Ply-based Sizing (Parameter) Optimization

Ply-based Laminate Modeling

Complimentary to the conventional property-based composite definition, a new ply-based modeling technique was introduced in OptiStruct 9.0. In this format, laminates are defined in terms of ply entities and stacking sequences, which reflect the native language of ‘ply-book’ standards to composite laminate modeling and manufacturing. This is also analogous with how a laminate composite is manufactured. The PLY card specifies the thickness, orientation and material data for each ply, as well as its layout in the structure. The STACK card ‘glues’ the PLYs together to produce the laminate structure. Properties of every zone of unique laminate lay-ups are uniquely, albeit implicitly, defined. This allows you to simply focus on the physical buildup of the composite structure and eliminates the burden associated with identifying patches (PCOMPs) of unique lay-ups, which can be especially complicated for a free-sizing generated design.

Ply-based Optimization

In property-based sizing (parameter) optimization, the designable entities are the ply thicknesses associated with the PCOMP(G) properties. In ply-based sizing (parameter) optimization, the PLY thicknesses are directly selected as designable entities. This approach greatly simplifies the design variables definition, since ply continuity across patches is automatically taken into account.

As with free-sizing optimization, several composite manufacturing constraints are available to control the thickness of the laminate or the thicknesses of specific orientations. These constraints are defined on the DCOMP card and should generally be inherited from the concept phase. A mechanism exists whereby the composite manufacturing constraints defined in the free-sizing phase are automatically carried over into the ply sizing (parameter) optimization phase. This is part of the same mechanism that also generates the input file for the ply based sizing (parameter) optimization (phase 2), containing ply bundles as explained in the section on Free-sizing Optimization. Through this, the ply bundles are automatically set up for optimization with the necessary DESVAR and DVPREL cards defined. The ply bundles are now ready to be sized to determine the optimum thickness per bundle per fiber orientation.

In addition, discrete optimization is automatically activated when TMANUF, the thickness of the basic manufacturable ply, is specified for the PLY associated with a given design variable. This feature forces ply bundles to reach thicknesses reflecting a discrete number of physical plies.

Therefore, from a ply bundle sizing (parameter) optimization, the number of plies required per orientation can be established.

Typically, additional behavioral constraints such as failure, strain, etc. are added to the problem formulation at this stage.

To proceed to the final phase, an input file for phase 3 can be automatically generated from running phase 2, i.e. ply bundle sizing (parameter) optimization.

Note: Automatic offset control is available in composite free-size and sizing (parameter) optimization wherein the specified offset values are automatically updated based on thickness changes. The offset values can be specified on the PCOMP(P/G) property entries or the CTRIA3/CTRIA6, CQUAD4/CQUAD8 element entries using the Z0 or ZOFFS fields.