Lab 1. Hardness Test Flashcards
Hardness is..
resistance of a material to localized plastic deformation, usually by indentation
resistance to scratching, abrasion or cutting.
hardness is the ability of a material
to resist plastic deformation under load
the greater the hardness of a material…. the greater its….
resistance to deformation
does hardness have units?
no units
why is hardness the most common test on materials?
it is simple, inexpensive. gives prediction of wear properties
gives us an idea about machinablity…. more hard harder to machine..
it is nondestructive simple test….
give idea about mechanical properties….. it can help predict tensile strength of metals
the higher the material’s hardness
the better its wear properties
hard materials can be inserted in mechanisms at
points of stress to improve the life of the parts
hardness gives the ideas about _____…
machinablity
generally there is an inverse proportion between
hardness and machinability
hardness can be measured 3 ways.
scratching
indenting
free fall of a diamond tip hammer on sample… measuring the bounce
scratch hardness
mohs scale
hardness measurments can be classified as ____ and ___ tests according to the forces applied and the displacements obtained
macrohardness and microhardness
macro hardness test (Rockwell, Brinell, Macro-Vickers)
are the most widely used methods for rapid routine hardness measurements. The indenting forces in macro-hardness tests are in the range of 5 to 3000kgf.
Micro-hardness test (micro-vickers, knoop)
is applicable when hardness ofcoatings, surface hardness, or hardness of differentphasesin the multi-phase material is measured. Small diamond pyramid is used as indenter loaded with a small force of 10 to 1000gf.
macrohardness
quick simple methods of obtaining mechanical property data for bulk material from a small sample
macrohardness test requile application of loads above
1kgf
commmon tests macrohardness include
rockwell and brinell hardness test
macrohardness is not effective for determining
coat and surface hardness properties
Brinell
10mm sphere of steel or tunsten carbide
vickers
diamond pyramid
rockwell ABC
diamond cone
Rockwell BFG
1/16in diameter steel sphere
test used in lab?
rockwell B. 1/16 inch ball… 100 kg
the following sample characteristics should be considered when selecting the hardness testing method to use
sample size cylindrical samples sample thickness scales Gage R&R
describe brinell testing
large area and deep penetration..
harden steel or carbide ball. usually 10 mm diamameter… surface condition not critical
microstructure heterogenous
best for achieving the bulk or macro-hardness of a material, particually those materials with heterogenous strucutres
can help predict tensile strength
what is brinell testing not suitable for
very hard materials may cause ball damage.. very thin materials.. .case harden materials.
Describe Rockwell testing
does not require visual measurements…. penetration depth is measured instead of penetration are…
it has a smaller indention then Brinell
no mathmatical relation to strength
surface condition is critical
Rockwell indentor….
The indenter may either be a steel ball (can be of different diameter) or a spherical diamond-tipped cone with a 1200 angle and 0.2 mm tip radius, called a Brale.
The type of indenter and the test load determine the hardness scale (A, B, C, etc).
Every 0.002 mm penetration causes hardness value to drop by 1.
when testing with rockwell how much load is originally applied?
10 kg
superficial tests are frequently performed on
thin specimens. shallow penetration
