If a type of G11 Expoxy Glass Laminate was fitted inside a steel cylinder, so that it pressed against the inner wall of the steel, how would you calculate the stiffness of the G11 glass? The glass does not have a specific Modulus of Elasticity, however, it does have a Flexural Modulus. Can this value be used to determine k?

For more context, my goal is to analyze the forces between steel and G11.


1 Answer 1


In ASTM D790 standard, the flexural modulus for an isotropic simple support beam with a load F at midlength and of length L, width w, and height H with a deflection d is defined as

$$E_{flexural}=\frac{L^3 F}{4wh^3 d}$$ Wich after comparing with the I, the 2nd-moment area of the beam simplifies to E, Young's modulus.


image by Adwilley

For very small strains in isotropic materials like glass, metal or polymer, flexural or bending modulus of elasticity is equivalent to the tensile modulus (Young's modulus) or compressive modulus of elasticity. However, in anisotropic materials, for example wood, these values may not be equivalent. Moreover, composite materials like fiber-reinforced polymers[4][3] or biological tissues[5] are inhomogeneous combinations of two or more materials, each with different material properties, therefore their tensile, compressive, and flexural moduli usually are not equivalent.

Quoted from Wikipedia. source

  • $\begingroup$ There is absolutely nothing isotropic about G11 laminates. $\endgroup$
    – Phil Sweet
    Commented May 7, 2023 at 13:46
  • $\begingroup$ @PhilSweet, Then as the quote says the flexural modulus is not the same and needs to be established by testing. I cover both cases as a guide. $\endgroup$
    – kamran
    Commented May 7, 2023 at 15:36

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