×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

static equivalent to a dynamic load

static equivalent to a dynamic load

static equivalent to a dynamic load

(OP)
I need some help converting a load.  Right now I have a dynamic load.  I have mass=76.5 kg, acceleration=6g's (58.8 m/s^2) and time=0.667 s.  The load is out on a cantilever and is being subjected to an impulse (there is no impact).

The setup is similar to someone on a diving board, quickly going from standing to crouching.  There is deflection at the end of the diving board, but there is no impact.  I do not think energy method can be applied here because, height is difficult to determine.

I know the current setup holds up under the above conditions.  I want to test the setup until failure. I would like to use a pull station to isolate this part.  I should be able to do this if I can turn the result of the static test into an equivalent impulse result.

I cannot remember how to convert a static load into an equivalent impulse.  Can anyone point me in the right direction?

RE: static equivalent to a dynamic load

For a quick "back of envelope" calculation:

Dyn Amplification factor = 1 / (1-fa/Fn)

Where fa is the frequency of the equipment and Fn is the natural frequency of the cantilever beam.  
 

RE: static equivalent to a dynamic load

from the data provided, why not F=ma ?  but i guess you'll say the acceleration isn't constant, maybe a sin (or cos ?) with 1/4 wavelength of 0.667s ??

if it is similar to a person quickly crouching ... isn't the person giving up potential energy (lowering their CG) ?  where does that energy go ?  strain energy in the diving board ??

RE: static equivalent to a dynamic load

(OP)
You are correct that the center of gravity lowers, but measuring that distance is not possible.

The acceleration is not constant, but I do have the acceleration profile over time.  This is a one shot test.  The setup has to survive once to "pass"...

Does the accelerometer data (6g's) take in to account the fact that this is an impulse?

RE: static equivalent to a dynamic load

accelerometers measure acceleration ...

but you can derive impulse from acceleration ...

RE: static equivalent to a dynamic load

Suddenly applied loads (not impact from a moving object with sizeable mass) are simulated by doubling the load.  I am away from my office so I don't have my original source (Terzaghi.) This was originally based on the observation that a suddenly applied load would result in a doubling of the elastic elongation of a steel rod as compared to the same load applied under static conditions.  While not accurate for relatively high energy transfer, it works for gravity-magnitude transactions for typical members.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources