Algor’s New Kinematic Elements Enable Mechanical Event Simulations Using CAD Solid Models or Assemblies

Michael L. Bussler
President
Algor, Inc.
Pittsburgh, PA

Prior to the availability of Algor’S kinematic finite elements, engineers were limited to performing static stress analyses on individual components of mechanical systems due to FEA software and hardware limitations. They had to analyze simplified models to obtain quicker processing speed and as a result were not able to examine the behavior of the entire mechanism in motion without building a prototype. Using kinematic elements with Algor’s Accupak family of products, FEA software that realistically simulates motion and flexing in mechanical events and eliminates the need to specify dynamic loads, engineers are no longer limited by a computer's analysis processing time. They can now simulate a mechanical event using a complete CAD solid model or assembly on a desktop computer in an efficient amount of time.

Kinematic elements are rigid elements that move like regular, flexible finite elements, but do not produce stresses, which dramatically reduces processing time. They possess mass, transmit forces and contain full contact capabilities. They can be constrained or loaded with force, traction, pressure and gravity. Kinematic elements are used in relatively rigid areas of a model while regular elements are used in areas of engineering concern to obtain stresses only where needed. Algor has compared the speed of kinematic elements to regular elements and preliminary test results have shown that kinematic elements can quicken processing speed by as much as 160 times.

This Mechanical Event Simulation of an automotive fastener was performed with Algor’s Accupak/VE software. The simulation yielded motion, dynamic loading and large displacement over time for the entire model. Flexing and stresses were produced at the hinges where regular, flexible elements were specified. Areas with kinematic elements appear gray because stresses were not calculated for those elements. Preliminary test results have shown that kinematic elements can quicken processing speed by as much as 160 times. The actual fastener assembly is shown in the top right corner.

An engineer analyzed this automotive fastener assembly (see Figure above) using kinematic elements to determine how it would function during real-world operation. After achieving a high quality FEA solid mesh with Algor, the engineer determined which elements should be defined as kinematic elements. When working with a mechanism, Algor’S rigid kinematic elements should be used to represent the stiffer members of the mechanism while flexible elements should be used in areas where stress information is important. Because stresses in the fastener mechanism’s hinges were important in this analysis, the engineer specified regular, flexible elements for the nine hinges and kinematic elements for the top and bottom components and the fastener arms. This was done by opening the "Element Type" data entry screen from Algor’s "Model Data Control" window in Superdraw III, Algor’s single user interface and precision finite element model-building tool. The engineer simply selected "Brick" as the element type for the hinges and "3-D Kinematic" as the element type for the remaining element groups.

The engineer then defined the remaining model parameters, including element types, material properties, boundary conditions (where realistic) and the duration of the event. The engineer was not required to input loading parameters because Accupak software calculates them based on the physics operating during the event. The engineer then ran the analysis and examined the results with Superview, Algor’s visualization program. The Mechanical Event Simulation yielded motion, dynamic loading and large displacement over time for the entire model. Flexing and stresses were produced at the hinges where regular, flexible elements were specified.

By performing a Mechanical Event Simulation with kinematic elements, the engineer learned how the fastener assembly design would function during real-world operation. The engineer gained accelerated design experience by building a virtual prototype of the entire mechanism using a computer rather than through more expensive and time-consuming physical prototype testing.