Oasys LS-DYNA Environment 8.1 VOLUME 3 ... - Oasys Software

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Oasys LS-DYNA Environment: User Guide (Version 8.1) contact search will then identify where contact to the tooling will occur and will adapt the blank mesh according to the curvature of the tooling. Although this can create somewhat more elements than the two pass option it does allow the single pass option to be used (adpass = 1) giving the most efficient result. This option works best with the _FORMING_ contact algorithm; it also requires a fairly frequent check (adpfreq should be set so that the tools move less than the value of adpene between adaptions). Adaptivity can be turned on and off during the analysis to reduce the additional cpu demand. The ioflag is useful to obtain the adapted mesh (with no displacements) at the end of the run. Mass scaling is generally used to prevent the small elements created by adaptivity from controlling the timestep. Metal forming is well suited to parallel processing and excellent speed up factors can be obtained with LS-DYNA. The number of processors to be used is set using *CONTROL_CPU. DATABASE CARDS It is essential that the strain tensor is included in the output; set the variable strflg to 1 on the *DATABASE_EXTENT_BINARY card. The compressed database option is worth considering as it will greatly reduce the size of the d3plot files because it will omit superfluous data relating to the rigid tooling. POST-PROCESSING Almost all of the useful data from a sheet metal forming simulation is in terms of strains; total plastic strain is insufficient to assess the success or failure of the process and even thickness strains do not, on their own, give an assessment of the likelihood of splitting. The strain tensor, projected into the plane of the blank, gives us the major and minor strains. These strains can be plotted on a Forming Limit Diagram and compared with the Forming Limit Curve for that material (for low carbon steels this can be estimated from the material thickness and n value; for other materials experimental data must be obtained). This diagram is used to indicate splits and contour plots of formability can be derived from this. Oasys D3PLOT allows display of the FLD and formability contours with the option to click on a point in the FLD to turn on the corresponding element label on the contour plot. The direction of major and minor strains is also very helpful to understand material flow. Strain paths for selected elements should also be checked to help understand the forming process. These and several other types of data (thickness value, thickness strain, blank edge movement, wrinkle visualisation using shading plus links to ray-tracing packages, for highly accurate visualisation of surface deflects etc.) can be viewed using Oasys D3PLOT. Strains are generally in true values, but can be plotted as engineering strains (in %) for FLD plotting. Oasys D3PLOT also includes a DIE-CLOSURE plot which calculates the distance of the blank to a selected tool or tools; this is very useful for checking for complete tool closure and for die filling in hydroforming simulations. KEYWORDS USED IN METAL FORMING Page 17.8
Oasys LS-DYNA Environment: User Guide (Version 8.1) ` AIRBAG - pressure in hydro forming ` BOUNDARY_PRESCRIBED_MOTION_RIGID ` CONSTRAINED_RIGID_BODY_STOPPERS ` CONSTRAINED_EXTRA_NODES_OPTION (drawbeads) ` CONTACT ` CONTACT_ENTITY (VDA or IGES data) ` CONTROL (implicit, adaptivity) ` DAMPING ` DATABASE ` DEFINE (i.c., box, co-ords, vectors etc) ` DEFORMABLE_TO_RIGID (def of tooling) ` ELEMENT ` INCLUDE ` INITIAL (esp stresses and strains) ` INTERFACE ` LOAD (pt load, pressure, gravity) ` MAT ` NODE ` PART ` SECTION ` SET ` TERMINATION (stop due to displacement or contact force) ` TITLE Page 17.9
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Oasys LS-DYNA Environment 8.1 VOLUME 3 ... - Oasys Software

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