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기술자료 Strand7 Problem of linear contact

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작성자 씨앤지소프텍
댓글 0건 조회 6,860회 작성일 21-01-27 15:48

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Problem of linear contact

 
An analysis is required to evaluate the complex state of stress just below the surface of a rail where localized contact stresses are induced in the head of the rail by a train wheel. The difficulty in modelling this particular contact problem is to devise a method whereby once the wheel makes contact with the rail surface it will not go beyond the boundary of the node line defining the rail surface. In addition to this condition, the nodes must be allowed to continue to move with the contact surface when the rail itself deforms. In the following picture the Strand7 mesh is shown.


Rail_1.gif
Mesh used for the linear contact analysis.


Rail_2.gif
Detailed view of the contact zone.


Rail_3.gif
Strand7 Dialog box for the definition of the contact element property.

To simulate these conditions using Strand7, we need to use Point Contact Zero-Gap beam elements. Since the gap is initially open these elements will be ignored by the solver (and hence the force they generate) during the first few iterations until the two surfaces contact. It is not until the wheel and rail make contact that the wheel will begin to induce a compressive stress in the gap beam element. At this point the gap beam element, now in compression, will be included in the solution.

The gap element can be considered in its simplest form as a line element joining two nodes at opposite points on two surfaces and, by knowing the initial distance between these two nodes, subsequent behaviour can be monitored. If contact is detected the elements possess an artificially high axial stiffness to prevent the wheel from intruding into the rail surface. A value for the initial stiffness of such elements must be entered in the dialogue box. If the Dynamic Stiffness option is set, Strand7 will update automatically that value during the computation.

The wheel and rail should be modelled using the four node quadrilateral plate element QUAD4 and set to either a 2D plane stress or 2D plane strain type solution. To check the integrity of the results (and hence the modelling technique), it is best to view the deformed plots using an absolute displacement scale of 1. The deformed shape of the rail as well as a Global XX Stress contour plot is shown below.


Rail_4.gif
Rail deformed shape and vertical dispacement contour plot.

This example has outlined the methodology used for analysing linear contact problems using Strand7. In many instances however, a contact problem will be both geometrically non-linear as well as a material non-linear problem. An example of a geometric non-linear contact problem is one in which the deformable part of the body will contact over a region which varies with load.


Rail8.gif
In Strand7, contours can be displayed on some parts of the model, while still drawing other parts without contours.

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