`__crash_absorber_support_area`

face set### Indice

# Fem Fundamentals and Chassis Design, spring 2022 course

## Lecture Notes

### Planar beam structure i.p. and o.o.p. loadings

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

### Symmetric and skew-symm. parts of a general load

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).

## Rollbar-like frame

Maxima worksheet v0001, v0002, rollbar_v0002_checkme_insert.wxmxv0003 v0004 v0005 a link rollbar_v0006.wxmx final version 2022

## Quarter ladder frame chassis

quarter_ladder_frame_ffcd2022a.wxmx

quarter_ladder_frame_ffcd2022b.wxmx

quarter_ladder_frame_ffcd2022c.wxmx

quarter_ladder_frame_ffcd2022d.wxmx

quarter_ladder_frame_ffcd2022e.wxmx

## OTW profile in torsion

profile_in_torsion_v014bis.mud

profile_in_torsion_v016_3d_hole.048.mud

profile_in_torsion_v017b.mud profile_in_torsion_v018b_href.mud profile_in_torsion_v018b_pref.mud profile_in_torsion_v019b_href.mud profile_in_torsion_v019b_pref.mud profile_in_torsion_v020b_href.mud profile_in_torsion_v020b_pref.mud

## A Phoney monocoque chassis

RBE3 connector: kinematics, moment distribution; RBE2 vs. RBE3 demonstrator model, screenshot.

Models:
v001,
v002,
v003^{1)},
monocoque_chassis_2022_v003b.mud,
v004,
v005 ^{2)},
v203,
v203motions,
v204,
v205,
v206,
v207.

### Properties

**Suspension link trusses**

Solid circular beam sections, ø12mm, aluminum. Essentially rigid with respect to other chassis structures.

**Rear framework**

Hollow circular section beam, aluminum.

Main structure: outer diameter ø40mm, wall thickness 1.8mm.

Stiffeners: outer diameter ø30mm, wall thickness 1.2mm.

**Composite monocoque**

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, `E=E_steel*1e4`

, `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.

### Frontal crash absorber collapse loadcase (inertia relief)

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).

### How to set a damped response

## Buckling

## Sparse material

## Videos

## Interesting stuff

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.

### Roller bearing questionable modeling

### Dynamics related stuff

** 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**

MSC.Mentat procedure for creating poor man harmonic response animations

MSC.Mentat procedure for creating poor man natural mode animations

**Structural damping references**

structural_damping_values_jdstevenson.pdf

damping_cross-reference_and_material_properties.pdf

f_orban_damping_of_materials_and_members_in_structures.pdf

tom_irvine_damping_in_bolted_and_welded_joints.pdf

estratto vol. 2, sezione 8 di Soovere, J., and M. L. Drake. Aerospace Structures Technology Damping Design Guide.LOCKHEED-CALIFORNIA CO BURBANK, 1985.

## Exercises

## Exam turns

^{1)}

^{2)}