Composite failure vs failure index

Hi Fede54,

When you are looking at composite failure you can see the Bond failure indices. So composite failure gives an insight of micro level results for the structure.

Where as Failure index is what deals with macro level results (individual ply failure index).

Ok thank you... so which index should be less than one in order to grant the composite resistance according to the classical failure criterions (Tsai-Wu ecc)?

Fede54, 

Failure index should be less than 1.

Failure index less than 1 indicates that failure of composite is not taken place.

Anyone of you please tel me the use of Max. stress failure theory and where we have to use this? And why we are not using the other failure theories instead of Max. stress theory?

Hi Jodha,

According to this theory, Failure occurs when the response stress reaches Ultimate stress in longitudinal/ultimate stress in transverse or ultimate shear stress.