Picture-frame testing of woven prepreg fabric: An investigation of sample geometry and shear angle acquisition

Krogh, Christian; White, Kari D.; Sabato, Alessandro; Sherwood, James A.

doi:10.1007/s12289-019-01499-y

Cited by 12 publications

(12 citation statements)

References 24 publications

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“…Three‐dimensional (3D) digital image correlation (DIC) and 3D point tracking (3DPT) systems have proven their efficiency in being able to perform noncontact inspections 29 . They provide accurate quantitative information of structural deformations, full‐field strain maps, geometry profiles, and modal parameters 30 over a wide range of civil and mechanical engineering systems such as rotating machinery, 31 bridges, 32 railroad tracks, 33 and composite materials 34 . In recent years, computer vision and stereophotogrammetry approaches have gained substantial popularity for WTB monitoring and dynamic behavior characterization because of their noncontact nature 35,36 .…”

Section: Introductionmentioning

confidence: 99%

Multicamera measurement system to evaluate the dynamic response of utility‐scale wind turbine blades

et al. 2020

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Wind turbine blade certification requires static and fatigue testing at a large-scale facility similar to the Wind Technology Testing Center (WTTC) located in Charlestown, Massachusetts. Usually, these tests are conducted by using wire-based sensors such as strain gages, accelerometers, and string potentiometers. These systems are expensive, require a time-consuming installation (e.g., up to 3 weeks and $35 k-$50 k for a strain gage system on a 55-m-long blade), are difficult to deploy on large-sized structures, require additional instrumentations (e.g., power amplifiers and data acquisition systems), and produce results only at a handful of a discrete number of measurement points. In this study, a multicamera measurement system is implemented and experimentally evaluated to obtain full-field displacement and strain over a~12-m-long portion of a~60-m utility-scale wind turbine blade. The proposed system has the potential to streamline the certification process by reducing the blade's preparation and sensor installation cost and time to a few hundreds of dollars (for painting equipment) and a few days for preparing the surface of the blade for the test. Furthermore, operational modal analysis was used in conjunction with the multicamera system to estimate the natural frequencies and mode shapes of the wind turbine blade. The obtained results have shown that the proposed approach can detect in-plane displacement as low as 0.2 mm, mechanical strain with an error below 3% when compared with measurement performed using strain gages, and the first five natural frequencies with an error below 2% when compared with data recorded using traditional wire-based accelerometers. This paper presents these results and provides a summary of the strengths and weaknesses of the proposed optical measurement approach in the context of streamlining the blade certification/testing process and performing vision-based structural dynamic measurements on large-scale structures. K E Y W O R D Sdigital image correlation, fatigue tests, operational modal analysis, stitched field of view, structural health monitoring, wind turbine blades

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Section: Introductionmentioning

confidence: 99%

Multicamera measurement system to evaluate the dynamic response of utility‐scale wind turbine blades

et al. 2020

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“…The parameters used for the model are listed in Table 2. The prepreg material used in this study exhibits nonlinear and rate-dependent behavior as was shown in previous publications [8,26]. The representation of, respectively, the bending and shear behavior through the constant moduli E and G deserve some elaboration.…”

Section: Air Pocket Evaluationmentioning

confidence: 61%

“…Concerning the bending behavior, the value of Young's modulus, E, was found by using the static deflection from a cantilever test [27]. Concerning the shear behavior, the value of the shear modulus, G, was found from the initial behavior recorded through bias-extension and picture-frame tests [8,26] and also from considerations on providing sufficient resistance against crumpling of the mesh. The coefficient of friction µ was measured in connection with a previous study [8].…”

Section: Air Pocket Evaluationmentioning

confidence: 99%

Will it Crease or Cease? A study of debulking of air pockets in automated prepreg composite layup

Krogh

Jakobsen

Wilm

2020

Composites Part A: Applied Science and Manufacturing

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Automatic draping of carbon-fiber prepreg plies for the aerospace industry is a promising technique for lowering the manufacturing costs and to this end, a thorough in-process quality control is crucial. In this paper, out-of-plane defects in the layup are investigated. After draping, air pockets are occasionally encountered. The question is, if such apparent defects can be mitigated sufficiently during vacuum debulking. The 3D topology is measured by means of a structuredlight 3D scanner and air pockets are segmented. An approximate mass-spring ply model is used to study the behavior of the air pockets during application of vacuum pressure. The model is computationally fast and will indicate online whether the air pocket will be removed or manual intervention is required. Upon comparing the model predictions with experimental data, it is shown that the system is capable of correctly predicting 13 out of 14 air pockets in a test layup.

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“…It is therefore important to employ a technique that correctly measures the actual shear angle, specifically during the bias extension tests in the so-called pure-shear zone. In contrast, the picture frame test does not require external shear angle measurement, because an overall uniform shear deformation exists within the acceptable limits over the entire specimen [10,16,17]. As a consequence, the determination of the material shear angle can be done using the rigid frame angle.…”

Section: Shear Angle Measurementmentioning

confidence: 99%

“…Despite the inherent drawbacks and delicacy of implementation, the two test methods are equally popular for measuring the shear properties of biaxial fabrics. The picture frame test is considered to create a uniform shear deformation of the entire specimen [10,11,16,17]. This deformation mode makes the post-test analysis relatively straightforward.…”

Section: Introductionmentioning

confidence: 99%

Shear deformability characteristics of a rapid-cure woven prepreg fabric

et al. 2020

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Formability of a continuous fiber-reinforced material is known to be influenced by its intraply shear behavior. This study investigates a 2 × 2 twill weave carbon fabric and the corresponding vinyl-based thermoset prepreg developed for press-cured structural parts. Intraply shear tests of bias-extension and picture-frame were conducted for a range of industrial-relevant processing conditions of temperature and shear rate. The dry fabric was characterized similar to the prepreg to isolate the influence of semi-cured resin on the woven prepreg fabric formability in shear. The shear deformation behavior of the prepreg, usually dependent on the fabric architecture, is found to be controlled by the state of the resin. The results clearly show the significance of the choice of process parameters on the prepreg shear behavior. It is demonstrated that preheating the prepreg to temperatures considerably lower than required to initiate cure can make the shear formability of the woven prepreg equivalent to the constituent (dry) reinforcement fabric. The actual shear angle measurement during the bias-extension tests demonstrates the level of inter-tow slippage for the prepreg fabric at relatively elevated temperatures. The comparison of normalized shear data from the two test methods helps to determine the improved procedure for prepreg fabric testing.

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Picture-frame testing of woven prepreg fabric: An investigation of sample geometry and shear angle acquisition

Cited by 12 publications

References 24 publications

Multicamera measurement system to evaluate the dynamic response of utility‐scale wind turbine blades

Multicamera measurement system to evaluate the dynamic response of utility‐scale wind turbine blades

Will it Crease or Cease? A study of debulking of air pockets in automated prepreg composite layup

Shear deformability characteristics of a rapid-cure woven prepreg fabric

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