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Stress is the force per unit area applied on a material, which can result in deformation or a change in shape. There are two types of stress: tensile stress and compressive stress.
- Compressive stress is a type of stress that occurs when a material is being compressed or squeezed together.
- Tensile stress occurs when a material is being pulled apart, and it results in the material becoming longer or stretched out.
Both compressive stress and tensile stress can cause materials to deform, and the extent of deformation depends on the magnitude of the stress applied and the properties of the material stressed. If the stress exceeds the material's strength, it can lead to failure, such as cracking or breaking.
| Table of Content |
Key Terms: Compressive Stress, Tensile Stress, Material’s Strength, Cracking, Elasticity, Pascal
Read More: Stress Formula
What is Compressive Stress?
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Compressive stress is a type of stress that occurs when a material is being compressed or squeezed together. It results in the material becoming shorter or more compact. The magnitude of compressive stress is calculated as the ratio of the applied force to the area of the material that is being compressed.
- Compressive stress is a common type of stress experienced by materials such as concrete, rocks, and metals when subjected to forces that attempt to squeeze them together.
- In construction and engineering, compressive stress is an important consideration when designing structures and materials that are intended to withstand weight, pressure, or other types of force.
- If the magnitude of compressive stress is too great, it can lead to deformation or failure of the material.
- The extent of deformation or failure depends on the properties of the material is stressed, including its strength, elasticity, and other factors.
- In some cases, compressive stress can be beneficial, such as when it is used to compact soil or strengthen concrete.
However, it can also be a source of concern when it is applied to structures or materials that are not designed to withstand it.
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|---|---|---|
| Tensile Stress | Thermal Stress | Yield Strength |
| Young's Modulus | Stress and Strain | Strain Energy |
Unit of Compressive Stress
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The unit of compressive stress is the same as that of stress, which is force per unit area. In the SI system, the unit of compressive stress is the pascal (Pa), which is equivalent to one newton per square meter (N/m2). Other common units of compressive stress include pounds per square inch (psi) and kilopascals (kPa).
For example, if a force of 1000 Newtons is applied on an area of 1 square meter, the compressive stress would be 1000 Pa (1000 N/m2). Similarly, if a force of 5000 pounds is applied on an area of 10 square inches, the compressive stress would be 500 psi (5000 lb/in2). The unit of compressive stress is important for measuring and comparing the strength and durability of different materials under compressive forces, such as in construction and engineering applications.
Dimensions of Compressive Stress
The dimension of compressive stress depends on the system of units being used to express the force and area. In the SI (International System of Units), the unit of force is Newtons (N) and the unit of area is square meters (m2). Therefore, the dimension of compressive stress in SI units is Newtons per square meter (N/m2) or Pascals (Pa).
In the English system of units, the unit of force is pounds (lb) and the unit of area is square inches (in2). Therefore, the dimension of compressive stress in the English system of units is pounds per square inch (psi).
In general, the dimension of compressive stress can be expressed as:
Dimension of compressive stress = [M][L]-1[T]-2
- Where [M] represents the unit of mass,
- [L] represents the unit of length, and
- [T] represents the unit of time.
Compressive Stress Formula
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The formula for calculating compressive stress is:
Compressive stress = Force / Area
Where:
- Force is the external force applied to the material
- Area is the cross-sectional area of the material that is being compressed.
- The unit of compressive stress is typically expressed in Pascals (Pa) or pounds per square inch (psi).
For example, if a 10,000 Newton force is applied to a cylindrical steel rod with a cross-sectional area of 0.01 square meters, the compressive stress can be calculated as follows:
Compressive stress = Force / Area
Compressive stress = 10,000 N / 0.01 m2
Compressive stress = 1,000,000 Pa or 145 psi
Therefore, the compressive stress on the steel rod is 1,000,000 Pa or 145 psi.
Compressive Stress Examples
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Compressive stress is a common type of stress experienced by materials in many different contexts. Here are a few examples:
- Building and construction: Compressive stress is an important consideration when designing and constructing buildings, bridges, and other structures. The weight of the structure and any loads it carries can create compressive stress on the materials used in its construction, such as concrete, stone, and steel.
- Geology: Compressive stress is a significant factor in the formation of rocks and the deformation of the earth's crust. When tectonic plates collide, they can create compressive stress that leads to the formation of mountains and other geological features.
- Manufacturing: Many manufacturing processes involve the application of compressive stress to materials to change their shape or properties. For example, forging and extrusion involve applying compressive stress to metal to shape it into a desired form.
- Soil mechanics: The weight of soil and other materials can create compressive stress on the ground beneath them, leading to deformation or settling. This can be an important consideration in civil engineering projects such as building foundations or roads.
- Packaging: Compressive stress can be a concern in packaging and shipping, as goods can be subjected to pressure and crushing forces during transport. Packaging materials such as foam or air-filled cushions can be used to protect items from compressive stress.
What is Compressive Strength?
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Compressive strength is the maximum compressive stress that a material can withstand before it fails or breaks. It is a measure of a material's ability to resist compressive forces and is an important property in materials science, engineering, and construction.
- Compressive strength is typically measured by subjecting a specimen of the material to a compressive force until it fails or fractures.
- The compressive strength is then calculated by dividing the maximum load applied to the specimen by its cross-sectional area.
- The compressive strength of a material is affected by many factors, including its composition, microstructure, porosity, and manufacturing process.
- Different materials have different compressive strengths, with some materials, such as concrete and rock, having very high compressive strength, while others, such as plastics and foam, have relatively low compressive strength.
Compressive strength is an important consideration in many applications, such as building and construction, where materials must be able to withstand the compressive forces of their own weight and any loads they carry. It is also an important factor in manufacturing processes that involve compressive stress, such as forging, stamping, and extrusion.
Also Read:
| Related Articles | ||
|---|---|---|
| Hooke's Law | Bulk Modulus | Derivation Relation Between Elastic Constants |
| Shear Modulus Formula | Shear Modulus | Bulk Modulus Formula |
Difference between Tensile Stress and Compressive Stress
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The differences between tensile stress and compressive stress are highlighted as below:
| Tensile Stress | Compressive Stress |
|---|---|
| Tensile stress tends to stretch or pull a material | Compressive Stress tends to compress or push a material |
| Positive sign | Negative sign |
| It shows linear deformation | It shows nonlinear deformation |
| It is concerned in applications such as cables, ropes, and bridges | It is concerned in applications such as building and construction |
| Tensile stress is caused by a force applied in the direction of the material's longitudinal axis | Tensile stress is caused by a force applied perpendicular to the longitudinal axis |
Things to Remember
- Compressive stress is a type of stress that occurs when a material is subjected to a compressive or squeezing force.
- Compressive stress is denoted by a negative sign, indicating that the stress tends to shorten or compress the material.
- The formula for compressive stress is force divided by the cross-sectional area of the material being compressed.
- Compressive stress can cause a material to buckle or deform in a nonlinear manner, depending on the material's properties and the magnitude of the compressive force.
- Examples of compressive stress include the weight of a building or bridge pushing down on its foundation, or the force of a hydraulic press compressing a piece of metal.
- The compressive strength of a material is the maximum amount of compressive stress it can withstand before it fails and is an important property in engineering and construction applications.
Sample Questions
Ques. Where does compressive stress occur? (3 marks)
Ans. Compressive stress can occur in any material that is subjected to a squeezing or compressive force. In engineering and construction, compressive stress commonly occurs in building and structural components such as columns, beams, and foundations that are subjected to the weight of the structure above them. Compressive stress can also occur in materials such as rocks and soil, when they are subjected to forces such as the weight of overlying material or external loads. In manufacturing, compressive stress is used in processes such as forging and extrusion to shape and deform materials by applying compressive forces.
Ques. Why is compressive stress important? (3 marks)
Ans. Compressive stress is important for the following reasons:
It is a fundamental concept in engineering and construction, as many structures and components are designed to withstand compressive forces. Understanding the properties of materials under compressive stress is crucial for ensuring the safety and reliability of buildings, bridges, and other structures.
Compressive stress is also important in manufacturing and materials processing, where it is used to shape and deform materials. Processes such as forging, rolling, and extrusion rely on compressive stress to shape metals and other materials into desired shapes and sizes.
The compressive strength of a material is an important property for engineers and materials scientists, as it indicates the maximum amount of compressive stress a material can withstand before it fails. Knowing the compressive strength of a material is essential for designing structures and components that will not fail under compressive loads.
Ques. What are the properties of compressive strength? (5 marks)
Ans. Compressive strength is a fundamental property of materials that describes the maximum amount of compressive stress a material can withstand before it fails or fractures. Some of the important properties of compressive strength include:
Compressive strength is a measure of a material's resistance to compression, and is typically measured in units of force per unit area, such as pounds per square inch (psi) or megapascals (MPa).
The compressive strength of a material is influenced by many factors, including the composition, structure, and grain size of the material, as well as the rate and direction of the compressive force.
Compressive strength is anisotropic, meaning it can vary depending on the orientation of the material relative to the direction of the compressive force.
In general, brittle materials such as ceramics and concrete have higher compressive strength but lower tensile strength than ductile materials such as metals and polymers.
The compressive strength of a material can be affected by environmental factors such as temperature and humidity, as well as by the presence of defects such as cracks and voids.
Ques. What is the nature of the restoring force? (5 marks)
Ans. The nature of the restoring force depends on the type of system being considered. In general, a restoring force is a force that acts to bring a system back to its equilibrium position when it is displaced from that position.
In a simple harmonic oscillator, such as a mass-spring system, the restoring force is proportional to the displacement of the mass from its equilibrium position and acts in the opposite direction to the displacement. The restoring force in this case is provided by the spring, which stretches or compresses as the mass is displaced.
In a pendulum, the restoring force is provided by gravity and acts to pull the pendulum back towards its equilibrium position. The restoring force in this case is proportional to the angle of displacement from the vertical.
In more complex systems, such as those involving friction or other dissipative forces, the nature of the restoring force may be more complicated. However, the basic idea remains the same: a restoring force acts to bring a system back to its equilibrium position when it is displaced from that position.
Ques. What does tangential stress do to an object? (3 marks)
Ans. Tangential stress, also known as shear stress, can cause deformation and failure in an object by causing it to shear or slide along a plane parallel to the direction of the applied force.
Tangential stress is caused by a force that is applied parallel to the surface of an object, which creates a shearing or sliding force along that surface. This can cause the object to bend, twist, or shear, depending on its geometry and the nature of the applied force.
If the tangential stress exceeds the strength of the material, it can lead to permanent deformation or failure, such as cracking or fracturing. In some cases, shear stress can cause materials to fail even when the applied force is relatively small, such as in the case of a thin sheet of metal being cut with a pair of scissors.
However, shear stress can also be beneficial in some cases, such as in the case of cutting tools, where the shear force is used to remove material from a workpiece in a controlled manner.
Ques. What are the different types of stress? (5 marks)
Ans. There are several different types of stress that can act on an object or material. The main types of stress include:
Tensile stress: This is a stress that stretches or elongates an object in the direction of the applied force. Tensile stress is common in materials like ropes, cables, and springs.
Compressive stress: This is a stress that compresses or shortens an object in the direction of the applied force. Compressive stress is common in materials like concrete, bricks, and columns.
Shear stress: This is a stress that causes one part of an object to slide or shear relative to another part. Shear stress is common in materials like scissors, blades, and cutting tools.
Torsional stress: This is a stress that causes an object to twist or rotate around an axis. Torsional stress is common in materials like shafts, gears, and turbine blades.
Bending stress: This is a stress that causes an object to bend or flex in response to an applied force. Bending stress is common in materials like beams, bridges, and cantilevers.
Each type of stress can cause different types of deformation and failure in an object, depending on the strength and properties of the material. Understanding the different types of stress is important in designing and analyzing structures and materials to ensure they can withstand the stresses they will experience in use.
Ques. What are the types of tests that are used to test compressive stress? (5 marks)
Ans. There are several types of tests that can be used to measure the compressive strength of a material or structure. Some of the most common tests include:
Compression test: This is a test where a sample of the material is subjected to an axial compressive force until it fails. The load and displacement are measured during the test, and the compressive strength is calculated from the maximum load and the cross-sectional area of the sample.
Shear test: This is a test where a sample of the material is subjected to a shear force until it fails. The load and displacement are measured during the test, and the shear strength is calculated from the maximum load and the cross-sectional area of the sample.
Flexural test: This is a test where a sample of the material is subjected to a bending force until it fails. The load and displacement are measured during the test, and the flexural strength is calculated from the maximum load and the dimensions of the sample.
Torsion test: This is a test where a sample of the material is subjected to a twisting force until it fails. The torque and rotation angle are measured during the test, and the torsional strength is calculated from the maximum torque and the dimensions of the sample.
Crush test: This is a test where a sample of the material is compressed between two plates until it fails. The load and displacement are measured during the test, and the crush strength is calculated from the maximum load and the dimensions of the sample.
These tests can be used to determine the compressive strength of materials like concrete, rock, ceramics, and metals, and can be used to evaluate the performance of structures like columns, beams, and walls.
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