A = 336.46 MPa

B = 342.66 MPa

C = 0.01

n = 0.41

m = 0.6

r = 2,770 kg/m³

q_m = 604 ^oC

K = 81 GPa

m = 28 GPa

c = 875 J/kg^oC

res_mesh

The material parameters above were inserted into a prepared finite element code to evaluate the effects of high-speed impact on the material. Two different types of failure are possible, plastic and brittle. The goal of this exercise was to determine impact times for plastic and brittle failures at 10, 20, 30, 40, 50, and 60 m/s. The results are plotted to determine the critical speed where the failure mode switches from brittle to plastic. Principal stresses were evaluated to determine t_brittle and Von Mises stresses were evaluated to determine t_plastic. t_brittle is defined as the time when the principal stress , s, reaches a certain value given by the following equation.

7039 Aluminum produces a value of 730 MPa for s. t_plastic is defined as the time where the Von Mises stress drops below 90% of its maximum value. The above information is determined from the graphical output of the FEA code.

At the impact speeds given, 7039 Aluminum did not reach the estimated s, thus an estimate of 500 MPa was made for finding t_brittle . The following is the graph of the brittle and ductile failure times versus impact speed.

The following example plots are the four output plots for an impact speed of 10 m/s.