FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 4. Metal Structure, Welding, and Brazing | 2. Testing of Metals | 4-18. Brinell Hardness Test
9/8/98
SECTION 2. TESTING OF METALS
AC 43.13-1B
4-16. HARDNESS TESTING. If the mate
rial type is known, a hardness test is a simple
way to verify that the part has been properly
heat-treated. Hardness testers such as Rock
well, Brinell, and Vickers can be useful to
check metals for loss of strength due to expo
sure to fire or abusive heating. Also, under
strength bolts can be found and removed from
the replacement part inventory by checking the
hardness of the bolt across the hex flats. Al
though hardness tests are generally considered
nondestructive, hardness testing does leave a
small pit in the surface; therefore, hardness
tests should not be used on sealing surfaces,
fatigue critical parts, load bearing areas, etc.,
that will be returned to service. These hard
ness tests provide a convenient means for de
termining, within reasonable limits, the tensile
strength of steel. It has several limitations in
that it is not suitable for very soft or very hard
steels. Hardness testing of aluminum alloys
should be limited to distinguishing between
annealed and heat-treated material of the same
aluminum alloy. In hardness testing, the thick
ness and the edge distance of the specimen
being tested are two factors that must be con
sidered to avoid distortion of the metal. Sev
eral readings should be taken and the results
averaged. In general, the higher the tensile
strength, the greater its hardness. Common
methods of hardness testing are outlined in the
following paragraphs. These tests are suitable
for determining the tensile properties resulting
from the heat treatment of steel. Care should
be taken to have case-hardened, corroded, pit
ted, decarburized, or otherwise nonuniform
surfaces removed to a sufficient depth. Exer
cise caution not to cold-work, and conse
quently harden, the steel during removal of the
surface.
4-17. ROCKWELL HARDNESS TEST.
The Rockwell hardness test is the most com
mon method for determining hardness of fer
rous and many nonferrous metals. (See ta
ble 4-5.) It differs from Brinell hardness test
ing in that the hardness is determined by the
depth of indentation made by a constant load
impressing on an indenter. In this test, a stan
dard minor load is applied to set a hardened
steel ball or a diamond cone in the surface of
the metal, followed by the application of a
standard major load. The hardness is meas
ured by depth of penetration. Rockwell super
ficial hardness tests are made using light minor
and major loads and a more sensitive system
for measuring depth of indentation. It is useful
for thin sections, very small parts, etc. Cali
bration of Rockwell hardness testers is done in
accordance with American Society of Testing
Materials (ASTM E-18) specifications.
4-18. BRINELL HARDNESS TEST. In
this test a standard constant load, usually
500 to 3,000 kg, is applied to a smooth flat
metal surface by a hardened steel-ball type in
denter, 10 mm in diameter. The 500-kg load is
usually used for testing nonferrous metals such
as copper and aluminum alloys, whereas the
3,000-kg load is most often used for testing
harder metals such as steels and cast irons.
The numerical value of Brinell Hardness (HB),
is equal to the load, divided by the surface area
of the resulting spherical impression.
HB = P
(π D [D − (D2 − d 2 ) ])
2
Where P is the load, in kg; D is the diameter of
the ball, in mm; and d is the diameter of the
indentation, in mm.
Par 4-16
Page 4-5