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Introduction to brittle deformation, condition to form and place for forming. Types of brittle deformation and effect of enviromental to brittle deformation. Đây chỉ là bài thuyết trình nhỏ và còn nhiều thiếu sót mong mọi người đọc và góp ý :)
Contents • Introduction • Classification of Brittle deformation • Effect of Environmental factors in failure Introduction What is brittle deformation? • Brittle deformation = the permanent change that occurs in a solid material due to the growth of fractures and/or sliding on fractures • A fracture is a surface of discontinuity (includes cracks, joints and faults) • Brittle deformation requires a loss of cohesion across a fracture, which only occurs when stresses exceed a critical value 1 Introduction What is brittle deformation? • Atomic structure of material: atoms and ions are connected to another by chemical bonds as tiny spring Recoverable Nonrecoverable Figure: The chemical bonds are represented by springs and the atoms by spheres Elastic strain fracture Introduction What is brittle deformation? • The two main classes of geologic structure resulting from brittle deformation are faults and joints Faults result from shear stresses, and joints result from tensile stresses: • shear = movement parallel to plane of contact • tensile = movement normal to plane of contact Introduction What is brittle deformation? Brittle deformation: Rocks behave like a brittle solid and fracture + Near surface conditions + Relatively low pressure and temperature + Result is faulting Factors in Rock deformation: Pressure, temperature, rocks composition, time,… 2: Categories of Brittle deformation processes • Depending on purposes of our discussion: Cataclastic flow Frictional sliding Shear rupture Tensile cracking Classification of Brittle deformation 2.1 Cataclastic • Cataclastic flow: This type of brittle deformation refers to macroscopic ductile flow as a result of grain-scale fracturing and frictional sliding distributed over a band of finite width Classification of Brittle deformation 2.2 Frictional sliding • Frictional sliding: sliding on a pre-existing fracture surface, not involving plastic deformation mechanisms Requires a shear stress sufficient to overcome frictional resistance to sliding (no surface is perfectly smooth) 2 Classification of Brittle deformation 2.3 Tensile Cracking • Tensile cracking: propagation of cracks into previously unfractured rock during tensile stress In a homogeneous stress field, tensile cracks propagate in their own plane Most common near the surface (joints and veins,) c: Shear rupture 2: Categories of Brittle deformation processes • This type of brittle deformation results in the initiation of a macroscopic shear fracture at an acute angle to the maximum principal stress when a rock is subjected to a triaxial compressive stress Classification of Brittle deformation Figure: Types of brittle deformation 3: Effect of environmental factors in failure a: Effect of fluids on tensile crack growth • Rocks contain pores and cracks Which contain fluids( water, gas or oil) • High degree of permeability in the rock=> water flow easily from pore to pore and in or out of rock layer => Tensile crack growth B: Effect of dimensions on tensile strength • Large simple content appropriately oriented and larger cracks that will begin to propagate when stress is applied => failure of the whole sample => larger rock samples are weaker than smaller rock samples D: Effect of intermediate principal stress on shear rupture • Fractures form parallel to σ2, and so the value of σ2 does not affect values of normal stress (σn) and shear stress (σs) • However, σ2 does have a relatively small effect on rock strength Thank you for your attention ... tensile = movement normal to plane of contact Introduction What is brittle deformation? Brittle deformation: Rocks behave like a brittle solid and fracture + Near surface conditions + Relatively... joints and faults) • Brittle deformation requires a loss of cohesion across a fracture, which only occurs when stresses exceed a critical value 1 Introduction What is brittle deformation? • Atomic... spheres Elastic strain fracture Introduction What is brittle deformation? • The two main classes of geologic structure resulting from brittle deformation are faults and joints Faults result from