The Abaqus user subroutine allows the program to be customized for particular applications unavailable through the main Abaqus facilities. You should write a user subroutine if you could not run your analysis by ABAQUS built-in models for materials, loads, properties, elements, etc., for example, if you need to model a user-defined nonlinear stress-strain relation, which is not provided by Abaqus, then look for UMAT user subroutine. A more advanced subroutine is UMATHT, which allows the creation of user-defined thermal-mechanical behaviour. If it is your first time writing a subroutine like UMATHT Abaqus, please read the Start Writing an Abaqus Subroutine: Basics & Recommendations article. After reading this post and watching this tutorial’s demo video, you will definitely decide to save time in Abaqus modeling and get this UMATHT Abaqus training package. If you have questions, ask here on our live chat on the left side of this page.

Basic steps to write a subroutine:

Generally, to write a newly developed UMATHT, you should follow these steps:

1. Knowing well the material model theory for our UMATHT 
2. Getting Familiar with UMATHT parameters (Inputs/Outputs)
3. Developing FORTRAN code of the UMATHT in Abaqus
4. Implementation in Abaqus & Compilation
5. Testing and debugging UMATHT subroutine
6. Examining UMATHT results and verification

1. Being a combustible material, wood’s safe usage in building will depend on a thorough understanding and modeling of the physical and chemical processes involved in pyrolysis, which determine temperature growth and, consequently, the performance of wood in fire. To more accurately describe the actual physical phenomena that occur when wood is exposed to fire, it is necessary to implement a predictive FE model via a user-defined subroutine in the appropriate commercial software. This is where the UMATHT subroutine comes in. Through gradually changing the thermo-physical properties of the timber, the research of pyrolysis is taken into account in the produced UMATHT.
2. It is generally known that the process of curing rubber products requires a lot of time and effort. This is primarily because rubber compounds have a low thermal diffusivity, which results in a very slow rate of heat absorption into rubber compounds and a very slow rate of heat release during the cooling process when compared to other materials used in the vulcanization system, such metals. As a result, a time-varying and non-uniform temperature field is produced, resulting in a distinct profile of state-of-cure for each place inside the rubber compound. Finite element code for general use the heat conduction equation and the rubber cure kinetics have been solved simultaneously using ABAQUS and a custom-written subroutine (UMATHT). It is utilized to mimic both the post-cure phase and the curing process for a thick rubber object in the mold.
3. Due to their superelastic characteristics, corrosion resistance, and biocompatibility, NiTi shape memory alloys (SMAs) are gaining popularity in a variety of medical applications. They do, however, exhibit notable sensitivity to hydrogen diffusion. For instance, a few months after being fixed to the teeth, fractures in NiTi orthodontic wires will manifest. The oral cavity’s absorption of certain hydrogen contaminants is what causes this embrittlement. Other processes working in hydrogen-rich environments might also experience this unfavorable effect on orthodontic wires. Superelastic NiTi shape memory alloys exhibit considerable changes in their thermomechanical behavior as a result of hydrogen’s unfavorable effects. According to experimental findings, hydrogen causes a delay in forward transition. In addition, it is also possible to see the expansion caused by hydrogen. According to the NiTi alloy’s absorption of hydrogen, these effects take place. The UMAT and UMATHT subroutines have constructed a linked diffusion-mechanical model of shape memory alloys that takes into account the impact of hydrogen on the thermomechanical behavior and transformation process of NiTi alloys.
4. To study the thermal response of carbon epoxy composites directly exposed to propane flame, a three-dimensional thermal response model is created. The model is built with heat transfer and energy conservation in mind, and the heat transmission takes the form of anisotropic heat conduction, matrix breakdown absorption, and gas diffusion. The decomposition of the materials is shown using the Arrhenius equation. For the sake of mass conservation, the diffusion equation for the decomposition gas is included. The temperature, density, decomposition degree, and decomposition rate can be derived from the thermal response model using the UMATHT and USDFLD subroutines of the ABAQUS code to analyze the process of material decomposition.