A plastic section modulus is a geometric property for a cross section of an object generally used in materials in which plastic behavior can be observed. This is only one of the two different types of plastic section modulus used in engineering and design. Plastic section modulus is the more uncommon form of plastic section modulus, and most general designs by engineers do not use it in their calculations.
A section modulus can be used when designing objects that have beams or pieces that are highly flexible and bendable, explains EngineersEdge.com. In most cases, the elastic form of the modulus is used. This can account for different types of objects, including metals. However, in certain specific cases a plastic section modulus is used to calculate these values and design the objects.
The plastic section modulus of a given object depends greatly on the plastic neutral axis of the object. This is an axis that splits the cross section in such a way that it sets the compression force from the area being compressed equal to the tension force from the area undergoing the tension. The plastic section modulus itself is derived by summing the areas of the cross section on either side of this axis.