Mervyn S. Paterson is an Australian engineer best known for his application of the principles of engineering and materials science to the analysis of the structures, fabric, and behavior of rocks, particularly those generated during brittle deformation.
-Plastic failure is defined as the flow of matter in response to stress. Instead of being confined to narrow, discrete zones of separation across which rock fragments are displaced, plastic failure involves the deformation of the entire body of rock in which grains are flattened, extended, and rotated without the concurrent development of discrete through-going fault planes or fracture surfaces. Recrystallization of minerals usually always accompanies plastic failure, and this is expressed in the development of foliation and, more strikingly, the development of folds. Plastic deformation occurs at depths within the Earth where rock materials are experiencing great heat, thusly reducing their internal strength (or competence). Metamorphic rocks almost always exhibit some degree of plastic failure or flow. Plastic flow is ubiquitous to the asthenosphere, the high temperature zone which directly underlies the lithosphere from its base to depths in excess of 700 kilometers.
Questions.
1. How does the study of the mechanical behavior of rocks benefit society? Cite specific
examples.
2. Define the term elasticity. Which type of materials exhibit elasticity? Can a material
exhibit unlimited elasticity? Explain.
3. Briefly explain the meaning and significance of the elastic constant.
4. Define the term plasticity. How does plasticity differ from elasticity? At what point does
elastic behavior become plastic behavior? Explain.
5. Briefly define yield stress. Explain its significance in terms of material behavior and what
sort of information about a particular material it provides.
6. Briefly define the term failure. Which sorts of features in a rock body indicate a history of
failure?
7. Briefly define and distinguish among the three basic types of permanent deformation. At
which location within the Earth do each of these types of deformation occur? Be
specific.
8. How is the Earth's lithosphere defined and characterized? How is the Earth's
asthenosphere characterized? What is the observed consequence of the lithosphere-
asthenosphere system? (THINK!)
9. Assign each of the following situations a proper deformation term:
a. Squeezing a sponge.
b. Bending a spoon.
c. Chopping wood.
d. Heating butter.
e. Melting ice.
f. Molding clay.
g. Sculpting stone.
h. Squeezing a styrofoam cup.
i. Swatting a baseball.
j. Tearing paper.
k. Shaping pizza dough.