Showing papers in "Strain in 1973"
TL;DR: In this paper, a variety of loadings were applied to reinforcing bars to study a range of initial strains and loading and unloading sequences from tension and compression, and it was found that a Ramberg-Osgood type function gave good agreement with the loading portions of the experimental curves except at very large strains.
Abstract: The stress–strain behaviour of mild steel under cyclic loading is examined. The results of tests are described in which a variety of loadings were applied to reinforcing bars to study a range of initial strains and loading and unloading sequences from tension and compression. The tests emphasize that when postelastic stress reversals take place the stress–strain relationship for steel becomes non–linear over much of the loading range owing to the Bauschinger effect. It is found that a Ramberg–Osgood type function gives good agreement with the loading portions of the experimental curves except at very large strains. The empirical constants in the function were determined from the experimental results by least squares analyses and were found to depend on the plastic strain in the previous loading run and the number of previous loading runs.
25 citations
TL;DR: In this article, it was shown that a softening of the model material with heat causing a variation in the value of Young's modulus can cause a significant increase in strain and deflexion.
Abstract: Analysis of structural problems with the aid of scale models constructed in low–modulus thermoplastic materials such as Perspex, Vybak and Darvic is now well established. Measurements of strain and deflexion are complicated, however, by the structure creeping under load and by the effects of changes in ambient conditions of temperature and humidity. Experience shows that these difficulties can usually be overcome by the use of suitable testing techniques, but strain measurements using resistance strain gauges are sometimes regarded critically because these measurements are said to be influenced by the heating effect of the bridge current and the low thermal conductivity of thermoplastics. One aspect of this could be a softening of the model material with heat causing a variation in the value of Young's modulus. At the Naval Construction Research Establishment, Dunfermline, thermoplastic model testing has for many years been a feature of the work in support of structural and theoretical analyses and the information derived from this work shows that the criticisms are unjustified.
12 citations
TL;DR: In this paper, the authors used nine independent measurements from which not only is a complete analysis possible by solution of the strain matrix constructed from these readings, but gross errors in individual readings may be identified and these readings discarded.
Abstract: Surface strain measurements of bulk concrete structures such as dams provide insufficient information and embedded strain measuring devices are necessary. For complete analysis six strain measurements are required. The device described indicates nine independent readings from which not only is a complete analysis possible by solution of the strain matrix constructed from these readings, but gross errors in individual readings may be identified and these readings discarded. An evaluation may be made of the errors in the results determined from the remaining gauges.
8 citations
TL;DR: In this paper, the authors used the frozen stress photoelastic technique to determine the stress intensity factors of a nuclear reactor vessel with a radial branch, and cracks of varying depth were introduced longitudinally.
Abstract: Stress intensity factors have been determined by means of the frozen stress photoelastic technique for nozzle corner cracks in pressure vessel models. The model geometry was chosen to represent a nuclear reactor vessel with a radial branch, and cracks of varying depth were introduced longitudinally. The results were compared to experimental data obtained from burst tests, thus extending their scope.
7 citations
TL;DR: In this article, the design and development of Manganin wire sensors for use at pressures up to 200 000 lbf/in2 (1.38 GN/m2) is described and data presented for an alternative wire, Zeranin.
Abstract: The design and development of Manganin wire sensors for use at pressures up to 200 000 lbf/in2 (1.38 GN/m2) is described and data presented for an alternative wire, Zeranin. A brief description of suitable bridge and digital read–out systems is given together with the design of a resistance strain gauge transducer suitable for control applications.
6 citations
TL;DR: In this article, a non-stroboscopic system for freezing high speed rotational motion has been developed by WaddelI. The system depends on the fact that the image of a stationary object (e.g., turbine disc, crankshaft, grinding wheel) can be made to rotate accurately about one axis only (i.e., no oscillation which will blur the image) when the image is passed through a certain prism.
Abstract: A non–stroboscopic system for freezing high speed rotational motion has been developed by WaddelI. The system depends on the fact that the image of a stationary object (e.g., turbine disc, crankshaft, grinding wheel) can be made to rotate accurately about one axis only (i.e., no oscillation which will blur the image) when the image is passed through a certain prism. The image of the object will rotate twice for one revolution of the prism. If the object now rotates, and a fixed velocity ratio is maintained between the object and the prism, the rotating image of the object is rendered optically stationary by the prism. The image is rendered stationary through 360 degrees of object rotation. A novel and inexpensive synchronising system has been evolved by Waddell to maintain a stationary image of the object for long periods and over a large range of speeds and to maintain that static image despite transients in the speed of the object.
3 citations
TL;DR: In this article, a surface mounted vibrating wire strain gauge for use in creep tests is described and some results on the stability of the gauge are presented, including a pressed one-piece clamp for holding the wire and provision for a secondary strain measuring system.
Abstract: The construction of a surface–mounted vibratingwire strain gauge for use in creep tests is described and some results on the stability of the gauge are presented. Novel features of the gauge construction include a pressed one–piece clamp for holding the wire and provision for a secondary strain measuring system. Relaxation of the vibrating wire caused relaxation of the gauge. There was no significant relaxation due to the clamping method. Cyclic straining of the gauge before use virtually eliminated zero displacement. The use of an unloaded control specimen, which is gauged at the same time and with the same wire tension as the creep specimen, is recommended. Alternatively, relaxation measurements on the wire can be used to correct measured strains. Either of these procedures will reduce the effect of gauge relaxation on creep strains to less than 3 μstrain.
2 citations
2 citations
TL;DR: The effect of temperature change on a strain gauge installation may be to produce strain readings of a magnitude greater than the mechanical strain being recorded as discussed by the authors, and some of the difficulties encountered in the measurement of strain.
Abstract: The effect of a temperature change on a strain gauge installation may be to produce strain readings of a magnitude greater than the mechanical strain being recorded. This paper discusses some of the difficulties encountered in the measurement of strain. In particular, the selection of the most suitable type of self–temperature compensated strain gauge for a particular specimen and its associated wiring technique are considered.
2 citations
TL;DR: In this article, the influence of transverse sensitivity factor n on errors in the measurement of strain is discussed and it is concluded that, provided the factor n is within £0015, its effect may be disregarded in all normal applications.
Abstract: The influence of the transverse sensitivity factor n on errors in the measurement of strain are discussed and it is concluded that, providing the factor n is within £0015, its effect may be disregarded in all normal applications. The determination of n on a gauge factor calibration rig is considered and an analysis made of the degree of accuracy attainable.
2 citations
TL;DR: In this article, the authors deal with the contact pressure between a belt and the pulley to which it transmits force and with the bending and membrane stresses in the belt, taking the anticlastic configuration of the belt into consideration.
Abstract: This paper deals with the contact pressure between a belt and the pulley to which it transmits force and with the bending and membrane stresses in the belt. The anticlastic configuration of the belt is also taken into consideration. The commonly known simplified approximate analysis of the pressure, as well as the results of a more elaborated theory, are presented. Also given in the paper are the description and evaluation of several experimental stress analyses methods that can be used to solve the problem. Two and three-dimensional photoelasticity, thickness measurements and electrical strain gages were found to be the most practical approaches. The correlation of results obtained using the theories and the experimental methods is discussed. It is estimated that the peak contact pressure is 3.5 times the one computed using the plane stress assumption. Results obtained will also have application in the design of wire-ropes or cables transmitting forces to sheaves, or drums.
TL;DR: In this article, a room temperature technique for experimental stress analysis in three-dimensional fiber reinforced plastics is proposed, which allows strains which are produced by loading to be permanently locked into the epoxy model by the curing process and enables slices to be cut for analysis without disturbance of the fringe pattern.
Abstract: A room temperature technique for experimental stress analysis in three–dimensional fibre reinforced plastics is proposed. The technique is verified experimentally in two dimensions for the particular case of a cold–curing epoxy resin subject to load before the resin has fully hardened. This technique allows strains which are produced by loading to be permanently locked into the epoxy model by the curing process and enables slices to be cut for analysis without disturbance of the fringe pattern. A simple three–dimensional model analysis is presented to demonstrate possible advantages of the technique.
TL;DR: In this paper, the results of experiments using cyanoacrylate IS 12 in cementing Perspex and Araldite are compared with the results using resorcinol formaldehyde.
Abstract: The development of the sandwich technique in photoelasticity necessitates a suitable cement. The results of experiments using cyanoacrylate IS 12 in cementing Perspex and Araldite are compared with the results of experiments using resorcinol formaldehyde. These show that cyanoacry/ate is much superior in strength and that it has other properties suitable for the purpose.
TL;DR: In this article, the dynamic response of a vertical cantilever structure exposed to the natural turbulent wind was observed, which consisted of a steel tube 2 743 m (9 ft) high on the top of which was mounted a closed drum.
Abstract: The paper describes an investigation in which the dynamic response of a vertical cantilever structure exposed to the natural turbulent wind was observed. The structure consisted of a steel tube 2 743 m (9 ft) high on the top of which was mounted a closed drum 609 6 mm (2 ft) diameter by 609 6 mm (2 ft) high. The deflexions of the drum on two orthogonal axes were measured and also the strains near the lower end of the steel tube. Wind velocity was measured with a hot–wire anemometer and all the measurements were recorded on a high speed ultraviolet recording galvanometer. The results are considered in two parts: (a) the response transverse to the wind direction (b) the response in the direction of the wind. The transverse displacements are accounted for by vortex shedding and the longitudinal displacements can be calculated from the wind velocity trace, given the requisite structural parameters. Many engineering structures can be considered as structures of one degree of freedom and it appears that the behaviour of all such structures can be predicted by the method used in this investigation.
TL;DR: In this article, the preparation of a liquid rubber formulation for both cold and hot casting of photoelastic models is explained, and suggestions are made for the development of approximate but rapid methods of analysis.
Abstract: The preparation of a liquid rubber formulation for both cold and hot casting of photoelastic models is explained. Membranes and thin–walled structural models are amongst the examples considered qualitatively. Suggestions are made for the development of approximate but rapid methods of analysis. Of necessity the applications outlined are based on brief trials only and further development work is required.