Showing papers by "City University London published in 1968"

An integral equation formulation of plate bending problems

Abstract: The mathematical theory of thin elastic plates loaded by transverse forces leads to biharmonic boundary value problems. These may be formulated in terms of singular integral equations, which can be solved numerically to a tolerable accuracy for any shape of boundary by digital computer programs. Particular attention is devoted to clamped and simply-supported rectangular plates. Our results indicate support for the generally accepted treatment of such plates and for the intuitive picture of deflection behaviour at a corner.

The Elastic Constants of Crystalline Native Cellulose

Abstract: A new theoretical analysis is made of the elastic constants of crystalline native cellulose. Primary interatomic forces are considered in the calculation of the Young modulus in the chain direction, where we retrieve a result identical to that of Treloar. Hydrogen bonds provide the main mechanism for determining all the other elastic constants, most of which are here calculated for the first time. The lateral Young moduli are found to be surprisingly high. Van der Waals interactions are assumed to play a subsidiary role to that of hydrogen bonds, but this factor remains to be quantitatively assessed. The relation of theory to experiment is critically examined.

Measurement of non-uniform bi-axial residual stresses by the hole drilling method

Abstract: The hole drilling method is used to evaluate bi-axial residual stresses varying with depth. Equations with experimentally determined calibration constants, given here for light-alloys, relate residual stresses to strain relaxations as the hole is drilled. Accuracy and limitations are assessed by application to known stress conditions. The method can be used on large structures and in field conditions.

Embedded strain gages for the measurement of strains in rolling contact

Abstract: The paper describes the use of the embedded-strain-gage technique for the measurement of the strain distribution below a circular surface of contact supporting normal and tangential forces while the bodies in contact are rolling together. A brief description is given of the method used for embedding strain gages at very small depths below the surface of a model sphere of epoxy resin. The rig used for pressing the model against another sphere of the same material, driving one of them and restraining the other, is also described together with the instrumentation. A preliminary series of static tests shows that the measured subsurface strains are in good agreement with Hertz's theory of contact. For tests under rolling conditions, the recorded results of a strain gage under different load levels are easily converted to a common nondimensional scale by photographic enlargement or reduction of the original recorded trace. A special Wheatstone-bridge configuration also permits the direct measurement of orthogonal shear strains by combining the output of the gages of embedded rectangular rosettes. Some typical results are given.

On the impulse response of an aquifer

Abstract: The impulse response and the response to a unit step function of the onedirectional semi-infinite aquifer is given, derived from the approximate partial differential equation of the ground water flow. An example is presented.

The Influence of Bends on Fluid Transients Propagated in Incompressible Pipe Flow

Abstract: The influence of a bend on the fluid transients propagated by a rapid valve closure in a long pipeline is examined by means of a short dimensional analysis and a comprehensive series of experimental tests designed to record the effects of varying in turn: the pipeline diameter to thickness ratio (7.35 to 48), pipe elasticity to fluid bulk modulus ratio (0.27 to 93.6), the restraint applied to the pipeline, the bend radius of curvature to pipe bore ratio (0 to 5), the included angle of the bend (0° to 135°) and the initial flow velocity.From these tests the influence of a bend is found to be solely dependent on its geometry. Empirical formulae are proposed which express the reflection and transmission of a transient at a bend in terms of the bend radius of curvature to pipe bore ratio and included angle. The formulae are tested by varying both the angle and curvature of a series of bends mounted in turn in a steel pipeline and found to be accurate within the limits of measurement possible.A method designed...

On a general method of compensation in strain gauge work

Abstract: If gauges or rosettes identical with those used in testing are affixed to a compensating bar under known stresses and of the same material as the test piece, the required stresses are obtained directly in terms of the known compensating stress and of the measured resistance changes. Cross-sensitivity, gauge factor and constants of elasticity of the test piece cancel out and errors due to inaccurate assumptions for their values are avoided. If the test strains, elastic or non-elastic, are required and the elastic compensating strain is known, Poisson's ratio of the compensator enters into the evaluation. A region of the test piece where stresses or strains are known may serve as a compensator. One compensating rosette or two single compensating gauges suffice for any number of identical testing gauges. Initial zero balance may not always be needed and special circuits facilitate evaluation, which lends itself to simple self-contained automation. An analogue unit suggested for incorporation in a strain meter allows direct display of principal stresses and directions from rosette measurements.

Some Aspects Of Vision in Infants

Abstract: Summary The development of visual acuity, refractive condition, and accommodation have been considered, comparing old-established concepts with a recent, prolific output of literature. It is shown that visual acuity probably advances at a greater pace than thought hitherto, and this also appears true of accommodation. A number of studies on the distribution of ametropia at birth and subsequent changes indicate that conventional teaching needs to be modified.

A simple heating arrangement for use in neutron scattering experiments

Abstract: A simple heating arrangement for use in neutron scattering experiments up to temperatures of 900°C is described as are its application to studies of liquid metal samples.