The polar moment of inertia J for a rectangular section is given by:

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Oxidation is a general chemical process that can occur independently of corrosion. Although it can cause corrosion of metals, oxidation is not always harmful and can be beneficial, as in the formation of protective oxide layers on metals such as aluminum.

Chemical reaction Oxidation process
Oxidation is a chemical process in which an atom or molecule loses one or more electrons. This process usually involves a reduction in which another substance takes the electrons released or lost by the oxidized material. Both of these processes are redox (reduction-oxidation) reactions. The following equation can represent the general form of an oxidation reaction:

M→M n+ +ne –

Where M is the metal or substance undergoing oxidation. M n+ is the oxidized form of the substance (a cation in the case of metals). n represents the number of electrons lost. For example, in the oxidation of iron, the reaction is as follows:

Fe→Fe 2+ +2e –

Oxygen is usually the oxidizing agent in most oxidation processes. This means that it gains the electrons that the metal or other substance loses. This can lead to the formation of oxides, such as

4Fe + 3O2 → 2Fe2O3​





For example, a highly acidic environment accelerates rust formation because oxidation accelerates under acidic conditions (low pH). Alkaline conditions also promote rust formation, but less vigorously than acidic conditions.












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J = (ab³)/3

This formula is only valid when the thickness is significantly less than the width.

Here, a and b are the dimensions of the first dataset rectangle measuring length and width respectively. When used as steel members for buildings and structures, rectangular sections are generally less torsionally stiff than circular sections, mainly when their aspect ratio is high, meaning that one side of the rectangle is more elongated than the other.

Example 2

Consider a thin-walled rectangular steel beam measuring 20 cm by 10 cm, with a length of 3 meters and a shear modulus G = 75 x 10 9 GPa. Determine the torsional stiffness GJ and the twist angle θ when a torque of T = 2000 Nm is applied.

Solution



The twist angle is given by

θ=(2000×3)/(2×10 7 =1.5×10 -4 radians

Hollow and complex sections:
Hollow circular sections such as tubes are also useful in engineering, as are non-circular sections such as I-beams and T-sections. Cylindrical shells offer good resistance to torsional forces and are relatively light. Cylindrical shells offer good resistance to torsional forces and are relatively light - they can be used in cars as drive shafts or in buildings as beams. The polar moment of inertia of a hollow circular section is given by the following formula:

J=π(r o 4 -r i 4 )/2