Definition: A pulling force that acts to elongate a material, stretching it in the direction of the force.
Imagine: Pulling a rope to extend it.
(ii) Shear Stress:
Definition: A force that tends to slide or deform one part of a material relative to another along a parallel plane.
Imagine: Sliding two bricks against each other, causing them to deform and potentially tear.
(iii) Compressive Stress:
Definition: A pushing force that squeezes or compresses a material, shortening its length in the direction of the force.
Imagine: Stacking heavy weights on top of a block, pushing it downwards and potentially crushing it.
(b) Components Experiencing Different Stresses in a Diesel Engine:
Tensile Stress:
Connecting rod: The pull of the piston on the connecting rod creates tensile stress throughout its length.
Cylinder head bolts: The pressure generated during combustion pushes outwards on the cylinder head, requiring the bolts to resist this tensile force.
Shear Stress:
Crankshaft bearings: The connecting rod rotates on the crankshaft bearing, creating frictional shear stress between the two surfaces.
Gear teeth: When gears mesh, their teeth slide against each other, generating shear stress at the contact points.
Compressive Stress:
Piston: The combustion pressure pushes down on the piston, creating compressive stress throughout its crown.
Cylinder walls: The pressure inside the cylinder also pushes outwards on the cylinder walls, subjecting them to compressive stress.
c) Component with Maximum Cyclic Stress in a 4-Stroke Diesel Engine:
The component in a 4-stroke diesel engine with a maximum recommended service life due to constant cyclic stress is the piston and its rings. These components experience repeated cycles of high pressure during combustion, followed by release of pressure during exhaust and intake strokes. This constant cycling, along with high temperatures and friction, contributes to wear and tear, necessitating a recommended service life for their replacement.
