Solves #4 (actually earlier commit just forgot to mention it)

src/UMAT.jl

@@ -162,7 +162,7 @@ function Materials.reset_material!(material::UmatMaterial)
     return nothing
 end
 
-include("umat_models.jl")
+include("gurson_model.jl")
 
 export UmatMaterial, UmatDriverState, UmatParameterState, UmatVariableState, UmatOtherState
 end # module

src/gurson_model.jl

@@ -0,0 +1,52 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/UMAT.jl/blob/master/LICENSE
+
+
+pkg_dir = dirname(Base.find_package("UMAT"))
+if Sys.iswindows()
+    lib_dir = joinpath(pkg_dir,"..","deps","usr","bin")
+else
+    lib_dir = joinpath(pkg_dir,"..","deps","usr","lib")
+end
+
+
+"""
+!STATEV(1)=f:Porosity
+!STATEV(2)=ep:equivalent plastic strain
+!STATEV(3)=DEp: Hydrostatic inelastic strain increment
+!STATEV(4)=DEp: Deviatoric inelastic strain increment
+!STATEV(5)...STATEV(10)=EELAS
+!STATEV(11)...STATEV(16)=EPLAS
+!STATEV(17)...STATEV(22)=X
+
+!Properties for porosity
+f0=PROPS(1)!f0,initial porosity[GJS-700:0.02,GJV-450:0.05,GJL-250:0.125]
+fc=PROPS(2)!fc,critical porosity[0.0325,0.08,1.0]
+ff=PROPS(3)!ff,failure porosity[0.25,0.1,1.0]
+fn=PROPS(4)!fn,volume fraction of graphite inclusions[0.04,0.1,0.25]
+sn=PROPS(5)!sn,standard deviation of graphite inclusions[0.001,0.001,-]
+en=PROPS(6)!en,mean value of graphite inclusions[0.0,0.0,-]
+qinf=PROPS(7)!Isotropic hardening amplitude
+b=PROPS(8)!Isotropic hardening exponent sflow=syield+qinf*(1-EXP(-b*ep))
+C=PROPS(9)!Cyclic hardening parameter
+ga=PROPS(10)!Cyclic saturation parameter. In von Mises plasticity C/ga=qinf,ga=b
+EE=PROPS(11)!Young's modulus
+nu=PROPS(12)!Poisson's ratio
+syield=PROPS(13)!Yield stress
+"""
+function GursonMaterial(initial_porosity=0.05, critical_porosity=0.08, failure_porosity=0.1,
+                        volume_fraction_of_graphite=0.1, sdev_of_graphite=0.001,
+                        mean_of_graphite=0.0, isotropic_hardening_amplitude=100.0,
+                        isotropic_hardening_exponent=1.0, cyclic_hardening_parameter=1.0,
+                        cyclic_saturation_parameter=1.0, Youngs_modulus=169000.0,
+                        Poissons_ratio=0.3, yield_stress=150.0)
+
+    umat_params= [initial_porosity,critical_porosity,failure_porosity,volume_fraction_of_graphite,
+                  sdev_of_graphite, mean_of_graphite, isotropic_hardening_amplitude,
+                  isotropic_hardening_exponent, cyclic_hardening_parameter, cyclic_saturation_parameter,
+                  Youngs_modulus, Poissons_ratio, yield_stress]
+
+    return UmatMaterial(NTENS=6, NSTATV=22, NPROPS=13,
+                        params=UmatParameterState(NPROPS=13, PROPS=umat_params),
+                        lib_path=joinpath(lib_dir,"libgurson_porous_plasticity." * dlext))
+end