Mechanical Engineering - Strength of Materials - Discussion

Suddenly applied load, having higher velocity compared to gradually applied load.

Twice stress why & which formula used this it may be more than twice or little less than twice.

When the load is applied slowly due to viscous dissipation by the atmosphere only half of the energy is stored as compared to the case when the load is applied suddenly.

In case of impact loading the dynamic force experienced by the body is given by P(dyn.) = W*[1+sqrt(1+2h/D)].

Here P = dynamic load experienced by the body.
W = static load which is impacting.
D = stact deflection due to above load.
h = height from which load is acting.

In this case h=0, So dynamic load experienced by the body is twice the load applied. As load to area is stress so stresses induced will be twice.

It is experimentally proved that the stress developed by impact load is twice than developed by gradually applied load.

Ya. As per the formula. Suddenly applied load doubled than gradully applied load.

When we loaded suddenly load 'w' then we consider 'w' load in stress while we loaded gradually load "w' then we consider average value of 'w' which will be w/2 in the stress calculation.

So we know that,
Stress = load/area.

So let p1 is stress when suddenly load and p2 is stress when load is gradually.

So p1 = w/area.

And p2 = (w/2)/area.

So p1/p2 = [w/aria]/[ (w/2) /aria].

So p1/p2 = 2.

p1 = 2p2.

Thats proves that suddenly loaded stress is double to the gradually loaded stress.

Because new load is P=P1+P2, where P1=P2 so the stress is twice.

@Aman.

How can you say that the average load is w/2?

In case w is split into 4 loads (w1+w2+w3+w4) applied gradually then average would come w/4.

In this case answer would come 4 times. Your method is completely wrong.

Stress do not depend on rate of application of force I prefer equal in both the cases.