Computer aided analysis of strain rosette data

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.     

ON A GENERAL METHOD OF COMPENSATION IN STRAIN GAUGE WORK

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.     

Apparent strains in unmounted strain gauges at high temperature

A detailed investigation into the source of the unmounted apparent strains in resistance strain gauges over a temperature range of 20°C to 550°C is presented. Different measuring systems give different values of unmounted apparent strain. Formulae for two different measuring systems relating the unmounted apparent strains to resistance values are derived. Values computed from these formulae using measured values of resistance are compared with values of unmounted apparent strains measured directly. In addition, formulae which are essential in order to relate the actual strain to the indicated strain are derived for each of the systems. It is shown using the derived expressions that the magnitude of the unmounted apparent strains can be reduced considerably by connecting a shunt resistor across the active element.     

电测法确定低强混凝土裂缝起裂和等效裂缝长度

该文设计了3种低强度混凝土三点弯曲切口梁,测试研究其双K断裂参数。试验中采用标距为5 mm和10 mm的应变片以半桥连接方式测量预制裂缝的起裂荷载,比较其工作性,发现应变片测量起裂荷载具有强度敏感性,短标距应变片更适宜测量本试验用低强度混凝土的裂缝起裂。试验中另沿韧带方向布置4组半桥应变片,根据各测点处拉应变回缩时的荷载与裂缝口张开位移,计算裂缝发展至测点高度时刻的等效裂缝长度,并与此时的实际缝长比较,结果表明双K断裂模型在预测裂缝长度方面具有较好的适用性。     

MEASUREMENT OF INTERNAL STRAIN IN CONCRETE

Methods of strain measurement in concrete have been investigated experimentally. This paper reports work on embedded resistance strain gauges mounted on concrete and other forms of gauge carrier, techniques for strain gauging embedded steelwork, results of gauge factor tests on briquetted and unbriquetted vibrating wire gauges, and gauge responses to temperature variations. Proposals are outlined for future work particularly on stress meters as distinct from strain gauges.     

A METHOD FOR MEASURING THE FRETTING MOTION OF FLYWHEELS

Araldite strips with bonded electric-resistance strain gauges are accommodated in pockets machined into the flywheel and are cemented to both the flywheel and the adjoining crankshaft. flange. Relative motion between the two components strains the strips and is indicated by amplified electrical output.     

Strain Measurement on Composites: Errors due to Rosette Misalignment

Abstract: Electrical resistance strain gauges are increasingly used for the determination of the strain field in composite components. The effect of the angular misalignment of a strain gauge rosette on the determination of the strains in a composite material is investigated in this paper. The theoretical analysis shows that the strain error along the principal material directions depends on the difference of principal strains, on the angular misalignment of the rosette and on the angle between the maximum principal strain and the fibre direction. The paper also shows experimental evidence for the theoretical analysis.     

A STRAIN GAUGE LOAD CELL FOR THE MEASUREMENT OF COMPRESSIVE LOADS UNDER

The design and development of a strain gauge load cell suitable for use under high hydrostatic pressures is described and the method of bonding the resistance strain gauges is given in detail.     

Ring gauge for biaxial strain analysis

The ring gauge performs the same function as a strain gauge rosette by providing three independent signals from which may be deduced the three unknowns in a biaxial strain system, viz. the magnitudes of the principal strains and the directions of the principal axes relative to a datum direction. It is analogous to a delta rosette but possesses advantages over the usual method of cementing three gauges to the surface of the material.     

CRACK TIP FIELDS UNDER NON-STEADY CREEP CONDITIONS—I. ESTIMATES OF THE AMPLITUDE OF THE FIELDS

Abstract— Under non-steady creep conditions, the stress and strain rate fields near the tip of a stationary crack can be described by the singular fields of Hutchinson, Rice and Rosengren for power-law creeping materials. Estimation formulae are presented for describing the amplitude of these fields under load and displacement controlled boundary conditions. For constant loading, the formulae reduce to the result of Riedel and Rice for short times after load application and to the steady state line integral C * for long times. At intermediate times, the estimate is validated by detailed finite-element computation. For displacement-controlled loading, the amplitude of the near-tip fields is shown to fall rapidly, consistent with finite-element analysis. The implications of the results for data collection and defect assessments are discussed in a companion paper.     

SOME NOTES ON THE DESIGN OF SIMPLE CANTILEVER TYPE TRANSDUCERS

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.     

Strain gauge readings on a programmable pocket calculator

Programs and command instructions are described for three readily available and established programmable pocket calculators which are an aid to the reduction of readings for rosette strain gauges both into principal strains and stresses, and also to the corresponding maximum shear stresses.     

Optimising strain gauge orientation for load measurement by means of rosette analysis

When measuring load by means of strain gauges attached to a structure it is not always obvious that the gauge position may be more sensitive to extraneous load components than had been assumed. This note describes a method of defining the orientation of the strain gauge in order to respond to the required load component, with minimum crosscoupling, as the principal strain direction changes.     

Some factors affecting long-term stability of strain measurements using metal foil gauges

The stability of long-term strain measurements is very much dependent on the correct selection of techniques, materials and equipment for the conditions under which the measurements are to be taken.
Temperature effects are also a major factor. Temperature-induced changes in resistance of the Wheat-stone bridge completion and balancing components can result in an output signal indistinguishable from that produced by change of gauge resistance due to surface strain. The signal conditioning and readout equipment can also be affected by temperature and become an additional source of instability.
The term 'instability', in strain gauging, generally refers to 'zero drift' and random deviations of readings when the loading conditions are stationary. In particular it refers to those situations where a measurement system has been balanced and measurements have been taken with a particular load condition which cannot be repeated to re-check the original zero.
In this paper the major sources of instability are identified and recommendations are made as to how best to obtain long-term stability of strain measurements using metal foil gauges.
Information on principal error sources in strain measurement systems using metal foil gauges is included for completeness and because an appreciation of these sources is also vitally important.     

THE MEASUREMENT OF STRAIN IN TUNNEL LININGS USING THE VIBRATING-WIRE TECHNIQUE

The article shows how the innate qualities of the vibrating-wire strain gauge: cheapness, long term stability and tolerance to electrical troubles make it particularly suitable for experiments in tunnels. A basic type of gauge is described and its working explained. Its application is then extended to use in concrete, wet situations, the use of large numbers of gauges and the measurement of bending. Finally, practical advice is given on the assembly and tuning of this kind of gauge.     

UTILIZATION OF STRAIN GAUGES OVER LONG PERIODS OF TIME AT ELEVATED TEMPERATURES

Tests are described for the evaluation of a particular strain gauge/cement combination under steady loading at elevated temperatures over long periods of time. Although the strain gauges showed a relaxation of their reading with time, due to creep of the gauge backing and cement, it proved possible to correct for this effect to within the scatter associated with the specimens and the instrumentation. It is concluded that application of such corrections to other strain gauge/cement combinations should be possible.     

CALIBRATION AND INSTRUMENTATION OF SEMICONDUCTOR STRAIN GAUGES

Characteristics of semiconductor strain gauges are explored experimentally and a procedure is given for calculating the gauge factor for strain measurement on a given test material at a known temperature. Results of experiments on suitable instrumentation are presented.     

The dislocation structures responsible for the optical effects in some naturally-deformed quartzes

The optical features in naturally deformed quartzites, namely undulatory extinction, deformation bands, deformation lamellae and sub-grains, can be related to dislocation structures in the quartz grains. Dislocation walls forming mosaics of sub-grains are the principal cause of all the optical features. The irrational deformation lamellae common in metamorphic quartzes are sub-grain walls; only those which lie on slip planes are slip lines and these are normally emprinted (superimposed) on sub-grain structures. The dislocation structures are indicative of recovery and thus optical features cannot be used as stress or strain gauges.     

小尺寸混凝土试件双K断裂参数试验研究

采用最大尺寸为680mm×160mm×40mm的标准三点弯曲梁试件,利用在初始裂缝两侧粘贴电阻应变片并利用混凝土裂缝扩展到此处时其应变回缩的方法测得了起裂荷载Pini,在此基础上根据Pini及初始缝长a0得到了起裂断裂韧度KIiCni;根据在试验中测得的最大荷载Pmax及对应的裂缝口张开位移CMODC计算了混凝土等效裂缝长度aC,据此计算了失稳断裂韧度KIuCn。结果表明:采用电阻应变片法可准确测定混凝土的起裂荷载Pini,且方法简单。试验结果还表明:在本试验范围内,三点弯曲梁法测得的混凝土双K断裂参数KIiCni、KIuCn与试件高度无关,进一步说明了混凝土双K断裂参数可以作为描述混凝土裂缝扩展的断裂参数。     

MEASUREMENT OF STATIC STRAIN UNDER RAPID HEATING

The behaviour of various strain gauges on unstressed aluminium under various heating rates is investigated systematically. Testing installations, gauge preparation, evaluation of tests and results are presented.