Fracture Toughness - Help with Units
Fracture Toughness - Help with Units
(OP)
Hi,
Has anyone worked with or seen the units kg/mm^1.5 for fracture toughness before? I am trying to convert these to Mpa.sqrt(m) which is typically what we use for all our calculations.
Is anyone familiar with a conversion from kg/mm^1.5 to Mpa.sqrt(m)?
Any help would be appreciated!
Thanks,
Mike
Has anyone worked with or seen the units kg/mm^1.5 for fracture toughness before? I am trying to convert these to Mpa.sqrt(m) which is typically what we use for all our calculations.
Is anyone familiar with a conversion from kg/mm^1.5 to Mpa.sqrt(m)?
Any help would be appreciated!
Thanks,
Mike





RE: Fracture Toughness - Help with Units
RE: Fracture Toughness - Help with Units
acc in m^2/s^2.
The acceleration division is probably just by gravity. Its just application of a fixed weight to open the crack which is actually silly as there is always stress concentration (simple geometry before considering crack effects) so the applied load in the testing method is not same as that experienced at the crack tip.
RE: Fracture Toughness - Help with Units
http://books.google.com/books?id=LC4E7OjnhuEC&...
RE: Fracture Toughness - Help with Units
RE: Fracture Toughness - Help with Units
Maui
www.EngineeringMetallurgy.com
RE: Fracture Toughness - Help with Units
To convert, I get x*9.807 MPa/(kg/mm2)*(1m/1000mm)1/2, or
MPa-m1/2 = 0.3101 kg/mm1.5
Aaron Tanzer
www.lehightesting.com
RE: Fracture Toughness - Help with Units
Maui
www.EngineeringMetallurgy.com
RE: Fracture Toughness - Help with Units
Pa = N/(m^2) = [kg*m/(s^2)]/(m^2) = kg/[m*(s^2)]
So for the units of fracture toughness we have,
Pa*(m^1/2) = kg/[(m^1/2)*(s^2)]
This contains units of seconds squared in the denominator.
Maui
www.EngineeringMetallurgy.com
RE: Fracture Toughness - Help with Units
I'm confused here. Stress units such as pascals/megapascals, or psi/ksi do not contain a time component (seconds) in their denominators. Where does this come from?
Aaron Tanzer
www.lehightesting.com
RE: Fracture Toughness - Help with Units
F = ma
where m is mass and a is acceleration. So the units of force are kg*[m/(s^2)]. This is where the time component originates from.
Maui
www.EngineeringMetallurgy.com
RE: Fracture Toughness - Help with Units
Aaron Tanzer
www.lehightesting.com
RE: Fracture Toughness - Help with Units
Clearly it's a stress of kg/mm^2 (not an uncommon unit, although assumes the mass is in an unspecified gravity field, assume 1 g here on Earth). kg/mm^2 * 9.80665 is MPa (1 kg weighs 9.80665 N down here so kg/mm^2 are smaller numbers than MPa).
Stress times root(a) with a in mm is a valid stress intensity (once you've accounted for the acceleration in the conversion of kg/mm^2 to MPa). Converting the length from mm to m needs multipying the mm^0.5 by 1/1000^0.5. Total conversion is then kg/mm^2*mm^0.5 * 9.80665 / 31.623.
kg/mm^1.5 * 0.31011 = MPa.root(m). As stated above before things got unclear.
RE: Fracture Toughness - Help with Units
Maui
www.EngineeringMetallurgy.com
RE: Fracture Toughness - Help with Units
RE: Fracture Toughness - Help with Units
http://en.wikipedia.org/wiki/Mars_Climate_Orbiter
Maui
www.EngineeringMetallurgy.com