Daylyt
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#1
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#1
Hello!
I have a tough semester project due in a few days and I'm struggling as all hell, if you can guide me through or even shed some light I would be deeply appreciative.
Link to question:http://imgur.com/a/VowNb
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Smack
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(Original post by Daylyt)
Hello!
I have a tough semester project due in a few days and I'm struggling as all hell, if you can guide me through or even shed some light I would be deeply appreciative.
Link to question:http://imgur.com/a/VowNb
Post what you've done so far so we can offer help.

What level is this by the way? School/college/university?
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Daylyt
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#3
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(Original post by Smack)
Post what you've done so far so we can offer help.

What level is this by the way? School/college/university?
Its a University Question for a kind of secondary course with a prerequisite of statics!
Here are some of my ideas some far but I still need help
I'm not sure how much you know about engines so I'll give a brief explanation. Functionally, at 0 deg the piston is Top Dead Center (maximum height) in the exhaust stroke. Meaning its pushed all of the exhaust gases out of the cylinder. This is why force is a minimum. 360 is the start of the power stroke, also at TDC, where the energy from the expended fuel is transferred to the crank shaft. This is why force is a maximum. It's also the area of interest and the force is known from your graph. The crank shaft is shaped in that fashion so that the piston rod (which is a link) can apply a torque to the rotating crank shaft (force * lever arm of crank). The crank shaft then transmits that torque through the transmission to the wheels.
Since stress concentrations are not of a concern and it can be assumed that your answer won't be affected much, I'd start with redrawing the dimensions of the part without fillets and with easier to handle dimensions. I would ignore bending moment from the fly wheel since those components are likely supported by bearings. I think I would also assume the engine has been running at 2000 rpm for some time, so that way you don't have to consider angular acceleration of the drivetrain components.
Consider the modes of failure. Torsion will develop from the torque in the shaft to accelerate or sustain the motion of the car. Shear will develop in the area where the connecting rod is attached to the crank. You will need to develop a combined stress equation. Then take that and find the von Mises stress. You can also find the power developed by the engine by multiplying angular engine speed (start with rpm) with the torque. Recall there will be some inefficiencies in the system. I'd start with a free body diagram of the crank shaft at 360 deg position, include all forces and resultant torques. Note that the force is divided into components, each will produce different stress modes in the part.
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Smack
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#4
(Original post by Daylyt)
Its a University Question for a kind of secondary course with a prerequisite of statics!
Here are some of my ideas some far but I still need help
I'm not sure how much you know about engines so I'll give a brief explanation. Functionally, at 0 deg the piston is Top Dead Center (maximum height) in the exhaust stroke. Meaning its pushed all of the exhaust gases out of the cylinder. This is why force is a minimum. 360 is the start of the power stroke, also at TDC, where the energy from the expended fuel is transferred to the crank shaft. This is why force is a maximum. It's also the area of interest and the force is known from your graph. The crank shaft is shaped in that fashion so that the piston rod (which is a link) can apply a torque to the rotating crank shaft (force * lever arm of crank). The crank shaft then transmits that torque through the transmission to the wheels.
Since stress concentrations are not of a concern and it can be assumed that your answer won't be affected much, I'd start with redrawing the dimensions of the part without fillets and with easier to handle dimensions. I would ignore bending moment from the fly wheel since those components are likely supported by bearings. I think I would also assume the engine has been running at 2000 rpm for some time, so that way you don't have to consider angular acceleration of the drivetrain components.
Consider the modes of failure. Torsion will develop from the torque in the shaft to accelerate or sustain the motion of the car. Shear will develop in the area where the connecting rod is attached to the crank. You will need to develop a combined stress equation. Then take that and find the von Mises stress. You can also find the power developed by the engine by multiplying angular engine speed (start with rpm) with the torque. Recall there will be some inefficiencies in the system. I'd start with a free body diagram of the crank shaft at 360 deg position, include all forces and resultant torques. Note that the force is divided into components, each will produce different stress modes in the part.
Okay I will have a quick look at this later, although I don't know an awful lot about engines.
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Daylyt
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#5
Report Thread starter 2 years ago
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(Original post by Smack)
Okay I will have a quick look at this later, although I don't know an awful lot about engines.
Any help is a great help, thanks!
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