文档介绍：Chapter 9: How Rock Bends, Buckles, and Breaks
龔源成
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Why Is Rock Deformed?
Tectonics forces continuously squeeze, stretch, bend, and break rock in the lithosphere.
The source of energy is the Earth’s heat, which is transformed into to mechanical energy.
Stress 應力(Force/Area)
Definition: the force acted on per unit of surface area, SI unit = Newton/m2=Pascal.
Uniform stress is a condition in which the stress is equal in all directions.
It is confining stress or confining pressure (圍壓) applied to rocks because any body of rock in the lithosphere is confined by the rock around it.
Differential stress is stress that is not equal in all directions.
Differential (Deviatoric) Stress
The three kinds of differential stress are:
Tensional stress (張應力), which stretches rocks.
Compressional stress(壓應力), which squeezes them.
Shear stress (剪應力), which causes slippage (滑移)and translation (位移).
Strain (應變)
Strain (應變) describes the deformation of a rock. It is dimensionless and defined by the change in length to the original undeformed length.
Normal Strain (正應變) (2) Compressional strain
(1) Tensional strain
Shear Strain (剪應變)
Figure
Stages of Deformation (變形)
When a rock is subjected to increasing stress, it passes through three stages of deformation in ession:
Elastic deformation (彈性變形) is a reversible change in the volume or shape of a stressed rock. Elastic stress is linearly proportional to elastic strain.
Ductile deformation (塑性變形) is an irreversible change in shape and/or volume of a rock that has been stressed beyond the elastic limit (彈性限度), that is, yield stress.
Fracture (破裂) occurs in a solid when the limits of both elastic and ductile deformation are exceeded.
Figure
Ductile Deformation Versus Fracture
A brittle (脆性) substance tends to deform by fracture.
A ductile (塑性) substance deforms by a change of shape.
The higher the temperature, the more ductile and less brittle a solid es.
Rocks are brittle at the Earth’s surface, b