SKRIPTA RIJEÅ ENIH ZADATAKA IZ OTPORNOSTI MATERIJALA

SKRIPTA RIJEÅ ENIH ZADATAKA IZ OTPORNOSTI MATERIJALA SKRIPTA RIJEÅ ENIH ZADATAKA IZ OTPORNOSTI MATERIJALA

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74 47. Zadatak Odrediti to����������������������������������������������������������������������������� m cm a m l kN F 2 , 0 20 5 10 = = = = ( ) 4 2 2 ' 4 2 2 3 2 2 3 ' 4 2 2 3 2 2 3 ' 2 2 2 2 2 2 2 2 3 1 6 5 6 7 2 3 2 0 6 5 2 6 7 2 0 12 11 6 5 2 12 2 6 5 2 12 12 11 6 7 2 3 2 12 2 6 7 2 12 6 7 3 2 3 2 2 6 5 3 2 2 3 2 a a a a a a a a a a a I a a a a a a a a a a a I a a a a a a a a a a a I a a a a a a z a a a a a a y a a a a A yz z y T T = ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − ⋅ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − ⋅ + + ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − ⋅ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − ⋅ + = = ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − ⋅ + ⋅ + ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − ⋅ + ⋅ = = ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − ⋅ + ⋅ + ⎥ ⎥ ⎦ ⎤ ⎢ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − ⋅ + ⋅ = = ⋅ + ⋅ = = ⋅ + ⋅ = = + ⋅ = Glavne osi momenata površine drugog reda : ( ) ( ) ( ) 0 12 7 3 1 12 11 4 5 3 1 12 11 3 1 12 11 3 1 2 2 1 12 11 2 2 1 4 2 1 2 1 45 90 2 0 3 1 2 12 11 12 11 3 1 2 2 2 4 4 2 4 4 1 4 4 4 2 ' 2 ' ' ' ' 2 , 1 4 4 4 4 ' ' ' = = = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − = = = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ± = ⋅ ± ⋅ ⋅ = + − ± + = ° = → ° = → ∞ = ⋅ − = − ⋅ − = − − = yz z y yz z y z y z y yz I I a a I I a a I a a a I I I I I I a a a a I I I tg α α α

75 Položaj neutralne osi : ° − = → − = − = ° − = − = 65 14286 , 2 7 15 45 12 7 4 5 4 4 ϕ α ϕ tg a a tg I I tg z y Ekstremna naprezanja su u to�kama B i D : MPa a Fl a Fl a a a a Fl y I z I M MPa a Fl a Fl a a a a Fl y I z I M D D z D y D B B z B y B 78 , 6 2 , 0 5 10 10 35 38 35 38 7 2 5 4 12 7 6 2 4 5 2 2 2 45 sin 45 cos 21 , 3 2 , 0 5 10 10 35 18 35 18 7 2 5 4 12 7 6 2 4 5 2 2 2 45 sin 45 cos 3 3 3 3 4 4 3 3 3 3 4 4 = ⋅ ⋅ = = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + = ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ + = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ° + ° = − = ⋅ ⋅ − = − = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + − = ⎟ ⎟ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎜ ⎜ ⎝ ⎛ + − = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ° + ° = σ σ σ σ a a a a a y a a a a a z a a a a a y a a a a a z D D B B 6 2 2 2 6 5 2 2 6 7 45 sin 6 5 45 cos 6 7 2 2 2 6 7 2 2 6 5 45 sin 6 7 45 cos 6 5 6 2 2 2 6 7 2 2 6 5 45 sin 6 7 45 cos 6 5 2 2 2 6 5 2 2 6 7 45 sin 6 5 45 cos 6 7 = − = ° − ° = = + = ° + ° = = + − = ° − − ° − = − = − + − = ° − + ° − =

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