(Confining Stress) 和应变速率(Strain Rate).PPT

Chapter 9: How Rock Bends, Buckles, and Breaks How 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 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). Stages of Deformation (變形) Strain (應變) describes the deformation of a rock. When a rock is subjected to increasing stress, it passes through three stages of deformation in succession: Elastic deformation (彈性變形) is a reversible change in the volume or shape of a stressed rock.. 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). Fracture (破裂) occurs in a solid when the limits of both elastic and ductile deformation are exceeded. Strain (應變) Normal Strain (正應變) Shear Strain (剪應變) Ductile Deformation Versus Fracture A brittle (脆性) substance tends to deform by fracture. A ductile substance deforms by a change of shape. The higher the temperature, the more ductile and less brittle a solid becomes. Rocks are brittle at the Earth’s surface, but at depth, where temperatures are high because of the geothermal gradient, rocks become ductile. Confining Stress Confining stress is a uniform squeezing of rock owing to the weight of all of the overlying strata. High confining stress hinders the formation of fractures and so