1. STRENGTH LIMITED DESIGN
1/24/2018 1/24/2018
STRENGTH LIMITED DESIGN
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2. A tie is a rod loaded in tension while a column is loaded in compression
The state of stress within both is uniform and the material remains elastic at stresses below the yield strength

3. If σmax exceeds σy then the
Figure 7.1
In bending, the maximum longitudinal stress on a beam or panel is:
ym – distance from the neutral axis
Ze – elastic section modulus
If σmax exceeds σy then the
component is no
longer elastic

4. At a moment well beyond the yield strength, a component will collapse by rotating about its plastic hinge
Figure 7.2
Maximum Moment FL
FL/4
FL/8

5. We can change the shape and properties of many metals by stressing them beyond their yield point – plastically deforming them
A lower limit for the torque T and power P required to deform a material by rolling is found from the plastic work σyεpl per unit volume
rolling
extrusion
forging (closed die)
sheet forming (deep drawing; stamping)

7. SUMMARY Elastic Design is focused on avoiding yield
This means the maximum stress anywhere in the object needs to be below its yield strength
Sometimes want controlled plasticity
Metal forming operations like forging, rolling, drawing rely on full plasticity of the piece being manufactured
Forces and power required depend on the yield strength and the temperature (which affects the yield strength)
VERY hard alloys cannot be manufactured in this way: their yield strength is too high.