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# AISI 4130 - Tangent modulus

## AISI 4130 - Tangent modulus

(OP)
What is a reasonable value of tangent modulus for AISI 4130 material? ( 1Cr 0.5Mo Temperature 350 F )

SUMATECH, INC.
www.sumacon.com

### RE: AISI 4130 - Tangent modulus

The Tangent Modulus is the slope of the stress-strain curve at a specific point. Therefore it is not a single value, but varies with the stress. At low stresses, the tangent modulus is the same as the normal Young's Modulus. As the stress approaches the yield stress, the modulus decreases, and this local modulus is called the Tangent Modulus. Since you need to know the stress to know the tangent modulus, it becomes an iterative problem. In a nonlinear material analysis, you can define the full stress-strain curve or use a bilinear approximation with a "hardening slope" which reduces the modulus to a constant single value after exceeding the yield stress.

### RE: AISI 4130 - Tangent modulus

(OP)
Thanks sdm919 .

I should have clarified. The Tangent modulus was
for bilinear-idealization. So the second slope,
after reaching the yield point is what I was
referring to.

SUMATECH, INC.
www.sumacon.com

### RE: AISI 4130 - Tangent modulus

Instead of asking us, plot a stress/strain curve from Et data and fit whatever curve you want.

### RE: AISI 4130 - Tangent modulus

sumacon2003

You need only 1 value of tangent modulus to define bi-linear material hardening behavior at the yield point.

One way to get reasonable value of Tangent Modulus is to calculate it with Ramberg-Osgood Equation. You can input the particular values of the stress and modulus at your required temperature.

Second way is to use ASME SEC VIII Div. 2-Annex 3.D approach to calculate Tangent Modulus for ASME code equivalent alloy steel.

Third way is to use the book- Atlas of Stress-strain curve by ASM international.

I don't know the fourth way yet.

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