Materials in Mechanical, Electrical and Manufacturing Applications
Materials in Mechanical, Electrical and Manufacturing Applications tests selection under fatigue, wear, creep and electrical duty, together with the process constraints that come with the chosen material.
Mechanical duty
Shafts and gears are fatigue-limited, so surface condition, notch geometry and residual stress dominate life. Case-carburised gears (16MnCr5/8620) give 58-62 HRC at the flank with a tough core; through-hardened bearing steel 100Cr6 runs near 60 HRC, with inclusion cleanliness controlling rolling-contact life. Springs rely on shot peening to place the surface in compression. Creep sets the high-temperature limits: carbon steel is unsuitable above roughly 400 C, where 9Cr steels or austenitics take over. Variable-amplitude design uses Goodman or Gerber mean-stress corrections with Miner's rule.
Electrical and electronic duty
Copper is the conductivity reference at 100% IACS (58 MS/m); electrical-grade aluminium is about 61% IACS and needs roughly 1.6 times the cross-section. Joints are the weak point: silver or tin plating, correct torque and suitable contact materials (Cu-W for arcing, Ag-SnO2 replacing Ag-CdO under RoHS) limit temperature rise. Insulation is temperature-classed - Class B 130 C, F 155 C, H 180 C - and XLPE cable must be protected from partial discharge and water treeing. In electronics, thermal-cycling fatigue of solder joints is driven by CTE mismatch; SAC305 is less compliant than the SnPb it replaced, which changed pad and joint design.
Manufacturing constraints
Casting needs shrinkage allowance, risers and a porosity acceptance standard; forging aligns grain flow with stress; fits use ISO 286 (H7/h6) and general tolerances ISO 2768 only for non-functional dimensions. Weldability is judged by carbon equivalent, approximately CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15.
Worked example
Steel: C 0.18, Mn 1.40, Cr 0.05, Mo 0.02, V 0.01, Ni 0.05, Cu 0.10. Then CE = 0.18 + 0.233 + 0.016 + 0.010 = 0.439. That exceeds a typical 0.40 threshold, so preheat and controlled heat input are required, post-weld heat treatment is considered for thick sections, and hydrogen-controlled consumables with clean, dry electrodes are mandatory.
Traps
Choosing the hardest material for wear and losing toughness; designing statically for a fatigue duty; ignoring CTE mismatch in a thermal cycle; using ISO 2768 for a bearing fit; assuming weld metal matches parent strength; ignoring stress relaxation in a preloaded bolted joint.