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Design and Stress Analysis of Extraterrestrial ... - The Black Vault

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Flexural stresses from centrifugal forces are used to compensate<br />

the flexural stresses from the: effect <strong>of</strong> gas-dynainic forces (see<br />

below). Torsional stresses r-e usually low <strong>and</strong> in tentative calculations<br />

can be disregarded.<br />

taken in<br />

<strong>The</strong> following system <strong>of</strong> coordinate axes (Fig. 3.15) has been<br />

the stress analysis <strong>of</strong> a blade foil.<br />

<strong>The</strong> Ox axis agrees, with the rotor's axis <strong>of</strong> rotation <strong>and</strong> is<br />

directed in the direction <strong>of</strong> the gas flow; the Or axis (or Oz) is<br />

perpendicular to the axis <strong>of</strong> rotation (Ox) <strong>and</strong> passes through the<br />

center <strong>of</strong> gravity <strong>of</strong> the root section <strong>of</strong> the blade; the Oy axis is<br />

perpendicular to the Ox <strong>and</strong> Or axes <strong>and</strong> is directed so that the<br />

smallest angle <strong>of</strong> turni ut to A c6incidence With the Or-ais 'is<br />

obtained with a turn in the direction <strong>of</strong> the angular velocity <strong>of</strong><br />

the rotor,<br />

Let us examine a method <strong>of</strong> determining stresses in the blade<br />

fo.Ll. from centrifugal forces in the example <strong>of</strong> a blade with a b<strong>and</strong><br />

web (Fig. 3.16).<br />

For convenience in determining stresses a in an arbitrary<br />

cross section (on radius r*) <strong>of</strong> a blade, let us divide the complete<br />

centrifugal force C acting on this cross section by the centrifugal<br />

force <strong>of</strong> the blade foil strictly COn <strong>and</strong> the centrifugal force <strong>of</strong><br />

the b<strong>and</strong> web C6, Obv.• usly,<br />

(3.3)<br />

Let us find these forces, for which we take an element <strong>of</strong> a<br />

blade wtth radiv- r <strong>and</strong> thickness dr.<br />

created by this blade element is<br />

d C<br />

= v U,')Frdr,<br />

<strong>The</strong>n the centrifugal force<br />

where p is the density <strong>of</strong> the blade material in kg/in<br />

2117

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