# 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'
one-eighth
one-fourth
one-half
four times
Explanation:
No answer description is available. Let's discuss.
Discussion:
12 comments Page 1 of 2.

Gowthamraj Mohan said:   8 years ago
1/4 times is correct.
(1)

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.
(1)

ROCKY said:   8 years ago
Section modulus proportional to strength.

Vijay said:   8 years ago
It is 1/4 times.

Vikram said:   7 years ago
The strength of shaft depends on torque transmitted.

So, A is correct.

Sweta said:   7 years ago
Can anyone explain this?

KAY said:   7 years ago
Z (sectional modules) is directly proportional to (d)^3.

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.

Shivam said:   6 years ago
Given answer is right and you are right @Meet.
It is asking for max. bending stress supported by beam.

Indian said:   5 years ago
After simplification strength=1/4 *d ofshaft i.e 1/2*1/4=18.