"FEA Finds Its Place," Feature Article, Oct. 2002

FEA finds its place

Engineers examine innovative ways to fold their analyses into their design cycles.

by Jean Thilmany, Associate Editor

Although many engineering companies currently use finite element analysis software programs, the practice of coupling analysis with everyday design is still relatively new. That's why engineers are often challenged to find the best way to integrate analysis into the design process. Engineers today are responsible for much of the analysis done on their own designs. Increasingly, engineers have to judge for themselves, based on their own analyses, which systems or components to include in a product and how best to tweak a part if analysis shows it doesn't meet specifications.

But because FEA—formerly the purview of highly trained analysts with Ph.D.s in the field—is still fairly new to most engineers, the analysis software may not yet be as smoothly incorporated into the design cycle as possible. One thing is certain: The demand now for faster and faster product turnaround time means that engineers must use every technology available to them to help meet compressed design schedules. By allowing mechanical engineers to simulate a variety of physical phenomena acting on a part and show the results via an intuitively understood graphical representation, FEA offers a means to help reduce design cycle time, according to engineers at Integrated Technologies Engineering, an FEA software vendor in Milford, Ohio.

By running analyses, engineers can predict, before physical prototyping, that a proposed design will meet specifications. If a design doesn't meet specifications in simulation, the engineer can modify the CAD drawing and analyze it again to see if the changes helped.

Fanuc Robotics North America Inc. recently coupled its FEA and CAD systems in order to run analysis on every part, a move that usually shaves about 28 days off the company's design cycle, according to a senior staff engineer. Previously, it had been designing many parts in two dimensions and analyzing them in three dimensions.

FEA use is growing at smaller companies that cannot afford to keep an analyst on staff. The growth is attributable to the rapid advances in computer technology in recent years. Commercial software now exists that can solve for sophisticated analysis. And engineers can use the software for more than structural analysis, which is what FEA was originally developed to do, according to Dermot Monaghan, a design engineer in Ireland with a Ph.D. from the finite element modeling group at Queens University in Belfast. Monaghan writes often about his engineering experience with FEA.

Originally developed for the aerospace and nuclear industries to study the safety of structures, FEA now has advanced to allow engineers to simulate the mechanical, electrical, and chemical forces that act on a part.

"The finite element method now has its roots in many disciplines," Monaghan said. "The end result is a technology so advanced it's almost indistinguishable from magic."
But Monaghan maintains that despite the proliferation and power of the commercial software packages available, engineers still need an understanding of the techniques and physical processes involved in analysis.

"Only then can an appropriate and accurate analysis model be selected, correctly defined, and subsequently interpreted," he said. "Computer-aided engineering is here to stay, but in order to harness its true power, the user must be familiar with many concepts, including the mechanics of the problem being modeled. All analyses require time, experience, and most importantly, careful planning."

It's not unusual for engineers to use a single CAD model to produce both engineering drawings and FEA analysis, he added. For this, engineers use a CAD application integrated with FEA software.

With the recent availability and stepped-up power of FEA, companies are regrouping to find the best way to fit the technology into the design cycle.

Fanuc Robotics North America Inc. of Rochester Hills, Mich., supplies robotic systems to a variety of industries. The company recently coupled FEA and CAD in order to run analysis on every part. The move commonly saves about 28 days of design development time, according to Don Bartlett, a Fanuc Robotics senior staff engineer.

To run finite element analysis on this human jaw, the jaw is first subdivided into a mesh of triangular-size sections with nodes that can be hidden later.

Because the company had been designing parts in two dimensions, parts had to be modeled in three dimensions from scratch if they required analysis in the FEA application that Fanuc Robotics used at the time, Bartlett said.

The model often had to be simplified during the transition from 2-D to 3-D in order to get it to mesh properly in the application. For FEA analysis, the part to be analyzed is subdivided into a mesh of finite-size elements with nodes. Where the nodes are displaced, the mesh shows strains and stresses on the structure.

To get around the need for converting the models for analysis, Fanuc Robotics installed the SolidWorks CAD program from SolidWorks of Concord, Mass., coupled with analysis software called Cosmos/Works from Structural Research Analysis Corp. of Los Angeles.

"The combination makes it easy to do an FEA and then to change dimensions of parts where required, which allows us to create better designs," Bartlett said. It takes about 15 minutes to run an analysis, he said.

He recently modeled a robot in CAD software, only to find when analyzing the part that a ball screw continually failed. "The problem was that the coupler was subjected to more angular deflection than we anticipated," he said.

By tweaking the design and then running analyses to see how the new design held up, Bartlett reduced the combined stress on the coupler by more than 60 percent to meet product specifications. He ran 20 FEA analyses to understand and solve the problem, he said.

"In fact, this project, which would have taken a month with the previous system, took only two days," he said.

Everyday Analysis

Of course, for some engineers the fact that the newer FEA software packages are easy to use just plain trumps the worry that engineer-run computer analyses might not be as complete, or yield as many answers, as simulations carried out by a formally trained analyst.

"As a designer, you're always guessing," said Robert McAnany, a design engineer at Hallmark Cards Inc. in Kansas City, Mo. He designs machinery for making the cards. "You can use these analysis tools to guess less and to get better answers up front. Once we had a little experience with analysis, we found that the answers maybe weren't perfect, but they were good enough. It's quick. And I can do it."

His company uses the Solid Edge CAD program from EDS in Plano, Texas, coupled with FEA software from SRAC. Because the two applications are integrated, McAnany doesn't have to translate the model into standard software languages, such as initial graphics exchange specification (IGES) or standard for the exchange of product model data (STEP) for the FEA software to read the CAD information, he said. Critical information can be lost in translation.

One reason suppliers, particularly automotive suppliers, are turning to FEA is that original equipment manufacturers are now putting design responsibility squarely on their suppliers' shoulders, according to Integrated Technologies Engineering. Suppliers with good FEA technology can better compete for business because they can use the technology to reduce design cycles. And reduced design time means a better chance at getting the OEM's contract.

Engineers at an air conditioning mounting bracket supplier used ITE's technology to carry out a series of analyses to help reduce the weight and cost of the vehicle maker's existing bracket, according to ITE. With the results, the supplier proved to the customer that it could handle more design responsibility, according to ITE.

Moving Beyond Engineering

Originally developed for the aerospace field, FEA these days isn't restricted to mechanical engineering, let alone aerospace. The technology has found application in many fields, from transportation to medicine. Researchers at Japan's Okayama University School of Dentistry used it to help upgrade an artificial jaw joint for patients whose joints break because of rheumatoid arthritis and others who have breathing difficulty because of a retreated lower jawbone.

Over the past decade, surgeons have used artificial jaw joints to give patients proper jaw function and proper shape to the mouth. Though none of the patients had problems such as a loosening of the artificial joint or absorption of surrounding bone, some patients reported they couldn't move their lower jaws properly, which affected normal jaw motions like chewing. To help these patients move their jaws more naturally, researchers at the university examined ways to produce a joint that allows for a fuller range of motion.

They wanted to find what kind of material would work best in the artificial jaw joints.

For their analysis, they used a coupled CAD and FEA technology to model the lower jaw. In this case, they used CAD technology from SolidWorks and FEA software from SRAC.

To accurately analyze stress generated in an artificial jaw joint, researchers should really create a model of the entire skull, according to Tomoaki Kawamoto of Okayama University, who was involved in the project. But that means surgeons would have to make a computer-aided tomography image of the patient's skull and then trace the image in order to make a model of the skull. The image would be hard to analyze because the human skull isn't a smooth surface and would require a complicated FEA mesh that reflected the bumps and variances.

This analysis run on a jaw with Cosmos/Works software shows how an artificial joint (at left) will absorb stress during a natural motion like chewing.

So researchers experimented with using the CAD software to create a model for the lower jawbone, which has a simpler form than the upper. They were able to get a 3-D model that roughly recreated the contours of the lower jawbone by using a CT image of a dried human skull available at the university's School of Dentistry.

The lower jaw is made up of two bones: the outer, harder bone, called the cortical bone, and the inner, softer bone, which is called the cancellous bone, according to Kawamoto. Because the two bones had different physical characteristics, the CAD model had to be able to discriminate between them. Models were also made for the bone-setting plate and screws used in artificial jaw joints that joined the fractured patients' jaws.

Researchers analyzed for strength three types of materials that plates and screws could be made from: titanium, stainless steel, and poly-L lactic acid, or PLLA. Normally, the metal parts that make up the artificial joints are removed several months after being implanted, after the fractured bone has fused and healed. In the case of PLLA, the material decomposes and is reabsorbed by the body.

The researchers analyzed for compressive stress in the upper section of the plates and tensile stress along the lower section of the plate. This helped them see what would happen to the plates when the patients chewed. The results showed that using different plates and screw materials produced different results. Stainless steel showed the most stress, PLLA the least.

In the future, researchers want to create models that will include the teeth and will represent the entire lower jawbone to more closely match the actual human process of chewing.

As FEA becomes more commonly available and more useful to mechanical engineers not specifically trained in the process, companies find new uses for the technology. Just like cell phones, VCRs, or personal computers, during the past two decades a once-esoteric technology has become an everyday tool.

FURTHER INFORMATION:

The following is a list of additional software analysis providers. Information is from Daratech, a market-research and analysis firm in Cambridge, Mass.

Algor Inc., 150 Beta Drive, Pittsburgh, PA 15238; (412) 967-2700; fax (412) 967-2781; www.algor.com.

Altair Engineering, 1820 E. Big Beaver, Troy, MI 48083; (248) 614-2400; fax (248) 614-2411; www.altair.com.

Ansoft Corp., Four Station Square, Suite 200, Pittsburg, PA 15219; (412) 261-3200; fax (412) 471-9427; www.ansoft.com.

Ansys Inc., 275 Technology Drive, Canonsburg, PA 15317; (724) 514-3304; fax (724) 514-9494; www.ansys.com.

Dassault Systemes S.A., 9 Quai Marcel Dassault, B.P. 310 92156, Suresnes Cedex, France; 33-1-40-99-40-99; fax 33-1-42-04-45-81; www.dassault-systemes.com.

EDS, 5400 Legacy Drive, Plano, TX 75024; (972) 604-6000; fax (972) 605-2643; www.eds.com.

EASi; 1551 E. Lincoln Ave., Madison Heights, MI 48071; (248) 582-3800; fax (248) 582-8523; www.easi.com.

FEDEM Technology Inc., 8700 Turnpike Drive, Suite 475, Westminster, CO 80031; (303) 650-5480; fax (303) 650-5481; www.fedem.com.

Hibbitt, Karlsson & Sorensen Inc., 1080 Main St., Pawtucket, RI 02860; (401) 727-4200; www.abaqus.com.

Imagine Software Inc., 233 Broadway, 17th Floor, Manhattan, NY 10279; (212) 317-7600; fax (212) 317-7601; www.imagine-sw.com.

LMS International, 1050 Wilshire Blvd., Suite 250, Troy, MI 48084; (248) 952-5664; fax (248) 952-1610; www.lmsintl.com.

MSC.Software Corp., 2 MacArthur Place, Santa Ana, CA 92707; (714) 540-8900; fax (714) 784-4056; www.mscsoftware.com.

MTS Systems Corp., 14000 Technology Drive, Eden Prairie, MN 55344; (952) 937-4000; fax (952) 937-4515; www.mts.com.

PTC, 140 Kendrick St., Needham, MA 02494; (781) 370-5000; fax (781) 370-6000; www.ptc.com.

SolidWorks, 300 Baker Avenue, Concord, MA 01742, (978) 371-5011, www.solidworks.com.

SRAC, 12121 Wilshire Blvd., Suite 700, Los Angeles, CA 90025; (310) 207-2800; fax (310) 207-7805; www.cosmosm.com.