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BigRHArrowBigRHArrowComputer Aided Engineering (CAE)  BigRHArrowFEA Case Study: Structural Analysis Types conc.

SmallLHArrow To perform the analysis technically correctly SmallRHArrow

The first analysis to perform would be natural freqeuncies of the wheel. Then the dynamic frequency response. This will yield if resonance has been induced. This would have to be done for a range of requencies to simulate different car speeds. Thirdly, a nonlinear dynamic transient response analysis. This will yield tyre and wheel interactions as well as any impulse effects. The final simulation would be a summation of the resonance loads and transient response loads.

 

SmallLHArrow A mountain of empirical test data is required SmallRHArrow

As it says above(!), accurate test data for material properties including stress/strain curves (Young's modulus), SN (fatigue) curves, poissons ratio, mass density and damping coefficients (very hard to gain accurate data) for all of the simulated components, frequency event for the dynamic frequency response analysis and the load/time function of impact for the dynamic transient response analysis. Working out the damping coeffcients in particular would be very difficult (expensive) to achieve accurately for all of the simulated components. Damping is the ability of a material to dissipate energy. Therefore the suspension is well damped (that's its job)! and should be damped at (or near) the critical level, the tyre is effectively acting as a spring with some damping - underdamped and the wheel has very little damping (effectively undamped). All this testing would be extremely time consuming and very costly to achieve, but with complex analysis, there is simply no point entering inaccurate data - rubbish in = rubbish out. If a true correlation between theory and pratice is required, I would advise to take this route (especially physical testing) so that your new product development can be done mostly in the CAE environment. Once these interactions and load sets are known, the problem can be massively simplified - see below.

 

SmallLHArrow A linear static approximation of nonlinear dynamic problem SmallRHArrow

Ask the question, what are we trying to achieve? We're just interested in finding peak stresses (via peak loads) of a pretty linear (cast aluminium alloy obeying Hooke's law) material (wheel) for optimisation and durability. Hence, this problem CAN be broken down into a linear static problem. How? If there is resonance, we can apply maximum load via a static vector load or loads, likewise any impulse effects can be applied as a maximum static vector load. We're not interested in the tyre or suspension stresses - we're just using them to react the load wihout causing peak stresses effects in the wheel. Hence the linear static approximation is the summation of all the dynamic loads.