Paper number 792


P Hopgood, J Cook, A Clarke

Mechanical Science Sector, Defence Evaluation and Research Agency (DERA), Farnborough, Hants, England, GU14 0LX

Summary Multi-axial stress states are common in structural components, yet failure of composites under multi-axial loading is relatively poorly understood. This situation has arisen because it has been extremely difficult to devise reliable multi-axial test methods. As a result, conservative failure criteria have to be used, and the effect has been to increase the mass of components. Since the mid 1970s, DERA has generated a large body of multi-axial test data using tubular specimens. However, this data cannot be directly applied to flatter composite laminates. DERA has recently made considerable progress in the use of flat cruciform specimens. These cruciform specimens have been used to obtain failures originating from open-holes, filled-holes, and the sites of impact damage over the full spectrum of biaxial loading. The development of the test method and the results of tests on open holes have been presented here. This includes a discussion of detailed fractography and failure mode investigations.
Keywords test, multi-axial, bi-axial, cruciform, test-machine, fractography, failure criteria.

Theme : Tests Methods and New Metrologies ; Mechanical Properties

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