Aerospace & Defense Technology - August 2023 - 37

Tech Briefs
ponents is the generation of complex
and thin-walled geometries for location-specific
performance otherwise
unachievable through conventional
manufacturing means. Yet, as a new
manufacturing process, AM leads to
unique microstructures that must be
properly assessed for material properties
and performance.
At times, regions of interest at the
component level will require subscale
specimen excision and evaluation for
proper characterization as witness coupons
may not fully capture locat
ion-specific performance. Other
industries, e.g., nuclear power, have
adopted non-standardized testing with
the goal of test specimen miniaturizat
ion so to character ize mater ial
response using minimal material volume
without the sacrifice of accurately
capturing bulk material properties.
Material scarcity, costs, and handling
hazards all motivate the need for developing
such a testing capability.
Two of the principal standards recognized
for elevated temperature tensile
testing of metallic materials are
ASTM E21 and ISO 6892-2. Notably,
these standards heavily pull from
their room temperature equivalents -
ASTM E8 and ISO 6892-1 - to specify
acceptable specimen geometries and
general test setup. However, none of
the standards directly addresses how
to approach the intricacies specific to
subscale specimen testing.
There are current efforts within ASTM
Subcommittee E28.04.01 (Task Group
on Small Specimens in E8/E8M) to
publish an annex providing guidelines
to uniaxial tensile testing of subscale
geometries. Yet, the annex has limited
scope to room temperature evaluation
only. Additional efforts are underway
through ASTM Subcommittee F42.01
(New Test Method for Additive Manufacturing
- Test Artifacts - Miniature
Tension Testing of Metallic Materials),
which seeks to develop a miniature
rectangular cross-section tension specimen
with a gauge length of 10-15 mm.
However, the title and scope of the
effort presently is in draft form.
ASTM E8 and ISO 6892-1 provide
guidance on acceptable standard tensile
specimen geometries. A generalized
Aerospace & Defense Technology, August 2023
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specimen layout is presented in Figure
1. The ratios have been established to
bound the design parameters to ensure
proportional response, i.e., interlaboratory
comparability. Often, standard
geometries serve as the basis for subscale
specimen design. ASTM E8 specifically
outlines a subsize geometry for
rectangular tension test specimens. The
subsize specimen has a gauge length of
25.0 mm, width of 6.0 mm, and variable
thickness not to exceed the width
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37
6/28/23 9:26 AM

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Aerospace & Defense Technology - August 2023

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