Mechanical properties of solids

It specifies numerous qualities of solids, such as deformation resistance and strength. Resistance to deformation refers to an object’s resistance to change in shape, whereas strength refers to an object’s capacity to withstand applied force.

Each atom or molecule in a solid is known to be surrounded by neighboring atoms or molecules. Interatomic or intermolecular forces hold them together and keep them stable equilibrium. When a material is deformed, the atoms or molecules are moved from their equilibrium locations, causing the interatomic (or intermolecular) distances to alter. When the deforming force is eliminated, the interatomic forces tend to return them to their previous places. As a result, the body returns to its natural shape and size. A model of a spring-ball system can be used to visualize the restoring process.

As a result, some of the mechanical properties of solids are as follows:

Elasticity: When we stretch an object, it changes shape, and when we release it, it returns to its original shape. Or, to put it another way, it is the ability to return to its previous shape once an external force is eliminated. Spring is an example.

 Plasticity: When an item changes shape and does not return to its previous shape even after an external force is eliminated, this is referred to as plasticity. It is a permanent deformation trait. Plastic materials are one example.

Ductility: An item has ductile characteristics if dragged in thin sheets, wires, or plates. It can be drawn into thin wires/sheets/plates. For instance, gold or silver.

Strength is defined as the capacity to bear imposed force without failing. Many types of items are more potent than others.

STRAIN AND STRESS

When forces are applied to a body while it is still in static equilibrium, it is deformed to varying degrees depending on the nature of the body’s material and the size of the deforming force. In many materials, the distortion is not visible, yet it exists. When a body is exposed to a deforming force, it develops a restoring force. This vital force has the same magnitude as the applied force but is directed in the opposite direction. Stress is defined as the restoring force per unit area.

Types of Stress

Longitudinal Stress: Because longitude refers to the length, it is also called the restoring force per unit area when the force applied is normal to the cross-sectional area of a cylindrical body. There is a change in the length of the item. For example, when a cylindrical rubber object is attached to a heavy object, longitudinal stress acts on it, causing the object’s length to vary.

Longitudinal stress is classified into two types:

• Tensile stress: In the above example, tensile stress emerges when force is used to stretch the cylinder.

• Compressive stress: When a force is exerted to compress an item, this is referred to as compressive stress.

Shearing or Tangential Stress It is the restoring force per unit area when the applied force is parallel to the body’s cross-sectional area. There is a relative displacement between the body’s opposing faces.

Hydraulic Tension

It is the restoring force per unit area when a fluid, such as water, applies force to a body or object. If a ball made of rubber (which can be crushed) is immersed in a river or sea, the pressure of the water exerts a force on the ball from all directions. As a result, the ball contracts somewhat.

Strain and Varieties of Strain

It is a deformation measure that can indicate the displacement of particles in a body relative to a reference length. Strain is a one-dimensional quantity. When a rubber item is stretched from both sides, the length change shows the strain.

Strains are classified into the following categories:

Longitudinal Strain: The change in length from the initial length of the body caused by longitudinal stress. It is the difference in length divided by the initial length.

Shearing strain is a measurement of the relative displacement of the opposing faces of the body caused by shearing force. Tan can be used to symbolize shearing tension.

Volume strain is the ratio of the change in volume to the original volume caused by hydraulic tension. It is defined as the volume change divided by the starting or original volume.

Hooke’s Law

It takes its name from the physicist Robert Hooke. Hooke’s Law asserts that, within an elastic limit, stress created is exactly proportional to strain produced in an item (if the object is elastic material). The elasticity of an item is its ability to return to its original shape. Hooke’s law thus applies to elastic things. It is not applicable to the flexibility of solids.

As a result, it may be written as Stress = k * Strain.

In this equation, k denotes the modulus of elasticity.

Stress-Strain Relationship

The stress-strain curve is a line formed between stress and strain. In the ideal scenario of Hooke’s law, a linear graph is generated when stress and stress are plotted along the y-axis and x-axis, respectively. When real trials are drawn, however, a curve known as the stress-strain curve is created, as illustrated below.

Stress-Strain Curve: The stress-strain curve is a curve that is drawn between stress and strain. In the ideal scenario of Hooke’s law, a linear graph is generated when stress and stress are plotted along the y-axis and x-axis, respectively. When real trials are drawn, however, a curve known as the stress-strain curve is generated.

A stress-strain curve can help you comprehend a material’s tensile strength. This curve changes depending on the substance. The stress-strain curve is depicted in the diagram below.

Explanation:

OA’s curve is a straight line. It shows that strain is proportional to stress. Hooke’s law is followed till point A. Point A represents the proportional limit.

Stress is not proportional to strain after point A. It is possible to produce an AB curved section. When the burden is removed, the body returns to its previous size.

Point B is the elastic limit, often known as the yield point. The yield strength is defined as the equivalent stress to point B.

The curve exhibits plastic deformation beyond B. In this case, strain grows faster than stress.

The tensile strength of a material is shown by point D on the curve. In the zone between B and D, the length of the wire rises without any extra stress. This is referred to as the plastic zone.

Conclusion

In conclusion, I hope that this brief guide has been helpful in understanding some of the basics of mechanical properties of solids as they apply to solids. Understanding how to calculate elasticity, pressure, and normal stress will be particularly useful in solving problems involving body forces. I trust that you will find these topics useful as well. Having a thorough understanding of the mechanical properties of solids can be helpful in optimizing the load path and building good structures, but there is more to it than meets the eye. There are other factors that affect how a structure performs under load, and not all materials are equal.