MAT-42

Griffith crack

Brittle fracture of a through-crack.

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GoverningGriffith crack

Governing equation

\sigma_f=\sqrt{2E\gamma_s/(\pi a)}

where

E: E (GPa)
g: g (J/m²)
a: a (mm)
sf: Griffith crack (MPa)

Lecture brief

Historical brief

Hooke (1678), Hall–Petch grain size, Arrhenius activation and Paris fatigue-crack growth are the spine of materials selection. The sheets relate stress, microstructure and life. This sheet (MAT-42 — Griffith crack) is the form associated with Griffith crack. Working symbols: $E$ , $g$ , $a$ $\rightarrow$ $sf$ . Brittle fracture of a through-crack. Pedagogical SI sheet with a live model and a swept parameter.

Purpose

Purpose: compute

sf

from

E

g

a

in Materials via

\sigma_f=\sqrt{2E\gamma_s/(\pi a)}

Brittle fracture of a through-crack. Use it when a real materials question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

E = 70.000\,\mathrm{GPa}

g = 10.000\,\mathrm{J/m^{2}}

a = 0.200\,\mathrm{mm}

, the governing relation

\sigma_f=\sqrt{2E\gamma_s/(\pi a)}

yields

sf = 47.203\,\mathrm{MPa}

. One governing identity, SI units, a single sweep on the sheet. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

E E70 GPag g10 J/m²a a0.2 mm

Outputs

Griffith crack sf47.203 MPa

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Narration of this film

One governing identity, SI units, a single sweep on the sheet.

Brittle fracture of a through-crack. Pedagogical SI sheet with a live model and a swept parameter.

Reading speed

Watch on YouTube