Through-Thickness test methods for Polymer Matrix Composites

Engineering designers need through-thickness strength and stiffness data for both 'thick' section applications and for 'thin sections' where there is concern that 2-dimensional analysis is inadequate. Although users of both simple and sophisticated analysis procedures may estimate stiffness values, they have even less confidence in estimating critical strength values.

Through-thickness properties are frequently needed for those 'difficult but real' aspects of the design where the composite, to perform its function, has to be shaped (e.g. flanged) and connected (e.g. bonded) to the remainder of a system. Features, such as holes, bolted connections, thickness changes etc. result in stress concentrations for which there are no adequate, validated design procedures generally available. Some features are being assessed by structural test elements (e.g. plate with hole), which may be suitable for standardisation.

Availability as a 'standard' method was considered by industry to be overall the most important factor in test method selection, followed by the ability to produce a consistent failure mode, the provision of strength data and application to a wide range of materials. Economic aspects were more important for QA test methods. No test method satisfied fully all these requirements.

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Three-dimensional property directions.

Short block (left) and C-Section (right) tensile specimens.

Short block (left) and waisted block or RARDE (right) compressive specimens.

Short beam shear or ILSS (left) and double notched shear (right) specimens.