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Strength/weight ratio question

  1. Dec 7, 2004 #1
    Quick question: Why does the strenght to wieght ratio increase for die cast parts with decreasing wall thickness?

    My view is that the weight decreases with nominal change in strength; however, a classmate of mine disagrees. Any thoughts?
  2. jcsd
  3. Dec 7, 2004 #2
    I can see how the stiffness/weight ratio can be improved in an I-beam. If you make the web thinner (but not so thin that it buckles) you'll not change the second moment of area much, so you'll have almost the same stiffness, but you will save weight. Conversely, you might make the web thinner but deeper, keeping the same overall weight but increasing the second moment of area and so the stiffness.
  4. Dec 7, 2004 #3
    Thanks. Additional delving into the topic showed us both that other factors such as porosity cooling rate grain structure and and mold flow are all 'typically' improved with thin wall castings versus thicker wall castings.

    Thanks for the response.
  5. Dec 7, 2004 #4


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    For a component like a pipe, recall that the contribution to the stiffness from any volume element goes like the cube (I think) of the radial position from the axis. However, the contribution to the weight goes only as the square of the radial position. So removing material from smaller radial positions improves the strength-to-weight ratio.

    That's why thin walled components are better for this.
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