The Grady Spall model can be used to model dynamic spallation of metals under shock loading. The critical spall stress for a ductile material can be calculated according to:

where:

ρ is the density

c is the bulk sound speed

Y is the yield stress at EPS = 0

ε _cis a critical strain value, usually set to 0.15

This critical spall stress is calculated for each element in the model at each time step and compared with local maximum principal tensile stress. If the maximum element principal tensile stress exceeds the critical spall stress, instantaneous failure of the element is initiated.

A typical value for the critical strain is 0.15 for aluminum.

Custom results variables available for this model:

**Material status indicators (1 = elastic, 2 = plastic, 3 = bulk failure, 4= bulk failure, 5 = failed principal direction1, 6 = failed principal direction 2, 7 = failed principal direction 3)