Local stiffness reduction in impacted composite plates from full-field measurements

Kim, J.-H.; Pierron, Fabrice; Wisnom, Michael R; Avril, Stéphane

doi:10.1016/j.compositesa.2009.09.024

Cited by 28 publications

(18 citation statements)

References 23 publications

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“…Indeed, if some diffuse damage occurred in certain parts of the field of view, then because the virtual fields are different from one time to the next, the weighted average of the modulus can be expected to be different. Unfortunately, the measurement resolution is not sufficient to explore spatial distributions of moduli, as in [18]. This is a future prospect for this work when UHS camera performances are increased.…”

Section: Identificationmentioning

confidence: 99%

Ultra‐High‐Speed Full‐Field Deformation Measurements on Concrete Spalling Specimens and Stiffness Identification with the Virtual Fields Method

Pierron

Forquin

2012

Strain

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For one decade, spalling techniques based on the use of a metallic Hopkinson bar in contact with a concrete sample have been widely employed to characterise the dynamic tensile strength of concrete at strain rates ranging from a few tens to hundreds of s−1. However, the processing method based on the use of the velocity profile measured on the rear free surface of the sample (Novikov formula) remains quite basic. In particular, the identification of the whole softening behaviour of the concrete material is currently out of reach. In the present paper, a new processing technique is proposed based on the use of the virtual fields method (VFM). First, a digital ultra‐high‐speed camera is used to record the pictures of a grid bonded onto the specimen. Then, images of the grid recorded by the camera are processed to obtain full‐field axial displacement maps at the surface of the specimen. Finally, a specific virtual field has been defined in the VFM equation to use the acceleration map as an alternative ‘load cell’. This method applied to three spalling tests with different impact parameters allowed the identification of Young's modulus during the test. It was shown that this modulus is constant during the initial compressive part of the test and decreases in the tensile part when microdamage exists. It was also shown that in such a simple inertial test, it was possible to reconstruct average axial stress profiles using only the acceleration data. It was then possible to construct local stress–strain curves and derive a tensile strength value.

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Section: Identificationmentioning

confidence: 99%

Ultra‐High‐Speed Full‐Field Deformation Measurements on Concrete Spalling Specimens and Stiffness Identification with the Virtual Fields Method

Pierron

Forquin

2012

Strain

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“…More details about the derivation of this equation can be found in [40]. The VFM has been used many times in the past on thin plates in bending [41][42][43][44][45][46][47] and the reader is also referred to these references for more details. Here, the VFM was used as a validation of the measurements as the elastic properties of the plate are known.…”

Section: Virtual Fields Methodsmentioning

confidence: 99%

Infrared Deflectometry for Slope Deformation Measurements

Toniuc

Pierron

2019

Exp Mech

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This paper presents an implementation of deflectometry in the infrared spectrum. Deflectometry consists in recording the specular image of a reference grid pattern onto the mirror-like surface of a test specimen. This technique has two main advantages, high sensitivity and direct measurement of surface slopes, which in the case of thin plate bending is only one spatial differentiation away from surface strains. The objective of imaging in the infrared spectrum is to mitigate the main limitation of deflectometry in the visible spectrum, which is to require an extremely smooth surface to provide dominant specular reflection. This paper explores IR deflectometry for the first time for deformation measurements. Two different infrared cameras were assessed for use in IR deflectometry, a short wave quantum detector one, and a long wave microbolometer (MB) array one. Different materials of varying surface roughness were imaged and it was verified that the Rayleigh criterion was appropriate to determine whether IR deflectometry was feasible on a given surface. With the MB camera, most off-the-shelf material surfaces proved reflective enough to perform IR deflectometry. Finally, several bending tests were performed on aluminium plates and the deformation fields were shown to compare remarkably well with finite element simulations. The experimental data were then used in the Virtual Fields Method (VFM) and the elastic stiffness components of aluminium were retrieved with excellent accuracy, further validating IR deflectometry.

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“…The slopes of the curvature profiles at x 0 are found to be w 000 d = À 5:52310 À7 m À2 for the damaged beam and w 000 b = À 2:39310 À7 m À2 for the baseline. The shear force ratio Q d =Q 0 is calculated based on equation (11), which is 0.987. So according to equation (12), the ratio of flexural stiffness D d /D 0 equals 0.43.…”

Section: Determining the Number And Length Of Delaminationsmentioning

confidence: 99%

Inverse methods for quantitative assessment of delamination damage based on vibrational response

Rose

Wang

2015

Structural Health Monitoring

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A novel two-step approach for quantifying laminar damages, such as delaminations in composites, is presented. This new approach first employs the gapped smoothing method to locate the edges of damage from the vibrational curvature data, followed by an inverse method to determine the through-thickness location of delaminations that provide the best match with the local reduction in bending stiffness over the damaged region. Practical aspects of the implementation of this procedure are discussed, and the approach is demonstrated using both simulated and experimental data. The role of sample spacing on the accuracy of damage location is investigated systematically and it is shown that an optimum spacing exists for experimental data containing noise. The inverse method is found to be able to provide detailed information of delaminations when the searching space is limited, and it can also be used to determine the effective flexural stiffness for complex delamination damage.

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Local stiffness reduction in impacted composite plates from full-field measurements

Cited by 28 publications

References 23 publications

Ultra‐High‐Speed Full‐Field Deformation Measurements on Concrete Spalling Specimens and Stiffness Identification with the Virtual Fields Method

Ultra‐High‐Speed Full‐Field Deformation Measurements on Concrete Spalling Specimens and Stiffness Identification with the Virtual Fields Method

Infrared Deflectometry for Slope Deformation Measurements

Inverse methods for quantitative assessment of delamination damage based on vibrational response

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