Physical Processes in Earth and Environmental Sciences Phần 4

Chương 3Hiển thị các đối tượng bị biến dạng đồng nhất phẳng (Hình 3.83b), các cạnh của hình vuông vuông góc với nhau, nhưng nhận thấy rằng cả hai đường chéo của hình vuông (a và b trong hình 3,83.) Ban đầu ở 90 đã biến dạng kinh nghiệm bằng cách cắt căng thẳng di chuyển đến vị trí a và b trong các đối tượng bị biến dạng.
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Physical Processes in Earth and Environmental Sciences Phần 4LEED-Ch-03.qxd 11/27/05 4:26 Page 88 88 Chapter 3 simple shear into a rhomboid, both the sides and the diag- (a) onals of the square have experienced shear strain. a b 90° 3.14.5 Pure shear and simple shear Pure shear and simple shear are examples of homogeneous strain where a distortion is produced while maintaining Angular shear γ the original area (2D) or volume (3D) of the object. Both (3) g = tan c types of strain give parallelograms from original cubes. g = tan c = tan –32° = –0.62 Pure shear or homogeneous flattening is a distortion which a converts an original reference square object into a rectan- –32° gle when pressed from two opposite sides. The shortening (b) produced is compensated by a perpendicular lengthening c b a 90° (Fig. 3.84a; see also Figs 3.81 and 3.83b). Any line in the object orientated in the flattening direction or normal to it does not suffer angular shear strain, whereas any pair of c perpendicular lines in the object inclined respect to these directions suffer shear strain (like the diagonals or the rec- (c) tangle in Fig. 3.83b or the two normal to each other radii in the circle in Fig. 3.84a). Simple shear is another kind of distortion that trans- 30° forms the initial shape of a square object into a rhomboid, so that all the displacement vectors are parallel to each other and also to two of the mutually parallel sides of the c rhomboid. All vectors will be pointing in one direction, g = tan 30° = 0.57 known as shear direction. All discrete surfaces which slide with respect to each other in the shear direction are named shear planes, as will happen in a deck of cards lying on a Fig. 3.83 Examples of measuring the angular shear in a square object table when the upper card is pushed with the hand (a) deformed into a rectangle by pure shear (b) and a rhomboid (c) (Fig. 3.84c). The two sides of the rhomboid normal to the by simple shear. displacement vectors will suffer a rotation defining an angular shear and will also suffer extension, whereas the ...