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PRODUCT SAFETY AND QUALITY | CUSTOM APPLICATIONS

the contact pressure between the chair,        contact problem: four points of contact         regions of the chair will be highlighted
loading plates, and oor, and predicted         between the chair legs and the oor,             to let the user know that the chair is
number of cycles to failure (see Figure 3).    then points between the seat and the            yielding. If the stress rises above the
                                               bottom loading plate, and the chair             tensile strength of the material, then
   “Setting up most of the model               back and the back loading plate,”               the chair has some form of catastrophic
was straightforward,” he added.                he continued. “We use the material              material failure, such as cracking and
“The structural mechanics, material            stiffness, yield stress, and coef cient of      fracturing,” Yeoman said. “The app will
properties, and load parameters                friction to help us accurately de ne the        automatically show a pop-up window
were relatively quick to implement in          contact parameters.”                            announcing that stress levels have gone
COMSOL® software.” Many mechanical                                                             above the material tensile strength and
factors in uence the pass or failure of        ð MAKING VIRTUAL                                the chair has failed.”
a chair test, but the contact study was        TESTING QUICK AND EASY
the tricky part, as Yeoman explained:                                                             This was exactly what the test house
“Contact analysis is inherently complex;       After completing and validating the             had been looking for, an application
it is highly dependent on the material         COMSOL model, the Continuum Blue                that allows chair manufacturers and
properties of the contact surfaces, the        team went on to build the customized            designers to import their own chair
coef cients of friction, and is highly         user interface, or application, that            geometry, select materials, de ne
nonlinear in nature.                           would allow a user to quickly run virtual       contact and loading conditions, and
                                               tests on chair designs by changing              check the results against the test
   “There are several points of contact        certain inputs and parameters related to        requirements to immediately see
that make this an inherently unstable          geometry, load conditions, and                  whether the design would pass or fail
                                               material properties.                            (see Figure 4).
FIGURE 3. Simulation showing deformation
(left), stress (center), and contact pressure     “We used the Application Builder                Through a local installation of the
(right) for a single chair during loading.     in COMSOL Multiphysics,” Yeoman                 COMSOL Server™ product, Yeoman
                                               commented. The Application Builder
                                               allows the app designer to arrange              “This will give them
                                               entry elds, results tables, buttons,             the ability to virtually
                                               drop-down options, and graphics.                 assess dozens of
                                               The resulting app runs the full                  designs before
                                               simulation, but the user — who may               deciding on a single
                                               have no background in engineering or             successful design to
                                               multiphysics modeling — has access to            prototype and test.”
                                               only the chosen inputs, not the model,
                                               physics, or analysis underneath.                — MARK YEOMAN, DIRECTOR AT
                                                                                                CONTINUUM BLUE
                                                  “For the test application we built
                                               for our client, we wanted the user              was also able to distribute the app to
                                               to be able to de ne various options,            different users, allowing them to log in
                                                                                               to a database and launch speci c apps.
                                                              like nonlinear materials.        The test house, in turn, intends to use
                                                              We parameterized all the         COMSOL Server in the future for sharing
                                                              model features so that they      test apps with their own clients all
                                                              were fully linked, and when      over the world.
                                                              someone changed one
                                                              parameter the simulation            “These apps will make it much
                                                              would update accordingly.”       simpler for designers and test engineers
                                                                                               to easily assess a chair’s performance
                                                                  “When the chair is loaded,   before production and physical testing,”
                                                              stress levels are assessed       Yeoman said. “This will give them the
                                                              against the yield and tensile    ability to virtually assess dozens of
                                                              strength of the material. If it  designs before deciding on a single
                                                              goes into permanent plastic      successful design to prototype and
                                                              deformation, the relevant        test, knowing with con dence that it
                                                                                               will meet the test requirements of the
FIGURE 4. The Continuum Blue app showing mesh             Mark Yeoman, Director at             quality standards, reducing the time
and input elds for a client to adjust according to their  Continuum Blue.                      and cost spent on building and testing
design needs.
                                                                                               physical prototypes.” v

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