How to Calculate Young's Modulus and Poisson Ratio if not given in Material Specs.

Hi All,

I could use some help.

I am a one man business and I do design and engineering for small companies.

As an engineer, I often have to work with these clients and often they will provide me with material data sheet for plastics that they want to use.

I have to perform FEA (ProMechanica) strucural simulation for them to show validatity of the design. So sometimes I have to show or record Young's Modulus, Tensile Modulus, Possion Ratio, Density, etc in my reports. Also I keep copies for ISO 9000 reasons.

A client has has me a question and I gave him an answer as below you will see my method of finding Young's Modulus and Poisson Ratio.

The question from client: "How do you or someone tell me how to calculate Young's modulus and Poisson Ratio if not given in the Material Specs."

I would appreciate if someone could validate my formula and use of numbers from Material Data Spec sheets.

One method I have used over the years.

Young's Modulus = Stress / Strain  ( Standard Text Book Answer)

Example: I have a material data sheet, attached. see "ABS_Data_Sheet.pdf"

Tensile Stress = 42.5Mpa

Strain at 50 percent yield = 23% (sometimes these values are stated; Strain at 50% elongation / 50mm/1minute

Young's Modulus =

math: 42.5Mpa / (23%/100) =     (Not knowing the forces but given a maximum strain I use the maximum strain as control factor)

math: 42.5Mpa / 0.23 =

math: 184,782,608.696 Pas.

math:: round 184.8e6 Mpa

Poisson ratio.

Possion Ratio is rarely given.

Could someone help me this this method given that most material suppliers never provide this value.

There must be values given from the material data sheets that can be plugged into a formula and then caluclate the resulting Possion Ratio.

If I remember correct Possion Ratio may not be a required value in ProMechanica (Could some confirm this as true or false)

Poisson's Ratio can be expressed as

υ = - ε_t / ε_l             (1)

where

υ = Poisson's ratio

ε_t = transverse strain

ε_l = longitudinal or axial strain

Strain can be expressed as

ε = dl/L             (2)

where

dl = change in length

L = initial length

For most common materials the Poisson's ratio is in the range 0 - 0.5.

What values do I use from the Material Data Sheet do I use to calucate the Poisson Ratio - not given any axial or transversial strain values. Or am I missing it and the values are there. Yeah, I can be tht stupid sometimes.

I have attached some Spec sheet that I often have to deal with

Thank in advance to all.

Dave