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6. Modulus of Elasticity
The measure of a material’s stiffness (without regard to material geometry) is known as the modulus of elasticity. In the case of metals, it is a function of metallurgy, and it is a mechanical property of the metal alloy. Modulus of elasticity varies widely among materials, and it varies significantly among metals; that is, some metals are considerably stiffer than others. Alloy groups tend to have the same modulus value; for example, the entire family of steels (carbon, low alloy and high alloy) all have the same modulus value of 30 x 106 lb/in.2.
Modulus of elasticity is an important parameter in structural design, and it is directly involved in the relationship between casting geometry and deflection. A larger modulus of elasticity means less deflection. For example, a steel casting would deflect less than an aluminum casting of identical geometry simply because steel is stiffer than aluminum.
One subtlety about modulus of elasticity is that it is not affected by heat treatment. However, heat treatment can affect the height of the elastic slope. This is very important because the height at which the elastic slope begins to curve is called the metal’s “yield stress.” This is the stress level at which plastic deformation begins and the metal is permanently affected. Stresses should be designed below this level so that deflections in the casting under load do not damage it.
--Mike Gwyn, Advanced Technology Institute
The author wishes to thank the following for their contributions to this work: Mark Armstrong, Duriron Co.; William F. Baker, Electric Steel Castings Co.; Leo Baran, Amerian Foundry Society; Malcom Blair, Steel Founders Society of America; Richard Heine, Univ. of Wisconsin-Madison; Jay Janowak, Grede Foundries Inc.; John Jorstad, CMI International; Raymond Monroe, Steel Founders Society of America; Mark Morel, Morel Industries; Tom Prucha, American Foundry Society; Fred Schleg, formerly of the American Foundry Society; and Jack Wright, consultant.
References:
"Basic Principles of Gating & Risering," AFS' Cast Metals Institute; "Risering Steel Castings (1973)," Steel Founders Society of America; R.W. Heine, "Comparing the Functioning of Risers to Their Behavior Predicted by Computer Programs," AFS Transactions 1985, vol. 93, p. 481; M.A. Gwyn, "Cost-Effective Casting Design," AFS; R.W. Heine, "Risering Principles Applied to Ductile Iron Castings Made in Green Sand," AFS Transactions 1979, vol. 87, p. 65; R.W. Heine, "Design Method for Tapered Riser Feeding of Ductile Irons," AFS Transactions 1982, vol. 90, p. 147; "AFS Risering System--Riser Sizer," developed at Univ. of Wisconsin-Madison, C.R. Loper Jr., R.W. Heine and R.A. Roberts, AFS Transactions 1968, p. 373.
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