Lecture 9 Flashcards
indentation used to measure
hardness and can estimate yield strength
indentation leads to … and how is it used to measure hardness
plastic yielding and size of indent used to measure hardness
adv and disadv of hardness test
simple and inexpensive to run, not destroying the material but are indenting which acts like a crack forms stress concentration and can be a weakness
Mohs scale how is it used to measure hardness
10 materials compares hardness
diamond = 10 diamond can scratch everything on scale
talc = 1 can not scratch anything
see if material can be scratched by one of the materials if i can its lower than that material on mohs scale
if not its higher
indication of how hard
issues with mohs scale
intervals between materials are not equal
hardness can also be measure of
whether one material can scratch another
brinell hardness indent using
hardened steel or tungsten carbide 10mm diameter ball
brinell hardness applied force (P) measured in
kgf 1kgf = 9.8N force exerted by 1kg
brinell hardness done by
pushing ball into surface leaving impression of circular indent measure two diameters of indent and take average
brinell hardness symbol and what does D and d stand for
Hb in kgf mm^-2, D is diameter of indent ball d is the diameter of the indent in mm!!
issues with brinell test
with high hardness material test can deform the ball
and work hardening can occur in material if you push into surface
want indent size do we want for brinell hardness
d is approximatley 0.375 * D
if d is bigger than D repeat using lower load
geometric constant for brinell test
P/D^2 = constant
maintain geometric similarity with different ball sizes
standard brinell test and how to report the result
10 mm diameter ball 3000 kgf 15s load duration
360 HB 10/3000/15
vickers hardness test uses what shape and why is this useful
pyramid diamond indenter - allows use diamond (which would be hard to form into a ball) very hard material to tests allows testing of very hard material
typical angle between opposite faces of a vickers test
136 degrees
what do you measure in vickers hardness
the two diagonals from corner to corner and take average to give you d
Why might you get different values each time you take a hardness test of the same material
different phases within material have different hardnesses may be measuring a different one each time - have to do multiple and take average
hardness is resistance to … what does this mean for its ductility
plastic flow
a hard material will not be ductile - very brittle
vickers hardness equation
Hv = F(or could be P)*1.854/d^2
measured in kgfmm^2
keep d in in mm!!
what is VHN and BHN
vickers hardness number and brinell hardness number
difference between hardness test and meyers hardness
use projected area written as Hmv for vickers and Hmb for brinell whereas brinell and vickers use actual surface area of indent
hardness is equal to
for what type of test is this relationship reliable
3 * yield strength
reasonable for vickers test as long as material doesnt significantly work harden (small indent)
what is the use of Hardness = 3* yield strength
can get a good estimate for yield strength without doing a tensile test
what doe hardness = 3* yield strength proove
materaisl with high hardness have high yield strengths therefore are brittle
what doe hardness = 3* yield strength proove
materials with high hardness have high yield strengths therefore are brittle
