Automated fine grid technique for measurement of large-strain deformation maps

Goldrein, H. T.; Palmer, S. J. P.; Huntley, Jonathan M.

doi:10.1016/0143-8166(95)00036-n

Cited by 59 publications

(40 citation statements)

References 6 publications

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“…Emission wavelength (nm) (7,5) Strain-induced spectral shifts are greatest for small roll-up angles (near-"zigzag") and smallest for large angles (near-"armchair"). Another important feature is that the peaks of one class of semiconducting SWCNTs (the "mod 1" nanotubes, for which mod (n-m,3) = 1) shift down in wavelength when they are axially stretched while the peaks of the other class ("mod 2") shift oppositely under the same deformation.…”

Section: Normalized Emission Intensitymentioning

confidence: 99%

“…8 The interferometric techniques, including holography, interferometry, speckle interferometry, etc., usually require a model of actual structure, tedious calculations to separate the values of principal stresses, and expensive equipment. Non-interferometric techniques like the grid method, 5 and digital image correlation (DIC) 6,7 suffer from some other limitations, such as the requirements for a random gray intensity distribution or speckle pattern distribution, heavy dependence on the quality of the imaging system, relatively low strain measurement accuracy in small deformation measurements, and the inability to measure strains induced when the object is not directly observed by the imaging system. Over the past two decades, Raman spectroscopy has been explored by many researchers in strain sensing applications.…”

mentioning

confidence: 99%

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Toward Practical Non-Contact Optical Strain Sensing Using Single-Walled Carbon Nanotubes

Sun

Bachilo

Nagarajaiah

et al. 2016

ECS J. Solid State Sci. Technol.

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Progress is reported in an emerging non-contact strain sensing technology based on optical properties of single-walled carbon nanotubes (SWCNTs). In this strain-sensing smart skin ("S 4 ") method, nanotubes are dilutely embedded in a thin polymer film applied to a substrate of interest. Subsequent strain in the substrate is transferred to the nanotubes, causing systematic spectral shifts in their characteristic short-wave infrared fluorescence peaks. A small diode laser excites a spot on the coated surface, and the resulting emission is captured and spectrally analyzed to deduce local strain. To advance performance of the method, we prepare S 4 films with structurally selected SWCNTs. These give less congested emission spectra that can be analyzed precisely. However, quenching interactions with the polymer host reduce SWCNT emission intensity by an order of magnitude. The instrumentation that captures SWCNT fluorescence has been made lighter and smaller for hand-held use or mounting onto a positioning mechanism that makes efficient automated strain scans of laboratory test specimens. Statistical analysis of large S 4 data sets exposes uncertainties in measurements at single positions plus spatial variations in deduced baseline strain levels. Future refinements to S 4 film formulation and processing should provide improved strain sensing performance suitable for industrial application. In structural health monitoring, routine inspection and maintenance are vital to ensure the safe operation and maximum service life of critical structures, including bridges, high-rise building supports, oil platforms, pipelines, pressure vessels, and airframes. Strain measured on the surface of any structure provides direct first-hand information about its health condition. Established strain sensor technologies, such as resistance strain gages and fiber Bragg grating (FBG) sensors, and some newer ones, including piezoelectric sensors, 1 MEMS doubleended tuning fork (DETF) strain gauges, 2 and nanotube films, 3 are all point-wise, unidirectional sensing methods that require physical connections to the sensor elements in order to obtain strain readings. They are therefore classified as contact strain sensing methods. By contrast, the focus of this report is a new technology for noncontact strain sensing.Some existing full-field non-contact optical methods have also been developed, such as interferometric techniques, 4 noninterferometric techniques, 5-7 and Raman spectroscopy. 8 The interferometric techniques, including holography, interferometry, speckle interferometry, etc., usually require a model of actual structure, tedious calculations to separate the values of principal stresses, and expensive equipment. Non-interferometric techniques like the grid method, 5 and digital image correlation (DIC) 6,7 suffer from some other limitations, such as the requirements for a random gray intensity distribution or speckle pattern distribution, heavy dependence on the quality of the imaging system, relatively low strain measurement accuracy...

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Section: Normalized Emission Intensitymentioning

confidence: 99%

mentioning

confidence: 99%

Toward Practical Non-Contact Optical Strain Sensing Using Single-Walled Carbon Nanotubes

Sun

Bachilo

Nagarajaiah

et al. 2016

ECS J. Solid State Sci. Technol.

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show abstract

“…In order that this can be converted to displacement in mm in the object plane, an appropriate scaling factor (mm / pixels) must be applied. This was determined by taking a radiograph of a grid of known pitch placed in the same plane as the specimen speckle pattern [54,58,59] and then performing a 2D…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

“…It is necessary to do a 2D Fourier transform since any rotation of the grid with respect to the spectral axes will result in the resolved components on each axis being a different frequency to the true grid pitch. The image is then inverse Fourier transformed and the phase is calculated and unwrapped [58,59] . The phase plane gradient gives the grid periodicity in pixels from which an accurate scale-factor for the imaged speckle pattern can be determined.…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

The use of digital speckle radiography to study the ballistic deformation of a polymer bonded sugar (an explosive simulant)

Prentice

Proud

Walley

et al. 2010

International Journal of Impact Engineering

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This paper reports an initial study into the benefits of determining two-dimensional flow fields for low velocity impact on a small-scale model of explosive reactive armour (ERA) using digital speckle radiography (DSR). The model system consisted of a polymer-bonded sugar (PBS) (otherwise known as a sugarmock) confined between two mild steel plates. The DSR technique relies upon creating a layer within the specimen that is seeded with lead particles. So although radiography itself is mechanically non-invasive, the lead layer needed may change the mechanical properties of the material. DSR revealed where regions of intense shear occurred in normal impact. These regions are likely to be where a polymer-bonded explosive (PBX) would initiate.

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“…Grids have been used to measure the deformation in hot rolling 7 and cold extrusion 8 and in general to calculate large strains during compression at room temperature. 9 Timothy et al 7 used an engraved insert embedded in a sample in a rolling experiment and the grid survived large deformation. If an insert is used, it is essential that the insert does not detach from the specimen during deformation since in that case, the grid would not be representative of the deformation of a sample without insert.…”

Section: Introductionmentioning

confidence: 99%

Measurement and prediction of deformation in plane strain compression tests of AA5182

Boldetti¹,

Pinna²,

Howard³

2006

Materials Science and Technology

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The present paper concerns the numerical prediction and experimental measurement of the distribution of strain in a plane strain compression test by means of a gridded insert. The insert was engraved with a 161 mm grid pitch and was embedded in an AA5182 sample. The tests were performed at 400uC with a reduction ratio of y20% and at a strain rate of 0 . 7 s 21. A thermocouple was used to record the temperature during the test. After the test, no detachment was observed between insert and sample, suggesting a close contact between them. The shape of the grid after deformation was analysed, and the in-plane component of the plastic strain calculated and compared with the numerical results obtained through finite element modelling of the test. In a comparison between experimental data and the results of a finite element (FE) model of the test that assumed perfect tool alignment, the fields of temperature agreed very well, while that for the in-plane component of strain was reasonable but inaccurate. However, significant misalignment of the tools was found in the experiments (a common occurrence in plane strain compression testing). When comparison was made with an FE model that included the geometry of the tool misalignment, the agreement was excellent. The paper discusses these effects and others such as the influence of 3D effects in the modelling.

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Automated fine grid technique for measurement of large-strain deformation maps

Cited by 59 publications

References 6 publications

Toward Practical Non-Contact Optical Strain Sensing Using Single-Walled Carbon Nanotubes

Toward Practical Non-Contact Optical Strain Sensing Using Single-Walled Carbon Nanotubes

The use of digital speckle radiography to study the ballistic deformation of a polymer bonded sugar (an explosive simulant)

Measurement and prediction of deformation in plane strain compression tests of AA5182

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