Energy balance for brittle crack extension
In a quasistatic elastic fracture model, crack extension releases mechanical potential energy at rateG=−∂Π/∂A per projected crack area.
Key knowledge
In a quasistatic elastic fracture model, crack extension releases mechanical potential energy at rateG=−∂Π/∂A per projected crack area. Extension becomes energetically possible whenG reaches the applicable resistanceG_c. For ideally brittle creation of two clean surfaces with surface energyγ each,G_c=2γ; real process-zone dissipation can raise the resistance. Flaw geometry and size therefore matter alongside remote stress.
Values and equations
G=−∂Π/∂A; G=G_c at the ideal extension threshold; G_c=2γ for ideally brittle surface creation
- G,G_c,γ
- energy release rate, applicable crack-growth resistance and one-surface energy J m⁻²
- Π
- mechanical potential under declared boundary loading J
- A
- one-face projected crack area m²
Conditions and scope
- DefineA as one-face projected newly cracked area andΠ as mechanical potential under the stated load/displacement boundary control. Linear elasticity outside a small crack-tip process zone and a specified crack mode/path are the bounded model.
- A threshold alone does not determine crack-growth stability, speed or whole-rock strength; compare how driving and resistance evolve under actual loading. Rock heterogeneity, frictional contact, fluid chemistry/pressure and larger plastic zones require further models. This is distinct from sliding an already formed fault.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- Introduction to Fracture Mechanics, printed2–4, energy-balance approach, surface energy and critical release rateDavid Roylance — MIT (2001), 3.11 course moduleReference guide · PDF
- PSG&T Chapter3, Stress Concentration, Griffith flaws and Frictional SlidingBen A. van der Pluijm and Stephen Marshak — University of MichiganReference guide
Evidence and review
Read actual MIT energy/surface balance andG_c extension for dissipation, plus Michigan crack/flaw and separate sliding discussion. G=−∂Π/∂A is the disclosed energy-rate notation for that balance, with one-face area convention. Excluded geometry-independent critical lengths, confusing unstable growth with every threshold crossing and unsourced universal crack-speed predictions.
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