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Aviation Structural Mechanic (H&S) 3&2 - How airplanes are built and how to maintain them | Next
Storage and Handling. |
THE ERNST PORTABLE HARDNESS
NOTE :
TESTER HAS A DIAMOND-TIPPED
MATERIAL MUST BE SOLIDLY SUPPORTED
PENETRATOR AND READS IN
FROM BEHIND.
PRESS DOWN WITH A
ROCKWELL OR BRINELL SCALES.
STEADY, EVEN FORCE.
Figure 1-31.—Ernst portable hardness tester.
ERNST TESTER
The Ernst tester is a small versatile tool that requires
access to only one side of the material being tested.
There are two models of the tester-one for testing
hardened steels and hard alloys and one for testing
unhardened steels and most nonferrous metals. It has a
diamond point penetrator, and it is read directly from the
Rockwell A or B or the Brinell scales, depending on the
model used. Figure 1-31 shows the Ernst portable
hardness tester and its proper use.
The correct procedures for using the Ernst tester are
as follows:
1. Solidly support the metal being tested by placing
a bucking bar behind the metal. This will minimize
flexing of the metal and yield a more accurate reading
of hardness.
2. The handgrip must be pressed down with a
steady, even force to ensure accurate readings.
3. Press down until the fluid column has stopped
moving. The hardness value is given at the point where
the fluid column has stopped moving on the scale.
As with other portable testers of similar type, the
material must be smooth and backed up so there will be
no tendency to sag under the load applied on the tester.
The test block supplied with each tester should be used
frequently to check its performance.
NONMETALLIC MATERIALS
Learning Objective: Identify properties of non-
metallic and composite materials used in
aircraft construction.
Transparent plastics, reinforced plastics, and com-
posite materials are common materials used in aircraft
construction. Sandwich construction is used for
radomes as well as for structural areas where strength
and rigidity are important.
TRANSPARENT PLASTICS
Transparent plastic materials used in aircraft
canopies, windshields, and other transparent enclosures
may be divided into two major classes, or groups,
depending on their reaction to heat. They are the
thermoplastic materials and the thermosetting materials.
Thermoplastic materials will soften when heated
and harden when cooled. These materials can be heated
until soft, formed into the desired shape, and when
cooled, will retain this shape. The same piece of plastic
can be reheated and reshaped any number of times
without changing the chemical composition of the
material.
Thermosetting plastics harden upon heating, and
reheating has no softening effect. They cannot be
reshaped after once being fully cured by the application
of heat. These materials are rapidly being phased out in
favor of stretched acrylic, a thermoplastic material.
Transparent plastics are manufactured in two forms
of material-solid (monolithic) and laminated. Lami-
nated plastic consists of two sheets of solid plastic
bonded to a rubbery inner layer of material similar to the
sandwich materials used in plate glass.
Laminated transparent plastics are well suited to
pressurized applications in aircraft because of their
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