How is interlaminar fracture toughness measured? Name two test configurations.

• A. Mode I via Double Cantilever Beam (DCB) and Mode II via End-Notched Flexure (ENF) or similar tests.
• B. Three-point bending and four-point bending.
• C. Tensile and compression tests.
• D. Izod impact and Charpy.

Answer: (A)

Interlaminar fracture toughness is about how resistant a composite is to a crack growing along the layer interfaces, quantified as the energy required to propagate that delamination in a given loading mode. To measure it, you use test setups that specifically promote the crack to advance in those modes.

For Mode I (opening), the Double Cantilever Beam configuration is used. The specimen has a pre-made delamination and is pulled apart at the ends, forcing the crack to open. From the load and crack growth data you obtain the mode I toughness, G_IC.

For Mode II (sliding/shear), End-Notched Flexure, or similar end-notched bending tests, are employed. The loading induces in-plane shear along the crack front, giving the mode II toughness, G_IIC.

Other test types like bending alone, tensile/compression, or impact tests measure bulk strength or energy absorption and do not isolate the interlaminar delamination resistance, so they aren’t used to determine interlaminar fracture toughness.