How do I determine the K value from a cantilever beam deflection test?

[Jason24]

Hi,

I am new to this type of material and am hoping that someone may be able to assist me.

In short I am putting a cantilever beam under test to determine its bending moment and stiffness (K value) in order to get a strain reading that can be related to an exact model in solid works.

The cantilever beam is 0.26m long and a weight is applied at 0.25m. It is obviously hinged at one end and has a point load of 4.9N (at 0.25m).

I have calculated a bending moment of 1.225x10-3 by summing -(0.0049)(0.25). I believe this is right?

From this I am trying to determine strain behaviour via M/I=Sigma/y

I have calculated I from bh3/12 as it is a rectangle giving me 43.94x10 6. Again I believe this is correct?

For the stress I assume I simply put the 4.9N that I applied? And I am unsure on how to calculate y?

Also how do i determine the K value from this?
It may also be worth mentioning that I have used a DTI to calculate a deflection of .11mm under loading

I appreciate any help, I am new to all of this and appreciate your patience

cheers,
Jason

 

[PhanthomJay]

If this is a homework question you have posted in wrong forum. Deflection of a cantilever under a point load P applied a distance L from the fixed support can be found in tables or determined from the calculus, where the stiffness is the inverse of the deflection under a unit point load. Watch your units is the load in N or kN? What are the beam dimensions ? Max stress occurs at extreme outer fibers at fixed end and where y for max stress location is the distance to the neutral axis .