Stress and strain

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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.

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Stress and strain

  1. 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. 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. 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. 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. 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.

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