Page 12 - COMSOL_News_2016
P. 12


Giving Furniture
Testing a Leg Up

In the furniture world, quality standards rule. Chairs that pass a physical
test are permitted to be sold on shelves, while a failed prototype means
it’s back to the drawing board for the engineers who designed the chair.

 by LEXI CARVER                                                                              FIGURE 1. Setup of the chair test. Overlaid,
                                                                                             geometry of the Continuum Blue chair model.
Behind every consumer product
         that hits the market is an iterative  for testing different chairs. This would      Permanent         Cracking
         process of designing, redesigning,    allow them to virtually predict whether       deformation       along edges
 prototyping, and testing that points to       a chair design would pass or fail prior to    & bending
 the work of researchers, engineers, and       the physical testing stage.
 specialists ensuring that an object is                                                      Surface cracking  Cracking where  Permanent
 ready for retail. To meet requirements           “Our customer wanted to explore                              legs meet base  deformation
 for safety and quality, manufacturers         whether they could develop simulation                                           & excessive
 must pass an assessment to verify that        applications for their test services,”                                          bending
 their product can be sold in stores.          explained Dr. Mark Yeoman, director of
                                               Continuum Blue. “Their clients would be       FIGURE 2. Schematic showing crucial points in
    For a chair to be allowed on the           able to log in remotely, upload various       the chair where failure typically occurs.
 shelves, this rigorous process involves       chair designs, and virtually test each
 con rming that it will hold a person’s        one. Only once they were con dent that        “It must survive a lifetime without
 weight, retain its shape, and not buckle      a chair passed the virtual test would         breaking, endure continued use with
 under certain conditions. A chair must        they manufacture the design and send a        no cracking, and the legs should not
 survive thousands of cycles of repeated       sample to the test house.”                    bend, splay apart, or bow too much. If
 loading over a lifetime and cannot                                                          cracking occurs in the corners where the
 suffer cracking, breaking, or bowing.            Such a test app would require a            legs meet the base, the chair will fail.”
                                               diverse range of functionality. It would
 ð TEST HOUSES LIGHTEN                         have to incorporate the quality criteria,     ð MEASURING UP TO THE
 THE LOAD FOR DESIGNERS                        be intuitive and usable for engineers         TESTING CRITERIA
                                               and designers at all stages of the
 Because this testing process can be           development process, and be exible            “The rst part of the test is a Static
 costly and time consuming for clients         enough to test different chair models,        Load Test to see if the chair can hold
 needing certi cation, an independent          shapes, and materials.                        a certain maximum load,” Yeoman
 assessment organization (a “test                                                            explained. “The test loads the chair over
 house”) is striving to lessen the burden      ð SIMULATION PAVES                            a 20-second period, initially loading
 on companies involved in chair                THE WAY TO QUICKER                            the base and then the back, to mimic
 production. They test hundreds of             FURNITURE ASSESSMENT                          a large person sitting down and then
 different chairs every year, and each                                                       leaning back. The second part involves
 design that fails to meet the European        Yeoman developed a numerical model            a fatigue evaluation, where the chair is
 and American quality standards (EN,           using COMSOL Multiphysics® software           repeatedly loaded and unloaded over
 BS, ISO, and ANSI standards) results in       that would predict a chair’s response to      thousands of cycles. This is equivalent to
 disappointment for chair producers and        a standard loading test. His simulation       the chair being used over many years.”
 thousands of dollars in design changes        included the chair geometry, oor,
 and re-testing.                               blocks to hold the legs in place, and            Yeoman’s model analyzed the
                                               loading plates for the back and base to       deformation during a person sitting
    To reduce the burden on                    mimic the physical test (see Figure 1).       down, the mechanical stress, and the
 manufacturers, a test house turned to                                                       earliest and likeliest points of failure
 Continuum Blue, a COMSOL Certi ed                Ultimately, the question the               (see Figure 2). The model also assessed
 Consultant helping companies develop          simulation needed to answer for many
 numerical simulation apps, to create a        different designs was, “will this chair fail
 tool the test house could offer clients       under the required load?”

                                                  “A chair has to hold up to scrutiny in
                                               quite a few areas,” Yeoman remarked.

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