Does anyone know how can the plastic strain be greater than unity? Such as in the benchmark manual 3.2.10 Indentation of a crushable foam plate: 

*CRUSHABLE FOAM HARDENING

 0.2000E6, 0.0000

 0.2577E6, 0.0094

 0.2760E6, 0.0258

 0.3053E6, 0.0452

 0.3267E6, 0.0655

 0.3623E6, 0.1084

 0.3891E6, 0.1540

 0.4250E6, 0.2405

 0.4568E6, 0.3812

 0.4738E6, 0.4600

 0.5170E6, 0.6391

 0.5862E6, 0.8570

 0.6503E6, 0.9857

 0.7470E6, 1.1324

 0.9820E6, 1.2965

 1.4702E6, 1.4808

 2.7262E6, 1.6609

 5.3911E6, 1.9000

As I Know that the formula for True strain is 

True Strain = ln(1+nominal strain)

and if we consider a compression process then nominal strain should not be greater than 1 and thus max true strain will be 

True Strain = ln(1+1)=ln(2)= 0.69

I know I am confusing somethings here, Kindly correct me