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: Is there any relation between hardness and rigidity
: Is there any relation between hardness and rigidity -- sanjeev_onearth	Post Reply	Top of thread	Forum

Posted by: tekinserdar ® 07/23/2008, 09:58:02 Author Profile eMail author Edit

thanks for your attention, but i can, comfartably, take the modulus of elasticity value of both a hardened bushing and its housing same, right?

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: Is there any relation between hardness and rigidity
: Is there any relation between hardness and rigidity -- sanjeev_onearth	Post Reply	Top of thread	Forum

Posted by: randykimball ® 07/02/2008, 23:45:16 Author Profile eMail author Edit

There is a relation between tensil and rigidity. Hardness is a different property. It is a bit like horse power and torque. They just are not the same thing. It is true that harder materials do tend to be stiffer. There are charts that attempt to offer ball park figures of tensil strength based on hardness scales, but they are just for ball park calculations and are not wise to use for engineering calculations. As an example: Some T6 aluminum tubing is very stiff and relates well or even better that a steel tube of similar cross section. However, the aluminum T6 is not nearly as hard as the steel counterpart. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Wed, Jul 02, 2008, 23:49:52

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: : Is there any relation between hardness and rigidity
: : Is there any relation between hardness and rigidity -- randykimball	Post Reply	Top of thread	Forum

Posted by: john2003 ® 07/24/2008, 21:29:15 Author Profile eMail author Edit

The way I understand it, the elastic modulus is the main factor that determines stiffness or rigidity. If you have two 3/8" OD X 2" long round steel dowel pins cantilever mounted to a steel support (both made of the same steel, but one hardened to 60 RC and the other non-heat treated) and you put 30 pounds on the ends of each of the dowels, both dowel pins will deflect by the same amount or distance. However, the heat treated dowel pin will be able to support a higher load (and thus deflect further) and still return to it's original position without becoming permanently deformed or bent. This is becasue yield strength goes up with hardness. Otherwise, you would notice no difference in deflection until you exceed the yield strength of the non-heat treated dowel. The elastic modulus for most steels is approximately 30,000,000.00 PSI and most Aluminum is around 10,000,000.00 so in general, aluminum only has 1/3 the rigidity of steel and therefore using the analogy with the dowel pin above, if one pin is made from aluminum it will deflect three times as far as the steel pin. The above elastic modulus figures are general figures for the majority of alloys but there are exceptions of course. Tungsten has a very high elastic modulus if I recall accurately. Even if the aluminum dowel had a higher yield strength than the steel, it will still deflect further for a given load, but it could handle a higher load before becoming permanently bent. John Modified by john2003 at Fri, Jul 25, 2008, 19:02:56

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