Showing papers in "Strain in 1991"

Towards full field automated photoelastic analysis of complex components

Abstract: The design of a automated system for photoelastic analysis of complex components is described, and an outline of the theory used in its operation is given. The potential of the system for providing detailed data over the full field of view is demonstrated by the analysis of a slice from a model of a bolt.

Contact stress distributions in a turbine disc dovetail type joint ‐ a comparison of photoelastic and finite element results

Abstract: Two dimensional photoelastic frozen stress techniques were used to investigate the stress distributions of an axially loaded dovetail joint as is found in the design of some turbine blade-disc fixings. The internal stress distributions were obtained by the shear difference method and were compared to results obtained by using the finite element method. It was found that steep principal stress gradients were present immediately below the contact surfaces in the zone adjacent to the fillet radius of the dovetail fixing, which could be an important consideration in the fatigue strength of the joint. The finite element model used gave the same trends of stress as the photoelastic model, predicted higher peak principal stresses and did not exhibit the same detailed variations of stress distribution.

The measurement of deformation of a bridge by moiré photography and photogrammetry

Abstract: Optical techniques offer advantages over mechanical methods for displacement measurement. A comparative study has been made between photogrammetry and moire 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.

Measurement of dynamic response and failure of pipework

Abstract: Pipework in nuclear power stations is designed to withstand the effects of earthquakes The current methods of design are known to be very conservative and lead to the inclusion of large numbers of pipework restraints These restraints are only included to limit stresses in the unlikely event of an earthquake but they can, under some circumstances, increase stresses during comparatively frequent thermal transients and thus their unnecessary inclusion is undesirable With the ultimate objective of reducing aseismic design conservatism the experimental work, described in this paper, has been conducted at Berkeley Nuclear Laboratories (BNL) to investigate the response and failure of pipework under high levels of dynamic excitation The initial work was aimed at response prediction, but it is now clear that the improvement of failure criteria is a preferred route to reduce design conservatism The measurement of high strains and dynamic yield performance of materials has necessitated the development of novel measurement techniques which have wider application in other areas This experimental work is now finished, and the results are being used to support a change in the design codes

Influence of measurement and evaluation parameters on stress distributions investigated by X‐rays

Abstract: The complete triaxial X-ray strain or stress analysis including gradients requires a physical description of the beam path through the superficial layer of the material for both the conventional ω and Ψ goniometer. Within this description, a theory has been developed for plane, cylindrical, spherical or any other convex or concave specimen topography which can be described by two different radii. All crystal structures are supported. Measurements and calculations are controlled by the independent in-situ determination of Poisson's ratio and the stress free lattice spacing. The physical boundary conditions are verified or can be postulated depending on the measurement quality. A complete internal strain and stress field analysis is discussed in terms of the ‘X-ray integral method’ on steel specimens of 100 Cr-6 (ASTM: A 295, BS: 97012), Al2O3 ceramics using conventional X-ray diffractometry and on NiO layers on a metal substrate by the use of synchrotron radiation and parallel beam optics.

The use of photoelastic coatings to investigate the pelvic strain variations resulting from the introduction of cementless metal backed acetabular cups

Abstract: An in vitro photoelastic coating study was initiated to investigate the influence of metal backed cementless acetabular cups on pelvic strain conditions in the immediately post operative state, for comparison with those related to normal hip joint conditions. A single dried bone hemipelvis was loaded to simulate the pelvic orientation at both the 47% stance and single leg stance. The problems associated with use of the photoelastic coating technique are discussed, particularly in relation to the analysis of the anisotropic pelvic bone. A number of critical areas were highlighted on the pelvis where high shearing strains occurred after the introduction of cementless metal backed acetabular cups.

A solution for the problem of load introduction in biaxial fatigue tests

Abstract: 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.

Errors in strain measurement at high frequency

Abstract: 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.

Quality assurance in dynamic testing

Abstract: 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.

Simulated seismic loading on reinforced concrete beam/column connections

Abstract: Laboratory tests to investigate the seismic behaviour of five reinforced concrete external beam/column connection specimens, by subjecting the beams to a series of slow load reversals, are described. The first three tests were undertaken as an extension of a static (non-seismic) test programme and were primarily carried out for the purposes of rig development. The two further test specimens contained additional links in the connection zone to make them representative of current seismic practice in the USA. These two specimens were subjected to a series of slow load reversals specifically intended to simulate seismic effects. With the first three specimens, complete destruction of the connection zone was achieved after only four or five cycles; the last two specimens withstood ten and twelve cycles respectively. One of these latter specimens failed due to the development of a plastic hinge at the beam/column junction, the other by plastic hinges forming in the column above and below the beam. Detailed information regarding the form of the reinforcement strain distributions developed during these tests is presented, data being obtained using reinforcement internally strain gauged with electric resistance strain gauges. Each specimen contained around 230 such gauges. (Author/TRRL) (Author/TRRL)

Computer aided analysis of strain rosette data

Abstract: In this paper a computer program has been developed for analysing the strain gauge rosettes by considering the transverse sensitivity of all gauges. The program is capable of calculating principal strains, maximum shear strain, principal stresses, maximum shear stress and principal directions from the data obtained by using strain gauge rosettes of various configurations. The gauge factor and transverse sensitivity of all gauges in the rosette must be the same.

Procedures for analysis of strain transfer in the acetabular region in vitro

Abstract: The failure of acetabular cups via loosening, migration or fracture is partially related to the stress distribution existing in the acetabular region. The complexity of the investigation of these stresses demands the application of a variety of model testing techniques involving combined embedded strain gauging, finite element analysis, transmission and reflective photoelasticity and crack propagation studies. The application of these procedures are described and the difficulties of obtaining representative loadings and restraints are commented upon.