# G10 GRE Tensile Modulus

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I've looked around on the web for the tensile modulus of G10/FR4, can't seem to find anything that quotes it, although there are many places that list it's other materials properties. I don't understand why not, perhaps someone here could shed some light on this. Again, it's the tensile modulus, not the flexural modulus I'm looking for.

TIA

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... and what exactly is that flexural modulus? and why people list this instead tensile modulus? Are these two related by some equation?

I always run into this problem trying to find material properties of plastic for FEA. And as for Poisson's ratio, this I have to guess...

thanks

Paul

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For well-behaved materials [homogeneous, isotropic] the three moduli are related in this way:

for sigma is Poisson's Ratio, for E is Young's modulus for n = E/(2(1 + sigma))...

Young's Modulus E = 9 n k / (3k + n)

Rigidity or Torsional modulus n = E /(2(1 + sigma))

Bulk modulus k = E / (3(1 - 2 sigma))

Express E, n k in N.m^-2

Brian Whatcott Altus OK

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Thanks,...but what is flexular modulus?

Paul

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Tensile modulus = Young's modulus

I entered "Flexural Modulus" in Google. The FIRST response of many was this: "Flexural modulus is the ratio of stress to strain within the elastic limit (when measured in the flexural mode) and is similar to the tensile modulus."

Brian W

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• posted

Paul thought carefully and wrote On 5/30/2004 10:21 AM:

I might be able to shed some dim light on the difference between tensile and flexural modulus particularly for a fiber-reinforced material like G10. I work in a university lab and we play around with tensile and bend testing of metals and plastics for an undergraduate strength of materials course.

The bottom line is that tensile testing of fiber-reinforced plastic is actually a very difficult thing to do. The biggest headache is that the grips holding of ends of the material usually crush the sample before dependable results can be found. This is a common problem and it usually takes a small development program to figure out the "right" way to perform a tensile test on a sample.

So to estimate the Young's Modulus (inelastic stress/strain ratio) of such a material we are forced to perform a bend test, measuring strains, forces and deflections to back-calculate a value for the modulus.

The accumulation of errors, deviations from assumptions, linear stress distribution, etc makes the bending modulus values "different" from the values obtained from a straight tensile test.

For real-world applications, the modulus results from a bend test (or the "flexural" modulus) is sufficient for most needs and there is no hue and cry for a real tensile modulus. Though I imagine someone, somewhere, has gone through the effort and gotten some values.

Lance

*****
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I think confusion may arise because in ceramics (and maybe in some other fields, too) the phrase "modulus of rupture" has traditionally been used to refer to the fracture stress in bending. Obviously, this isn't really a "modulus" in the way that the tensile or shear moduli are, and I don't know how the term originated, but it has been in use for a long time.

Anyway, these days, the term "flex strength," which is more correct, is starting to see some use. However, some people get the two terms mixed together and say "flex modulus" when they really mean "flex strength."

Since the units for strength and stiffness are the same, when someone says "flex modulus," you're best off asking them which they mean (unless it's already obvious from the number).

Dave Palmer

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