material iterative_stiffness_reduction [
	 name = test_mat_2
	 rho = 2.7e-9   # density
	 E   = 60e9 # young's modulus
	 nu  = 0.3    # poisson's ratio
	 Sc = 5.7e6
	 prescribed_dam = 0.1
	 max_damage = 0.9999
	 Gf = 160
	 crack_band_width  = 1
	 max_reductions = 10	 
]