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

Flexural stresses at any point' of the cross section are
determined by the relation
Al" . 11
(3.15)
where I and I are the principal moments of inertia for the cross
section of the blade, m
The signs of the bending moments in this equation must be
considered positive if they cause a bend deformation convex to
the side of the positive direction of the corresponding axis. The
signs of coordinates g and n correspond to the direction of the
axes.
Fig. 3.19. Determining bending y
moments relative to the principal
axes of inertia.
In writing formula (3.15) we assume the following rule of
signs for bending moments and stresses: tensile stress is assumed
positive and compressive stress negative.
Usually in turbine machines the principal moments of inertia
for blade cross sections are connected with the relationship
I > (10-15)IV, while the values of bending moments are of the same
order. Therefore, bending stresses, for example, at point A, can be
determined approximately from fnrmula
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