Showing papers in "Strain in 1984"
TL;DR: In this article, the authors examined non-linear interactions between a pair of beam modes in forced vibration of a simple structure and obtained steady state solutions for the nonlinear system equations.
Abstract: Small non-linear interactions of the type referred to as autoparametric may have a considerable effect on the pattern of forced vibration response of certain categories of structures exhibiting low damping characteristics. Under conditions of internal resonance these may bring about a complete neutralisation of the normal forced vibration resonance curve with a transfer of energy to an indirectly excited mode. The paper examines non-linear interactions between a pair of beam modes in forced vibration of a simple structure. Steady state solutions are obtained for the non-linear system equations. Measurements of vibratory acceleration and strain on a laboratory model are shown to give good confirmation of the analytical results and show clearly the substantial effects of internal resonance.
24 citations
TL;DR: In this paper, an annealing cycle for polycarbonate sheets is proposed, and tests carried out on 0.75-3.00 mm thick sheets show the good reliability of the technique.
Abstract: An annealing cycle for polycarbonate sheets is proposed in this paper. Tests carried out on 0.75–3.00 mm thick sheets show the good reliability of the technique. Further confirmation can be found in practical applications reported in other papers.
13 citations
TL;DR: In this article, a modified back computation procedure for the analysis of parting-out strain gauge data is developed and presented with numerical results, and the validity of the straight line assumption is examined over a range of conditions.
Abstract: One method for measuring through the thickness residual stress distributions in welded pipes involves a destructive, three step laboratory procedure consisting of parting out, splitting, and layer removal operations. In the parting out step, a coupon of material is removed from the wall of the pipe while strain gauges on the inner and outer surfaces are monitored. In back computing the through the thickness residual stresses from the parting-out strain gauge data, it is generally assumed that stress changes through the thickness of the coupon vary as a straight line. If the circumferential dimension of the coupon is large compared to the thickness, this assumption is valid. However, in the case of a pipe, the circumferential dimension is usually limited to reduce curvature effects during the subsequent splitting and layer removal steps. If this dimension is too small, the assumption of straight line stress changes through the thickness can lead to serious inaccuracies. In this paper, the validity of the straight line assumption is examined over a range of conditions. To handle cases where the straight line assumption is not valid, a modified back computation procedure for the analysis of parting-out strain gauge data is developed and presented with numerical results. (Author/TRRL)
9 citations
TL;DR: In this article, a new Moire method is proposed to map partial slope contours of laterally loaded reflective plate models, where the beam of light reflected by the plate is collected by a field lens and is optically sheared by a thin glass plate at the focus to produce slope modulated gratings at the image plane.
Abstract: A new Moire method is proposed to map partial slope contours of laterally loaded reflective plate models. The beam of light reflected by the plate is collected by a field lens and is optically sheared by a thin glass plate at the focus to produce slope modulated gratings at the image plane. No real grating is used. Sensitivities an order higher than those of classical Moire methods are obtained.
7 citations
TL;DR: In this paper, a complete separation of stresses throughout the entire stress concentration region near notches in plane, isotropic, linearly elastic plates is achieved using only isochromatic (difference of principal stresses) data.
Abstract: A complete separation of stresses throughout the entire stress concentration region near notches in plane, isotropic, linearly elastic plates is achieved using only isochromatic (difference of principal stresses) data. These data, which are obtained easily by conventional photoelastic techniques, are analysed by a non-linear least squares technique based upon previously derived equations describing the asymptotic character of the rapidly varying stress field near the root of the notch. This paper demonstrates that isochromatic data of typical experimental accuracy from relatively few, arbitrarily located data points within the highly stressed region is sufficient to accurately predict the entire stress field, including location and magnitude of critical stress(es).
6 citations
TL;DR: Using a two-dimensional photoelastic technique, hole shapes have been optimized in diametrically loaded circular discs with two neighboring holes leading to minimum s.c.f as discussed by the authors.
Abstract: Using a two-dimensional photoelastic technique, hole shapes have been optimised in diametrically loaded circular discs with two neighbouring holes leading to minimum s.c.f. Results are given for a range of disc diameter/hole diameter ratios (15.39 $ D/d $ 3.74). In comparison with circular holes, the s.c.f's have been reduced upto about 21 per cent at regions where peak stresses act. The results include the stress distribution around the holes, optimum geometries developed and the effect of tilting the load direction.
5 citations
TL;DR: A data collection system is described which utilizes the products of separate manufacturers to give a cheaper and more flexible system than could be achieved by buying a single ‘all in’ package.
Abstract: A data collection system is described which utilizes the products of separate manufacturers to give a cheaper and more flexible system than could be achieved by buying a single ‘all in’ package.
A description of the software requirements of such a system is given along with a description of its use in a typical logging application.
4 citations
TL;DR: In this article, the authors describe an experimental technique which permits shakedown/ratchetting tests to be undertaken at elevated temperatures for stainless steel type 316, which is required to operate at temperatures of about 500d C.
Abstract: The necessity for reliable shakedown/ratchetting data for stainless steel type 316 arises from its widespread specification in nuclear power plant. In such applications this material is required to operate at temperatures of about 500d C. This paper details an experimental technique which permits such shakedown/ratchetting tests to be undertaken at elevated temperatures.
4 citations
TL;DR: In this paper, the residual stress state between the austenitic surface and a region below the Austenitic/ferritic interface was determined using an incremental analysis to a depth of 8 mm.
Abstract: For an austenitic clad ferritic steel plate it was necessary to determine the residual stress state between the austenitic surface and a region below the austenitic/ferritic interface.
The thickness of claddings was 6 mm and to determine the stress variation between the surface and 8 mm an incremental analysis is required. Any material removal en masse in conjunction with small hole residual stress measurements would have resulted in a stress redistribution and hence a distortion in the stress field being measured. In conjunction with strain change measurements on the other face the sensitivity would not have been sufficient. These two options assume that a thin layer of material over relatively large areas can be removed by a non-stress inducing technique.
A blind hole residual stress measurement using a 13 mm diameter hole 13 mm deep will facilitate accurate incremental analysis to a depth of 8 mm.
The end mill method of hole forming cannot be used with stainless steels because of the random damage effect which is induced in the readings. The airabrasive method which induces no damage effect was used.
The standard airabrasive method of hole forming produces a 2 mm diameter and a 2 mm deep hole.
The modification of the standard airabrasive system is discussed which enables 13 mm diameter and 13 mm deep holes to be formed.
A deviation from the standard hole/gauge layout geometry has been investigated due to non-availability of suitable standard rosettes, and a significant increase in sensitivity has been obtained.
The incremental stress results for the austenitic layer and the austenitic/ferritic interface are discussed using the results from 1.6 mm, 3.2 mm and 13 mm diameter/deep holes.
3 citations
TL;DR: Moreton-Moffat as mentioned in this paper examined the computational techniques of Mendelson and that proposed by Moreton Moffat to derive post yield stresses from strain gauge readings and compared them with the fundamental Prandtl-Reuss approach.
Abstract: The paper examines the computational techniques of Mendelson1 and that proposed by Moreton-Moffat2 to derive post yield stresses from strain gauge readings and compares them with the fundamental Prandtl-Reuss approach. Although the approach by Mendelson is extensively used in one form or another in elasto-plastic analysis its application in the experimental stress analysis field is less common. Moreton-Moffat highlighted this application and modified Mendelson's method claiming that it was unnecessary to use the post yield constitutive law. In this latter respect their approach is shown in general to be inadequate. The technique based on the Mendelson approach1 is found to be an accurate and useful solution especially when modified to incorporate the slope of the constitutive law at the mean stress of any particular finite step. Although the method is an approximate strain analogue of the Prandtl-Reuss equations the approximation is excellent for practical step sizes.
2 citations
TL;DR: In this paper, the authors present the benefits of strain measurement techniques and a number of initiatives which have been taken by the BSSM in relation to quality and reliability which have included meetings held in conjunction with other organisations, the BssM Certificate Scheme and involvement in standards for strain gauge measurements.
Abstract: This paper reviews the very important role of the BSSM in contributing to the wide understanding and application of experimental stress analysis in product design evaluation and testing.
The paper presents the benefits of strain measurement techniques and a number of initiatives which have been taken by the BSSM in relation to quality and reliability which have included meetings held in conjunction with other organisations, the BSSM Certificate Scheme and involvement in standards for strain gauge measurements.
The paper concludes with some facts and figures related to Quality Assurance, and costs of failure and fracture, from authoritative published sources in the UK and USA.
TL;DR: In this article, it is shown that for any light path, the positions of the optical elements for an absolute minimum in intensity of the light emerging from the analyser are unique, and conditions for the determination of the isoclinics and isochromatics are obtained.
Abstract: Conventional polariscope set-ups like the plane polariscope or the dark or bright field set-ups specify the positions of the various optical elements with respect to the polarising axes of the photoelastic model for determining the isoclinic and isochromatic parameters.
In this paper, it is shown that such specification is not necessary since, for any light path, the positions of the optical elements for an absolute minimum in intensity of the light emerging from the analyser are unique. To illustrate this, the case of a general retarder introducing a retardation 2δ at an azimuth θ with respect to the axis of the polariser is discussed and the conditions for the determination of the isoclinics and isochromatics are obtained.
TL;DR: In this article, it was shown that the Moire fringe vector of deformation is the vector sum of those due to extension and rotation, and that it is the most similar vector to ours.
Abstract: Moire fringes are represented as vectors and their characteristics established using vector algebra. It is shown that the Moire fringe vector of deformation is the vector sum of those due to extension and rotation.>
TL;DR: In this article, the photoelastic model has a line of symmetry and is made from a stress frozen sheet, and it is shown how the isoclinics can be obtained from isochromatic measurements only.
Abstract: If the photoelastic model has a line of symmetry and is made from a stress frozen sheet, then it is shown how the isoclinics can be obtained from isochromatic measurements only. The accuracy is investigated with experimental examples. The method should have applications in transient problems and where the sandwich method is used.