Lubricant effects on strain fields of seven wire strands subjected to tensile load

As a part of an extensive analysis on strand behaviour the lubricant effect in strain fields was examined. The strains were measured by using electrical resistance strain gauges. The results obtained, by loading the unlubricated and lubricated sample both statically and quasi-statically, showed relevant effects caused by different contact loads developed among the wires. By examining the strains measured during the severing of one helical wire the inapplicability to the strands of one Italian regulation relative to wire ropes, was also confirmed.     

Early days of the resistance strain gauge

The earliest developments in the use of electrical strain gauges as a means of quantifying the measurement of stress in materials are recalled by the author, whose own involvement was associated with the early developments in the mechanised production of strain gauges. The manufacture of batch quantitities is vividly recounted following the realisation that strain gauges would lend themselves to commercial exploitation.     

The design of a multi-purpose multi-component strain gauge dynamometer

The design, construction and calibration of a multi-purpose multi-component strain gauge dynamometer is described. The dynamometer was constructed for use with a free surface water channel, which can also be used as a water tunnel or a cavitation tunnel. In this experimental facility, the large speed range available (0·03 to 6·1 m/s) and the variety of projects encountered require the measurement of a wide range of loads in several different configurations. The dynamometer system has been based on a unit block concept so that the blocks can be assembled into a suitable configuration and complexity of components to suit each particular problem.
The basic design concept is described together with the calibration results and the magnitude of the interactions. It is concluded that the overall accuracy of the dynamometer blocks and the absence of interaction coupled with the versatility of the system confirm the choice of the original design.     

Comparison of dynamic initiation toughness measured by strain gauges and the shadow optical method

The deformation and fracture behaviour in dynamically loaded Charpy specimens of BS11 rail steel were studied by two different measuring techniques. The transient records obtained from straingauges were compared with results obtained simultaneously by the shadowoptical method. Good agreement was obtained when measuring and comparing the stress intensity factor K in the initial stages of deformation behaviour prior to crack initiation. During fast fracture, the shadow optical method indicated the influence of dynamic effects on crack propagation.     

The Reinforcement Effect of Strain Gauges Embedded in Low Modulus Materials

The reinforcement effect of electrical resistance strain gauges is well‐described in the literature, especially for strain gauges installed on surface. This paper considers the local reinforcement effect of strain gauges embedded within low Young modulus materials. In particular, by using a simple theoretical model, already used for strain gauges installed on the surface, it proposes a simple formula that allows the user to evaluate the local reinforcement effect of a generic strain gauge embedded on plastics, polymer composites, etc. The theoretical analysis has been integrated by numerical and experimental analyses, which confirmed the reliability of the proposed model.     

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

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.     

The role of strain measurement technology in structural evaluation

This paper describes the importance of structural evaluation to the process of design assessment and outlines the significant role played by strain measurement technology in extending the scope of strain history data collection and facilitating strain monitoring of full-scale structures in the laboratory. After some general discussion of the various models of structural behaviour, it then proceeds to give a brief historical account and outlines the principles of thermoelastic stress analysis (TSA). A general desciption is provided of a specific TSA technique namely Stress Pattern Analysis by Thermal Emission (SPATE).
Despite the level of innovation and development in strain measurement technology, the use of bonded strain gauge elements is still by far the most commonly used strain measurement and monitoring technique in structural evaluation work at NEL. The paper highlights several recent test programmes carried out at NEL in the form of case studies which demonstrate different aspects of measuring, monitoring and validation of this and other strain measurement techniques; and verification of analytical models.     

Experimental evaluation of a method for separating axial and bending stresses from strain gauge measurements taken on one surface by three-element rosettes

A method is described and results presented for the separation of axial and bending components of stress taken on one surface of a structure with a two-tier, three-element rosette assembly.     

A numerical and experimental study of the yield surfaces in cross shaped aluminium plates

The behaviour of metals can be described through knowledge of its yield surfaces and constitutive relationships. Starting from this point, numerical and experimental analyses were developed about the yield surface evolution in aluminium cross shaped sheets subjected to incremental hardening. The results of using both the Szczepinski & Miastkowski experimental technique and an F.E.M. code for solving non-linear stress and strain problems, which uses a macro-programming language, were compared. The influence of the chosen offset and of the loading path on the shape and evolution of the yield surfaces were analysed. The determination of such surfaces and their evolution with the increase in plastic deformation is still of great importance.     

Use of the Southwell method to predict buckling strengths of stringer stiffened cylindrical shells

This paper presents the results of some tests that were conducted on stringer stiffened epoxy cylindrical shells. The object of the investigation was to determine if the Southwell technique for estimating buckling loads could reasonably be used for the nonlinear collapse of cylindrical shells. The results showed that the technique provides a useful estimate of the buckling load provided care is taken in interpreting the results. In some instances the estimate is likely to be greater than the actual load. Where two buckling modes are encountered at the same time the Southwell technique appears to predict the critical load associated with either mode depending on the deflection parameter being measured as well as on the interpretation of the results.     

Development of temperature compensated high elongation resistance strain gauges for use up to 250°C

The paper describes the development and evaluation of temperature compensated high elongation resistance strain gauges for use from room temperature to 250°C. These gauges could be temperature-compensated on steels with coefficient of thermal expansion α = 11 ppm/°C. Thermal output within 250°C was about 1 μm/m/°C and maximum standard deviation of 5 gauges was 34 μm/m. Strain limit was > 4% at room temperature and at 250°C. Gauge factors of different strain ranges at R.T. and at 250°C are tabulated. Some applications are stated.     

Prediction of stress and displacement fields in stress concentration regions by least squares asymptotic analysis of displacement data

This paper demonstrates that highly accurate predictions of the stress fields, including the peak stress of a stress concentration region, can be obtained easily by a least squares asymptotic analysis (LSAA) of even a relatively sparse set of displacement data from points in this zone lying sufficiently far from the boundary to avoid 'edge effects'.     

Error analysis and method of accuracy evaluation of strain gauge factor testing apparatus based on pure bending moment beams

For the appraisal of accuracy of strain gauge factor testing apparatus based on pure bending moment beams, the common means adopted since the 1960s and still in use internationally today are by application of the strain definition to measure directly the strain on the calibration beam surfaces. However, because of the imperfect measuring principle and inadequate resolution and accuracy of instruments available, etc., this problem has not been solved satisfactorily. This paper proposes a unique way by introducing two new concepts, i.e. the shape errors of the cylindrical surfaces and deflection errors of the bent calibration beam, in accordance with the features of the forces acting on the beam, and the geometric shape and dimensions of the beam in operation, to analyse and classify the various accidental and systematic errors involved. Through the two concepts, the task of appraisal of accuracy is simplified as the appraisal of the cylindricality of the cylindrical surfaces of the bent calibration beam and the appraisal of the three main parameters in the strain formula.     

Sensitivity of the virtual fields method to noisy data

This paper deals with the application of the virtual fields method (VFM) to the identification of constants governing anisotropic constitutive equations. After a short recalling of the main features of the VFM, its sensitivity to noisy data is addressed. The study focuses on the random component of the noise which always adds to the actual fields in experimental full-field measurements. The uncertainty of the identified constants due to this random component is derived analytically. The obtained closed-form expression is set as a criterion for grading virtual fields. The least sensitivity to noise leads to the best identification. The grading procedure is implemented directly in the VFM algorithm, providing systematically the virtual field which minimizes the sensitivity to random noises. Examples are provided for validating the approach with numerically simulated noisy data. Finally, the grading procedure is applied for adjusting the geometry which leads to an optimal use of the three-point bending test for identifying the elastic constants of a composite material. It shows that the criterion sensitivity to noise characterizes quantitatively the identifiability of one or several parameters. Future applications appear quite promising within the design of novel test methods for composites using the VFM.The authors would like to express deep gratitude to Professor Michel Fogli whose help was crucial for formulating rigorously the mathematical approach of this paper.     

An analysis of the transient stresses in a heavy duty switching unit

An analysis has been made of the transient bending and shear stresses set up in the drive shaft of an 11 W ring main switch unit manufactured by South Wales Switchgear Ltd. The analysis compares theoretical bending and shear stress plots along the main shaft with experimental values obtained from electrical resistance strain gauges.     

Effect of Lüders strain on engineering crack opening displacement estimations for leak-before-break analysis: finite element study

As a companion paper to our previous paper [ Fatigue Fract. Engng Mater. Struct. 24, 243–254], this note provides further validation on the engineering crack opening displacement (COD) estimation equation based on the enhanced reference stress method against three-dimensional, elastic–plastic finite element (FE) results using actual tensile data of three typical ferritic steels exhibiting a wide range of Lüders strain. Furthermore, the resulting FE results are also compared with the GE/EPRI COD predictions. It is found that the proposed enhanced reference stress method gives overall more accurate and robust COD results than the GE/EPRI method, compared with the FE results.     

Assessment of strain gradients affecting the performance of 3-D strain rosettes – relevant to the analysis of cement mantle strains in total hip replacements

A large scale model analysis, using embedded strain gauges, of the strain distribution in the cement mantle surrounding a femoral prosthesis is underway. In order to predict, and so avoid, positions of locally high strain gradients in this model, a finite element and experimental analysis of a similar problem was undertaken. For this purpose, a loose fitting rectangular steel insert inside a surrounding rectangular epoxy sheath was used to model an extreme case of the torsional and bending components of hip joint load. The axial component of joint load was modelled using an axisymmetric finite element model of a tapered shaft. The finite element results were used to determine suitable positions for embedding gauges in the experimental model. Results showed that the finite element analysis failed to adequately model the close sliding fit between the steel insert and epoxy. Altering the experimental model to artificially replicate the finite element contact conditions produced good correlation in bending, with experimental strains agreeing with simple bending theory to within 6%. Satisfactory correlation under torsional loading was not obtained, but strain magnitudes were low. Predicted positions for embedding gauges give conservative results, lessening the possibility of strain gradient induced error in the large scale model test of the cement mantle and prosthesis.     

Random errors caused by temperature in magnitude of principal strains evaluated ith 3-element strain gauge rosettes

The effects of the uncertainties associated ith the apparent strain and gauge factor data, given by the manufacturer, in the evaluation of principal strains are examined. Principal strains are obtained by a reduction of the strains measured ith electrical resistance strain gauge rectangular or delta rosettes. The theoretical analysis points out the relevance of the effects caused.     

多点激励下绝对位移直接求解算法的误差频域分析

多点激励地震响应分析时,相对运动法将结构内部节点绝对位移分解成拟静位移和动态位移两部分分别进行求解,而绝对位移直接求解法直接对内部节点绝对位移进行求解,在两种求解算法中,阻尼分别假定与内部结点相对速度、绝对速度成比例。两种算法的阻尼假定不同可能会引起计算结果误差,在瑞利阻尼、单元阻尼模型下,采用随机振动方法对两种算法计算结果误差在频域内进行了理论分析,指出了瑞利阻尼模型下两种算法求得的结构动态内力功率谱密度误差主要受结构阻尼比、激励频率与结构基频率比值影响,但单元阻尼模型下两种算法得出的动态内力功率谱密度不存在误差。最后从概率意义上指出：瑞利阻尼模型下,两种算法得出的结构内力响应方差的误差随结构阻尼比的增大而增大,当结构阻尼比不大于5%时,两种算法计算结果误差很小。     

Use of digital image correlation to measure strain recovery in particle toughened thermoset resins

A methodology for finding the yield point of epoxy resins, both neat and particulate toughened, is described. Trends of the effect that particulate filling has on the time dependent response of these materials were constructed from observations made with stereo‐based digital image correlation (3D–DIC), namely, creep and stress relaxation at constant load. The use of 3D–DIC also enabled the observation of differences in deformation mechanisms resulting from the particle addition. The focus is put on the technique's potential to characterise materials and produce clear relationships between composition and mechanical strain response. The methodology proposed herein allows the observation and study of multiple deformation mechanisms from a single test, and thus can potentially minimise the number of specimens needed for a comprehensive test campaign.