the maximum values determined.

Deformation analysis of skew ruled surface shells by moiré interference

Abstract: The use of thin film grids coated on surfaces is described in relation to the determination of deformations in doubly curved shells. The technique is called the coating film moire interference method and employs a laser holographic approach.

Comparison of dynamic initiation toughness measured by strain gauges and the shadow optical method

Abstract: The deformation and fracture behaviour in dynamically loaded Charpy specimens of BS11 rail steel were studied by two different measuring techniques. The transient records obtained from straingauges were compared with results obtained simultaneously by the shadowoptical method. Good agreement was obtained when measuring and comparing the stress intensity factor K in the initial stages of deformation behaviour prior to crack initiation. During fast fracture, the shadow optical method indicated the influence of dynamic effects on crack propagation.

Stress‐strain analysis of a biaxial tension cruciform specimen for tests under creep conditions

Abstract: A flat cruciform specimen for experimental tests either in the elastic or the inelastic range is investigated Mutually perpendicular biaxial tension forces applied to the edges of specimen arms produce in its thinnest part in plane biaxial stresses The stated goal of the study is to assess the extent to which a uniform stress state is achieved within the thin, central gauge area of the specimen It is shown, by applying the FE code ABAQUS, that in the transition between the thin and the thick part of the specimen stress concentrations occur and that the redistribution of stress due to creep will not produce a more uniform stress state An isotropic, elastic - viscoplastic constitutive description has been employed within the context of small deformations The calculations were carried out for three different ratios of biaxial loading The results are displayed for both the initial (ie immediately following load application) stress distribution and the steady state stress distribution within the specimen Experimental validation is discussed