MECHANICAL TESTING

Open Hole Fatigue - ASTM D 5766

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Method ASTM D 5766 is designed to determine the open hole tensile strength of polymer matrix composite laminates reinforced by high-modulus fibers. The composite material forms are limited to continuous-fiber or discontinuous-fiber reinforced composites in which the laminate is balanced and symmetric with respect to the test direction. The standard test laminate is of the [45/0/-45/90] ns stacking sequence family, where the sublaminate repeat index n is adjusted to yield a laminate thickness within the range discussed in 8.2.11. Other laminates may be tested, however, the test method is unsatisfactory for unidirectional tape laminates containing only one ply orientation.

A uniaxial tension test of a balanced, symmetric laminate is performed in accordance with the test method D 3039 / D 3039M, although with a centrally located hole and without strain or displacement transducers. Ultimate strength is calculated based on the gross cross-sectional area, disregarding the presence of the hole.

ASTM D5766 is designed to produce notched tensile strength data for material specifications, research and development, and quality assurance. Factors that influence the notched tensile strength include the following: material, methods of material fabrication, accuracy of lay-up, laminate stacking sequence and overall thickness, specimen geometry, specimen preparation (especially of the hole), specimen conditioning, environment of testing, specimen alignment and gripping, speed of testing, void content, and volume percent reinforcement.

Reference: ASTM D5766 - Standard Test Method for Open Hole Tensile Strength of Polymer Matrix Composite Laminates

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