{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"e2366605f0bb760162b47452eca58071ffbb48c02c77ab346e751433870506d2","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"97dbb709e5468868618baf99bedc998a073403e843b3cb713e8b7392f0237140","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":"1","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":null,"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":"e78bfe90db080ebe4f05460ebebe6c1ecd9eb9abbe035dcdb9122cce699033c5"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"91c06e4b6eeec748fd5c9c57c5ebe3ccb656ad2a8d46730cf3ef06eee58c905e","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"ebb64e989a7cdf98b41bb7c1f4eb5f624e404115a4869144b5d319de6a7d50bb","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"tiPrVA6Djruaixsg6Hvm6CX_1W20oTkrk0TNBJBnkzHYpy2k1gtxYeeWq60v9DNt6LmmrMwsQ7r3HD5H_EoPDw"},"schema":"pubphys.envelope/1"},"record_hash":"91c06e4b6eeec748fd5c9c57c5ebe3ccb656ad2a8d46730cf3ef06eee58c905e","leaf_index":727}