Thin-skinned Structures
The SCB geometry can't be used because the skins are too flexible.
Instead, a centre-notch flexure (CNF) test can be used.
A hole is drilled above the lower skin and a bar is inserted.
A force is applied to ends of bar and the crack extends towards the supports.
The P- δ curve is similar to the SCB and P, δ and ‘a' are measured.
The equations used for the thick skinned sandwich structures are used to determine Gc.