# Relation between tensile strenght and young's modulus

1. Jun 1, 2010

### balajiperumal

Hi friends,

My work is related to simulation of the practical testing processes to the software testing methodologies using CAE

In short, I have an assembly(3d model or CAD data) for which I have to simulate the practical testing process to the software testing and compare the results of both the cases. But the issue I am facing now is : For assigning the actual material properties for the assembly in the software, the software allows me with only 3 physical properties they are: young's modulus, poission's ratio and density.

Where as in the actual case I am provided with only tensile strength and yield strength.

Is there any relation(or say formulae) between tensile strength and young's modulus from where I can get the value of young's modulus?

Till now for obtaining the young's modulus value we performed the Tensile strength test for couple of parts using UNIVERSAL TESTING MACHINE(UTM). But, in the assembly there are nearly 22 parts. Performing the tensile strength test for all the parts may take much longer time and money also. So for avoiding such a long process, I have entered this forum for getting better suggestions. Please help me out with this as early as possible.

2. Jun 1, 2010

### Mapes

Hi balajiperumal, welcome to PF. Unfortunately, there's no simple relationship between strength and stiffness (Young's modulus). However, the Young's modulus doesn't depend much on alloying, so if you know the materials involved (for example, steel is predominantly iron; aluminum alloys are predominantly aluminum), you can use the Young's modulus for the base element without much error. Does this answer your question?

3. Jun 1, 2010

### balajiperumal

hi thanks for the quick support given by you.
Actually, I too felt the same of using the same steel's young's modulus for the steel related parts. But, as our customer is asking for the accurate matching of results with the practical test reports we are under the process of getting the young's modulus values for all the individual parts seperately.

And more over as you said, we dont find much difference with the use of steel's young's modulus to the steel related parts. But to satisfy the customer we are under this process.

Ok and apart from getting the value of young's modulus from the tensile strength, are there any other procedures for getting the value of young's modulus or poisson's ratio?

4. Jun 3, 2010

### Matcon

Agreeing with Mapes, it may be useful to know why there is no simple relationship.

For an elastically isotropic material, the strength would be Shear Modulus x angle through which an atom moves to get to its neighbour's position. The existence of dislocations makes this estimate hopelessly too high.

Also, bear in mind that tensile strength is just a number to help engineers design things; it is not a fundamental material property like conductivity or elastic modulus. When a metal fails under stress, a whole lot of irreversible processes are going on at the same time; dislocations are generated, getting locked together, widening, narrowing etc.

5. Jun 4, 2010

### balajiperumal

oh ok.

Now I understand clearly, thanks for your clarification
so to get the young's modulus especially for my software purpose I should calculate the young's modulus for all the components in the assembly through UTM.

6. Jun 9, 2010

### Studiot

Are you a software engineer?

Hardware engineers use the yield strength not the ultimate tensile stength because once a ductile test specimen passes the yield point you have to decide whether to use absolute or engineer's stress to measure and report. The material behaviour in the region between yield and eventual failure is no indicator of behaviour up to yield and very different from it.

Brittle materials do not posses a yield point so you cannot be discussing these.

Are you quite sure you need the ultimate tensile strength?
If so which one?

7. Jun 16, 2010

### balajiperumal

HI.

Yes, I am a software Engineer.

I need the value of young's modulus from the tensile strength value which I have for ductile materials and not for brittle materials.

From the previous threads I understand that both the tensile strength and young's modulus are of two modes, we cannot correlate them.

The reason for the need of young's modulus value is, because the software I use identifies the material based on three physical properties those are youngs modulus, poisson's ratio and density.

8. Jun 16, 2010

### Studiot

Well I don't see much of a problem then.

The ultimate tensile strength is of no value to you.

You must be able to determine young's modulus from the tensile test you have described, or you could not tell when the yield point is reached.

I think the density is a very easy property to measure separately and often done in materials testing as it is quite useful

I don't think you can readily measure poissons ratio but it is sensibly constant for a whole range of materials so I would just input an appropriate figure here.

9. Jun 17, 2010

### balajiperumal

Exactly, now you understand the issue I am facing here.

As you said I am calculating young's modulus from the tensile test using Universal testing machine.

But, the reason for posting thread is that to avoid such long process of tensile test, Is there any other procedure other than tensile test for calculating young's modulus using ultimate strength and tensile strength values?

10. Jun 17, 2010

### Studiot

Hardness testing is often used as a quick method.

11. Jun 18, 2010

### Astronuc

Staff Emeritus
12. Jun 18, 2010

### Matcon

..or acoustic emission or any acoustic method. People were getting good results relating Young's Modulus to acoustic properties with WW2 technology, so it should be possible to do the same job quicker and more cheaply today.

It's worth consulting an expert, though, because there are some snags with interpretation.

The only other material property I can think of that correlates with elastic moduli is latent heat of evaporation...let's not go there.

13. Jun 18, 2010

### Studiot

I am still not sure what the OP is trying to achieve; he has not properly answered my questions.

The ultrasonic method is difficult but for the record the formulae required are

For a compression wave

$${V_c} = \sqrt {\frac{{E\left( {1 - \sigma } \right)}}{{\rho \left( {1 + \sigma } \right)\left( {1 - 2\sigma } \right)}}}$$

For a shear wave

$${V_s} = \sqrt {\frac{E}{{2\rho \left( {1 + \sigma } \right)}}}$$

Where

V is the sonic velocity
E is youngs modulus
$$\rho$$ is density
$$\sigma$$ is poissons ratio

On the face of it these formulae link the desired variables, but I would be interested to see how the technique was to be used to deduce them.

Eddy current techniques are another useful NDT technique, but we really need more input from the OP.

14. Jul 14, 2010

### aprillove20

I totally agree with with Mapes,you can use the Young's modulus for the base element without much error.