Calculate Bending Moment & Stress of Axle w/ 300N Load

In summary, the limit stress for this loading case is F = 300N/m. If you cut into the half of the rotating machine, you would get a bending moment equation of M(b)=-325*F*500.
  • #1
teng125
416
0
Calculate the bending moment in the centre of the axle??
What limit stress is valid for this loading case ?

may i know how to form the moment eqn??
F=300N

picture - http://files.filefront.com//;5410274;;/

pls help
thanx
 
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  • #2
Did you show your work? Homework helpers will not assist with any questions until you've shown your own effort on the problem. Remember, we help with homework, we don't do your homework. We already passed those classes; it's your turn to do so.

What do you think? Try to form the equation on your own and we will inspect it.
 
  • #3
i have try it many times but i don't know.
if in mechanics,this have to use the heaviside function,but this is machine design.therefore ,i don't know what to use.

i assume it is F(1) <x-175>^0 + F(1)<x-825^0>...
but i think this is incorrect
 
  • #4
Well, heaviside functions aren't needed here.

Step 1: Determine the value of [tex]F_{1}[/tex] using equilibrium condition along the vertical (y-axis).

Step 2: By considering half part of the rotating machine (cut machine into two at the centre), write down the bending moment equation of either side using [tex]\sum\vec{F}l=\vec{M_{b}}[/tex]. It will be the same for the other half since it is symmetrical.
 
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  • #5
if i cut into the half,then i'll get F * 325mm = M(b) rite??am i correct??

if it is correct,in order to find limit stress = bending moment / W , where W= pi (d^3) / 64 right??
how can i find the diameter and which shaft should i consider??
 
  • #6
Bending_Moment.jpg


Your answer isn't correct. Try writing down the moment at C. Then we discuss the rest of the question.
 
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  • #7
then it should be M + (F1*325) - (1/2F * 500) =0 right??am i correct??

if it is correct,in order to find limit stress = bending moment / W , where W= pi (d^3) / 64 right??
how can i find the diameter and which shaft should i consider??
 
  • #8
Bingo.

How did you obtain the W? The correct axial section modulus W is [tex]W=\frac{\pi*d^3}{32}[/tex], assuming that the cross section of the axle is not hollow.

Setting [tex]\sigma_{all}=\frac{\sigma_{lim}}{n_{s}}=\frac{M_{b}}{W_{by}}[/tex] and solve for the diameter d as you have found [tex]M_{b}[/tex] in the first part, [tex]\sigma_{lim}[/tex] can be found in a strength data table, depending on the material given and the safety factor should be, well, leave the diameter in terms of [tex]n_{s}[/tex] if it isn't stated.
 
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  • #9
ok...thanx...pls help me in the other question in the engineering side...thanx
 

1. What is the formula for calculating bending moment and stress of an axle with a 300N load?

The formula for calculating bending moment is M = F * d, where M is the bending moment, F is the applied force, and d is the distance from the force to the point of interest on the axle. The formula for calculating stress is σ = M * c / I, where σ is the stress, M is the bending moment, c is the distance from the neutral axis to the outermost point of the axle, and I is the moment of inertia of the axle.

2. How do I determine the distance from the force to the point of interest on the axle?

The distance can be measured directly if the force is applied at a specific point on the axle. If the force is applied at an angle or distributed along the axle, you can use trigonometry or integral calculus to determine the distance.

3. What is the neutral axis of an axle and how do I determine its location?

The neutral axis is an imaginary line along the center of the axle where there is no bending or stress. Its location can be determined by finding the centroid of the cross-sectional area of the axle, which is the point where the area is evenly distributed in all directions.

4. What is the moment of inertia and why is it important in calculating stress?

The moment of inertia is a measure of an object's resistance to changes in its rotational motion. In the context of an axle, it represents how spread out the mass of the axle is and how it affects its ability to resist bending. It is important in calculating stress because it is a key factor in the formula for stress and can greatly affect the overall strength and stability of the axle.

5. Are there any safety factors or considerations to keep in mind when calculating bending moment and stress of an axle?

Yes, it is important to consider the maximum allowable stress for the material of the axle, as well as any potential weak points or areas of stress concentration. It is also recommended to use a safety factor of at least 1.5 to account for any unexpected or dynamic loads that the axle may experience.

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