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Critical Strain Determination Based on the Euler-Fresnel Jig

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Title: Critical Strain Determination Based on the Euler-Fresnel Jig
Authors: Koussios, S, Overig, Tazelaar, K, Docent, Roozen, NB, Overig, Beukers, A, Overig
Contributors: Domein Techniek, Ontwerpen en Informatica, Hogeschool Inholland, Groot Composiet, Hogeschool Inholland, Slimme Materialen voor de Energietransitie, Hogeschool Inholland@@@Domein Techniek, Ontwerpen en Informatica
Source: 20th International Conference on Composite Materials.
Publisher Information: Hogeschool Inholland, 2015.
Publication Year: 2015
Subject Terms: composiet, vezels
Description: When considering a composite strip or plate under certain thermal and environmental conditions and loadings, there is a minimum strain threshold for the appearance of the first micro crack. The associated strain level is defined here as 'critical strain'. There are various active displacement methods to measure this strain level (by tension and bending). The registration of the first micro crack is however challenging. Therefore, some alternative methods have been developed like the Bergen ellipse [1]. With this method, a relatively thin strip is forced by clamping to 'follow' the elliptical contour of the jig. The strip undergoes various strain levels from 0% to 2% or 3%. However, the strain distribution as a function of the strip length is far from linear. This causes inaccurate readings and high error sensitivity for certain areas on the ellipse. To overcome this problem, a novel jig design is introduced here; this design is based on a perfectly linear strain distribution along the strip’s length. The resulting curve is a classical one known as the Euler-Fresnel curve [2]. The linearity and the constant, low sensitivity to measurement errors guarantees high accuracy. Only at the beginning and the end of the strip, the measured strain might deviate from the real one, especially when the thickness of the strip is moderately less (Dh > 0.1 [mm]) than the height of the slot, Figure 9. The jig is a low cost device that can easily be placed in climate cabinets for e.g. cryo-cycling. In this paper we focus on the mathematical derivation of the jig, compare it to the Bergen ellipse, and provide the full consideration of the associated primary and secondary forces and moments. In addition, a comprehensive strength analysis of various lay-ups is provided for the maximum strain level of 2%. The paper ends with some key conclusions and recommendations.
Document Type: contribution To Periodical
Language: English
Access URL: https://surfsharekit.nl/public/3dec769a-f977-47e7-93cf-91c60c929baf
Availability: http://www.hbo-kennisbank.nl/en/page/hborecord.view/?uploadId=sharekit_inholland:oai:surfsharekit.nl:3dec769a-f977-47e7-93cf-91c60c929baf
Accession Number: edshbo.sharekit.inholland.oai.surfsharekit.nl.3dec769a.f977.47e7.93cf.91c60c929baf
Database: HBO Kennisbank
Description
Abstract:When considering a composite strip or plate under certain thermal and environmental conditions and loadings, there is a minimum strain threshold for the appearance of the first micro crack. The associated strain level is defined here as 'critical strain'. There are various active displacement methods to measure this strain level (by tension and bending). The registration of the first micro crack is however challenging. Therefore, some alternative methods have been developed like the Bergen ellipse [1]. With this method, a relatively thin strip is forced by clamping to 'follow' the elliptical contour of the jig. The strip undergoes various strain levels from 0% to 2% or 3%. However, the strain distribution as a function of the strip length is far from linear. This causes inaccurate readings and high error sensitivity for certain areas on the ellipse. To overcome this problem, a novel jig design is introduced here; this design is based on a perfectly linear strain distribution along the strip’s length. The resulting curve is a classical one known as the Euler-Fresnel curve [2]. The linearity and the constant, low sensitivity to measurement errors guarantees high accuracy. Only at the beginning and the end of the strip, the measured strain might deviate from the real one, especially when the thickness of the strip is moderately less (Dh > 0.1 [mm]) than the height of the slot, Figure 9. The jig is a low cost device that can easily be placed in climate cabinets for e.g. cryo-cycling. In this paper we focus on the mathematical derivation of the jig, compare it to the Bergen ellipse, and provide the full consideration of the associated primary and secondary forces and moments. In addition, a comprehensive strength analysis of various lay-ups is provided for the maximum strain level of 2%. The paper ends with some key conclusions and recommendations.