Nonlinear FEA-Based Simulation Software

—by Terry Bender, president, Applied Concepts

As a mechanical engineering consulting firm, the mission of Applied Concepts, Medina, MN, is to help companies make better, safer products at a lower cost by providing analytical documentation to support design decisions. Simulation software based on the finite element analysis (FEA) method is our tool of choice because building virtual prototypes on the computer is faster and cheaper than working with physical prototypes. FEA is applicable to structures of any size, from small, biomedical devices to large, industrial structures or machines. Our experience has shown that even proven designs can be improved with FEA.

The mechanical engineering discipline involves many areas of inquiry: strength of materials, mechanism kinematics and dynamics, collisions, fluid dynamics, heat transfer, functional design and manufacturing processes. Over time, the FEA method has been expanded to consider most physical phenomena and FEA-based simulation can include all of the multiphysics interactions without the need to make over-simplified assumptions that can lead to questionable results.

Although most engineers immediately call linear static stress analysis to mind when they think of FEA, most real-world problems involve complex interactions that are not fully captured with a linear static analysis. Linear static FEA has traditionally been the most common type of engineering analysis because of the perception that nonlinear and dynamic analyses are time-consuming and require greater expertise. While simplified linear approximations may require less processing time, the resulting solutions are not always valid. Today’s designs require optimization for cost, strength, wear, manufacturability and many other parameters. These requirements often involve second-order effects such as fatigue that are not visible with linear stress analysis results that assume a perfectly elastic material and only represent one moment in time.

Nonlinear FEA-based simulation enables users to more closely simulate actual responses observed in the real world. After all, failures are far more common in dynamic situations, in which nonlinear effects such as large deformations, buckling and plastic deformations typically occur. Understanding how product failures occur is a key step toward preventing them and designing better products.

We have found that FEA-based simulation software that calculates the effects of nonlinear materials and the motion of designs over time produces the most accurate results. This type of FEA-based simulation accounts for the bending, twisting, stretching, squashing and inertial effects of a model while simultaneously calculating rigid- and flexible-body motion. The results are based on physical data, rather than calculated or assumed loads and constraints, including dynamic or contact forces and users do not have to input constraints that do not exist in the real world (i.e. free-falling objects).

Consider a common problem such as a drop test: With linear static stress analysis, the engineer would have to guess about the orientation of the design at the moment of impact and apply an estimated impact load. Using nonlinear FEA-based simulation software eliminates the guesswork. The problem is set up in virtual space with initial translation and rotation, velocities and orientations, and then the software performs the drop test. The results account for linear and nonlinear material behavior and flexible joints and links. This type of simulation includes dynamic effects such as the vibration of parts, and may incorporate environmental factors such as heat, electrostatics and the effects of fluids. By simulating actual engineering problems including any nonlinear effects that may occur, engineers can more accurately predict real-world behavior, test fewer physical prototypes, speed up time to market and make better, safer products at a lower cost.

Applied Concepts uses nonlinear FEA-based simulation software from ALGOR Inc because it has an easy-to-use interface, provides a wide range of analysis capabilities including a powerful implicit nonlinear solver and is affordable. ALGOR’s simulation capabilities include static stress and Mechanical Event Simulation (MES) with linear and nonlinear material models, linear dynamics, steady-state and transient heat transfer, steady and unsteady fluid flow, electrostatics, full multiphysics and piping. These analysis capabilities are all available within a complete interface, FEMPRO, which supports a wide range of CAD solid modelers and includes finite element meshing and model-building tools.

Algor, 
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