All modern medium and slow speed diesel engines have components assembled via bolts that are tensioned hydraulically, both for removal and reassembly. When using such hydraulic devices, to what metallurgical state are you subjecting such bolts?
• Elastic limit vs plastic deformation in metals under tensile load • Purpose of hydraulic tensioning of large engine bolts (e.g., repeatability and clamping force) • Relationship between working stress in a bolt and its long-term fatigue life
• Think about what engineers want the bolt to do after the hydraulic pressure is released: should it spring back fully, or stay permanently stretched? • If a bolt is taken beyond its elastic limit during service tightening, what happens to its dimensions the next time you measure and reuse it? • For critical engine components (like cylinder head or main bearing bolts), what kind of stress region on a stress-strain curve is usually targeted for safe, repeatable operation?
• Review the definition of elastic limit and what happens to metal loaded above vs below this point • Consider the goals of hydraulic tensioning: uniform preload, reusability of bolts, and avoidance of permanent deformation • Ask whether a bolt that regularly works at or beyond its elastic limit would be acceptable in terms of fatigue life and safety on a main engine
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