0xyz 3221 Ñaëc ñieåm heä noäi löïc Heä noäi löïc thay ñoåi theo vò trí maët

0xyz 3221 ñaëc ñieåm heä noäi löïc heä noäi

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(0xyz). 3.2.2.1. Ñaëc ñieåm heä noäi löïc: -Heä noäi löïc thay ñoåi theo vò trí maët caét ngang. -Heä noäi löïc toàn taïi khi ngoaïi löïc toàn taïi. -Tính chaát heä noäi löïc phuï thuoäc tính chaát heä ngoaïi löïc. 3.2.2.2. Caùc thaønh phaàn noäi löïc: Xaùc ñònh heä toïa ñoä Cartesian vuoâng goùc 0xyz tam dieän thuaän ñoái vôùi phaàn vaät beân traùi, tam dieän nghòch ñoái vôùi phaàn vaät coøn laïi. Chieáu vector chính vaø vector momentt chính (ñaõ B A 6 P 5 P 4 P 1 P 2 P 3 P ) a A 6 P 5 P 4 P ) b 0 P n ) d x y z z M y Q x Q x M y M z N ) c z x M z M y M y x x Q y Q z N
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Giaùo Trình CÔ CHÖÔNG 1: KHAÙI NIEÄM CÔ BAÛN VEÀ CÔ HOÏC VAÄT RAÉN BIEÁN DAÏNG 62 TS. Vuõ Coâng Hoøa thu goïn veà troïng taâm 0), toång quaùt coù 6 thaønh phaàn noäi löïc. Qui öôùc teân goïi, kyù hieäu vaø chieàu nhö sau: * Ñoái vôùi vector chính: - Hình chieáu leân truïc x, y: löïc caét Q x , Q y . - Hình chieáu leân truïc z: löïc doïc truïc N z . * Ñoái vôùi vector moment chính: - Hình chieáu leân truïc x, y: moâmen uoán: M x , M y . - Hình chieáu leân truïc z: moâmen xoaén M z . Ghi chuù heä toïa ñoä ñòa phöông treân maët caét ngang: -Chieàu döông truïc z theo chieàu phaùp tuyeán ngoaøi cuûa maët caét. -Hai truïc x, y laø heä truïc quaùn tính chính trung taâm cuûa maët caét. -Ñoái vôùi phaàn vaät beân traùi, heä toïa ñoä ñòa phöông treân maët caét laø heä toïa ñoä thuaän vaø laø heä toïa ñoä nghòch ñoái vôùi phaàn vaät beân phaûi. 3.2.2.3. Xaùc ñònh caùc thaønh phaàn noäi löïc treân maët caét ngang: Vì heä noäi löïc caân baèng vôùi heä ngoaïi löïc cuûa phaàn ñang xeùt, neân: chieáu hình trình phuông 3 Coù 0 M M M löïc ngoaïi : e ; löïc noäi : i löïc ngoaïi Toång löïc noäi Toång chieáu hình trình phuông 3 Coù 0 F F F 0 e 0 i ej ij (1.1) Hay ta coù 6 phöông trình xaùc ñònh 6 thaønh phaàn noäi löïc: ) F ( m M ; ) F ( m M ; ) F ( m M F Q ; F Q ; F N ej z z ej y y ej x x ejy y ejx x ejz z (1.2) 3.2.2.4. Töông quan giöõa noäi löïc vaø ngoaïi löïc: Xeùt moät ñoaïn thanh dz trong baøi toaùn phaúng. Giaû söû ngoaïi löïc taùc duïng leân thanh naèm trong maët phaúng yoz vaø coù phöông vuoâng goùc vôùi truïc z. Nhö vaäy choû coù 2 thaønh phaàn noäi löïc: Q x , M x . Trong ñoaïn thanh ñang xeùt coù ngoaïi löïc phaân boá q, vì dz voâ cuøng beù neân coù theå xem q = const trong dz.
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