Simulation of SMA in Abaqus with UMAT

What are shape memory alloys (SMAs)?

Shape Memory Alloys (SMAs) are unique materials, often composed of nickel-titanium, copper-zinc-aluminum, and copper-aluminum-nickel. They exhibit a remarkable ability to return to their original shape, thanks to superelasticity and the shape memory effect. The shape memory effect is a phenomenon in which a deformed material returns to its original shape when heated. This occurs as the crystal structure of the material rearranges itself into a more stable configuration upon heating. Superelasticity is another characteristic of shape memory alloys that enables them to recover their original shape after undergoing significant deformations, without the need for a change in temperature. It differs from the shape memory effect, which relies on heating. Superelasticity is the result of reversible changes in the crystal structure of the material due to stress-induced transformations. Researchers have been studying SMAs for over 40 years, primarily due to the interest in their special shape-recovery ability, which is rooted in these two characteristics.

SMAs have several advantages over traditional materials. They are lightweight, strong, and cost-effective, making them suitable for various applications. In fields such as structural and mechanical engineering, SMAs are used in self-sensing systems, robotics enhancement, and energy dissipation systems. They also play a role in reducing noise in aerospace jet engines. Interestingly, SMAs have found applications in the medical and biomedical sciences, demonstrating their unique abilities and adaptability across different industries. In this package, we will thoroughly explore their features and applications, providing valuable insights.

How do SMAs behave?

Shape Memory Alloys (SMAs) can exist in two different phases: Austenite and Martensite. The behavior of SMAs when subjected to heat and mechanical stress is determined by transformations between these phases, which control the shape memory effect. For example, when you heat a deformed SMA after unloading, it transitions from the Martensite to the Austenite phase, and returns to its original shape. This unique ability distinguishes SMAs from other materials.

Now, consider an SMA, stable in the parent (Austenite) phase under a constant temperature. When we apply stress, the SMA experiences significant deformations, causing it to transform into the Martensite phase. This phase is not stable due to the absence of cooling the specimen. If we unload it, it will transform from Martensite to its parent phase and recover its original shape without the need for heating. This phenomenon is known as the superelasticity effect. The superelasticity effect can be valuable for various applications, such as eyeglass frames and biomedical stents, as discussed in the package.

In this package, we will take a closer look at the phase transformations in SMAs, especially for those new to the concept. We will also review a reliable model that explains how SMA wires behave during these transformations, with a specific focus on its use within this package. This model includes a constitutive equation that describes the material’s behavior during phase transformations, which is essential for simulating SMAs. In this package, you will also learn how to define the constitutive equation in Abaqus to simulate SMA wires.

If you think that you are not satisfied with this package about SMAs and want to know more about them and their applications, I recommend this course: “Constitutive Modeling and Applications of Shape Memory Alloys (SMAs)“

UMAT for modeling SMA wires

Sometimes, materials can be very complex, and the standard models in Abaqus software may not be sufficient to simulate their behavior. This complexity applies to SMAs as well. In such cases, you can use the Abaqus user-defined material behavior framework, called the UMAT subroutine. It is a general and powerful tool that allows you to define different mechanical behaviors when the existing material models are not suitable. We have used this subroutine to develop the SMA model in this package.

In this lesson, you will learn how to use UMAT to define the desired constitutive model in Abaqus. To make learning easier, we have provided a flowchart that explains the steps to be taken in the subroutine in a straightforward manner. After completing this, you will have a clear understanding of what to do. Then, the package offers a step-by-step guide on writing the UMAT subroutine in the Fortran language to simulate SMAs.

SMA Abaqus Simulation with UMAT subroutine package is an all-in-one solution for engineers looking to simulate SMA. This solution contains a full set of Abaqus subroutines and capabilities to cover anything from creating a static simulation to dynamic simulations. With easy setup instructions, anyone can get up and running with this product in no time.

The subroutine is based on the “Finite element simulation of shape memory alloy wires using a user material subroutine: Parametric study on heating rate, conductivity, and heat convection” Article.