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

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We increase the loading time <strong>of</strong> a part in each segment TI,<br />

**., Tk an identical number <strong>of</strong> times so that at the end <strong>of</strong> the k-th<br />

loading stage the part ruptures. <strong>The</strong>f 4ihe quantity indicating how<br />

many times the time segments T 1 , T 2 , ... , Tk must be increased<br />

so that rupture occurs at the end <strong>of</strong> the mode is the coefficient <strong>of</strong><br />

longevity reserve. We designate this new loading time for each<br />

segment with an asterisk:<br />

n ~.nr,; T 2 f 1 2 ,. ;f!,<br />

<strong>The</strong>n<br />

I. I<br />

k<br />

k<br />

I<br />

where ,T is the operating time <strong>of</strong> the part.. Hence, substituting<br />

rel.ationships (1.33) into (1.31), we obtain the formula for the<br />

coefficient <strong>of</strong> longevity reserve:<br />

& -- -- .(1.34)<br />

Tip<br />

To determine a coefficient <strong>of</strong> strength reserve under nonstationary<br />

loading we assume that stresses a 1 , a 2 , ... , ak are increased an<br />

identical number <strong>of</strong> tfmes n so that at the end <strong>of</strong> the new mode<br />

p<br />

rupture occurs. <strong>The</strong>n in expression (1.31), taking into account<br />

formula (1.24),<br />

Ti A 1 1<br />

• ;= (1.35)<br />

(n@)1 *<br />

where Tip is the stress necessary for rupture after time Tf. It<br />

i i.<br />

is found from the stress-rupture strength curve <strong>of</strong> the mater•ial<br />

under various temperatures.<br />

78

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