# Mechanical Engineering - Strength of Materials - Discussion

Discussion Forum : Strength of Materials - Section 7 (Q.No. 3)

3.

Two shafts '

*A*' and '*B*' are made of same material. The shaft '*A*' is of diameter*D*and shaft '*B*' is of diameter*D*/2. The strength of shaft '*B*' is __________ as that of shaft '*A*'Discussion:

12 comments Page 1 of 2.
MUHAMMAD NABI said:
3 years ago

As we know, the strength of the shaft is measured by polar modulus.

Polor modulus = j/r.

Here solid shaft is given so for solid shaft.

π/16 (d) ^3.

Now as db =d/2.

And da=d.

So,

π/16 (db) ^3 divide by pi/16 (da) ^3.

After a cancellation we get.

(db/da) ^3.

Put db= (d/2) ^3=d^3/2^3=d^3/8.

Now.

(d^3/8) /d^3.

=1/8.

Polor modulus = j/r.

Here solid shaft is given so for solid shaft.

π/16 (d) ^3.

Now as db =d/2.

And da=d.

So,

π/16 (db) ^3 divide by pi/16 (da) ^3.

After a cancellation we get.

(db/da) ^3.

Put db= (d/2) ^3=d^3/2^3=d^3/8.

Now.

(d^3/8) /d^3.

=1/8.

(1)

Meet said:
7 years ago

The strength of the shaft means torque transmitting capacity of the shaft without any plastic deformation.

&tTau; = 16*T/π* d^3.

As per this equation, T proportional to d^3.

&tTau; = 16*T/π* d^3.

As per this equation, T proportional to d^3.

Shivam said:
6 years ago

Given answer is right and you are right @Meet.

It is asking for max. bending stress supported by beam.

It is asking for max. bending stress supported by beam.

Vikram said:
8 years ago

The strength of shaft depends on torque transmitted.

So, A is correct.

So, A is correct.

Ayesh said:
4 years ago

Shaft strength depends upon polar modulus. So the answer is 1/8.

Indian said:
5 years ago

After simplification strength=1/4 *d ofshaft i.e 1/2*1/4=18.

Manjunath said:
4 years ago

T1= τ*z= pi*d^3/12.

T2= τ*z=pi*(d/2)^3/12= 1/8*T1.

T2= τ*z=pi*(d/2)^3/12= 1/8*T1.

KAY said:
7 years ago

Z (sectional modules) is directly proportional to (d)^3.

ROCKY said:
8 years ago

Section modulus proportional to strength.

Sweta said:
7 years ago

Can anyone explain this?

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