FEA question (stuck): Stress analysis on this Connecting Rod

• Engineering
• Smushiehippo
In summary, this lattice truss is designed to have high pressure in the red zone, where the stresses are greatest, and low pressure on the other zones to help distribute the stress.
Smushiehippo
Homework Statement
1) Explain where the first point of failure is likely to originate, and why.
2) An analysis of the studies, do you think that they will be an accurate representation of what will
happen in practice? how would you improve it.
Relevant Equations
none
Hey

Im doing FEA and got stuck on question. The diagram go me stuck, because looking through the workbook it says high stresses are in red and low in blue, whereas they included both different kind of stresses on the same diagram and no data.

Note: High Compressive strains are noted by blue, high tensile strains are noted in red, low strains are noted as light
blue/green/yellow.

What I Put
I think first point of failure would be located at the small end, where there is high tensile stress. the high tensile stress would cause deformation and fatigue fractures leading to failure.

For part 2 of the question - I layed out how FEA works, what the accuracy of the data depended on. i stated different methrod of checking (check with other collugues, past results, rerun simulations).

I believe comparing this result with past results ran the diagrams show a high level of accuracy, but cannot be 100% certain of accuracy. I do believe areas on the diagram may give errors in results, big end due to zero radius omitting tensiles stress. Ways to improve to include data on the stress to see if it exceeds yeild stress and put different stress on different diagrams.

Smushiehippo said:
Note: High Compressive strains are noted by blue, high tensile strains are noted in red, low strains are noted as light
blue/green/yellow.
I think that is incorrect.
I believe the connecting rod is shown under compression only. The highest pressure is where the gudgeon = piston pin, presses against the inside of the small end, shown as red. The big end has a greater area on the crank, so less stress. The blue is zero or neutral. The outer ends of the rod carry no load when under compression.

As the tapered rod is compressed, the narrower sections have greater stresses. That explains the colours changing along the length of the rod. The rod must be tapered to connect the small piston pin to the crank bearing.

The piston pin bearing has a low surface speed, and only swings through a small angle. It may have only splash lubrication. The big end has a higher bearing surface velocity, but also has forced lubrication. Red is an obvious problem.

DeBangis21 and Lnewqban
Baluncore said:
I think that is incorrect.
I believe the connecting rod is shown under compression only. The highest pressure is where the gudgeon = piston pin, presses against the inside of the small end, shown as red. The big end has a greater area on the crank, so less stress. The blue is zero or neutral. The outer ends of the rod carry no load when under compression.

As the tapered rod is compressed, the narrower sections have greater stresses. That explains the colours changing along the length of the rod. The rod must be tapered to connect the small piston pin to the crank bearing.

The piston pin bearing has a low surface speed, and only swings through a small angle. It may have only splash lubrication. The big end has a higher bearing surface velocity, but also has forced lubrication. Red is an obvious problem.
That's what I thought about the diagram and notes being wrong. But unicourse only gave me the diagrams with those notes and won't respond to my emails about it being potential wrong so kind of stuck

This looks like an old design of an equal-space lattice truss whose strains are not supported to equalize the strain. Especially the outer triangles are the weakest.
More like this

The Red zone has the highest pressure but this needs pressurized oil on the sleeve bearing during the low pressure up stoke to fill the red zone. I added two gray oil holes on the opposite side of the high force bearings which will allow oil to be pumped and forced down to the red zone.

1. What is FEA and how does it work?

FEA (Finite Element Analysis) is a computer-based method used to analyze the structural behavior of a component or system. It works by dividing the component into smaller, finite elements and solving for the stresses and strains within each element, taking into account the material properties and boundary conditions.

2. What is stress analysis and why is it important?

Stress analysis is the process of determining the internal forces and stresses within a component or structure. It is important because it allows engineers to understand how a component will behave under different loading conditions, and to ensure that it can withstand those loads without failure.

3. What is a connecting rod and what is its function?

A connecting rod is a component in an engine that connects the piston to the crankshaft. Its function is to transfer the linear motion of the piston into rotational motion of the crankshaft, which ultimately powers the engine.

4. What factors affect the stress analysis of a connecting rod?

The stress analysis of a connecting rod is affected by factors such as the material properties of the rod, the geometry and dimensions of the rod, the loading conditions (e.g. engine speed and torque), and any constraints or boundary conditions applied to the rod.

5. How can FEA be used to improve the design of a connecting rod?

FEA can be used to simulate and analyze the behavior of a connecting rod under different loading conditions, allowing engineers to identify potential areas of high stress or failure. This information can then be used to optimize the design of the connecting rod, such as adjusting the material or dimensions, to improve its strength and performance.

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