The beam structure centroidal axis lies on a plane, which is also a symmetry plane for the cross-sections.
Symmetric and skew-symmetric loads with respect to such a plane are called in-plane and out-of-plane loads, respectively.
If the superposition of effects holds (e.g., if the structure behaves linearly) each load set only induces an associated subset of the possible components of internal action, see
A general load is applied to a symmetric structure in a); in b), c) the loads applied on each half structure is treated separately. In d), e) the action on the loaded portion is halved, and symmetrically propagated to the other portion; those symmetric actions are accumulated in the symmetric part of the load f). In g), h) the action on the loaded portion is halved, and skew-symmetrically propagated on the unloaded portion; those skew-symmetric actions are accumulated in the skew-symmetric part of the load i).
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Suspension link trusses
Solid circular beam sections, ø12mm, aluminum. Essentially rigid with respect to other chassis structures.
Hollow circular section beam, aluminum.
Main structure: outer diameter ø40mm, wall thickness 1.8mm.
Stiffeners: outer diameter ø30mm, wall thickness 1.2mm.
Thicker backbone: 1.8mm aluminum sheet, 25.4mm aluminum honeycomb 3003, density 5.2 lb/ft^3 (hex-3003-td.pdf), 1.8mm aluminum sheet.
Thinner panels: 1.8mm aluminum sheet, 6.75mm same aluminum honeycomb, 1.8mm aluminum sheet.
Frontal shock absorber support plate: provisionally as thinner panels, to be defined based on shock.
Sway (anti-roll) bar
outer diameter ø25mm, wall thickness 2mm, extremely stiff (Super-alloy Z,
nu=0.3); it may be mechanically isolated at need by deactivating one of the connecting elements to the wheel hub carriers.
Such a “deformable but extremely stiff” linkage modeling should be discouraged in favor of an actual kinematic constraining – i.e. an MPC, since excessive stiffness badly impacts the system matrix condition number (or the integration time step, in the case of explicit dynamic simulations); nonetheless, it allowed for a very straightforward implementation.
Inertial elements modeling
The following spreadsheets are used in defining the equivalent rectangular cuboids for each inertially relevant rigid body: engine, wheel assemblies. The driver inertia is modeled through an 80 kg steel bar spanning roughly from the sternum to the pelvis.
At the element faces belonging to the
crash_absorber_bearing_area set (an approx. 155×320 mm area at the front bulkhead), a 25 psi = 0,172 MPa distributed pressure is applied which is due to the honeycomb absorber crushing (see datasheet).
Reference L-shaped cross section, to verify the coupled bending formulas: maxima worksheet, Oxy and G12 oriented MSC.Marc/Mentat linear models. Large rotation, animated hiE lowE models, gif animation.
free_anticlastic_vs_cylindrical_bending.wxmx maxima worksheet for the four point bending test discussion.
On the relevance of constraining in dynamic analyses back view side view relevance of (improper) constraints on the dynamic behaviour of a structure. Design is reliable in actual operational conditions (link). Added constraints stiffen up the structure, thus increasing natural frequencies. However, a 0 Hz rigid body mode natural frequency may rise to a finite value due to added positioning constraints; the associate natural mode may be excited in resonance by dynamic loads.
Poor man dynamic response animated view
Structural damping references
estratto vol. 2, sezione 8 di Soovere, J., and M. L. Drake. Aerospace Structures Technology Damping Design Guide.LOCKHEED-CALIFORNIA CO BURBANK, 1985.