Failure in engineered materials is extremely difficult. In composites, damage originates at the microscale and is then propagated to the global scale. While Finite Element Analysis is a powerful tool, it is limited to the global scale because the mesh refinement needed to get down to the microscale is not feasible in FE programs. At MultiMechanics, we consider this to be a true multiscale problem, since damage at the microscale needs to be assessed and relayed to the macroscale.
What tools are available?
Most commercial material modeling and simulation tools rely on analytical methods to understand the stresses and strains within an element. Until recently, analytical methods were much faster than traditional FE2, as they relied on approximations to get results in a reasonable timeframe. These generalizations of a material assume that the material is perfect. For example, a fiber reinforced composite will be represented as a matrix with all fibers equally spaced from one another, which is far from the actual distribution of fibers.
The MultiMech for ANSYS tool utilizes the extremely detailed and accurate FE2 theory. Using this theory, an engineer can have a global scale model with a part that is subjected to different loadings and boundary conditions. The stresses and strains within this part are transferred to a specified microscale finite element model, which represents every integration point within the global scale model. Once the microscale model is solved, that information is passed to the global scale, enabling much more realistic results than simply approximations. This method is truly representative due to the fact that microscale damage will lead to stiffness reduction in global scale elements, distributing stress concentration to different elements.
How does it work?
MultiMech is integrated within the ANSYS native user interface, making it very simple to convert an existing ANSYS model into a full TRUE multiscale model. After the MultiMech extension is installed, the option to designate a material as a "MultiMech Microscale RVE (UPF)" is available. After this MultiMech material is created, a user has the ability to create a microstructure model and define its constituent material properties, all within ANSYS.
The microstructure generation is located in ANSYS Mechanical. After the extension is installed, a MultiMech toolbar will be present in ANSYS Mechanical, as seen in the image below. Selecting the "Add MultiMech Material" button will populate the model tree with a MultiMech section.
This is where all the MultiMech options and utilities are located. A user has the ability to import complex fiber orientations, define the microstructural outputs, and create, edit, or import a microstructural model.
When creating a new microstructural model or editing an existing model, the MultiMech GUI window will appear and give the user the ability to make any changes.
Once the microstructural model is ready, selecting "Solve" will then run the full multiscale simulation, ensuring that the MultiMech material is designated to the part geometry. The part level can still be post-processed the same as any other ANSYS model, but the MultiMech extension also gives the ability to post-process the microstructure. The user can then observe how the microstructure behaves and rigorously investigate where damage originates at the microscale. From here, a structural analyst can try different geometries or orientations to improve overall part performance.
MultiMech for ANSYS is a tool that gives engineers and scientists the ability to observe microstructure properties. These multiscale analyses used to be too computationally expensive, as the solve time and memory were not practical for commercial applications. With MultiMech for ANSYS, multiscale analysis is now feasible and allows engineers to make design choices based on the high fidelity multiscale simulation that pinpoints the origin of failure at the microstructure. This tool also allows material manufacturers to virtually test new materials without the cost and time necessary to manufacture physical prototypes and destructively test different loading scenarios. Finally, MultiMech, being seamlessly integrated with ANSYS, allows structural engineers to easily run multiscale analyses and quickly derive value from this simulation method.