CHÖÔNG 2 ÖÙNG SUAÁT VAØ BIEÁN DAÏNG 85 TS Vuõ Coâng Hoøa 3324 Phöông cuûa

Chöông 2 öùng suaát vaø bieán daïng 85 ts

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CHÖÔNG 2: ÖÙNG SUAÁT VAØ BIEÁN DAÏNG 85 TS. Vuõ Coâng Hoøa 3.3.2.4. Phöông cuûa vector phaùp tuyeán cuûa maët nghieâng cho trò öùng suaát tieáp lôùn nhaát laø phöông PE vaø PF (kyù hieäu min max n , n treân hình 2.10b). Ñeå yù goùc < EPF chaén nöûa cung voøng troøn, vaäy min max n n hay caùc maët chöùa öùng suaát tieáp lôùn nhaát vuoâng goùc nhau. Ngoaøi ra: 2 / ) ( R MC JC R PJ JF tg 2 / ) ( R MC PM R MC JC R PJ EJ tg y x xy min y x xy max (2.67) 3.3.2.5. Goùc ôû taâm chaén cung AE laø 90 0 , vaäy caùc phaùp tuyeán naøy hôïp vôùi nhau goùc 45 0 . Töø ñaây suy ra maët chính vaø maët chöùa öùng suaát tieáp cöïc trò hôïp vôùi nhau goùc 45 0 . 3.3.2.6. Töø caùc bieåu thöùc (2. 63) ta suy ra: y x min max (2.68) töùc toång öùng suaát phaùp treân 2 maët vuoâng goùc nhau laø moät haèng soá. 3.3.2.7. Töø hình 2.10b ta coù: 2 / ) ( min max max (2.69) 3.4. Caùc traïng thaùi öùng suaát phaúng ñaëc bieät: 3.4.1. Neáu 0 , 2 1 (neùn): Voøng troøn Mohr naèm hoaøn toaøn phía traùi truïc - (hình 2.11.a); ñieàu naøy laø lyù töôûng cho vaät l ieäu chòu keùo keùm (ñaù, beâtoâng,…). Hình 2.11 2 1 2 1 2 1 2 1 E F ) b ) a
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Giaùo Trình CÔ CHÖÔNG 2: ÖÙNG SUAÁT VAØ BIEÁN DAÏNG 86 TS. Vuõ Coâng Hoøa 3.4.2. Neáu ) neùn ( 0 & ) keùo ( 0 2 1 : Voøng troøn caét truïc - ôû 2 ñieåm E, F treân ño = 0ù (hình 2.11.b). 3.4.3. Neáu 0 & 0 2 1 : Ta coù traïng thaùi keùo thuaàn tuùy, (hình 2.12.a). 3.4.4. Neáu 0 & 0 1 2 : Ta coù traïng thaùi neùn thuaàn tuùy, (hình 2.12.b). 3.4.5. Neáu 2 1 : Voøng troøn coù taâm ñaët ôû goác toaï ñoä vaø ta coù traïng thaùi öùng suaát thuûy tónh. Luùc naøy moïi maët ñeàu chòu moät öùng suaát ñôn, (hình 2.12c). 3.4.6. Neáu 0 2 1 : Voøng troøn coù taâm ñaët ôû goác toaï ñoä vaø ta coù traïng thaùi öùng suaát tröôït thuaàn tuùy. Treân caùc maët nghieâng 1 goùc 45 0 so vôùi phöông chính (E, F), caùc öùng suaát phaùp = 0 vaø öùng suaát tieáp 1 (hình 2.12.d). Hình 2.12 1 2 2 1 1 2 1 2 1 2 1 1 2 1 0 E F ) d ) c ) b ) a
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Giaùo Trình CÔ CHÖÔNG 2: ÖÙNG SUAÁT VAØ BIEÁN DAÏNG 87 TS. Vuõ Coâng Hoøa 4. BIEÁN DAÏNG: 4.1. Chuyeån ñoäng, chuyeån vò vaø bieán daïng: Khaûo saùt moät vaät theå ñaøn hoài chòu löïc. Goïi laø hình thaùi ban ñaàu trong heä toaï ñoä 0xyz luùc chöa chòu löïc, vaø / laø hình thaùi cuûa vaät khi chòu löïc (hình 2.13).
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