中国地质大学：《构造地质学》课程PPT教学课件（英文版）Lecture 19 Stress（1）

Lecture 19 Stresses (1)

Lecture 19 Stresses (1)

F orce Force is a kind of mechanical action between different objects it tends to change the shape, volume or movement state of the object with a force upon it Force is a vector quantity, and thus possesses both magnitude and direction; it can be represented by an arrow whose length specifies the magnitude and whose orientation specifies the orientation of the force Force mass X acceleration (kg m s-2)INewtonIINI Unit. Newton Newton=I kilogram meter per second squared scalar (on ly magnitude vector

Force Force is a kind of mechanical action between different objects, it tends to change the shape, volume or movement state of the object with a force upon it. Force = mass × acceleration (kg m s-2 ) [Newton][N] Force is a vector quantity, and thus possesses both magnitude and direction; it can be represented by an arrow whose length specifies the magnitude and whose orientation specifies the orientation of the force. F Unit: Newton 1 Newton = 1 kilogram meter per second squared vector scalar (only magnitude)

F A B Resolution and resultant of forces A Force F resolved into two components F, and F B Two forces F and F2 represented by resultant F

Resolution and resultant of forces A Force F resolved into two components F1 and F2 . B Two forces F1 and F2 represented by resultant F F1 F2 F F1 F2 F A B

Surface forces and body forces Surface forces: the forces acting on the contact surface between adjacent parts of rock system, between adjacent blocks or adjacent lithosphere plates. The contact surface may be or may be not a visible material boundary It can be a imaginary surface inside the object considered

Surface Forces and Body Forces Surface forces: the forces acting on the contact surface between adjacent parts of rock system, between adjacent blocks or adjacent lithosphere plates. The contact surface may be or may be not a visible material boundary. It can be a imaginary surface inside the object considered

Body forces Body forces: the forces can work at a distance and depend on the amount of material affected, so, we can call body forces distant forces. Gravitational force is an example of body forces. The gravitational force on a rock body of mass m is F=m where g is the acceleration of gravity. g varies with depth in the earth and with position on the earths surface, but for the purpose of structural geology, it is a constant 9.8m/sec2

Body forces: the forces can work at a distance and depend on the amount of material affected, so, we can call body forces distant forces. Gravitational force is an example of body forces. The gravitational force on a rock body of mass m is F = mg where g is the acceleration of gravity. g varies with depth in the earth and with position on the earth’s surface, but for the purpose of structural geology, it is a constant 9.8m/sec2 . Body forces

Nonuniform forces Imaginary plane Uniform forces F N=F Uniform Internal Forces ONA=FA External forces Internal forces and stresses Stress on a plane: internal forces acting on unit area of the given plane within the considering body

Uniform forces Nonuniform forces External forces Imaginary plane Uniform Internal Forces a b a F F F  N=F =N/A=F/A Internal forces and stresses Stress on a plane: internal forces acting on unit area of the given plane within the considering body. x

External forces △P m △E △P Internal △F forces area p stress △Pcp limar D △F->0 △FdF

p dF dp F P F = =    → lim 0 m Interna l forc e area F P P— F— External forces Internal forces area stress

Normal stress and shear stress Stress acting at a point m on a plane n is a vector, it can be resolved into two components o and t, o is normal to the plane, called normal stress, t is tangential to the plane, called shear stress

Stress acting at a point m on a plane n is a vector, it can be resolved into two components  and ,  is normal to the plane, called normal stress,  is tangential to the plane, called shear stress. Normal stress and shear stress

Magnitude and Units of Stress Magnitude of stress Stress=Force/Area, limit Area approaching zero Units of stress I Newton/m2 or a ' Pascal'l, or simply say"Pa That is 1 pascal= 1 newton per square meter newton=1 kilogram meter per second squared(1 kg m- a more commonly used unit is the bar or the kilobar, Where 1 bar=10 pascals=0. 1 MPa

Magnitude of stress Stress = Force / Area, limit Area approaching zero Units of stress [ Newton / m2 or a ‘Pascal’], or simply say ‘Pa’ That is 1 pascal = 1 newton per square meter. 1 newton = 1 kilogram meter per second squared (1 kg m s-2 ) A more commonly used unit is the bar or the kilobar, Where: 1 bar = 105 pascals = 0.1 MPa Magnitude and Units of Stress

Normal and shear stresses at a fault plane(a) and a bedding plane during flexural slip folding(B)

Normal and shear stresses at a fault plane (A) and a bedding plane during flexural slip folding (B)