{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"ceb4bf59252d1716473cfc1c68fef8973d451d556577ea6da8fd218f660b70c0","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["91c06e4b6eeec748fd5c9c57c5ebe3ccb656ad2a8d46730cf3ef06eee58c905e","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"a364aea3d6f0fc28355294ca171d066719e78216a567c39378ebb32be9784a97","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"bio.amorphous-plasticity.crack-microbranching","kind":"phenomenon","literature_status":"partially-resolved","n":"2","parents":[],"plain":"A fast crack moving through glass or plastic becomes unstable and develops small side branches at a speed well below that predicted by classical fracture theory. The cause of this threshold in three-dimensional samples is not explained.","posed_since":"","precise":"In brittle amorphous materials (silicate glass, PMMA, polyacrylamide gels), single cracks become unstable to microbranching at velocities of roughly $0.4 c_R$ ($c_R$ the Rayleigh wave speed), below the branching velocity predicted by linear elastic fracture mechanics. Determine the 3D mechanism and critical velocity from a theory including near-tip nonlinear elasticity and dissipation, and predict the branch length and spacing.","problem_ref":"91c06e4b6eeec748fd5c9c57c5ebe3ccb656ad2a8d46730cf3ef06eee58c905e","references":"","settled_by":"A theory and 3D simulations predicting the microbranching velocity and branch statistics that agree with measurements in at least two materials.","status_note":"In thin gel sheets an oscillatory crack instability near the Rayleigh speed was explained by weakly nonlinear elasticity in the 2010s; the 3D microbranching threshold lacks a first-principles explanation (2026).","title":"What triggers microbranching of fast cracks in brittle amorphous solids?","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"fbe98eedd9868b3ec2ed9aa22ac7a4c6dc1b7caa284953d3172057c596d50199","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"b9b847d6aa0f8ed2e086a61e9b4decdbd24f71ea87f9ee31262f0cd0722314e8","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"Z4aczajL5cDH0v6rBnQmISeArbVJ_adZprUhIm2JyvSM6E0VbS5vzOkTU36NJ0QHh5oG1ABmQWarqM0sCS3xBw"},"schema":"pubphys.envelope/1"},"record_hash":"fbe98eedd9868b3ec2ed9aa22ac7a4c6dc1b7caa284953d3172057c596d50199","leaf_index":2554}