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Why hollow shaft can transmit more power than solid shaft

When comparing a solid shaft with a hollow shaft of equal section modulus, both will

transmit the torque with equal stress levels, but the hollow shaft will be stiffer, or rather will

deflect less under the same overhung moment. This translates to longer allowable shaft

lengths at a given stress level, and less weight at a given shaft length. Less weight means lessthrust transmitted to the drive bearings, and a longer expected bearing life. Less weight and

higher stiffness also helps avoid critical speed, frequently a limiting factor in mixer design.

What is the difference between engineering

stress and true stress?

The difference between true stress & engineering stress is summarised as follows:

ngineering stress assumes that the area a force is acting upon remains constant, true stress

ta!es into account the variation in the cross sectional area as a result of the stress induceddeformation "strain# of a material. $or example a steel bar in tension once its yield point or

stress is reached will start to %nec!%. ec!ing is the locali'ed concentration of strain in a

small region of the material, causing a reduction in cross sectional area at this point.

ngineering stress and strain "also sometimes called nominal stress and strain# are calculated

based on the original dimensions of the material in question.

True stress and strain are calculated based on the actual dimensions of the material.

(o when you do a tension test, the bar will begin to get thinner as it stretches. ngineering

stress would be the force divided by the original area for the duration of the test. True stress

would be the force divided by the actual area, at every time that a measurement is ta!en.

)oments

The moment (or torque) of a forceabout a turning point is the force multiplied by the

perpendicular distance to the force from the turning point.

Moments are measured in newton metres (Nm).

The principle of moments.When an object is in equilibrium the sum of the anticlocwise moments about a turning

point must be equal to the sum of the clocwise moments.

sum of anticlocwise moments ! sum clocwise moments

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