Lecture 9

Question 1

indentation used to measure

Answer 1

hardness and can estimate yield strength

Question 2

indentation leads to … and how is it used to measure hardness

Answer 2

plastic yielding and size of indent used to measure hardness

Question 3

adv and disadv of hardness test

Answer 3

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

Question 4

Mohs scale how is it used to measure hardness

Answer 4

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

Question 5

issues with mohs scale

Answer 5

intervals between materials are not equal

Question 6

hardness can also be measure of

Answer 6

whether one material can scratch another

Question 7

brinell hardness indent using

Answer 7

hardened steel or tungsten carbide 10mm diameter ball

Question 8

brinell hardness applied force (P) measured in

Answer 8

kgf 1kgf = 9.8N force exerted by 1kg

Question 9

brinell hardness done by

Answer 9

pushing ball into surface leaving impression of circular indent measure two diameters of indent and take average

Question 10

brinell hardness symbol and what does D and d stand for

Answer 10

Hb in kgf mm^-2, D is diameter of indent ball d is the diameter of the indent in mm!!

Question 11

issues with brinell test

Answer 11

with high hardness material test can deform the ball

and work hardening can occur in material if you push into surface

Question 12

want indent size do we want for brinell hardness

Answer 12

d is approximatley 0.375 * D

if d is bigger than D repeat using lower load

Question 13

geometric constant for brinell test

Answer 13

P/D^2 = constant

maintain geometric similarity with different ball sizes

Question 14

standard brinell test and how to report the result

Answer 14

10 mm diameter ball 3000 kgf 15s load duration

360 HB 10/3000/15

Question 15

vickers hardness test uses what shape and why is this useful

Answer 15

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

Question 16

typical angle between opposite faces of a vickers test

Answer 16

136 degrees

Question 17

what do you measure in vickers hardness

Answer 17

the two diagonals from corner to corner and take average to give you d

Question 18

Why might you get different values each time you take a hardness test of the same material

Answer 18

different phases within material have different hardnesses may be measuring a different one each time - have to do multiple and take average

Question 19

hardness is resistance to … what does this mean for its ductility

Answer 19

plastic flow

a hard material will not be ductile - very brittle

Question 20

vickers hardness equation

Answer 20

Hv = F(or could be P)*1.854/d^2
measured in kgfmm^2
keep d in in mm!!

Question 21

what is VHN and BHN

Answer 21

vickers hardness number and brinell hardness number

Question 22

difference between hardness test and meyers hardness

Answer 22

use projected area written as Hmv for vickers and Hmb for brinell whereas brinell and vickers use actual surface area of indent

Question 23

hardness is equal to

for what type of test is this relationship reliable

Answer 23

3 * yield strength

reasonable for vickers test as long as material doesnt significantly work harden (small indent)

Question 24

what is the use of Hardness = 3* yield strength

Answer 24

can get a good estimate for yield strength without doing a tensile test

Question 25

what doe hardness = 3* yield strength proove

Answer 25

materaisl with high hardness have high yield strengths therefore are brittle

Question 26

what doe hardness = 3* yield strength proove

Answer 26

materials with high hardness have high yield strengths therefore are brittle