NUMERICAL SIMULATION OF CHEVRON FOLDS IN MULTILAYERS

The unique geometric features of chevron folds, such as straight limbs and narrow hinge zones, indicate specific deformation mechanisms during folding. It is commonly understood that either flexural slip, material anisotropy, or the hinge migration of kink bands or box folds can lead to the development of chevron folds. In this study, 2D finite element analysis of visco-elastic multilayer buckle folding is used to simulate the development of chevron folds for a variety of conditions. For effective material anisotropy (i.e. for layers of alternating competence), chevron folds are successfully simulated and form in the center of the multilayer fold stack. Key control parameters for the development of chevron folds are the viscosity contrast of competent to incompetent layers, the number of layers, and the thickness ratio of competent to incompetent layers. For numerical simulations of effective single layer folds (based on sinusoidal initial perturbations) involving flexural slip, chevron folds are not reproduced. In addition to sinusoidal initial perturbations, random (white noise) and chevron shaped initial perturbations are applied to investigate if flexural slip contributes to the development of chevron folds. Since several studies report that flexural slip occurs in the later stages of chevron folds, usually at an interlimb angle of 60-70 degrees, additional model setups are tested to find the contributing mechanisms to form chevron folds.