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Article
Publication date: 1 February 2001

D.W. Lloyd, D.G. Neilly and D.B. Brook

Almost all end-uses of fabrics make use of the ability of fabrics to suffer strains that are very large compared to engineering strains. This paper is the first of a…

Abstract

Almost all end-uses of fabrics make use of the ability of fabrics to suffer strains that are very large compared to engineering strains. This paper is the first of a series devoted to the measurement of large strains in fabrics. This paper considers some of the problems of fabric strain measurement and describes the use of piezoelectric polyvinylidene fluoride film as the active element in an extensible strain sensor. Strain sensors based on this film are suitable for use with many industrial fabrics, for measuring strains that vary over time with periods of a few seconds or less.

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Research Journal of Textile and Apparel, vol. 5 no. 1
Type: Research Article
ISSN: 1560-6074

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Article
Publication date: 5 June 2007

Gao Zhan‐feng, Du Yan‐liang, Sun Bao‐chen and Jin Xiu‐mei

The purpose of this article is to suggest that Fraby‐Perot optic sensor is a practical measurement gage to monitor the strain of great structures such as railway bridges.

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Abstract

Purpose

The purpose of this article is to suggest that Fraby‐Perot optic sensor is a practical measurement gage to monitor the strain of great structures such as railway bridges.

Design/methodology/approach

A remote strain monitoring system based on F‐P optic fiber and virtual instrument is designed to monitor the strains of a railway bridge.

Findings

The application results show that the Fraby‐Perot optical fiber sensors can accurately measure strain and they are suitable for the long‐term and automatic monitoring. In addition, the system has several advantages over conventional structural instruments including fast response, ability of both static and dynamic monitoring, absolute measurement, immunity to interferences such as lightning strikes, electromagnetic noise and radio frequency, low attenuation of light signals in long fiber optic cables.

Practical implications

Health monitoring of structures is getting more and more recognition all over the world because it can minimize the cost of reparation and maintenance and ensure the safety of structures. A strain monitoring system based on F‐P optic fiber sensor was developed according to the health monitoring requirements of Wuhu Yangtze River Railway Bridge, which is the first cable‐stayed bridge with a maximum span of 312 m carrying both railway and highway traffic in China. It has run stably in the monitoring field more than two years and fulfilled the monitoring requirement very well. Now the system has been transplanted successfully to the Zhengzhou Yellow Railway Bridge for strain monitoring. So the work can be referenced by other similar health monitoring projects.

Originality/value

Long‐term, real‐time monitoring of strain using FP fiber optic sensors in railway bridge is an innovation. A remote strain data acquisition and real‐time processing are another character of the system. The work studied can be referenced by other structures monitoring, such as tunnel, concrete bridges, concrete and earth dams.

Details

Journal of Quality in Maintenance Engineering, vol. 13 no. 2
Type: Research Article
ISSN: 1355-2511

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Article
Publication date: 25 January 2011

Sari Merilampi, Toni Björninen, Leena Ukkonen, Pekka Ruuskanen and Lauri Sydänheimo

The purpose of this paper is to develop a wireless strain sensor for measuring large strains. The sensor is based on passive ultra high‐frequency radio frequency…

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1528

Abstract

Purpose

The purpose of this paper is to develop a wireless strain sensor for measuring large strains. The sensor is based on passive ultra high‐frequency radio frequency identification (RFID) technology and it can be embedded into a variety of structures.

Design/methodology/approach

Silver ink conductors and RFID tags were printed by the screen printing method on stretchable polyvinyl chloride and fabric substrates. The development of the strain‐sensitive RFID tag was based on the behavior of the selected antenna and substrate materials. Performance of the tags and the effect of mechanical strain on tag functioning were examined.

Findings

The results showed that large displacements can be successfully measured wirelessly using a stretchable RFID tag as a strain‐sensitive structure. The behavior of the tag can be modified by selection of the material.

Research limitations/implications

New tag designs, which are more sensitive to small levels of strain and which have a linear response will be the subject for future work. Tag performance under cyclic loading and in a real environment will also be investigated. Future work relating the investigation of practical applications and the system designing for the strain sensor will also be required.

Practical implications

Printing is fast and simple manufacturing process which does not produce much waste or material loss. The sensor is a new application of printed electronics. It also provides new opportunities for system designers.

Originality/value

The paper provides a new kind of wireless strain sensor which can be integrated into many structures (i.e. clothes). The sensor is a new application of printed electronics and it is made from novel materials.

Details

Sensor Review, vol. 31 no. 1
Type: Research Article
ISSN: 0260-2288

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Article
Publication date: 1 February 1944

J.C. King

DURING recent years strain gauges have been used more and more in the aircraft industry as a means of assessing the loads in aircraft structures, both in structural…

Abstract

DURING recent years strain gauges have been used more and more in the aircraft industry as a means of assessing the loads in aircraft structures, both in structural testing laboratories and in flight. This increased use can be mainly attributed to the satisfactory development of successful electrical strain gauges of the resistance type and to the demand by engineers for a more complete knowledge of the load distribution in modern aircraft structures. Electrical strain gauges, although requiring accurate apparatus and a large amount of electrical wiring in addition, are much more easily attached to the structure than mechanical gauges and have the great advantage that they can be mounted in positions inaccessible to most mechanical gauges. This increased use of such gauges has been applied to the determination of the loads in tubes under combined bending and direct loading and to obtaining the direct and shear stresses in sheets and panels. The results of all this has been that more engineers have had reason to use the basic formulae for determining these quantities from the measured strains on three or more gauge lines.

Details

Aircraft Engineering and Aerospace Technology, vol. 16 no. 2
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 July 1955

B.R. Noton

A two‐spar cantilever box beam with forty‐five degrees sweep and oblique ribs placed parallel to the root clamping section was the subject of a series of static tests…

Abstract

A two‐spar cantilever box beam with forty‐five degrees sweep and oblique ribs placed parallel to the root clamping section was the subject of a series of static tests. Stress and strain distributions were determined, primarily in a region distant from the root and tip disturbances, to permit a stringent comparison with three well‐known swept wing theories and the simple theory of bending. Torsional and flexural stiffnesses were also measured and compared with these theories. The sequence of calculation for each method is presented and it is found that two of the theories provide accurate predictions of the stresses, strains and stiffnesses. The influence of rivet slip and rivet flexibility on the stiffnesses of the box is mentioned. As a secondary aim of the investigation, the distribution of normal and shear strain has been measured in the cover skin and spar webs at the root connexion. The design of swept box examined has been the subject of research in a number of establishments and a review of this other work is included.

Details

Aircraft Engineering and Aerospace Technology, vol. 27 no. 7
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 February 2002

D.W. Lloyd, C.D. Price, C. Wild and D.B. Brook

The method of measuring strain fields in fabrics, described earlier, is applied to an example of heavy industrial fabrics. The example chosen is that of heavy woven…

Abstract

The method of measuring strain fields in fabrics, described earlier, is applied to an example of heavy industrial fabrics. The example chosen is that of heavy woven conveyor belts. Conveyor belts are limited in their load rating and fatigue life by the means used to join them together. Two forms of joint are used, mechanical joints and spliced joints. Experimentally determined strain fields are used to explain the mechanisms of failure of each type of joint, and to assess the effectiveness of a modified joint. Measurements of strains through the thickness of spliced joints are used to contribute to the understanding of failure mechanisms in such joints.

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Research Journal of Textile and Apparel, vol. 6 no. 1
Type: Research Article
ISSN: 1560-6074

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Article
Publication date: 3 May 2016

Julián Sierra-Pérez and Alfredo Güemes

The purpose of this paper is to study techniques of pattern recognition in the strain field as structural health monitoring tools. The changes in the strain field may be…

Abstract

Purpose

The purpose of this paper is to study techniques of pattern recognition in the strain field as structural health monitoring tools. The changes in the strain field may be very intense at the tip of a crack but smooth out very quickly. So trying to get information about damage occurrence from strain measurements is a difficult task, as the detected strain changes may be very small and masked by temperature drifting, load changes or any other environmental factor.

Design/methodology/approach

It drives to the need to include a large sensor array into the structure, which is not difficult when using optical fiber sensors. Experiments were done on a simple cantilever beam, instrumented with 32 sensors and submitted to loads and progressive damage conditions. The same approach was applied to a more complex structure, the wing of an unmanned air vehicle (UAV) made in composite materials.

Findings

Algorithms based on principal component analysis (PCA), damage indices and damage thresholds were used and shown to be simple and robust enough for this task.

Originality/value

The data treatment was done in a fully automated approach; an algorithm to compare and extract information from the multiple strain measurements was developed for this task.

Details

Aircraft Engineering and Aerospace Technology: An International Journal, vol. 88 no. 3
Type: Research Article
ISSN: 1748-8842

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Article
Publication date: 1 February 2001

D.W. Lloyd

Deformations in the plane of a fabric, because of their nature, are almost invariably expressed as "percentage extensions", i.e., as changes in length per unit original…

Abstract

Deformations in the plane of a fabric, because of their nature, are almost invariably expressed as "percentage extensions", i.e., as changes in length per unit original length. Such measures of strain only exhibit tensor transformation behaviour when the strains are infinitesimally small; this is rarely the case with textile fabrics. With the growth of engineering end-uses and related design techniques, plus the drive to achieve the virtual reality catwalk, there is a need for deformations of fabrics to be expressed as true finite strains. A method of calculating such strains from experimental data is described, based on the finite element stress analysis methods widely used in engineering. The method involves measuring the displacements during deformation of a grid of points marked on the fabric.

Details

Research Journal of Textile and Apparel, vol. 5 no. 1
Type: Research Article
ISSN: 1560-6074

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Article
Publication date: 1 November 2010

V. Richter‐Trummer, P.M.G.P. Moreira, S.D. Pastrama, M.A.P. Vaz and P.M.S.T. de Castro

The purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The…

Abstract

Purpose

The purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The technique is based on digital image correlation (DIC) combined with an overdetermined algorithm.

Design/methodology/approach

The linear overdeterministic algorithm for calculating the SIF based on stress values around the crack tip is applied to a strain field obtained by DIC.

Findings

As long as the image quality is sufficiently high, a good accuracy can be obtained for the measured SIF. The crack tip can be automatically detected based on the same strain field. The use of the strain field instead of the displacement field, eliminates problems related to the rigid body motion of the analysed structure.

Practical implications

In future works, based on the applied techniques, the SIF of complex cracked plane stress structures can be accurately determined in real engineering applications.

Originality/value

The paper demonstrates application of known techniques, refined for other applications, also the use of stress field for SIF overdeterministic calculations.

Details

International Journal of Structural Integrity, vol. 1 no. 4
Type: Research Article
ISSN: 1757-9864

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Article
Publication date: 28 March 2008

Dimitrios Karalekas

The objective of this study is to investigate the use of a fibre Bragg grating (FBG) sensor for measuring of curing strains that develop during the solidification of a…

Abstract

Purpose

The objective of this study is to investigate the use of a fibre Bragg grating (FBG) sensor for measuring of curing strains that develop during the solidification of a photocurable resin used in 3D microfabrication.

Design/methodology/approach

The followed approach consists of embedding a 1,300 nm FBG into a cylindrical specimen, fabricated into a transparent mould, being exposed to ultraviolet laser light. The further development of the cure induced strains under thermal treatment was also studied by post‐conditioning the cylindrical specimen in an oven at 70°C.

Findings

The experimental results demonstrate the capability of the FBG sensor to provide useful information on the strain build‐up during laser solidification and their post‐cure evolution under the presence of a thermal environment.

Research limitations/implications

Future work should involve the use of smaller diameter FBG sensors in microstereolithography built parts.

Practical implications

It is shown that considerable cure strains are developed at the end of the photo‐polymerisation process that eventually can affect the structural resolution of final parts fabricated by microstereolithography.

Originality/value

The presented method can be used to investigate other photopolymers used in micro‐stereolithography.

Details

Rapid Prototyping Journal, vol. 14 no. 2
Type: Research Article
ISSN: 1355-2546

Keywords

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