Guest Post/Tutorial by Best Engineering Aids and Consultancies Pvt. Ltd. (BEACON India)
Abaqus is a powerful finite element analysis (FEA) software widely used in engineering and scientific communities to simulate complex physical phenomena. While the software offers extensive built-in capabilities, certain advanced analyses require customization beyond the standard features. This is where Abaqus subroutines come into play. Subroutines are user-defined code snippets, typically written in Fortran, that allow users to define their own material behavior, boundary conditions, loading scenarios, element formulations, and other specialized features. They provide the flexibility needed to model complex, nonlinear, or user-specific behavior that cannot be captured through Abaqus’s default settings. This write-up explores the various types of Abaqus subroutines, their applications, and the workflow for implementing them in a simulation environment. Abaqus subroutines support FORTRAN, C, C++, etc.
Abaqus consists of two sets of subroutines. Abaqus standard subroutines which are utilized in static to implicit dynamics procedures whereas explicit subroutines are used for explicit dynamics steps. Some of the important subroutines and their significance are mentioned below.
DFLUX
DFLUX subroutine can enable a moving heat flux source. This is most suitable in case of welding simulation where moving heat source is required. The heat source can be given as a function of time, position or temperature etc. An example is shown below.
DLOAD
DLOAD subroutine allows you to simulate moving loads. The load can be varied based on time, position or temperature etc. The scenarios such as moving vehicle loads on a road or bridge, dynamic loading in aircraft can be simulated with the aid of DLOAD subroutine. An example is shown below (displacement with respect to load).
UEL
The UEL subroutine in Abaqus allows users to implement their own finite element formulations by defining the element’s stiffness matrix, residual vector, and other element-level behavior. It is used when standard Abaqus elements cannot capture the required physics or numerical approach, such as in advanced materials, multiphysics problems, or novel element types. UEL is often used to model fracture propagation in rock formations using cohesive elements or extended finite element methods (XFEM). Engineers implement custom fracture mechanics algorithms to simulate crack initiation and growth during hydraulic fracturing operations.
UMAT
UMAT is a user-defined subroutine in Abaqus that allows engineers to implement custom material models by defining the stress-strain behavior, internal state variables, and evolution laws under various loading conditions. It is widely used in the aerospace industry to simulate the complex, nonlinear, and often anisotropic behavior of advanced composite materials in structures such as aircraft wings and fuselages, where standard material models are insufficient.
UGENS
UGENS enables users to define the general section behavior of beam elements by customizing the stiffness, coupling effects, and nonlinear responses of cross-sections. This subroutine is commonly applied in civil engineering, particularly for simulating non-standard or composite beam sections in bridge decks, tall buildings, or towers, where interaction between bending, shear, and torsion must be captured accurately.
UMESHMOTION
UMESHMOTION is used to control the movement of the finite element mesh in simulations involving deforming geometries or moving boundaries, typically in Arbitrary Lagrangian-Eulerian (ALE) or coupled fluid-structure interaction problems. It finds important industrial applications in processes such as blow molding of plastic containers and simulating the dynamic motion of oil tankers over ocean waves, where mesh motion must follow physical boundaries precisely.
The subroutines used in Abaqus Explicit are like above. The difference is that explicit time integration will come into picture (new and old-time steps) and names will be changed in such a way that VDLOAD, VDFLUX, VUMAT etc.
Guest Post/Tutorial by Best Engineering Aids and Consultancies Pvt. Ltd. (BEACON India)
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