Figure 7-69.Rupturing fillet weld test plate.
(fig. 7-69) until a break occurs in the joint. This force
may be applied by hydraulics or hammer blows.
In addition to checking the fractured weld for
soundness, now is a good time to etch the weld to check
The ETCHING TEST is used to determine the
soundness of a weld and also make visible the boundary
between the base metal and the weld metal.
To accomplish the test, you must cut a test piece
from the welded joint so it shows a complete transverse
section of the weld. You can make the cut by either
sawing or flame cutting. File the face of the cut and then
polish it with grade 00 abrasive cloth. Now place the test
piece in the etching solution.
The etching solutions generally used are hydrochlo-
ric acid, ammonium persulfate, iodine and potassium
iodide, or nitric acid. Each solution highlights different
defects and areas of the weld. The hydrochloric acid
dissolves slag inclusions and enlarges gas pockets,
while nitric acid is used to show the refined zone as well
as the metal zone.
Tensile Strength Test
The term TENSILE STRENGTH may be defined as
the resistance to longitudinal stress or pull and is meas-
ured in pounds per square inch of cross section. Testing
for tensile strength involves placing a weld sample in a
tensile testing machine and pulling on the test sample
until it breaks.
Figure 7-70.Standard tensile test specimen.
The essential features of a tensile testing machine
are the parts that pull the test specimen and the devices
that measure the resistance of the test specimen. Another
instrument, known as an extensometer or strain gauge,
is also used to measure the strain in the test piece. Some
equipment comes with a device that records and plots
the stress-strain curve for a permanent record.
The tensile test is classified as a destructive test
because the test specimen must be loaded or stressed
until it fails. Because of the design of the test machine,
weld samples must be machined to specific dimensions.
This explains why the test is made on a standard speci-
men, rather than on the part itself. It is important that the
test specimen represents the part. Not only must the
specimen be given the same heat treatment as the part
but it also must be heat-treated at the same time.
There are many standard types of tensile test speci-
mens, and figure 7-70 shows one standard type of speci-
men commonly used. The standard test piece is an
accurately machined specimen. Overall length is not a
critical item, but the diameter and gauge length are. The
0.505-inch-diameter (0.2 square inch area) cross section
of the reduced portion provides an easy factor to ma-
nipulate arithmetically. The 2-inch gauge length is the
distance between strain-measuring points. This is the
portion of the specimen where you attach the exten-
someter. In addition, you can use the gauge length to
determine percent elongation.
The tensile test amounts to applying a smooth,
steadily increasing load (or pull) on a test specimen and
measuring the resistance of the specimen until it breaks.
Even if recording equipment is not available, the testis
not difficult to perform. During the test, you observe the
behavior of the specimen and record the extensometer
and gauge readings at regular intervals. After the speci-
men breaks and the fracturing load is recorded, you
measure the specimen with calipers to determine the
percent of elongation and the percent reduction in area.
In addition, you should plot a stress-strain curve. From
the data obtained, you can determine tensile strength,