Structural Micro-Layered Ceramics with Surfaces under Tension and Compression with Increasing Apparent Fracture Toughness

Two different designs of high fracture toughness micro-laminate ceramics were produced containing 50 μm thick Si3N4 layers and 100 μm thick Si3N4 + TiN layers. The first design with external tensile layers had a predicted maximum apparent fracture toughness of 10.5 MPa m1/2. The second design with external compressive layers had a predicted maximum apparent fracture toughness of 18.0 MPa m1/2. The fracture toughness of these micro-laminates was tested by the SEVNB method. A stiff testing machine was used to measure the R-curve behavior by observing crack growth in single notched specimens. A soft testing machine was used to measure the R-curve behavior using several specimens with notches at different depths.

The Plane-Strain Compression Behaviour of Glass and Carbon/Epoxy Laminates

A test jig has been developed for the compression of flat plate laminates between parallel dies, making use of an ultra-stiff testing machine. Preliminary experiments have been carried out using this plane strain compression arrangement for a variety of laminates of differing fibre and matrix composition and with different specimen/die geometries. For all of the laminates investigated it was possible to determine a measure of elastic modulus, but strength could only be assessed for unidirectional layups owing to the yield/fracture strength of the steel dies themselves being exceeded for the woven composites. The results obtained compare well with those from the literature using more conventional compression tests.