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A pendulum impact test on a specified notched specimen, commonly used to measure absorbed energy as a function of temperature. A transition curve characterizes a ductile-to-brittle transition, but its energy is not itself a fracture toughness value.^[ref]

Loss of mechanical integrity associated with retained helium, including the growth and coalescence of gas-containing cavities at grain boundaries. Gas location, trapping, temperature, stress and the initial microstructure influence the result. It can occur in austenitic steel without the ferritic ductile-to-brittle transition.^[ref]

An official technical note explaining Charpy impact test transition curves. Section2 describes absorbed energy, lateral expansion and fracture-appearance measures of the ductile-to-brittle transition.

For mild steel, the corresponding bounds areA relatively low yield stress increases the thickness needed to carry pressure, but a favorable toughness-to-yield-strength ratio can give a much larger leak-before-break upper bound. This tradeoff often makes a tough structural steel more attractive than choosing the highest strength alone.

For Arctic service, the ductile-to-brittle transition is crucial. A room-temperature toughness cannot be assumed to persist below the transition, and welding, constraint and loading rate affect the comparison. A suitably qualified low-temperature steel can be practical; the word mild alone does not establish that qualification.

TODO: numerical thickness cannot be completed without the unavailable 2018 NST Data Book values. The temperature and state of the tabulated toughness must also be identified before making a numerical service claim.

For Ti–6Al–4V, use its own fracture toughness and yield stress inThe same unit-conversion formulas from part(i) apply. A feasible yield-limited screening interval requires $t_{\mathrm{yield}}<t_{\max }$, using consistent crack geometry and low-temperature properties.

High specific strength and corrosion resistance can be attractive, but cost, fabrication, joining and toughness must also be assessed. The label HCP is not a sufficient rule that every titanium alloy has the same sharp ductile-to-brittle transition as ferritic steel; actual low-temperature alloy and microstructural data are needed.

TODO: numerical thickness cannot be completed without the unavailable 2018 NST Data Book's Ti–6Al–4V property pair. No historical value or material-specific Arctic toughness is invented.

The characteristic effect is an irradiation-induced upward shift of the ductile-to-brittle transition in ferritic steel. A component previously used above its transition can then fail by cleavage fracture at the same service temperature, with much less warning from plastic deformation.

Ferrite has a body-centered cubic lattice. At low temperature, dislocation glide becomes difficult enough that brittle crack propagation can precede substantial plastic relaxation. Irradiation hardening raises the yield strength by introducing obstacles to dislocation glide; the competition with cleavage fracture consequently shifts toward brittle failure. Austenite, with its face-centered cubic lattice, does not normally show this same sharp cleavage transition. This does not make austenitic steel immune to loss of ductility, helium embrittlement or other radiation damage in materials.

Examine the fracture surface for cleavage fracture facets and river patterns, and compare Charpy impact test energy-versus-temperature curves from exposed material and an unirradiated reference of the same composition and heat treatment. The reference is important: a low impact energy from one failed specimen cannot establish an irradiation-induced shift. Transition curves can also use lateral expansion or the proportion of ductile fracture appearance.^[ref]

A direct fracture toughness test over the transition region complements the Charpy impact test; the two measurements are not interchangeable. Combine these observations with exposure history, local temperature, microstructure and crack location. Brittle appearance supports the failure mechanism, while a measured transition shift and suitable controls support its attribution to irradiation.