Tensile Strength vs Yield Strength
Tensile strength and yield strength are two very important topics discussed in engineering and material science. Tensile strength is a measurement of the maximum deformation a certain material can take without necking. Yield strength is a measurement of the maximum amount of elastic deformation a material can take. Both of these concepts are very important in fields such as structural engineering, mechanical engineering, material science and various other fields. In this article, we are going to discuss what yield strength and tensile strength are, their definitions, the applications of yield strength and tensile strength, the similarities between these two, and finally the difference between yield strength and tensile strength.
What is Tensile Strength?
Tensile strength is the common term used for the ultimate tensile strength (UTS). When a material is pulled it stretches. The force, which is stretching the material, is known as the stress. The ultimate tensile strength is the maximum stress a material can withstand before necking.
Necking is the event of the cross section of the specimen becoming significantly small. This can be explained using the intermolecular bonds of the specimen. When stress is applied, the intermolecular attraction forces act in the opposite direction, to keep the specimen in shape. When the stress is released, the specimen fully or partially returns to its initial state. When the necking starts the molecules are stretched apart so that the intermolecular forces are not enough to hold them together. This causes a sudden strain due to the stress and necking happens.
Tensile strength is also a property of the material. This is measured in Pascal, but larger units such as Mega Pascal are used in practical conditions.
What is Yield Strength?
When a material is stretched with an external force, the first part of the stretching is elastic. This is known as elastic deformation. Elastic deformation is always reversible. After a certain amount of force is applied, the deformation becomes plastic. A plastic deformation is not reversible. The point where the elastic deformation becomes plastic deformation is a very important property of the material.
Yield strength is defined as the amount of stress where a predetermined amount of plastic (irreversible) deformation occurs. If the applied stress is lower than the yield strength, the deformation is always elastic.
Yield strength is always lower than the ultimate tensile strength. This means any necking effect occurs after plastic deformation. Necking is not possible in the elastic deformation region.
Yield strength can be measured using methods such as the divider method.
Tensile Strength vs Yield Strength
- Ultimate tensile strength is the strength where the necking effect begins. Yield strength is the strength where the deformation turns from an elastic deformation to a plastic deformation.
- Yield strength is always lower than the ultimate tensile strength.
- When the amount of stress reaches the yield strength, there is a very small amount of plastic deformation due to the measuring threshold value.