First of all, Connecting rod bolts are not given a uniform crosssection from bottom to top TO PREVENT STRESS CONCENTRATION, and FRETTING. shank of the bolt is less in diameter at the botttom core by a marginal 10% which reduces stress concentrations in the bolt, and increases EXTENSIBLITY. note the term extensiblity used here. it accounts for elongation of the bolt wen needed, and thus increases fatigue strenght. it inturn reduces the area in direct contact with the bolt, reducing fretting.
The main design feautures of the bolt are:
- High UTS alloy steel having higher fatigue strength.
- Long thin elastic bolts for higher percentage of elongation and fatigue strength.
- High degree of surface finish bolts is used to reduce stress concentration.
- Bolts are free with very little fitted portion, to reduce stress concentration.
- Shank of bolts is less in diameter than the core diameter at the bottom of the thread by 10 %, which increases extensibility.
- Well-formed fillet at place of change of section and between the shank and bolt head to prevent stress concentration.
- Bolt has smooth change of section.
- Bolt stiffness is less than component stiffness.
- Rolled thread and three or four additional thread and gradual transition.
- Dowel pins are fitted to reduce shear load on bolts and bolts are provided with interlocking arrangements
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