| Abstract |
- The fracture toughness is a critical material property that determines engineering performance.
However, as is well known for crystalline materials, if certain sample geometry and size
requirements are not met, test results become sample-size dependent and difficult to compare
among different studies. Here, the room-temperature fracture toughness of the Zr-based bulkmetallic
glass (BMG) Zr₅₂.₅Cu₁₇.₉Ni₁₄.₆Al₁₀Ti₅ (Vitreloy 105) was evaluated using compacttension,
as well as single-edge notched bend, specimens of different sizes to measure KIc values
according to ASTM standard E399 and JIc values according to ASTM standard E1820. It is
concluded that the ASTM standard E399 sample-size requirements should be cautiously
accepted as providing size-independent (valid) KIc results for BMGs; however, it is also
concluded that small sized samples may result in a wider scatter in conditional toughness KQ
values, a smaller yield of valid tests, and possibly somewhat elevated toughness values. Such
behavior is distinct from crystalline metals where the size requirements of ASTM standard E399
are quite conservative. For BMGs, KQ values increase and show a larger scatter with decreasing
uncracked ligament width b, which is also distinct from crystalline metals. Samples smaller than
required by ASTM standards for KIc testing are allowed by the J-integral based standard E1820; however, in this study on BMGs, such tests were found to give significantly higher toughness
values as compared to valid KIc results. Overall, the toughness behavior of BMGs is more
sensitive to size-requirements than for crystalline metals, an observation that is likely related to
the distinct size-dependent bending ductility and strain softening behavior found for metallic
glasses. It is concluded that toughness values measured on BMG samples smaller than that
required by the KIc standard, which are common in the literature, are likely sample size- and
geometry-dependent, even when they meet the less restrictive valid JIc requirements.
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