Showing papers in "Strain in 1970"

Measurement of thermally induced preloads in bearings

Abstract: Strain gauge bridges and thermocouples on a waisted section of the shaft, with heated potted amplifiers rotating with the shaft, measure changes in preload due to bearing temperature changes in an experimental simplified mainspindle assembly.

Theoretical aspects of residual stress measurements by x‐ray diffractometry

Abstract: This paper is the first in a series of three covering (1) theoretical considerations, (2) experimental features, and (J) practical applications of X-ray diffractometer techniques to the accurate determination of residual macrostresses.

Measuring strains under welds by the moiré fringe technique

Abstract: A method of measuring strains very close to weld deposits has been developed using moire fringe technique and mismatch gratings. It is necessary to compromise between accuracy and gauge length, but an accuracy of 100μin/in (-10-4) can be achieved with a gauge length of 0.2 in (5mm). Strains parallel to the weld deposit can be measured right up to the fusion line, but in the direction normal to the weld deposit the first strain reading is controlled by the gauge length, as defined by the distance between successive fringes.

TRIANGULAR AND v 2 GRATINGS FOR THE MOIRÉ TECHNIQUE

Abstract: Methods for constructing two new types of grating for the moire technique are described, their use is illustrated in application to a simple beam, and the range of measurable strains is established. In certain circumstances the use of these gratings presents a means of accurate analysis without recourse to elaborate equipment.

Analysis of photoelastic data for three‐dimensional stress separation

Abstract: The principles of stress separation, by the classical and by Tesar's methods, from observations on slices of frozen-stress photoelastic models are explained with illustrations for axisymmetric and general three-dimensional problems and for problems with a plane of symmetry.

The effect of cross‐sensitivity on the determination of stress by strain gauges

Abstract: Some free-filament wire strain gauges used at high temperatures have a higher than normal cross-sensitivity so that errors in the principal stress calculated by standard formulae may be significant. The magnitude of the error is shown and the formulae are modified to obtain true principal stresses. As the modifications are simple, all results obtained from electrical resistance strain gauges can be corrected similarly.

Stencil methods for preparing moire grids

Abstract: Three methods are described for depositing moire grids on specimens by means of thin metal meshes produced by electroforming. The methods involve printing, electro-etching, vacuum deposition, with the mesh used as a stencil, and they are capable of accurately reproducing grids with line densities of 2000 lines/in (80 lines/mm) and of giving good contrast.

Some notes on the design of simple cantilever type transducers

Abstract: A nomogram is derived that permits a quick selection of steel or Al-alloy cantilever beam dimensions for the design of a transducer required to measure by means of strain gauges a given deflection or a given force. Examples show the application of the nomogram and important factors for optimum design are discussed.

The strain gauge: an aid to the development of marine transport

Abstract: Strain gauges measure directly strains in models and marine components and are parts of torque and thrust transducers and of force and moment balances. Six-component balances of strut and shear-plate design and special sliprings are described.

A 3-dimensional investigation of shrink-fit stress distributions

Abstract: The paper gives an account of the experimental procedures adopted in investigations concerning shrink-fit stress distributions in epoxy resin model assemblies. The use of the stress-freezing technique is discussed with reference to the shrink-fit problem. Information on model material properties is also presented, with particular emphasis on an assessment of the creep level.

A universal instrument for fringe multiplication

Abstract: Expenditure of time for conventional photoelastic analysis of two-dimensional models under load and of frozen-stress slices is minimised and the applications of materials of low optical sensitivity either for stress or for strain are extended by the use of this instrument, which is designed for incorporation in any conventional transmission bench. Data may be analysed directly by travelling microscope or deduced from photographs. The light may also be passed into a separate darkroom unit and the faint images projected on to a screen for observation and for recording of information on photographic paper which is then rapidly processed.

Triaxial analysis of the “poker‐chip” test

Abstract: Axial compression of thin circular discs made of plasticized epoxy resin was studied. The plane faces were cemented to platens rigid compared with the material of the discs so that the constraint due to cementing created in the discs a three-dimensional state of stress. The internal strain distribution was measured by the moire method which yielded enough data for an evaluation of this state of stress. The influence of the aspect-ratio of diameter D to thickness t of the disc was investigated.

Izod impact machine for a wide range of single and repeated impact tests

Abstract: A pneumatically operated lifting mechanism and a fluidic control system have been added to an Izod impact testing machine for automatic repetition and counting of impacts from an adjustable preset striking height of the pendulum hammer and for automatic stopping of the machine on failure of the specimen.

A direct reading flexible strain gauge

Abstract: A scale and a vernier, which are photographed on two strips of copying film on a flexible high-stability polyester backing, can freely slide over each other so that, if affixed to the test piece at opposite ends, they form a strain gauge of minimal stiffness measuring up to 12% strain with a sensitivity of 0.1% strain. Effects of curvature are taken into account by calculation.

A rapid method for calculating the transversal strain in the moire technique along sections of symmetry

Abstract: An approximate rapid method is described for calculating in the moire technique the transversal strain directly from the longitudinal strain distribution across sections of symmetry. The method is based on evaluation of the load transmitted through the section and is corroborated by two examples.

Prediction of zero strain vectors in dynamometer rings

Abstract: A simplified theory for the prediction of points of zero strain in dynamometer rings under diametral loads has been verified by experiment and found to give very good results. These points can be used for the separation by strain gauge indications of the effects of two mutually perpendicular forces.