1. Strength of a material

Strength is a measure of the stress a material can withsand.

Two different values are typically used to define the strength of a material, the ultimate strength and yield strength.

2.Material Stress and Straina

First, we need to explain some of the physical concepts behind the mechanical properties. The main one is stress. Stress tells you how big of a force applies to an area. In mechanical engineering, it is mostly expressed in MPa’s or N/mm2. Those two are interchangeable. The formula for stress is:

σ=F/A, where F is force (N) and A is area (mm2).

The second important concept is strain. Strain has no unit as it is a ratio of lengths. It is calculated as follows:

ε=(l-l0)/l0, where l0 is starting or initial length (mm) and l is stretched length (mm).

A.Young’s Modulus

From those two concepts we get to our first mechanical properties – stiffness and elasticity as its opposite. It is an important factor for engineers when solving physics problems (material suitability for a certain application).

Stiffness is expressed as Young’s modulus, also known as modulus of elasticity. As one of the primary mechanical properties of materials, it defines the relationship between stress and strain – the bigger its value, the stiffer the material.

This means that the same load would deform two equally-sized parts differently, if they have varying Young’s moduli. At the same time, lesser value means that the material is more elastic.

B.Yield Strength

Yield stress or yield strength is the value most often used in engineering calculations. It gives a material a stress value in MPa it can take before plastic deformation. This place is called the yield point. Before it, a material regains its former shape when lifting the load. After exceeding the yield point, the deformation is permanent.

There is a good reason for using yield stress as the most important factor in mechanical engineering. As can be seen from the stress-strain curve, when stress goes beyond the yield point, the damage is not yet catastrophic. That leaves a “cushion” before a construction fails completely to the point of breaking.

C.Tensile Strength

Ultimate tensile strength, or just tensile strength, is the next step from yield strength. Also measured in MPa’s, this value indicates the maximum stress a material can withstand before fracturing.

3,Toughness of material

Toughness is the ability of a material to absorb energy up to fracture. Materials that can absorb a lot of energy before fracturing have high toughness.

Toughness can be thought of as the area under the stress-strain curve. If the area is large, the material will have high toughness and will be able to absorb a large amount of energy before fracturing.