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  • Every the machine has is in operation as like lever or screw or like a complex machine like aircraft piston engine, the hydraulically operated landing gear of aircraft, all those machines their parts and piece experience stress.
  •  There a lot of external forces are applying on any object like a weight pushing on the end of the lever and the reaction occurs into an object like stress, in SI the stress is measured in pound per square foot or psi pound square inch, there are forces is acting on the object and causing stress to manifest itself if in one of five forms, those five forms are tension, compression, torsion, bending, shear.

 Tension :

  • Is defined as a force able to pull an object apart, for example, the block and tackle system , the upper of the block that house two fixed pulleys were secured to an overhead beam, and the movable lower block and it’s two pulleys were hanging by ropes and also the weight is hanging below the entire assembly, so the weight being lifted would make ropes and blocks under the force of tension.

Compression :

  •  These forces try to crush an object, for example when a sheet metal airplane is assembled using the fastener is called rivet , this rivet passes through the hole drilled in a piece of aluminum and rivet gun on one side and bucking bar on the other apply a force and this applied forces tries to crush the rivet and makes it expand to filling the hole and securing hold the aluminum piece with each other.

Torsion :

  • Is defined as stress an object experiences when it is twisted, that happen when torque is applied to a shaft, and this force is made up of two other stresses is tension and compression exactly when a shaft is twisted, the tension creates a diagonal to the shaft and compression acts 90° to the tension of this force, for example, the turbine the shaft on a turbofan engine that is connected to the compressor in order to drive it is under the force of torsion.

Bending :

  • On aircraft this force is applied on the wing as aerodynamic lift tries to raise the wing and this force causes the skin on the top of the wing to compress and the skin on the bottom of the wing is under torsion, and when the aircraft on the ground the force of gravity is trying to bend the wing downward.

Shear :

  •  During the time to applying this force an object, the force rues to slice through as an knife cutting through butter, for example, the clevis bolt that is used to secure a cable to a part of the airframe and there is an act of stress on it.

 Strain :

  • This force is causing the object to damage it’s shaped to become distorted, one characteristic of matter is that it tends to be elastic, is called strained when any object becomes distorted by applying this force on it.

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