Strength of printed parts

[last updated: 2019-01-30]
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measuring part strength
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• Strength of parts can be categorized in several ways, depending on how force is applied to the part:
• Tensile:
  • This is 'pulling', or stretching the part.
  • Tensile strength is quoted in the web at ~ 30 MPa for ABS and ~ 55 MPa for PLA
  • Tensile strength is usually measured by plotting a stress-strain curve:
  • Stress is the force applied, and strain is the deformation (as ratio of change in length/total length)
  • The highest point on the stress-strain curve is the UTS (ultimate tensile strength).
  • Measured tensile strength does not depend on size of the part being tested
  • Units of measurement (international system) is MPa, or mega pascal, a unit of force/area.
  1 pascal is 98.0665 g/cm2
• Compression:
  This is 'squeezing' the part
• Torsional:
  This is 'twisting' the part.
• Bending:
  This is like you'd do to break a stick in your hands, bending both ends down. This mode is affected by both tensile and compressive strength of the part, because one side of the part is in tension (the 'top' of the part as you bend it), and the other side is in compression (the 'bottom' of the part as it is bent).
• Stiffness/flexibility:
• Another property relevant to actual use of printed parts is how stiff/flexible they are. That is, how much do they deform under applied stress.
• This property is quantified as 'elastic modulus' or "Young's modulus" (tensile elasticity)
• Values reported in web:
  ~ 180 MPa for ABS and ~ 3400 MPa for PLA
• See also: (link to:) wikipedia
• Heat tolerance:
• There surely is a proper term for this, just don't know what it is at this time...
• This refers to the tendency of a part to deform under stress as it is heated.
• Basically stiffness/flexibility as above, but at elevated temperature.

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• Strength of parts varies due to a lot of factors:
• testing conditions, specifically direction of applied force, ie. perpendicular or parallel to plane of printed layers
• composition of filament:
• PLA vs. PET vs. ABS vs. ...
• printing parameters:
• layer height
• nozzle orifice diameter
• nozzle/extruder temperature
• infill percentage and pattern

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• Strength of parts can be measured:
  Lots of stuff on the web related to strength of printed parts. Some notable sites:
• (link to:) Hackaday project measuring 'stiffness', ie. resistance to bending under force
• (link to:) Well-done study at Michigan Technological Univ.
In the end, however, I decided to set up a test of my own. Here is my project to measure part strength:

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• Strength of parts can be increased with Heat Treating:

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