Other experimental measurements made on the chassis related to the handling behavior of the car include torsional stiffness, which can range from 15,000 to 40,000 N m/°; flexural stiffness; and engine fitting local stiffness. This test is made to check if the rear wall of the chassis is stiff enough to avoid a “hinge effect” at the interface with the engine, where there is a very high stiffness change. Once the safety targets are met, the global stiffness requirements typically are satisfied.
Basically, all of the tests listed above are simulated in a finite element analysis (FEA) environment. Some of them can be replicated closely, while others cannot (e.g. the penetration test). Where a realistic simulation of the test cannot be done, a simplified correlated calculation has been set up and validated with many years of experimental data fitting.
The CAE group at Minardi consists of seven people who cover FEA, CFD (computational fluid dynamics), multibody, and hydraulics design and analysis. It takes approximately two months for two CAE operators to come to the first definition of the chassis structure. Then, including optimization, refining, and other changes, 25% of the CAE potential is dedicated to the chassis during a racing season. The workflow of the monocoque chassis structural design, from the conceptual phase issues to the regulation checks and the optimization process, requires accurate and easy-to-use analysis.
Currently, NEiNastran is used as general-purpose FEA software for static analysis (stress, stiffness), buckling (linear-nonlinear, especially on crash cones), and surface contact (roll-bar crush). All of the calculations are correlated with experimental measurements, thus enabling a continuous refinement of methodologies and material data.
In order to reach the targets defined above, several optimization runs are made by modifying material choice, layup sequences, local reinforcements, foams, bulkheads, and inserts. In this phase, it is important that the FEA package be productive in managing and editing the existing FE model, solving the problem, and giving accurate and detailed postprocessing information, so effective modifications can be decided by the engineers.
During the six-month evaluation of NEiNastran, one of the main benefits found was reduced modeling time. Using FEMAP and Smart|Browser/Smart|Laminate features, the creation of the FE model of the chassis was done in about half the time required by the previous FE package. Another benefit was training and technical support. With very focused custom training, Minardi was productive on the new FE platform in a few weeks.
A surface contact feature enabled a more general and accurate approach to some of the regulation test simulations that were solved through a more approximated scheme in the past. During the transition phase, where NEiNastran and the previous Nastran package co-existed, the input and output data generated could be shared without incompatibility issues.
This work was performed by Paolo Marabini, Analysis and Calculation Chief Engineer at Minardi F1, Faenza, Italy, using NEiNastran analysis software from Noran Engineering, Westminster, CA. For more information on NEiNastran, contact Noran Engineering at 714-899-1220, ext. 207; email: info@noraneng. com; or visit www.NENastran.com.