Short Answer:

Energy absorbed under impact is the amount of energy a material or body can take in when a sudden load or impact force acts on it before it breaks or deforms permanently. It shows how well a material can resist shock or impact loading. Materials that can absorb more energy under impact are considered tough, while those that absorb less energy are brittle and likely to fail easily.

In simple terms, it is the capacity of a material to take up energy during sudden loading without fracturing. This property is very important in designing machine components, tools, and structures that face impact forces in their operation, such as gears, springs, and automobile parts.

Detailed Explanation :

Energy Absorbed Under Impact

Energy absorbed under impact refers to the total amount of work done or energy taken up by a material or specimen when it is subjected to a sudden load, blow, or shock before failure. This energy represents the material’s ability to resist sudden fracture and is also known as impact energy or toughness under impact.

When an impact load is applied, the material experiences a rapid deformation within a very short time. The kinetic energy of the striking body is converted into strain energy in the material being struck. If the material is tough, it will absorb more energy before breaking; if it is brittle, it will absorb very little energy and break almost instantly.

The ability to absorb impact energy is an essential mechanical property, especially for materials used in applications like automotive components, machine tools, rail tracks, bridges, and aircraft parts. These components often face dynamic or shock loads, and hence must withstand impact without failure.

Concept of Impact Energy

When an object is suddenly struck, a large force acts on it for a very short period. The energy absorbed by the body during this process is called the impact energy. This energy depends on both the mass and velocity of the striking body and the toughness of the material being hit.

Mathematically,

or, in terms of toughness,

where,

•  = applied impact load,
•  = deformation before fracture.

In most cases, energy absorbed under impact is determined through impact testing, which measures the energy required to fracture a specimen in one blow.

Impact Testing Methods

Two common tests used to measure energy absorbed under impact are:

1. Charpy Impact Test:
   • In this test, a notched specimen is supported horizontally on both ends.
   • A swinging pendulum hammer strikes the center of the specimen opposite to the notch.
   • The difference in potential energy of the hammer before and after impact gives the energy absorbed by the specimen.
2. Izod Impact Test:
   • Here, the specimen is held vertically as a cantilever.
   • The hammer strikes the specimen at a fixed height above the notch.
   • The energy required to break the specimen is recorded as the impact energy.

Both tests help determine the toughness of materials under dynamic loading conditions. Tough materials such as mild steel show high energy absorption, while brittle materials such as cast iron or glass show very low energy absorption.

Factors Affecting Energy Absorbed Under Impact

Several factors influence the amount of energy a material can absorb under impact:

1. Material Type: Ductile materials absorb more energy due to their ability to deform plastically before breaking.
2. Temperature: Materials become brittle at low temperatures and absorb less energy.
3. Notch Effect: A notch or crack reduces the energy absorption capacity by concentrating stress at a specific point.
4. Strain Rate: The faster the load is applied, the higher the impact energy required to cause failure.
5. Size and Shape of Specimen: Larger specimens with more volume can usually absorb more energy.

Importance in Engineering Applications

Understanding the energy absorbed under impact is crucial for designing components that can survive shocks and sudden loads. For example:

• Automobile bumpers are designed to absorb high impact energy during collisions to protect passengers.
• Tools and machine parts must resist sudden blows during operation.
• Structural members in bridges or buildings are designed to absorb energy during earthquakes or accidents.

By selecting materials with higher impact toughness, engineers can improve safety and durability in various applications.

Energy Absorbed and Toughness Relationship

The toughness of a material is its ability to absorb energy up to fracture. The area under the stress-strain curve represents the energy per unit volume that a material can absorb. Hence, the greater the area under the curve, the tougher the material, and the higher the energy it can absorb under impact.

Materials like steel, copper, and aluminum alloys are known for high impact energy absorption, whereas materials like cast iron, ceramics, and glass have low impact toughness.

Conclusion

Energy absorbed under impact represents the total energy a material can take before it fractures under a sudden load. It measures the toughness and resistance of a material against shock or impact loading. This property is vital for the safe and reliable design of machine components and structures subjected to dynamic forces. The higher the energy absorbed, the tougher and more durable the material will be.