Most real world problems require performance of both linear and nonlinear finite element simulations. While the linear FEA is faster and less complex, many times it does not provide analysts and engineers with the true behavior of the structure and needed accuracy. This becomes more relevant when analyzing parts and assemblies made out of complex composites, rubber and other nonlinear materials. The main assumptions inherent to a linear analysis are based on the fact that deflections and strains are small and materials have a linear elastic behavior. However, with the rise in the use of newer elastomers, plastics, and metals that exhibit nonlinear responses, it is important to detect sources of these nonlinearities and detect their effect on the design process.
Hundreds of companies who started using linear static and dynamic capabilities of MSC Nastran are now utilizing SOL 400 to perform advanced nonlinear simulations with MSC Nastran, because it is saving them many hours in their design and engineering process. Geometric nonlinearities manifest when the structure undergoes a large displacement or rotation, for example large rotation of cantilever beam and shell type structures, buckling, or snap through. This violates the small displacement assumptions that are inherent to the equations of linear analysis. MSC Nastran SOL 400, uses advanced element technology with the ability to handle large deformations and rotations, while maintaining an accurate nonlinear strain-deformation relationship.
In a linear analysis, stress is assumed to be linearly proportional to strain, which is a reasonable approximation when the deformations are very small. However, for many engineering applications that exhibit large strain and large displacements, this assumption is inadequate and would lead to incorrect results. Advanced composite, plastic, and rubber materials require nonlinear simulations to be performed in order to better predict the real behavior of the structure and increase quality of stress results.
When a certain failure criterion is met, the material fails and no longer sustains the load bearing capacity. In FEA, this means that the element at which the material reaches the failure limit loses its ability to carry load. Different materials experience different failure characteristics and SOL 400 in MSC Nastran provides multiple failure criteria options. SOL 400 supports linear and nonlinear fracture mechanics in order to determine the conditions under which crack propagation occurs. By investigating stability of the crack propagation, speed of crack growth, and possibility of crack arrest with nonlinear fracture mechanics, users can then modify the designs to achieve longer product life.
In assembly models that interact with multiple parts, contact between those parts is also a nonlinear phenomenon. During the simulation when two parts come into contact due to an applied load, or are connected via glue to simulate welding or by other means, like bolts or clamps, a nonlinear FEA will provide a much more accurate simulation result. The analysis of contact behavior is complex because of the requirement to accurately track the motion of multiple geometric bodies, and the motion due to the interaction of these bodies after contact occurs. The general contact methods implemented in MSC Nastran SOL 400 focus on ease of set up with the ability to handle simple to highly complex contact scenarios. SOL 400 can be used to solve a wide array of contact scenarios without the need for additional contact elements, accurately predicting the physical response of the structural assemblies.