Classification Society Tests For Hull Materials

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Both mild steel and higher tensile steel plates and sections built into a
ship are to be produced at works approved by the appropriate classification
society.

Destructive tests are made on specimens obtained from the same product as
the finished material in accordance with the societies’ requirements which may
be found in the appropriate rules. These tests usually take the form of a
tensile test, and impact test.

Tensile Test

A specimen of given dimensions is subjected to an axial pull and a minimum
specified yield stress, ultimate tensile stress, and elongation must be
obtained. In order to make comparisons between the elongation of tensile test
pieces of the same material the test pieces must have the same proportions of
sectional area and gauge length.

Impact Tests

The Charpy V notch test or Charpy U notch test is commonly specified and
therefore described in this text. The object of the impact test is to determine
the toughness if the material.


In the figure above, the principle of the Charpy test machine is illustrated
and also is the standard test specimen for a Charpy V notch test. This specimen
is placed on an anvil and the pendulum is allowed to swing so that the striker
hits the specimen opposite the notch and fractures it. Energy absorbed in
fracturing the specimen is automatically recorded by the machine. Basically,
making allowances for friction, the energy absorbed in fracturing the specimen
is the difference between the potential energy the pendulum possess before
being released and that which it attains in swinging past the vertical after
fracturing the specimen. A specified average impact energy for the specimens
tested must be obtained at the specified test temperature.


Aluminium Alloy Tests

Aluminium alloy plate and section material is subject to specified tensile
tests. Bar material for aluminium alloy rivets is subject to a tensile test and
also a dump test. The latter test requires compression of the bar until its
diameter is increased to 1.6 times the original diameter without cracking
occurring. Selected manufactured rivets are also subjected to the same dump
test.

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