ASC Moves to ‘Design-Analyze-Confirm’ Process with Integrated Simulation Tools - Part 2

In Part 1 of this article, Stephen Doncov, CAE specialist at ASC International, described the need to address critical design issues and tradeoffs for their open-air automotive engineering mechanisms by using MSC Software's SimDesigner for CATIA as a key element of their Virtual Product Development (VPD) process. The ASC design engineering team determined that an integrated CAD-CAE environment provided by an embedded CAE tool like SimDesigner was best suited to help solve linear, nonlinear, and dynamic problems and allow early validation of operational effort, load capacity, and abuse testing for their products. Mr.Doncov explained how a complex convertible top header latch, modeled in the V5 environment with 3D contacts, joints, flexible bodies, and multiple material properties, was simulated using the analysis tools in SimDesigner's Motion workbench without leaving the CATIA environment.  

The second and final installment of this article describes ASC's use of the Nonlinear workbench capabilities in SimDesigner to simulate the effects of high nonlinear stress ranges that are experienced by their products in real use.

Nonlinear Analysis: Abuse—Vertical Force

The abuse analysis was used to determine if the handle would break when an opening (vertical) force of 600N was applied. If the handle bent, it was not considered a failure. A linear analysis was run to determine which parts could be omitted to save nonlinear analysis computing time. Parts not reaching their yield strength and not critical for maintaining the integrity of the mechanism, such as connecting pins, were eliminated, reducing processing time.

Figure 1 . Latch handle abuse analysis using SimDesigner's Nonlinear workbench on the modified design indicated the handle satisfied the vertical abuse specification.

Initially, all the parts were meshed with Tetrahedron 4 elements (tet4's), which are linear brick elements. They are very stiff elements that reduce compute time. Since the nonlinear analysis determined all the high-stress area hot spots were located in the handle, all the parts were kept as tet4's. The handle was set to tet10, a higher-order element.

Using the local mesh feature, a finer mesh was used in the critical stress areas. Local sag conditions were implemented around the area of contact and hot spots. The ability to use localized, refined meshing provides higher accuracy results in the critical areas identified during the linear analysis and substantially reduces processing time.

SimDesigner's Nonlinear workbench allows different types of contact between bodies to be defined. For example, when looking for tangency, contact, or an impact, it allows two bodies to be constrained as always glued together, intermittent contact, or never touch. This allows the user to decide how the individual parts will interact, which makes the solver more efficient and further reduces processing time.

The clamp mounting bracket and both handle-to-idler hinge pins were constrained. For bodies that do not collide and bodies contacting themselves, contact was set to inactive, eliminating their consideration. The bodies that did not need to rotate in relation to one another were set to glue. The bodies that could come in and out of contact with one another or would need to rotate relative to one another were set to touch. A 600N load was applied in the vertical direction of the face near the end of the handle.

For the material properties, ZA-8 zinc, the same material used in production parts, was used for all the components, except the connector pins, which were 1010 steel. ASC and MSC Software provided the nonlinear material properties. Although the curves were not validated with physical testing, this can be an important consideration. Any cold-working or heat treatment of the parts can lower or raise the yield and ultimate strength, dramatically affecting the nonlinear material curve.

The contact bias was set at 90%, allowing the solver to converge faster because it doesn't have to drive down to an exact solution. Contact bias is a numerical method to help convergence in contact analysis using Marc, the nonlinear solver used by SimDesigner. For some applications, the contact bias helps improve stability in contact analysis. Coulomb friction was activated because friction affects material deformation or material flow on the contact boundary. This in turn is reflected in force and stress, etc. Additionally, friction generates heat, which affects material properties in thermal-coupled analysis.

As mentioned earlier, the physical prototype was made of ZA-12, which is not as strong as the production material ZA-8. VPD tools enabled the use of ZA-8 production material properties, which with satisfactory correlation would provide data for determining the performance of production parts. The handle design was simulated using ZA-12 and ZA-8 material properties. Additionally, a physical prototype was made with ZA-12 and tested to validate the results. The vertical abuse test of the initial design indicated the ultimate stress was exceeded in the handle using ZA-8 at approximately 60% of the load. The actual results were:

The handle design was modified and another simulation performed using ZA-12 and ZA-8 material properties. Another physical prototype was made with ZA-12 and tested for correlation. The actual results were:

The redesign using ZA-8 material properties provided an approximately 200% safety margin, which satisfied the vertical abuse specification. Additionally, a simulation was run using the ZA-12 material properties, which indicated a failure at 600N. The physical test using the ZA-12 material determined that failure would not occur until 130% of the load was achieved (approximately 780N). This was within 25% of the simulation results, which was within ASC's correlation target.

Abuse—Side Load

Normally, a failure happens when somebody applies too much force on the handle. Therefore it was important to know what would happen if the handle was left half open and got caught on somebody's shirt, or what would happen if somebody tried to muscle open the latch with too much force. Would the handle bend or break off? The same boundary conditions, constraints, material properties, meshing, and solver settings were used for the 294N side load analysis as in the vertical load analysis. The original design satisfied the side load abuse design requirement.

Alternate Failure—Maximum Load Analysis

The alternate failure analysis was a customer-required test to make sure the hook could withstand a high-impact event. In this case, the hook had to withstand a maximum load of 4900N in the latch stroke direction. As in previous simulations, linear analysis was used to determine which parts could be omitted from the nonlinear analysis. In this case, all the parts were eliminated except for the clamp body, hook, roll pin 1, and receiver.

All of the parts were meshed with tet4 elements and, as earlier, a nonlinear analysis was run to identify the hot spots for high stress. The first simulation was used to refine the mesh. The receiver and roll pin remained tet4 elements. However, the clamp body and hook were re-meshed with tet10 elements. The local meshing and sag conditions were implemented around the contact areas and hot spots.

An advanced restraint was applied to roll pin 1, allowing only translational displacement in the latch stroke direction. The two translation degrees of freedom (DOF) in the non-stroke (loading) direction were removed. The same contact constraints were used as in the 600N latch abuse analysis, including inactive, glue, and touch. A distributed force of 4900N was applied across the roll pin in the latch stroke direction. The material properties for the latch analysis were set as follows:

As in the nonlinear abuse analysis, the solver was set for contact bias at 90% and Coulomb friction was activated. To meet the 4900N load, more expensive materials had to be used for this customer than before. For example, the receiver had been made of plastic, as it is for many other customers. However, the 4900N load requirement is significantly higher and required changing the receiver from plastic to steel. This increased material and process costs.

Since the earlier system had passed all of the requirements, it was possible that the use of a steel receiver was over-engineering. Using simulation, it was relatively easy to compare the customer's earlier design to the current version. By comparing the ultimate strength of the earlier system to the new design, the 4900N requirement was determined too severe. By changing the receiver from steel back to plastic, the new design was as strong, if not stronger, than the earlier system, and a competitive price point was maintained.

New Process, New Advantages

ASC's product development processes are expanding. In the past, normal operating conditions were the focus. However, customers are now asking which parts might fail under extreme conditions. When a mechanism fails a physical test, it can be embarrassing for the engineers and troubling for the customer. By using SimDesigner for CATIA, designers and analysts share one common interface and database. Multiple iterations can be virtually tested in the computer without building anything and investing in tooling. Failures and iterations occur virtually, are fixed virtually, and then when the best design is identified, verified with physical testing.

Moving from the old school of ‘design, build, test, break' to ‘design, analyze, and confirm,' ASC engineers identified and addressed the failure points in the handle without going through several stages of physical prototyping and testing. Physical testing is becoming the last step for verification. Using embedded analysis tools earlier in the design process, ASC's design engineering team was able to determine weak areas in the initial design before physical prototyping and testing, saving a substantial amount of time and money.

For more information on ASC International: http://www.ascglobal.com

For more information on SimDesigner: http://simdesigner.mscsoftware.com

Web Conferencing is Not Collaboration: Maximize PLM and Accelerate Customer Support with Next-Gen Collaboration Tools

Robert de Monts is VP Marketing and Business Development at Imera Systems, and a former executive at Dassault Systemes.

The global marketplace, with its borderless economy, places increasing pressure on enterprises to deliver products faster and at lower cost. Today, it's common for organizations to consist of a global workforce representing local and outsourced department functions, and to support a geographically dispersed customer and partner base. The new face of business requires that cross-enterprise and cross-geography teams constantly interact to design new products, support customers or work with partners, suppliers, and vendors. Despite these compelling drivers, most workers lack even basic tools to compete and collaborate in a global marketplace.

Do you recognize yourself in the following situations?

•  Do you think that scheduled web conference meetings are not entirely satisfactory because of the time it takes to set them up, and/or coordinate with colleagues or partners?

•  Do you wish you had a solution that replicated the ease of walking into a colleague's cubicle to resolve the issue on the spot; e.g., , to check your colleague's presence at his or her desk, ask a question, use a whiteboard or piece of paper, or view a display screen?

•  If you support customers, do you think you need the ability to view your customer desktops immediately without having to provide a UID or PW for a web session, and/or walk your customers through yet another web conferencing user interface?

•  As a user of Enovia and Smarteam, do you need to discuss / view / be connected at all times not only with colleagues within your company, but also with colleagues at partner, supplier, or customer locations?

•  Do you want to be able to use the same communication tools for both inside and outside yet be assured they are fully secure?

•  If you already use IM, web conferencing, and the telephone, wouldn't you like to have all these options integrated within one application, so you don't have to use different tools?

The following white paper reviews the issues facing the distributed team, historical methods to enable collaboration, and the next generation solutions that are addressing the critical problems enterprises face in their goal of uniting virtual teams. To download click on the following link:

http://www.imera.com/products/collabpaper.html