material BilinearDP (1) (2) (3) (4) (5) (6) (7) (8) [9]
# (1) int, unique material tag
# (2) double, elastic modulus
# (3) double, poissons ratio
# (4) double, \eta_y
# (5) double, \eta_f
# (6) double, \xi
# (7) double, cohesion
# (8) double, hardening ratio
# [9] double, density, default: 0.0
