Exam Question

A crankshaft in a two-stroke engine is subjected to several types of stresses during normal operation. These stresses arise due to gas pressure, inertia forces, centrifugal forces, and torsional effects, and they influence the strength, durability, and fatigue life of the crankshaft.
Types of Stresses Acting on the Crankshaft
Torsional (Shear) Stresses: The turning moment produced by gas pressure acting on the piston causes torsional shear stresses in the crankpin, webs, and journals. These stresses may be further increased by torsional vibrations, particularly when the engine operates at or near resonant speeds.
Bending Stresses: The crankshaft is subjected to bending moments between the main bearing supports due to gas forces and inertia forces of the reciprocating parts. These bending moments cause alternating tensile and compressive stresses in the crankshaft as it rotates.