AMERICAN RECREATIONAL VEHICLE MANUFACTURER USES FINITE ELEMENT
ANALYSIS SOFTWARE TO IMPROVE CONTEMPORARY DASHBOARD DESIGN
Coachmen's 1999 Sportscoach
is more modern, aerodynamic
and ergonomic than previous
September 4, 1998, Pittsburgh, Pennsylvania -- Recreational Vehicle (RV) camping ranks second only to wildlife
viewing in satisfaction among participants in outdoor activities, exceeding hiking, biking, boating and other sports,
according to a 1997 survey conducted by the Go RVing Coalition. To stay competitive in the growing RV market, RV
manufacturers must design safe, aesthetic vehicles that require minimal maintenance. They must road test RVs for safety
and durability to verify all components' functionality. A leading American RV manufacturer, Coachmen Recreational
Vehicle Company, recently used finite element analysis (FEA) software by Algor, Inc. to test an innovative new dashboard
under loading conditions experienced in an RV on the road. Analyzing the dashboard on the computer saved the company
time and money on physical prototype testing.
Coachmen Recreational Vehicle Company in Middlebury, Indiana recently introduced its Sportscoach model motorhome, a
contemporary, affordable vehicle that has an aerodynamic design and more features and ergonomic considerations than any
other Coachmen product. One of the innovations in the new Sportscoach is a plastic-molded, automotive style dashboard to
replace the outdated, vinyl dashboards of older motorhomes. Coachmen used Algor's linear static stress analysis software
to analyze the new dashboard's steel support structure after subjecting it to a static load using the computer. The company
optimized the structure's geometry by locating and strengthening its weak areas and shortened the length of its design cycle
in time to introduce the Sportscoach at the biggest RV industry trade show of the year.
Modernized Dashboard Must Withstand Weight of Human
The Sportscoach's new ABS
plastic dashboard has a more
contemporary, automotive style
than its vinyl and wood
Coachmen Recreational Vehicle Company designs and manufactures RVs including motorhomes, travel trailers, fifth
wheels and truck campers for sale primarily in the United States and Canada. Coachmen's Class A Motorhome Series is
marketed to those who wish to explore the great outdoors for months at a time, but who also want to travel with the
comforts of home.
Coachmen's top-of-the-line Sportscoach was constructed more efficiently and ergonomically than previous models. Its new
ABS plastic dashboard is tool molded in one piece rather than assembled from numerous pieces like the conventional vinyl
dashboard. The dashboard is smaller and lighter, increasing cabin space and RV capacity, which enables customers to
purchase additional features. It also gives drivers greater road visibility and its gauges and instrument panel are larger and
placed in the driver's line of sight.
Because the dashboard can be up to 96 inches wide, it requires a support structure beneath it. The steel support bracket that
Coachmen designed for the plastic dashboard consists of four parallel bars that extend approximately 18 inches into the
cabin from the front of the vehicle. They are connected by two perpendicular bars, one is mounted to the front bulkhead of
the vehicle and the other extends across the width of the dashboard.
Coachmen needed to test the strength of the new dashboard support structure to locate potential stress because the
dashboard's collapse could cause extensive injury or maintenance costs. Coachmen realized that the RV's low, wide
dashboard invites people to sit or lean on it. The company determined that simulating the weight of a person sitting on the
dashboard's midsection and the weight of a person leaning on the dashboard's side section above the glove box would
represent the most severe stress profile experienced by an RV dashboard. Designing towards this profile would ensure that
the dashboard could withstand other RV experiences, such as vibration during road travel.
"Producing and testing a dashboard prototype can cost $40,000 so the entire dashboard design, including the steel support
structure, must be as close to the final design as possible when a prototype is constructed," said Jim Keough, engineering
design manager. "Using FEA software to test the support bracket allowed us to quickly pinpoint problems with our design
and saved us the time and cost of two prototype tests."
Coachmen had little time to spare because they intended to introduce the new Sportscoach at the Recreational Vehicle
Association's annual trade show, which was quickly approaching.
Preparing for the Stress Analysis
To prepare for the support structure's stress analysis, Scott Schrock, product designer at Coachmen, designed a model of
one-half of the dashboard support bracket using AutoCAD 14. He modeled the passenger side in order to analyze stress
results for the area above the glove box. Jim Keough imported the model into Algor to prepare for a finite element analysis
that would replicate the application of weight on the support bracket and reveal resulting stress. Keough used Algor's
Supergen meshing tool to create a four-node quadrilateral mesh.
"Algor's Supergen automatic meshing engine quickly made the elements symmetrical in non-uniform areas, which saved me
a lot of time," said Keough. "In the past, I created a mesh around critical features like holes by hand and made certain that
the elements matched."
Keough chose 3-D plate elements to best represent the steel bracket's thin-walled material and orientation. "It was
convenient for me to quickly alter the material's thickness to optimize the design when it became necessary," said Keough.
To determine the steel material's yield point, Keough chose the Tresca stress yield criterion because of its conservative
yield calculation for combined stress. Keough then applied steel material properties to the model based on standard steel
purchasing requirements. He applied boundary conditions at the interface between the bracket and the front bulkhead of the
Keough applied a 200-pound static load to the left bar of the support bracket model, or "arm", that represents the center of
the dashboard support and a 100-pound static load above the glove box. The 200 pounds represented the average weight of
a person sitting on the midsection of the dashboard and the 100 pounds represented stored material in the glove box as well
as a person leaning on the passenger side of the dashboard. The goal of the analysis was to determine if these heavy
cantilevered loads would exceed the yield stress of the steel bracket. If its yield stress was exceeded in the analysis, the
bracket would fail to support the plastic dashboard covering under similar real-world conditions.
In the first analysis, Keough found excessive stress in the cross bar above the glove box. He increased the stiffness of the
entire bracket support by increasing its material thickness. The stress remained excessive in the same area in the second
analysis so Keough added a one-inch flange to the cross bar above the glove box to increase its strength and reduce stress.
| ||Coachmen's Algor model was
one-half of the original design.
The analysis results to the left
follow the addition of a
one-inch flange to the cross bar
above the glove box (lower
right). Stress remains excessive
in the cross bar and begins to
appear in the arm of the
support bracket (left).|
The third analysis revealed a new problem as a result of the thickened cross bar; some of the stress from the cross bar had
shifted to the arm of the bracket support model. It also showed that the one-inch flange did not eliminate excessive stress
above the cross bar. Keough added another one-inch flange to the top of the arm to compensate for the shifted load and also
added a Z channel to the length of the cross bar to stiffen the entire bracket assembly.
The final analysis showed that stress levels had been reduced below Coachmen's limit of 25,000 PSI except at the tip of
the arm, which Keough attributed to point loading over a small area. Keough had successfully reduced stress by
strengthening the support bracket in critical areas. He had completed crucial redesign steps before creating one physical
| ||The final analysis showed that
stress levels decreased below
the required limit of 25,000 PSI
except at the tip of the arm,
which was attributed to point
loading over a small area.
Engineering design manager
Jim Keough had removed stress
by strengthening the support
bracket in critical areas.|
"The weakest point in the model was identified in each analysis. I was able to easily work the weak point out of the design
in each iteration to arrive at the final configuration," said Keough.
Coachmen's advanced development department proceeded to manufacture a dashboard prototype. They tested the prototype
in their laboratory, checking its fit, function and response to loading. The results correlated closely to Algor's software
results. A final RV prototype was created and subjected to a lifetime durability test at an automotive test ground. The test
simulates actual road events such as railroad track crossings and other rough terrain. The road test also confirmed Algor's
software analysis results.
Coachmen Saves Time and Money with Algor Software
"The virtual manipulation of the design was much more cost effective and timely than the trial and error method of
prototyping and testing each concept," said Keough. "The evaluation of the bracket design would have taken weeks longer
without the Algor analysis."
Keough also appreciated being able to share the visual results with his company with minimal effort. "To locate an area of
interest, I don't have to scroll through tables with elements and node numbers," he said. "I can obtain a colored stress
output, convert it to a bitmap file and place it in a word processing document for easy presentation to my colleagues."
Coachmen did not study the effects of dynamic stress on the dashboard, such as vibration, because the company designed it
with the most severe static load in mind. The support bracket inherently handles lighter loads like everyday vibration from
road conditions. But Coachmen is expanding their design processes in the future to include composites, nonlinear and
An Algor customer for eight years, Coachmen reports good correlation between the analytical and practical results.
Coachmen used Algor's linear static stress analysis software to improve other parts of the Sportscoach including the RV's
sidewall that is 38 feet long and only 1 ½ inches thick to ensure that it could withstand the handling and assembly process.
They also used Algor to analyze the RV's bumper attachments and various brackets for mounting appliances.
The Sportscoach model achieved the highest number of new product sales ever recorded at the Recreational Vehicle
Association trade show in Louisville, Kentucky last December 1997. "We cannot make them fast enough," reports its
designer, Eric Johanson.
The Industrial Designers Society of America, an organization sponsored by Business Week magazine, recently awarded
Coachmen a 1998 Bronze Industrial Design Excellence Award (IDEA) in the transportation category for the Sportscoach.
The Sportscoach was judged on its design innovation, user benefits, ecological responsibility, aesthetics and appeal. It
competed against 1,031 entries in 47 categories.
"Algor finite element analysis has become a requirement for all structural evaluations in Coachmen Recreational Vehicle
Company's design processes," said Keough. "We are training additional personnel in the use of Algor to further support the
growing demand for the analysis tool. Our commitment to providing quality products to our customers begins with Algor
software at the early stages of design."