Thermal Stress

Stress

Stress is a physical quantity described in physics and engineering as the force per unit area experienced by a material internally as it attempts to recover its shape when an external force is applied. Though people were aware of stress in materials, the concept of stress and its measurement were mostly empirical until the 17th century. Even before then, it was used to make composite bows, glass bowing, and other items. Using capitals, arches, domes, and trusses, people have built and utilised wood beams and stone blocks to withstand and distribute stress to prevent the structure from collapsing over time.

Thanks to the work of scientists such as Galileo Galilei and Isaac Newton, Augustin-Louis Cauchy, a French physicist and mathematician, developed the first mathematical model for stress in a homogeneous medium. Newton used a differential formula to calculate the stress involved in liquids. Stress is a fundamental quantity since it is produced from a fundamental quantity like force and a geometric quantity like area. Stress will always act in the opposite direction as the deforming force is applied.

The unit of stress in SI is the pascal (Pa). The resulting stress is one pascal when one newton of force is applied to a unit surface area of one metre squared.

Types of Stress

1. Normal stress: If the direction in which the stress acts is perpendicular to the cross-sectional area of the material, it is considered to be normal stress. Longitudinal stress and bulk stress, often known as volumetric stress, are two types of normal stress.

2. Longitudinal stress: When equal and opposite forces are applied to the two separate cross-sectional areas of a cylinder, the stress that the cylinder experiences is known as longitudinal stress. The deforming force acts along the length of the body, causing the length and diameter of the body to vary slightly. Tensile stress and compressive stress are two types of longitudinal stress.

3. Tensile stress:Tensile stress occurs when the acting deforming force increases the length of the body on which it is applying.

4. Compressive stress: Compressive stress occurs when a deforming force is applied that reduces the length of the body it is acting on.

5. Bulk stress: Bulk stress, also known as volumetric stress, is a type of stress that acts across the object’s dimensions and changes its volume.

6. Shearing stress: When the direction of the applied deforming force is parallel to the area of cross-section and modifies the shape of the item it acts on, it is known as tangential stress.

Thermal Stress

Thermal stress is defined as stress generated by a change in an object’s temperature, which causes it to expand or contract.

The application of thermal stress in mechanics and thermodynamics is extensive.

These stresses may cause the object to fracture or break. As the temperature changes, the level of stress increases.

Let’s look at a thermal conductive rod as an example. It will expand as the temperature rises. The restoring force will act on the rod if it is kept at room temperature before returning it to its original position. Furthermore, if stored at a cold temperature, it will begin to contract.

Thermal stress is often used in the construction of railway tracks. The train is able to move because of the space between two railway tracks. They grow in the summer as the temperature rises, while they contract in the winter when the temperature drops. Thermal stress keeps these circumstances in check, allowing the train to stay on track.

Formula of Thermal Stress

Assume a thermal rod is subjected to thermal stress.

Let the rod be A. 

Original length of the rod = L₀

The increase in temperature of the rod = ΔT

New length of the rod = L

Hence, 

L – L₀= L₀∝ΔT 

Here,

∝= coefficient of linear expansion of the material of the rod. 

L = L₀(1+∝ΔT) 

F/A= Y(L – L₀) /L₀ 

Here,

Y is young’s modulus of a given rod

F/A=Y ∝ΔT  

Causes of Thermal Stress

Thermal Stress is a mechanical process caused by a change in an object’s internal temperature, according to the rules of thermodynamics. Any increase in temperature produces more stress in normal circumstances. However, in addition to tension, thermal shock can occur, resulting in an object’s rapid fracture or breaking.

Effects of Thermal Stress

If thermal stresses are not properly considered, they can have a considerable impact on structural strength and stability. Because of a lack of awareness of thermal stress, there is a risk of creak fractures and breaks in numerous areas of severe weakness.

The shattering of glass that occurs when it is heated to a high temperature and then dipped in cold water is one of the most common examples of thermal stress. The glass crack and fracture that occurs as a consequence of the impact are not the same as those that occur as a result of the impact.

Conclusion

Stress is the internal restorative force acting per unit area of a deformed body. These internal forces of a distorted body are always equal and opposite to the deforming forces in an equilibrium state. If the deforming force is removed, the internal restitution force restores the body’s natural shape.

Stress is the internal restorative force acting per unit area of a deformed body. These internal forces of a distorted body are always equal and opposite to the deforming forces in an equilibrium state. If the deforming force is removed, the internal restitution force restores the body’s natural shape.

Thermal stress is defined as stress generated by a change in an object’s temperature, which causes it to expand or contract.