A brief description about the concept of stress and strain as a basis to understand rheology. This is part of IMK 209 - Physical Properties of Food, a second year level course in Food Technology, School of Industrial Technology, Universiti Sains Malaysia. Lecturer: Prof. Abd Karim Alias.

1. 1
We all deal with stresses and strains in
our daily lives, but the way food
materials respond to stress and strain
impacts processing, appearance,
and most importantly texture
Stress & Strain
Rheology is mainly
concerned with
relationship between
strain, stress, and time
This
work
is
licensed
under
a
Crea3ve
Commons
A7ribu3on-­‐NonCommercial
3.0
Unported
License.

2. 2
Turning around to look
for blemishes on the
apple; it does not tell
you anything about the
texture…
A Simple Rheology Experiment
Pressing with the finger will
deform the apple (dented)
and this will provide some
basic information on the
firmness of the apple – a
simple rheology experiment!

3. 3
• Strain is simply a quantitative measure of the
extent to which an element of material has
been deformed
• Deformation implies a change of shape (i.e.
dimensional change).
Definition of Strain

4. 4
When you press the apple,
you are actually applying a
force, or stress, with your
finger to deform the apple
Definition of Stress
• We can think of stress as a normalised
force, i.e., force acting on a unit area.
• think of stress as the intensity of force
Stress is simply defined as a force
per unit area

5. 5
Force intensity is different
when you press your finger
on the pencil than that of
the pin
Definition of Stress
Stress is higher with the pin
than that of the pencil,
assuming the same force
magnitude is applied.