# Torsional strength of shaft 35 mm dia grade 1020 and 4140

#### yhshah

I have a grade specific query. We are currently using 35 mm dia shaft of 1020 grade steel. We want to upgrade to 4140 steel of same diameter. Researching on google and this forum i found out the ultimate tensile strength of 1020 grade is 710 MPa and UTS of 4140 grade is 1080 MPa. But thats general Strength i want to calculate Torsional strength for 35 mm dia and length of 680 mm for both the grade. how do i make comparison ? Urgently required the solution so thanking all of you in advance....I also read Torsional strength is .6 of UTS but does it apply to all grade of steel ???

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#### minger

For torsion you're going to want to compare your calculated stress numbers to the shear strength of the material. There are general tables which relate shear strength to tensile strength if you're material properties don't explicitly state the number. This table may be useful to get your shear strength:
http://www.roymech.co.uk/Useful_Tables/Matter/shear_tensile.htm

#### CFDFEAGURU

You might also want to check the values listed here.

http://www.matweb.com/

You can calculate the shear modulus with knowledge of the elastic modulus and Poisson's ratio.

Here is the equation for that.

G = E / (2*(1 + v))

where

E is the elastic modulus
v is Poissons ratio

Thanks
Matt

#### FredGarvin

You may want to double check what material properties you currently have. 700 MPa for Sut sounds a bit too high for plain old 1018 or 1020.

Have you considered just a heat treatment instead of a material change?

#### CFDFEAGURU

Off topic:

Fred, I have to ask you here because you can't accept messages. What is your avatar picture of? (Not the one Kurt Russel from Big Trouble in Little China.)

lol

Thanks
Matt

#### FredGarvin

It's a picture of myself with two fellow hookers in Suadia Arabia for Desert Shield on the ramp of our aircraft.

#### CFDFEAGURU

Ohh you mean those kind of hookers .... yeah there cool too. LOL

Matt

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