Re: My stop sign broke

From: Guy Allen Brady (
Date: Wed Mar 11 1998 - 19:41:30 EET

Two words: fracture mechanics.

You're extending a fatigue crack in the material - each little flex
lengthens a crack and I would venture to guess this little trinket has
quite a stress concentrator at the base of the "sign" near the stem. It is
this stress concentration which takes your tiny applied moment and
magnifies it at the crack tip. Once the crack has lengthened to a critical
value: "bink", two pieces.

          G. Allen Brady -- Graduate Research Assistant
Materials Science and Engineering - The University of Michigan
2219 H.H. Dow Bldg. 2300 Hayward Street Ann Arbor, MI 48109-2136
work: 313/936-0177 fax: 313/747-4807 email:

On Wed, 11 Mar 1998, Candy Barone wrote:

> I had the same problem with my stop sign toy that was made with the new
> ABS-like resin. I try to separate the two halves and one of my tabs
> cracked. I don't believe I forced it past its plastic state.
> *******************************************************************************
> Candy Barone
> Graduate Student - Environmental Engineering (MSEV)
> Rapid Prototyping Center - Research Assistant
> Milwaukee School of Engineering
> 414/277-7189 (w)
> 414/224-9569 (h)
> *******************************************************************************
> On Wed, 11 Mar 1998, Robert Zubrickie wrote:
> > Did anybody elses stop sign toy from the NASUG break? Mine seemed to get extreamly
> > brittle one week later. It could have been the cycling of the material or something
> > else. My stop sign broke then the next day one of my latches broke and I didn't flex
> > them past the plastic state.
> >
> > For more information about the rp-ml, see
> >
> For more information about the rp-ml, see

For more information about the rp-ml, see

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