Strain Hardening Behavior Exercise - Example Answers

What is the value of flow stress at strain = 1?

s = K

s = K.
On the stress-strain plot a value of n can be set and different values of K tried. It will be seen that the value on the stress axis for strain = 1 is equal to the value of K chosen.
A more easily seen answer can be obtained by by setting a value for K and trying various values of n.

Which material parameter, K or n, has a larger effect on material strength?

For example, using a value of e = 2
with K = 200 MPa

for n = .2 the flow stress is about 225 MPa
for n = .4 the flow stress is about 250 MPa
a ( 250 - 225 ) / 225 change of 11%
with n = .4
for K = 200 MPa the flow stress is about 250 MPa
for K = 400 MPa the flow stress is about 575 MPa
a ( 575 - 250 ) / 250 change of 130%
Answering this question requires defining "strength" and deciding on a method for comparing values of strength. One possibility is to define strength as the flow stress at a particular value of strain and ask, does doubling the value of K or n have a larger effect on flow stress?

If the value of K is doubled, by how much does the flow stress change?

The effect of doubling the value of K at n = .4 and e = 2 was determined above.

with n = .2 and e = 2

for K = 200 MPa the flow stress is about 250 MPa
for K = 400 MPa the flow stress is about 525 MPa
a ( 575 - 250 ) / 250 change of 130%

If the value of n is halved, by how much does the flow stress change?

Again, flow stress depends on K and e as well as on n so the answer will vary with the values of K and e at which the comparison is made.


Back to Strain Hardening Solution Procedures
© 2001 by Barney E. Klamecki. All rights reserved