DN Staff

July 19, 1999

4 Min Read
How to combine kinematics, kinetics, and stress analysis

Engineers have a variety of virtual product development (VPD) software tools, including CAD, finite element analysis (FEA), and kinematic and simulation software, to aid them in developing product designs. However, only the integration of VPD tools into a single what-you-see-is-what-you-get environment will enable an engineer to fully understand dynamic mechanical systems within shorter time frames and reduce the need for physical prototyping. Mechanical event simulation (MES), the latest development in VPD products, combines the capabilities to replicate motion (kinematics), dynamic loading (kinetics), and flexing (stresses) of parts of an assembly of interconnected components (mechanisms) during a virtual "event."

The concept of combining stress analysis with dynamics (kinematics and kinetics) in a single process was pioneered because the skills required to manipulate stand-alone solutions were difficult and error prone. Traditional mechanism programs used for load determination show the motion of mechanisms but do not calculate stresses or show how components flex as a result of motion. Because they require the engineer to assume that all linkages in the assembly are rigid, one must laboriously transfer the dynamic loads to a stress analysis program, transfer".

Once the loads are transferred to a static program, the FEA software calculates stresses but only at a single instant in time. The motion load transfer methodology requires the engineer to build separate FEA and mechanism models. Often, each model must be analyzed with a different software package, making data transfer a difficult task subject to errors.

MES, on the other hand, allows engineers to create only one model and work in only one analysis package. MES products eliminate the two-step process by providing one software tool that replicates motion, flexing, and stresses in a single process, thus providing an analysis of the complete event on the computer as it may occur in the real world. MES intrinsically calculates the loads and stresses as motion takes place at each instant in time throughout the event, facilitating a more efficient design process because the need to estimate and specify forces is eliminated.

With the ability of MES software to replicate motion, dynamic loading, and flexing, the number of design scenarios available is virtually unlimited. MES has successfully been used for many applications, including impact and drop testing, contact between multiple objects, mechanical linkages, damping, in-plane motion, elastic deformation, hydrodynamic effects on a structure, local buckling, snap-through buckling, and fracture.

This automotive fastener was analyzed using kinematic elements for all of the rigid areas (shown in gray). Regular flexible elements show flexing and stresses at the hinges.

This suspension shows Algor software analyzing mechanical linkages and dashpot damping. The program's kinematic elements reduce run time for the MES of this detailed CAD solid assembly.

MES enables engineers to understand how their designs will function during real-world operation and develop safe, efficient, cost-effective designs and to reduce expensive and time-consuming prototype testing. Most software vendors offer interfacing between software packages to enable engineers to use two or more packages together, a CAD system with FEA software, for instance, or kinematic system with FEA software. Algor software offers the combination of stress analysis with dynamics (kinematics and kinetics) in a single process. In the Release 12 version of Algor software, MES capabilities are available in two packages in the Accupak family of products: Accupak/VE and Accupak/MES. While Accupak/MES is suited for scenarios in which material nonlinearity is not a concern, Accupak/VE can additionally take into account material nonlinearities.

Kinematic elements are especially useful in large CAD models and assemblies. They are rigid elements that move and dynamically behave like finite elements, but for which stresses are not calculated. Algor offers kinematic elements in an add-on package to any of the products in the Accupak family to accelerate MES processing time. Says Keith Orgeron, of Integra Engineering (Houston, TX), "This tool allows my engineering consulting firm to perform PC-based simulations and analyses that conventional finite element analysis packages just do not offer.

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