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Mechanical Properties

Mechanical Properties. MFG 355. Forces and Responses. Tensile – applied loads “pull” the sample. Tensile Forces. Gripping Zone. Gripping Zone. Failure Zone. ¾ inch. ½ inch. 8 ½ inches. Forces and Responses. Compression – applied loads “squeeze” the sample. Forces and Responses.

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Mechanical Properties

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  1. Mechanical Properties MFG 355

  2. Forces and Responses • Tensile – applied loads “pull” the sample

  3. Tensile Forces Gripping Zone Gripping Zone Failure Zone ¾ inch ½ inch 8 ½ inches

  4. Forces and Responses • Compression – applied loads “squeeze” the sample

  5. Forces and Responses • Flexural – applied loads “bend” the sample

  6. Forces and Responses • Shear – applied loads are offset

  7. Forces and Responses • Torsion – applied loads “twist” the sample

  8. Mechanical Behavior • Impact (toughness) – applied loads “hit” the sample • Impact (charpy, dart)

  9. Mechanical Behavior • Creep

  10. Elastic Solid • Stress-strain • What happens when force is removed? • Recovery

  11. F/A = ŋ dv/dx = ŋγ Shear Thickening Shear Thinning Newtonian Viscous liquid • Tensile forces? – cannot exist (like pulling water) • Shear forces • What happens when force stops? • Viscous flow • Newtonian and non-Newtonian

  12. Measures of Viscosity • Equation F/A = τ = ŋ (dv/dx) • Viscometer

  13. Viscoelasticity • Time/temperature dependant • Plastic stress-strain • a) start point • b) proportional limit • c) yield • d) recovery • e) ultimate failure

  14. Dashpot Permanent Deformation (sandpaper) Spring Mechanical Model of Plastic Behavior

  15. Intermolecular relationship Intermolecular relationship Interpretation of Plastic Behavior

  16. Time Dependence of Plastics Increasing shear rate Stress Strain

  17. Reinforcements • Increase mechanical properties • Generally fibers • Composites

  18. Fillers • Reduce cost • Can potentially decrease mechanical properties • Can improve • UV stability • Thermal stability • Wear resistance • Electrical conductivity • Flame resistance • CTE

  19. Toughness Modifiers • Increase impact strength • Increases the potential for movement within the plastic on impact (creep) • Example – ABS

  20. Thank You

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