STRUCTURAL GEOLOGY HATCHER 6 Flashcards
Three end members of deformatio
Elastic
Plastic
Viscous
Objects with materia memory
Elastic
permanent strain that occurs without loss of cohesion and is the result of rearrangement of chemical bons in crystal lattices in minerals by one or more DISLOCATION CREEP MECHANISMS
Plastic
Behaviour of fluids such as water or magma or any other substances with LITTLE INTERNAL STRUCTURE and is perasive, permanent and involves dependence of strain rate on stress
Viscous
Another term for elastic behaviour
HOOKEAN
This implies failure in the elastic range particularly in breaching the elastic limit
Brittle behaviour
this best describes LINEAR ELASTIC BEHAVIOR in an isotropic Homogenous material and states that elastic strain is directly proportional to the stress applied
Hooke’s Law (Robert Hooke)
Mathematical equation of Hookes Law
Applied stress = Youngs modulus * strain
Therfore what is the formula for the elastic constant aka youngs modulus?
E= Stress/Strain = F/A / (L1-L0)/L0
Elastic behaviour under shear stress
Shear stress = Rigidity Moduls* Shear Strain
Thus rigidity modulus is equal to
G = Shear stress/Shear strain
This is where the stress strain curve changes slope abruptly which denotes area where hooke’s law is no longer applicable and beyond which the material begins to undergo permanent defomrtaion or ruptures
Yield point/Elastic Limit
This is the highest point in a stress strain curve
Ultimate strength
Rocks theoretically begins to fracture at this point or value of ultimate strength
Half of the ultimate strength
A measure of compressibility of PR = - E1 (Lengthening )/ E3 (Change in h (- shorthening) which is always positive
Poissons ratio
Poission’s ratio of water and its implication
0.5 = incmpressible
Possons of Halite
<0.5 low compressibility
Possons of less than 0.5 means
VOLUME Decreased
Formula of possons using Vp compressional and Vs Shear wave velocity
0.5 [1- (1/(Vp/Vs)^2-1)]
Beyond elastic limits the behaviour of solid and liquids respectively are
Solid: Plastic = liquid: Viscous
Stationary fluids that does not transmit shear stress
Perfect Fluids
Fluids in which there is linear proportionality between the differential stress or shear stress and shear strain rate
Newtonian Fluids
Si unit for Viscosity?
Poise
Equivalent of poise to stress units of Pa
10 poise = 1 Pa*s
Viscosity is
Differential stress/shear strain rate
Shear stress in fluids exists only when they are in?
Motion
aka ideal plastic behaviour that begins at yieald point
Saint Venant Behaviour
(Adhemar Jean Claude Barre de Sain Venant)
This pertains to the process when material increases resistant to deformatio as strain increases after the yield point
Strain hardening
This pertains to process when material decreases resistance to deformation as strain increases
Strain Softening
aka of elastiviscous behaviour
Maxwell Behaviour
Therfore what is the formula for the elastic constant aka youngs modulus?
Total shear strain = elastic shear strain + viscour shear stran
Suggested term for materials that deform like fluids (viscous strain is 100x the elastic strain)
Rheid
The phenomenon when Rocks behaviour vary in space and time by concentration of defromation into specific parts of a rock mass by different behaviour or mechanism
Strain Partioning
