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National Advisory Committee for Aeronautics, Technical Notes - Nondestructive Test Methods for Spot Welds in Aluminum Alloys

This report presents the_results of a study and research
investigation of nondestructive'test methods'for spot welds
in aluminumwalloy sheets. The purpose of the research-was to
investigate proposed nondestructive test methOds-for spot
welds in aluminum alloys, to determine the feasibility of
such. tests, and to recommend those- research methods found
suitable for development and redu ction to practical applica—
tion.

Investigation was made of approximatelv 50 proposed non-
destruc_tive methods of testing spot welds, including electric—
current conduction-tests, eddyscurrent~tests,-thermal tests,
sonic and vibration tests, material—property tests, penetra—
tor tests, X—ray tests, and mechanical—proof tests. Prelim—
inary tests and analysis of the requirements of a suitable
nondestructive test indicated that penetrator, electrical,
and X~ray tests showed the most promise, and extensive devel—
opments of each of these test methods were carried out} Each
of these test methods then was tried on groups of several
hundreds of industrially made spot welds, and the reliability
and accuracy with which weld sise, strength; and—fiuality were
predicted by each test were determined. Complete descrip—
tions of test equipmeht and the results of measurements are
included in this report, in many cases in the form of graphs.
Also included are photographic tables of data on spot—weld
nomenclature and metallurgy, weld classification, and the
effects of conditions of welding upon weld size and structure.

It was found that, in terms of reliability, the most
promising nondestructive test method is the radiographic in~
spection of spot welds, which can probably measure weld—nug—
get diameter and the presence of defects, such as cracks,
porosity, and sp1tting. The most reliable non- radiographic
test is the ring—penetrator or profile—penetrator test .
which can measure weld—nugget diameter reliably under normal
conditions of production welding. It does not measure the
nature or extent of cracking. porosity. and spitting, except
insofar as these_defects change the depth of penetration un—
der load. Neither the electri.cal Inor the penetIrator tests
are capable of determining the extent of the alclad inclusion
into the weld nugget at. the faying plane. or the decrease in
weld strength resulting from this cause.