tailieunhanh - Physical Processes in Earth and Environmental Sciences Phần 4

Chương 3 Hiển thị các đối tượng bị biến dạng đồng nhất phẳng (Hình ), 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. | 88 Chapter 3 Fig. Examples of measuring the angular shear in a square object a deformed into a rectangle by pure shear b and a rhomboid c by simple shear. shows the object deformed by homogeneous flattening Fig. the sides of the square remain perpendicular to each other but notice that both diagonals of the square a and b in Fig. initially at 90 have experienced deformation by shear strain moving to the positions a and b in the deformed objects. To determine the angular shear the original perpendicular situation of both lines has to be reconstructed and then the angle can be measured. In this case the line a has suffered a negative shear with respect to b. The line a perpendicular to b has been plotted and the angle between a and a defines the angular shear. The shear strain is calculated by the tangent of the angle . The same procedure can be followed to calculate the strain angle between both lines plotting a line normal to a . Note that in this case the shear will be positive as the angle between b and a is smaller than 90 . In the second example Fig. the square has been deformed by simple shear into a rhomboid both the sides and the diagonals of the square have experienced shear strain. Pure shear and simple shear Pure shear and simple shear are examples of homogeneous strain where a distortion is produced while maintaining the original area 2D or volume 3D of the object. Both types of strain give parallelograms from original cubes. Pure shear or homogeneous flattening is a distortion which converts an original reference square object into a rectangle when pressed from two opposite sides. The shortening produced is compensated by a perpendicular lengthening Fig. see also Figs and . Any line in the object orientated in the flattening direction or normal to it does not suffer angular shear strain whereas any pair of perpendicular lines in the object inclined respect to these directions suffer shear strain like the .