Critical Section Location in Stepped Shaft Under Torque Load

[teng125]

What are the cases for section 1 and 3??
this is a stress concentration factor of notched or fillet bars problem.
From the picture,how can we choose whether it is t=tension,z=compression or b=bending??


http://files.filefront.com//;5410211;;/

and

http://files.filefront.com//;5410216;;/


pls help.i really need it.
thanx

 

[Astronuc]

Without knowing the load distribution, one cannot tell if the local stress is tension, compression, bending or shear. Are there other considerations.

If a shaft is rotating between two bearing which are not properly aligned, on could have alternating states of tension and compression, with bending, during the cycle of rotation.

Also, I think ImageShack ( http://imageshack.us/ ) is a better place to put images/graphics files.

 

[teng125]

Rp0,2 = 450 MPa, Rm = 1000 MPa. It is loaded by a bending moment Mb = 6,0 kNm and a torque T = 3,0 kNm.

than is all data give.is it possible to solve??

 

[teng125]

pls help...

 

[teng125]

pls help...

 

[Astronuc]

Well, the bending moment would produce bending in the shaft, but the torque would produce torsion. It does not appear that there is a tensile or compressive load.

For the bending moment, one would use the appropriate b-stress concentration factor.

From the figure viewer1.bmp, there should be some other data besides the three columns: z, b, t There is usually a relationship between the diameter ratios, the fillet radius and the stress concentration factor.

Are there no examples in the course textbook?

 

[teng125]

nono,but from the shaft can we know whether it is torsion or bending stress that occur at the location 1 and 3??

 

[Astronuc]

If a torque is applied to a shaft, then the shaft experiences torsion.

If a moment (bending force) is applied to the shaft, the shaft will experience bending stress (moments) along its length. The magnitude of bending will depend on the magnitude of bending force and the distance between point of application and point of interest. Also, more bending would tend to occur in the smaller section.

The change in cross-section results in a reduction of area which increase the magnitude of stress in the smaller cross-section. The objective of the rounded shoulder fillet is to reduce the stress concentration which would occur if there was a sharp corner or transition from the greater diameter section to the smaller diameter section.

Then the matter becomes one of determining the magnitude and location of stress, and comparing it to technical limits like yield/proportional stress (practical upper limit of elastic range) or ultimate tensile stress, and performing a fatigue analysis.

 

[teng125]

while if the question ask where is the critical section if a torque is acting??

 

[teng125]

' where is the critical section in the stepped shaft if a torque is acting '