Anisotropy of hygrothermal damage in fiber/polymer composites: Effective elasticity measures and estimates

Measured elasticity moduli of a highly (68%) glass-fiber reinforced epoxy matrix for different amounts of fiber/matrix interface weakening and debonding, due to different hygrothermal ageing stages, are compared to estimated ones. Ultrasonic measurements provide seven of the nine elasticity moduli o...

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Bibliographic Details
Published in:	Mechanics of materials Vol. 38; no. 12; pp. 1143 - 1158
Main Authors:	Yann, Ricotti, Damien, Ducret, Rachid, El Guerjouma, Patrick, Franciosi
Format:	Journal Article
Language:	English
Published:	Lausanne Elsevier Ltd 01-12-2006 Amsterdam Elsevier Science New York, NY Elsevier
Subjects:	Acoustical measurements and instrumentation Acoustics Applied sciences Composite Composites Damage Elasticity Engineering Sciences Exact sciences and technology Forms of application and semi-finished materials Fracture mechanics (crack, fatigue, damage...) Fundamental areas of phenomenology (including applications) Hygrothermal ageing Interphase Physics Polymer industry, paints, wood Solid mechanics Static elasticity (thermoelasticity...) Structural and continuum mechanics Technology of polymers Ultrasonics Elasticity Composite Damage Interphase Hygrothermal ageing Ultrasonics Hygrothermal variation Polymer fibers Fiber reinforced material Epoxy resin Coatings Modeling Composite material Finite element method Ultrasonic control Delamination Ultrasound Damaging Acoustic measurement Deformation modulus Ageing Thermomechanical properties Orthotropic material Matrix fiber interface Anisotropy Homogenization methods Interface crack Glass fiber Effective medium model
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Summary:	Measured elasticity moduli of a highly (68%) glass-fiber reinforced epoxy matrix for different amounts of fiber/matrix interface weakening and debonding, due to different hygrothermal ageing stages, are compared to estimated ones. Ultrasonic measurements provide seven of the nine elasticity moduli of the orthotropic material samples, including all the moduli significantly affected by damage. Theoretical estimates combine homogenization modeling techniques and Finite Element (FE) calculations, the latter when the effect of observed partial debonding on effective moduli is to be specified. These estimates are performed under different assumptions for the composite structure, with special attention to the existence of a fiber–matrix interphase. Analytical comparisons for the undamaged composite establish that matching US measurements with estimates cannot be obtained, regardless of the chosen model, without the assumption of an interphase layer of modified resin coating the fibers. This coating resin, when in relevant concentration with regard to literature data about fiber coating thickness, typically conserves the epoxy moduli transversally to the fiber orientation, while, in the fiber direction its moduli approach those of the fibers. The comparison of the US measurements on damaged samples to FE calculations assuming progressive one-directional debonding shows that most of the composite stiffness loss can preferentially be due to an initial interphase weakening, while the fiber/matrix debonding seems more likely delayed to long H-ageing times. This is consistent with physical interpretation of damage by water pooling through silane bridges bonding epoxy to glass. The calculations also provide the effective stiffness, at different damage stages, of the “Undamaged Equivalent Inhomogeneity” for this damaged inclusion type.
Bibliography:	ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23
ISSN:	0167-6636 1872-7743
DOI:	10.1016/j.mechmat.2006.02.001