Design, development, and implementation of test methods for determination of through thickness properties of laminated composites

Test methods for the measurement of through thickness elastic and strength characteristics of laminated composites in tension, compression, and shear have been investigated. Each method studied involved finite element analysis and practical testing on unidirectional carbon-epoxy laminated specimens. Tensile and compressive methods involved the direct loading of a parallel sided block for determination of elastic constants and a waisted specimen with square cross-section for the measurement of elastic constants and strength. Experimental results validated the numerical studies. The shear method consisted of a specimen bonded between steel plates, which were loaded in compression, inducing shear stresses in the specimen. Two specimen designs were developed. The first, for measurement of shear moduli only, was a parallel sided block. Specimen length and thickness were optimised for two fibre directions. The second design, for measurement of shear strengths, was a waisted specimen sandwiched between two epoxy blocks and subjected to a combination of sheer and transverse compressive loading. Tests confirmed the validity of the shear moduli measurements. However, it was found that a purl shear failure mode was not achievable. Failure always occurred by a combination of sheer and transverse tension.