Hardness Testing in FEA 1

[vtmike]

Hi,

I have the following material properties & wanted to carry out a hardness test in ANSYS to measure maximum deformation when indented by a hard diamond tip,

1) 4340 Steel Case 1
Yield Stress = 69 ksi
Ultimate Tensile Stress = 108 ksi
Elongation = 22%
Density = .283 lb/in^3
Youngs Modulus = 3E7 psi
Poissons Ratio = .29

2) 4340 Steel Case 2
Yield Stress = 135 ksi
Ultimate Tensile Stress = 149.1 ksi
Elongation = 17.7%
Density = .283 lb/in^3
Youngs Modulus = 3E7 psi
Poissons Ratio = .29

I would have to use a bilinear isotropic hardening material model, but what would be the difference in the two material models? The slope of the tangent modulus? How do I calculate the tangent modulus & am I missing any data to calculate the tangent modulus for the two material models mentioned above?

Any help either directly or links to some references would be very helpful & highly appreciated.

Thanks,
Mike

 

[EdR]

The tangent modulus is ET = (Delta sigma)/(delta epsilon) from a uniaxial stress curve...

You apparently have enough information to compute what you want......

Based on your question I would suggest you get someone who knows something about FEA to solve this problem.....It's not as simple as you might think....You probably need to run actual hardness tests rather than try and simulate a test with FEA....particularly if the results are to be used for anything practical.....

As for references look at any undergraduate Mechanics of Materials book.

Ed.R.

 

[vtmike]

Let me begin by saying that I am solving this problem to understand more about FEA. I have some understanding of plasticity and the reason I was asking this question is to get some different points of views from some experienced users. I am NOT claiming to be an expert here!

There are references that cite different approaches to calculating the tangent modulus and I simply wanted to know what approach would provide the most accurate fit based on available data. I haven't found any formula in my mechanics of materials book but did find one in my undergrad theory of plasticity one which simply tells you to assume the tangent modulus as E/10.
Another approach is to use the following formula,

E_tan_Calculated = [(1+%EL/100)*S_ult - S_yield ]/ [(ln(1/(1-%RA/100)))
- (S_yield/E)]

But is this the most accurate approach to model hardness with available data or is there a better way?

Mike

 

[ishvaaag]

Here you have two printouts of some worksheets related to steel's tangent modulus; they are engineering steel properties and ay not be applicable to your work.

 

[ishvaaag]

the other