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Showing papers in "Strain in 2000"


Journal ArticleDOI
01 May 2000-Strain
TL;DR: The study shows that a relatively small number of sensors can be used to detect reliably impacts on a composite plate and is solved here by means of a Genetic Algorithm.
Abstract: The problem of impact detection in composite panels using artificial neural networks is addressed in this paper. The data were taken from an experiment in which time dependent strain data were recorded on a network of surface-mounted piezoceramic sensors when the plate was impacted. Neural networks were trained to locate and quantify the impact event when presented with features extracted from the measured data. An important problem for detection systems like this is that of optimal sensor placement; this is solved here by means of a Genetic Algorithm. The study shows that a relatively small number of sensors can be used to detect reliably impacts on a composite plate.

133 citations



Journal ArticleDOI
01 May 2000-Strain
TL;DR: In this paper, the mechanical properties of a typical stereolithography resin are determined and the effect of environmental variations, post-cure time and batch to batch variations on the properties is investigated and discussed in detail.
Abstract: The mechanical properties of a typical stereolithography resin are determined. The effect of environmental variations, post-cure time and batch to batch variations on the properties is investigated and discussed in detail. The amount of anisotropy in the cured material is evaluated for each batch of material and the implications discussed in the context of experimental stress analysis

64 citations



Journal ArticleDOI
M. Ermini1
01 May 2000-Strain
TL;DR: In this article, the dependence of the calibration constants A and B on the biaxiality ratio (Ω) between the principal stresses and on the angle (β) between principal direction of stress and the direction of the strain gauge was discussed.
Abstract: A recent paper touched on some important aspects of residual stress measurement by the blind hole drilling method in the presence of an intense stress field. This technical note discusses some significant issues raised in that paper, and presents a different viewpoint. The issues concern the problems regarding a yield condition of the material near the drilled hole. In the presence of plasticity effects, we discuss the dependence of the calibration constants A and B on the biaxiality ratio (Ω) between the principal stresses and on the angle (β) between the principal direction of stress and the direction of the strain gauge.

22 citations


Journal ArticleDOI
01 May 2000-Strain
TL;DR: In this article, the in-plane load effects on the static behavior of CFRP laminated composite panels when subjected to transverse load were studied and it was shown that the energy absorbed by the panel to failure is approximately constant with respect to inplane load.
Abstract: Static tests with various in-plane loads from 0 to 30 kN were conducted, to study in- plane load effects on the static behaviour of CFRP laminated composite panels when subjected to transverse load. The panels were 32 ply with the unidirectional carbon epoxy plies in a quasi-isotropic lay up. It is shown that panel stiffness and maximum load increase with increasing in-plane load and that a failure mode transition occurs with increasing in-plane load. It is also shown that the energy absorbed by the panel to failure is approximately constant with respect to in-plane load. Experimental information on load v deflection histories, surface strain histories and different failure modes together with material properties are presented in the paper, which could be used for analytical and numerical simulations of the problem.

13 citations


Journal ArticleDOI
01 Aug 2000-Strain
TL;DR: In this paper, an extension of polarization-optical time domain reflectometry (POTDR) is presented to measure the distribution of any parameter external to the optical fiber, which can modify its polarization behavior.
Abstract: Fully-distributed optical-fibre sensing (FDOFS) systems are developing rapidly and are offering significant advantages for measurement functions in a variety of structural applications, especially in the oil industry, the power supply industry, the aerospace industries and civil engineering construction. Polarization techniques are well established in FDOFS, and in the analysis of polarization-mode dispersion (PMD) for optical-fibre telecommunications. However, a major problem has been that of determining, from one end of the fibre, the distribution of the full polarization properties of a monomode optical fibre, along its length, with some specific spatial resolution. This paper will present a new technique for providing this full information, and thus for measuring the distribution of any parameter, external to the fibre, which can modify its polarization behaviour. As a result, for example, it becomes possible to measure simultaneously the distributions of temperature and of a strain field comprising, in the latter case, the longitudinal and the two transverse components of direct strain, plus the transverse shear strain. The technique comprises an extension of polarization-optical time domain reflectometry (POTDR) [16], and necessitates on-line processing. Details of the physical principles, the algorithms and the polarimetry will be presented, together with results illustrating the measurement accuracies which can be achieved.

13 citations


Journal ArticleDOI
01 Aug 2000-Strain
TL;DR: In this article, the measurement accuracy in a composite laminate is found to be influenced by the formation of cracks in adjoined layers, interface between fibre sensor and host materials and nonuniform stress fields.
Abstract: Fibre Bragg grating sensors have been developed as a strain measurement technique. With regard to practical applications, there is growing knowledge and experience. However, many application issues remain unsolved. These issues include signal interpretation, confidence in measurement accuracy, calibration, and zero-strain definition. This paper reports some issues which have been encountered in practical measurements and application trials. The investigation covers various aspects of strain measurement. The measurement accuracy in a composite laminate is found to be influenced by the formation of cracks in adjoined layers, interface between fibre sensor and host materials and nonuniform stress fields.

9 citations


Journal ArticleDOI
01 Aug 2000-Strain
TL;DR: An overview of the principal approaches to optical fiber strain measurement can be found in this article, where the authors highlight some of the more novel applications which are enabled through the use of fibre optic strain transducers.
Abstract: Optical fibres have emerged as versatile strain transducers. They can function as direct but topologically simple replacements for a range of strain gauges or can implement new measurements in distributed and integrating formats. Like all strain measurement techniques the properties of the transducer dictate its suitability for specific applications. In the case of optical fibres some of these applications are entirely new and in particular facilitate the techniques of smart structures fabricated from new advanced materials. This paper presents an overview of the principal approaches to optical fibre strain measurement and endeavours to set these into an applications context. In particular we shall highlight some of the more novel applications which are enabled through the use of fibre optic strain transducers.

8 citations



Journal ArticleDOI
01 Aug 2000-Strain
TL;DR: In this article, a variety of approaches have been discussed that have led to recent development of multicore, temperature-insensitive vector bend sensors and shape-sensing fiber-optic sensors.
Abstract: Optically broadband interferometric techniques have been developed into cost effective and practical systems that enable the discrimination of strain and temperature in fibre optic sensors. Recent developments of temperature-insensitive strain and shape-sensing fibre-optic sensors are described. A variety of approaches are discussed that have led to recent development of multicore, temperature-insensitive vector bend sensors.

Journal ArticleDOI
01 Feb 2000-Strain
TL;DR: In this article, a least square inverse problem solution for the case of photoelastic fringes around a hole in a biaxially loaded plate for two problems is presented.
Abstract: This paper presents a least squares inverse problem solution for the case of photoelastic fringes around a hole in a biaxially loaded plate for two problems. Problem 1 relates to an infinite plate in which the circular hole is drilled first and then the loads are applied. Problem 2 is the residual stress problem in which the hole is drilled after the biaxial load is applied to the infinite plate. This hybrid experimental numerical approach permits utilisation of as many points of information as desired, away from the edge of the hole and the axes of symmetry. Also, no a priori knowledge is needed as to the orientation of the principal axes of symmetry. Its implementation, using simulated photoelastic fringes, yields accurate predictions of the magnitude and orientation of the far field stresses.

Journal ArticleDOI
01 Nov 2000-Strain
TL;DR: In this paper, a finite element (FE) and experimental data of cracked, 88.9 mm outside diameter, 5.49 mm thick, short radius, carbon steel piping elbows under displacement controlled, opening bending are reported.
Abstract: Finite element (FE) and experimental data of cracked, 88.9 mm outside diameter, 5.49 mm thick, short radius, carbon steel piping elbows under displacement controlled, opening bending are reported. Short and long defects with depth-to-thickness ratios ranging from shallow to through-wall, axially or circumferentially centred about the bend crown centreline or intrados respectively, are considered. The FE predicted general deformation mechanisms and overall strain distributions compare well with the experimental observations. Also, the strains agree well with the experimental values away from the defects. However, in the immediate vicinity of the defect, the FE strain data give much more detail about the initiation and spread of plasticity as the loading is increased towards plastic collapse of the component, but specific integration point strain data reveals that the variations are large and that steep strain gradients are evident even within individual elements. This explains the poor comparisons with experimental data in these regions. Using the above type of data, in conjunction with the twice-elastic slope (TES) method for the determination of plastic loads for the cases investigated, it has been shown that values lower than those obtained from similar global measurements (load-displacement plots) are consistently obtained.


Journal ArticleDOI
01 Aug 2000-Strain
TL;DR: In this article, the principles of fiber optic strain sensing based on the use of in-fibre Bragg gratings are presented with emphasis on advances in the grating inscription technology.
Abstract: The principles of fibre optic strain sensing based on the use of in-fibre Bragg gratings are presented with emphasis on advances in the grating inscription technology. Multiplexed array techniques for structural health monitoring are described with reference to modern industrial applications. Recently established techniques for improving the multiplex density, for extreme strain monitoring, and for high sensitivity measurements using long period gratings are addressed.

Journal ArticleDOI
01 Nov 2000-Strain
TL;DR: In this article, an attempt has been made to compare the analytical shear stress values in the adhesive layer obtained in previous analytical work with those obtained by modelling the laminated beam using finite elements.
Abstract: Laminated beams fabricated from strips with intermediate adhesive bonding layers are frequently used. The evaluation of the shear and normal stresses in the adhesive layer along the length of the beam is important and both analytical as well as experimental investigations for these stresses have been previously documented. In the present paper, an attempt has been made to compare the analytical shear stress values in the adhesive layer obtained in previous analytical work with those obtained by modelling the laminated beam using finite elements. It is also shown that the analytical approach may be extended to the approximate analysis of coupled twin shear walls.

Journal ArticleDOI
01 Feb 2000-Strain
TL;DR: In this paper, the authors describe the implementation of an experimental technique that allows one to optimise the efficiency of layout design for ropes, tendons, etc in prestressed structures.
Abstract: The present paper describes the implementation of an experimental technique that allows one to optimise the efficiency of layout design for ropes, tendons, etc in prestressed structures. An application with a certain grade of complexity has been developed, i.e. a stiffening partition wall in hollow sections, with a central opening. This structural typology is normally used in bridges.


Journal ArticleDOI
01 Feb 2000-Strain
TL;DR: In this article, the authors investigate leak detection systems with the aim of devising a suitable system for power station use, and present the problem is contained by conducting rigorous but selective NDT at each shutdown on a representative sample of the critical welds.
Abstract: A large number of power stations worldwide contain steam pipework where welded joints can be susceptible to circumferential cracking close to or in the heat affected zone between the weld metal and the parent material. On occasions, cracks have grown significantly around the circumference of the welds and have penetrated through the pipework wall to produce small leaks. Although these leaks were detected before significant damage could occur, there is concern that violent failures could occur from undetected cracks. At present the problem is contained by conducting rigorous but selective NDT at each shutdown on a representative sample of the critical welds. However, numbers of steam leaks have been successfully reduced, but it has not proved possible to eliminate them completely. Consequently, there remains a need to detect, and respond to those leaks which do occur as quickly as possible. A programme of work was commissioned to investigate leak detection systems with the aim of devising a suitable system for power station use.

Journal ArticleDOI
Fumio Nogata1
01 Feb 2000-Strain
TL;DR: In this article, a cell-based mechanosensing power and adapting modelling mechanism for detecting the external mechanical strain/stress induced by external loads is described, and three types of sensors are investigated: tension sensitive, compression sensitive and compression sensitive.
Abstract: This paper describes a cell based mechanosensing power and adapting modelling mechanisms found in plants. Biological structures consist of mechanical load carriers, which are strongly optimised in terms of mechanical strength and minimum mass. It is shown that bamboo structures are designed to have uniform stresses at all positions, applying various sizes of bamboo fibre at the optimal locations. As a significant biological design system, a biological sensing power for detecting the strain/stress induced by external loads can be accepted. The mechanosensing system can be regarded as that in which live cells detect the external mechanical strain/stress as biological electric signals generated by the motions of various ions throughout and/or into the channels of the cell membrane. The modelling mechanism is a cell based mechanosensor that depends on the kind of plant. Three types for detecting the mechanical strain/stress (tension sensitive, compression sensitive, and tension and compression sensitive types) are investigated. Changes in electrical signals at the local portion of a plant body due to the mechanical deformation of cell membranes, affect the modelling of a plant's tissue to fit external mechanical environments.

Journal ArticleDOI
01 Nov 2000-Strain
TL;DR: In this article, a hybrid technique employing a boundary element method for determining individual stress components in two-dimensional arbitrarily shaped domains from experimental isopachics only is presented, which consists of a numerical solution of two Poisson equations representing equilibrium for 2D plane-stressed solids with zero body forces.
Abstract: This paper presents a development of a hybrid technique employing a boundary element method for determining individual stress components in two-dimensional arbitrarily shaped domains from experimental isopachics only. The procedure consists of a numerical solution of two Poisson equations representing equilibrium for two-dimensional plane-stressed solids with zero body forces. An existing technique is employed for smoothing interior thermoelastic data and enhancing boundary information. The algorithm of stress separation has been implemented with the help of commercial codes. The whole procedure has been tested through a complete post-processing example of thermoelastic stress analysis data.