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The three-point bending flexural test provides values for the modulus of elasticity in bending, flexural stress, flexural strain and the flexural stress–strain response of the material. This test is performed on a universal testing machine (tensile testing machine or tensile tester) with a three-point or four-point bend fixture.
Fig. 3 - Beam under 3 point bending. For a rectangular sample under a load in a three-point bending setup (Fig. 3), starting with the classical form of maximum bending stress: = M is the moment in the beam; c is the maximum distance from the neutral axis to the outermost fiber in the bending plane
For a 3-point test of a rectangular beam behaving as an isotropic linear material, where w and h are the width and height of the beam, I is the second moment of area of the beam's cross-section, L is the distance between the two outer supports, and d is the deflection due to the load F applied at the middle of the beam, the flexural modulus: [1]
Water (H 2 O) is an example of a bent molecule, as well as its analogues. The bond angle between the two hydrogen atoms is approximately 104.45°. [ 1 ] Nonlinear geometry is commonly observed for other triatomic molecules and ions containing only main group elements, prominent examples being nitrogen dioxide (NO 2 ), sulfur dichloride (SCl 2 ...
3, and the sulfite ion, SO 2− 3. In organic chemistry, molecules which have a trigonal pyramidal geometry are sometimes described as sp 3 hybridized. The AXE method for VSEPR theory states that the classification is AX 3 E 1. Phosphine, an example of a molecule with a trigonal pyramidal geometry.
For many cases, such as trigonal pyramidal and bent, the actual angle for the example differs from the ideal angle, and examples differ by different amounts. For example, the angle in H 2 S (92°) differs from the tetrahedral angle by much more than the angle for H 2 O (104.48°) does.
This increased p character in those orbitals decreases the bond angle between them to less than the tetrahedral 109.5°. The same logic can be applied to ammonia (107.0° HNH bond angle, with three N(~sp 3.4 or 23% s) bonding orbitals and one N(~sp 2.1 or 32% s) lone pair), the other canonical example of this phenomenon.
In fluoromethane (CH 3 F), for instance, the experimental F–C–H bond angle is 109°, which is greater than the calculated value. This is because according to Bent's rule , the C–F bond gains p-orbital character leading to high s-character in the C–H bonds, and H–C–H bond angles approaching those of sp 2 orbitals – e.g. 120 ...