×
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

impact force question

impact force question

impact force question

(OP)
I am designing a saftey cage for a bulldozer that is used in deforestation.  I need to find the force that is created when a tree falls over and strikes the cage.  The trees are 30m tall and have a diameter of 1m....the density is 12 KN/m^3.  I know these are bigger and denser than the trees in yuor back yard but this is in a jungle and this is the design criteria.

I have tried useing mechanics...but the forces I am coming up with are astronomical so I don't think I'm useing mechanics correctly.

I am grateful for any help

RE: impact force question

You're describing a 64,000 lb object falling on a vehicle whose roof is not that substantial, so I'd believe that the cab would get crushed in most case.

There have been already some discussions about this type of analysis, with about the same title, so you might try search, e.g.:
Thread404-74498
Thread507-86811
Thread507-69901

TTFN

RE: impact force question

Those threads are mostly to do with elastic collisions. I strongly suspect that you will only be able to absorb that sort of impact by designing a plastic (ie deformable) structure.

If this so then you can use an energy balance to determine the final deflection, as most crash structures use a constant force construction, crudely this just gives you masstree*g*.5*height=F*d

Alternatively you could use a spring and damper to hold the roof up, in which case you could use the impact solution for a single degree of freedom system.

You need to do a bit of work to establish the striking velocity and the worst bit of the trunk to be hit with (the top is moving faster, but the middle has more effective mass). This has got something to do with baseball bats.

Cheers

Greg Locock

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