Under longitudinal compression and shear, matrix damage due to shear may not occur

[acbergan]

The model is implement so that only one damage mode (fiber tension, fiber compression, or matrix damage) is activate at each integration point. Under combined stress cases, the first failure criteria to be satisfied determine which damage mode is activated.

When the following conditions are satisfied, matrix damage will not occur when it would be expected:

• matrix damage and fiber kinking theory are enabled
• a small amount of longitudinal compressive strain is introduced (>1e-6)
• the element size is larger than the width of the kink band so that the fiber kinking decomposition is required

A work around for this issue in structural models is to use the alternating section definition method (Hyder et al, 2018) with the strips of elements designated for matrix cracking having the fiber kinking model disabled.

Fundamentally, a better understanding of the material behavior under combined longitudinal compression and shear is needed.