I'm reading the Wikipedia page on flexural modulus. It is said:
Ideally, flexural or bending modulus of elasticity is equivalent to the tensile modulus (Young's modulus) or compressive modulus of elasticity. In reality, these values may be different, especially for polymers.
But how can they be different? Young's/elastic modulus is measured in the tensile test, by pulling a sample of the material and measuring the stress/strain response. In the bending test we bend the sample instead, but the fibers at the bottom (as seen in the picture) are in tension. Thus, if we inspect as small sample at the bottom of the beam, it is subject to tensile forces only and it should therefore behave in the same way as if the sample was being subjected to the tensile test. How does the sample know it is part of a beam being bent instead of being a part of a beam being pulled? How can the two moduli be different? The article mentions polymers specifically, but do the moduli differ for metals as well?