Stress is defined as “The restoring force per unit area of the material”. Stress is neither scalar nor a vector quantity; rather, it is a tensor quantity.
Stress is symbolised by σ, and Pascal or N/m2 is the measuring unit.
Mathematically, stress can be expressed as –
σ = F/A
Where,
- F denotes the restoring force in Newton,
- A represents the area of cross-section m2.
- σ denoted the stress measured in N/m2 or Pa.
Normal Stress
When the direction of the distorting force is perpendicular to the cross-sectional area of the body, then such type of stress is known as Normal Stress. The stress will be normal if the length of the wire or the volume of the body changes.
Longitudinal Stress:
To understand longitudinal stress, let us take an example of a cylindrical rod. When two equal and opposite forces are applied to the cross-sectional areas of the cylindrical rod, then the stress experienced by the cylindrical rod is termed longitudinal stress.
Longitudinal Stress can be additionally classified into two types based on the direction of distorting force because it either stretches the object or compresses the object along its length.
- Tensile Stress: If the object’s length increases on applying distorting force or applied force, then this resulting stress is named tensile stress. For instance: Apply equal and opposite outward force on a bar or wire at both ends.
- Compressive Stress: If the object’s length decreases on applying distorting force or applied force, then this resulting stress is named compressive stress.
Volume Stress or Bulk Stress
When the volume of an object changes after applying a distorting force that acts from all dimensions, then such stress is called Bulk Stress or Volumetric Stress. In brief, volumetric stress is a distorting force that changes the volume of a body when applied to it.
Tangential Stress or Shearing Stress
The stress experienced by an object when the direction of the external force or distorting force is parallel to its cross-sectional area is termed as tangential stress or shearing stress; the shape of the body changes when tangential stress is applied to it.
Important Questions on Stress
1) In an elastic deformation region, the slope or gradient of the stress-strain curve is known as ________.
a) Plastic modulus
b) Section modulus
c) Poisson’s ratio
d) Elastic Modulus
Correct Option: (d)
Explanation: The slope on the curve of the stress-strain graph will be termed as the elastic modulus because it is the ratio of stress and strain.
2) What is the stress-strain curve?
a) The difference between stress and strain
b) The relationship between stress and strain
c) The percentage of stress and stain
d) None of these
Correct Option: (b)
Explanation: The stress-strain curve represents the change in stress with the change in strain; therefore, on a graph, the relationship between stress and strain is known as stress-strain curve.
3) After the proportionality limit, which point occurs on the stress-strain curve?
a) Elastic limit
b) Plastic limit
c) Upper yield point
d) Ultimate point
Correct Option: (a)
Explanation: Up to the proportionality limit, the curve will be stress-strain proportional. And the elastic limit will occur after this limit.
4) Which among the following is the correct unit for stress?
a) Nm
b) Nm3
c) N/m2
d) N2m
Correct Option: (c)
Explanation: Stress is nothing but the force upon a unit area. Therefore, the dimension of force divided by that area is the unit for stress which is N/m2. The dimension for force is N, and the dimension of the area is m2.
5) Which of the following relations is stated in Hooke’s law?
a) Stress and strain are proportional to each other
b) Stress and strain are inversely proportional to each other
c) Square of strain is directly proportional to stress
d) Square of strain is inversely proportional to stress
Correct Option: (a)
Explanation: Hooke’s law states that the stress and strain are directly proportional to each other, and their ratio is denoted by Y, which is termed as Young’s Modulus of elasticity.
6) Stress is like pressure which is always perpendicular to a plane. Is it true or false?
a) True
b) False
Correct Option: (b)
Explanation: Pressure is always perpendicular to a unit area, but stress can be parallel or perpendicular to the plane; that’s why it is of two types is shear stress and normal stress.
7) Strain can be negative. Is it true or false?
a) True
b) False
Correct Option: (a)
Explanation: Strain can be negative because there can be situations when volume or length decreases when an object is compressed. Since the change in length or volume divided by initial length or volume, respectively, is termed as strain.
8) What do you mean by Normal stress?
When the direction of the distorting force is perpendicular to the cross-sectional area of the body, then such type of stress is known as Normal stress. The stress will be at normal if the length of the wire or the volume of the body changes.
9) What is Tangential Stress or Shearing Stress?
The stress experienced by an object when the direction of the external force or distorting force is parallel to its cross-sectional area is termed tangential stress or shearing stress; the shape of the body changes when tangential stress is applied to it.
10) Define tensile stress
If the length of an object increases on applying distorting force, this resulting stress is called tensile stress. For instance: Apply equal and opposite outward force on a bar or wire at both ends.
Practice Questions
1) Define stress and strain.
2) What is normal stress?
3) What is young’s modulus of elasticity?
4) What is volumetric stress?
5) What is Hooke’s law?
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