Mechanical Properties

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Mechanical Properties - PowerPoint PPT Presentation

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

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
• Flexural – applied loads “bend” the sample
Forces and Responses
• Shear – applied loads are offset
Forces and Responses
• Torsion – applied loads “twist” the sample
Mechanical Behavior
• Impact (toughness) – applied loads “hit” the sample
• Impact (charpy, dart)
Elastic Solid
• Stress-strain
• What happens when force is removed?
• Recovery

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
Measures of Viscosity
• Equation

F/A = τ = ŋ (dv/dx)

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

Dashpot

Permanent Deformation (sandpaper)

Spring

Mechanical Model of Plastic Behavior
Time Dependence of Plastics

Increasing shear rate

Stress

Strain

Reinforcements
• Increase mechanical properties
• Generally fibers
• Composites
Fillers
• Reduce cost
• Can potentially decrease mechanical properties
• Can improve
• UV stability
• Thermal stability
• Wear resistance
• Electrical conductivity
• Flame resistance
• CTE
Toughness Modifiers
• Increase impact strength
• Increases the potential for movement within the plastic on impact (creep)
• Example – ABS