| Abstract: | The paper deals with the displacement and stress distribution in boudinage structures. To analyze this, the finite-element method is used. Four models are examined.The first model treats three homogeneous bands. The displacement of the central band produces a barrel-shaped structure. The tension is greatest in the central part of this band and decreases almost continuously towards the shorter edges. If the band ruptures, the rupture will occur in the central part.The second model treats a quarter of a total structure that is already in part a developed boudinage. This development is followed through 19 iterative steps. The displacement analysis demonstrates that the boudin is displaced towards the free short edge and becomes more barrel-shaped, thinner and wider. The mean stress has two, local, tensilestress maxima inside the boudin at the upper boundary: one in the gap area and the other in the matrix at the outer, short edge of the boudin.The third model treats a quarter of a developed boudinage with two materials in the matrix. Displacement analyses demonstrate that the barrel shape of the boudin becomes more pronounced when the competence contrast between boudin and matrix decreases.One axis of principal stress has a direction in every element close to the x-axis of the model. In the area marked PbS (model 6A), this axis shows a local tensile-stress maximum and a local compressive-stress maximum. In model 6B, these points are still extreme points, but the local compressive-stress maximum has changed to a local tensile-stress maximum.The fourth model treats a boudinage in which one boudin is rotated. Displacement analyses demonstrate that the boudins tend to rotate to a position in which they are parallel, diverging a little from a right angle to the angle of the applied pressure. The mean stress demonstrates a pressure shadow in the PbS area, with a slight displacement downwards in the area beside the rotated boudin.The stress distribution corresponds to the mineral distribution of the boudinage from the Udden Mine. The investigation indicates a direct relationship between grain size and stress distribution. |
