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DISCLAIMER:I never completed any of these classes upon first drafting this work, but these are continuously updated as a I venture into the topics in class, on my own, and as I encounter them in LHRS as a whole. 👍
Statics
Start here → Statics Lecture.pdf
Pictured here is an explanation of moment as it pertains to the example of a brake pedal. The force at A causes a moment around B with the distances of 240mm and 100mm.
Moment
Firstly, many different static and dynamics ergonomics parts will experience various forces and moments when in use on the car.
For example, you have the driver putting force (causing a moment) on the brake and throttle pedals with his legs, while applying a grip force on the steering wheel, all while the equal and opposite contact forces from the seat and harness keep the driver at equilibrium and safe within the occupant cell.
- Force → load applied at a point, causes pressure and by extension stress (force over an area), displacement, work, etc.
- Moment → measure of a force times a perpendicular distance from a point (I.e. tendency of a force to rotate around an axis of an arbitrary point)
Takeaways from this → Each part takes on different loads and moments that we must tailor each design and mechanism for to take on
Inside each part, internal forces are present, which can cause different effects (i.e. compression → buckling, shear force → shearing, bending moment →bending stress, etc.)
- When designing a part, especially when FEA and additional analysis is required, one must consider the different types of forces acting on the part, and how each one can affect the overall part (i.e. where are the weakest points in the structure based on the loads placed on it?). Some parts may experience only one of these cases (think of a seat only experiencing shear forces caused by the gravity of the occupant), while some parts may experience multiple at the same time (think of a brake pedal with both compression and bending moment caused by the force of the driver's foot).
Axial Forces
- Axial forces (forces parallel to the center axis of the part) can cause compression or tension in a part, which can essentially be broken down into squeezing or stretching
- Too much of either tension or compression can lead to either plastic deformation or buckling
- Most parts are resistant to axial forces as compared to shear forces or bending moments (this can vary on the material, shape, and size of the part however)
- Buckling is more common in longer, less stiff parts (I.e. shorter, stiffer part → less chance of buckling)
Shear Forces
- Shear forces (forces perpendicular to the center axis of the part) can cause the shearing of a part
- Think of it as a cutting force, like scissors cutting paper, a force perpendicular to the part can sort of “cut” the part in half
Bending Moments
- Bending moments (forces that cause a rotation around a fixed point, causing bending) can cause bending stress (this is the root of most all problems in a lot of design)
- You can think of bending moments as the worst case scenario, not only are you getting normal stress loads, but you are getting transverse shear stress as well
- Bending moments have a lot to do with load pathing (i.e. if your load path is a straight line, no bending moment is caused (forces are only axial), but as soon as you introduce an angled path, bending moments are caused)
Torsional Forces
- Torsional (or twisting) forces occur when torque is applied about the longitudinal axis of a part
- A good way to visualize this would be when the driver continually tries to turn the steering wheel after they have reached the steering stops
- No more allowed rotation → torque is opposed → torsion (albeit not that much unless our driver is Bruce Banner or something) occurs
Supports will come in later when you take Statics/are introduced to FEA.
- Supports assume infinite stiffness in specific degrees of freedom. Some supports (like fixed) have reactionary forces and moments in all DOF, some like (roller and pinned) have reactionary forces and moments in only specific DOF
- All that matters is that different types of supports resist different types of forces/moments, which you can use to solve/isolate forces and understand the reactions happening in a system
- Supports are integral to setting up a simulation right. If you have too many constraints, your sim will be too stiff and you will have inaccurate results. Too little constraints, same problem, inaccurate results, that can cause you to falsely presume your part is safe/effective.
Friction is also present in some capacities within the Ergonomics system, with the main part being the braking system.
- Friction is the force that resists or opposes either
- a) relative motion → Kinetic Friction (although relative motion can be at rest so potentially Static Friction)
- b) impending motion → Static Friction
- Friction is made up of the coefficient of friction which is determined by the surfaces and materials you are working with and the normal force, the force pressing the contacting surfaces together.
- Friction is also most often associated with heat energy, meaning that when friction occurs, heat dissipation is likely to follow. Think of this as when you rub your hands together → friction occurs → heat follows shortly after
- As an example, friction is present in the braking system as when the driver pushes the brake pedal and shifts the braking fluid, which sends hydraulic pressure to the brake caliper, which cause the brake pads to contact the brake rotor, thereby causing friction, which then slows down the rotor and wheels, while also releasing some of the transferring kinetic energy as heat to the atmosphere.
Two Force Members
- A two force member in our case would be a tube with forces only acting in two locations, with the forces being equal opposite and colinear.
Topology Optimization
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