Does anyone know how to use the hypoplasticity and high cycle accumulation model as a subroutine in Abaqus? Papers and manuals suggest to apply the different phases of the models as steps. However, I am not understanding if I am applying the steps in the correct way. For example, Niemunis et al. (2005), the HCA models author, reccomend to apply the following phases:

´´The fortran subroutine umat has three modes of operation:

1. Implicit mode: umat delegates the calculation to the implicit umat treated as a subordinated procedure. As the implicit umat we use a version of the hypoplastic constitutive model with the so-called intergranular strain (cf. [29] and [3, Sections 2.5, 4.1 and 4.3.6]). The material constants used in calculations are listed in Table 3. The implicit mode is used to find the initial state equilibrium and to perform irregular cycles. The numerical implementation of hypoplasticity is discussed in [3, Section 4.1.3].

2. Recording mode: umat works in the implicit mode (hypoplasticity) but additionally the strain path is memorized. Only a few characteristic states need to be recorded. Several filtering criteria have been devised to economise on the computer memory. The recording mode provides the input data for the calculation of the field of strain amplitudes.

3. Pseudo-creep mode: umat calculates stress increments explicitly using (5) and (7). Before the first increment is executed in this mode, the amplitude A is evaluated.

Does it mean that I should create 3 steps in Abaqus and ask to run the umat? The first step is the initial predefined condition stress state. The second is only one cyclic periodic load. The third will be the cyclic load for 100,000 cycles time period step? 

The other question is related to the umat file. How can I run umat files composed of different modulus? One modulu call the other ones, which are in different fortran files codes. Should I only run this file that call the other ones?

Thank you very much!