A connecting rod is a key component in an engine that connects the piston to the crankshaft. Its small end is connected to the piston pin, and its big end is connected to the crankpin on the crankshaft. The connecting rod transmits the force acting on the piston to the crankshaft and converts the piston’s reciprocating linear motion into the rotational motion of the crankshaft.
During operation, the connecting rod is subjected to compressive, tensile, bending, and impact alternating loads. Therefore, it must meet high requirements for strength, stiffness, and fatigue life. Connecting rods are typically made from medium carbon steel (such as 45# steel), alloy steel (such as 40Cr), or quenched and tempered steels (such as 40MnB and 40MnVB). They are formed by die forging or roll forging, followed by machining and heat treatment. The shank is usually made with an I-beam cross-section to reduce weight while maintaining sufficient strength and stiffness. To further improve fatigue strength, shot peening is often applied to the surface.
Structurally, the small end, shank, and big end form an integrated load-bearing body. The small end carries the alternating load from the piston pin, the big end carries the rotational and impact loads from the crankpin, and the shank bears tensile, compressive, and bending stresses. Therefore, material selection, forging quality, heat treatment, and surface strengthening all directly affect the service life of the connecting rod and the reliability of the engine.