{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"93fd4949d62a9cc463709f791365a0cf81532005059ca97dfa4ee001df98d802","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["2818c1c6781ac5fd849bf3d8394c34c851fd90dc2dedfe5f3cc3f7e1838f36f7","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"e7489a1b6e65004f3901485096870f5818a7c3338b0bb9ec241bfddbf0694dd9","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"cm.crystal-plasticity.psb-crack-initiation","kind":"phenomenon","literature_status":"open","n":"2","parents":[],"plain":"Under repeated small loads, metals form thin bands of concentrated slip with a ladder-like dislocation structure, and cracks begin where these bands meet the surface. How the bands push out surface ridges and start cracks has not been derived from dislocation physics.","posed_since":"","precise":"In cyclically loaded Cu single crystals, persistent slip bands with dislocation ladder walls spaced about $10^{-4}$ cm carry localized plastic strain and produce surface extrusions and intrusions where cracks nucleate. Determine the mechanism producing extrusions (vacancy generation by annihilation of edge dislocation dipoles, as in the Essmann-Gosele-Mughrabi model, or irreversible slip) and predict the number of cycles to crack initiation versus plastic strain amplitude. An answer is a model validated against measured extrusion growth rates and initiation lives.","problem_ref":"2818c1c6781ac5fd849bf3d8394c34c851fd90dc2dedfe5f3cc3f7e1838f36f7","references":"","settled_by":"In situ measurement of extrusion growth and point-defect content in persistent slip bands, compared with a dislocation-based model predicting initiation life.","status_note":"","title":"How persistent slip bands initiate fatigue cracks","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"f80afe64922e07afd9fcbc797821a5283e43b19714a5a6bbba7c4dbd3e5bee8b","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"93688044a878c0c4bc4328ea2fa9c2292b246a5ba81ea47177cd4a826e5018da","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"vFvQwMac14HpHI_qQWaJmPQEwKSfhcukrQolQsnBa6whjvIjIL2aHNpgfQbed5J_nn5Fkzj75nC5yBWbLTEJCA"},"schema":"pubphys.envelope/1"},"record_hash":"f80afe64922e07afd9fcbc797821a5283e43b19714a5a6bbba7c4dbd3e5bee8b","leaf_index":2718}