OLGA

Optimization of Laminates using a Genetic Algorithm

ADOPTECH's composite laminate design tool, referred to as OLGA (Optimization of Laminates using Genetic Algorithms) allows the user to design monolithic composite laminates for minimum weight subject to buckling and/or strength constraints. The program can also design constant thickness laminates for maximum buckling and/or strength failure loads. The user can design multiple laminates simultaneously , and optionally find the best blended laminate design such that continuity of the stacking sequence from one laminate to another is maintained (see further explanation below)

OLGA is powered by an advanced Genetic Algorithm (GA) optimization code, called DARWIN, which has been tailored specifically for designing laminated composite structures. Composite laminate design problems are inherently discrete in nature, since ply thicknesses, materials, and orientation angles are usually restricted to a discrete set of values due to manufacturing considerations. Because GAs are one of the few optimization algorithms that work directly with discrete design variables, they are well suited for composite laminate design. Additinally, "blended" laminates (structures composed of several contiguous laminates that contain common layers to aid in the manufacturing process) can be designed using the features of the GA.

The main console shows DARWIN's operational status and information about each of the top designs. For each design the following information is displayed:

• The material key (which indicates the material used for each ply)
• Total number of plies in the laminate
• Laminate stacking sequence
• Laminate weight
• Critical load factor and failure mode

Information displayed on the main console can be updated at any point during the optimization run by pressing the Update button, which updates the best designs printed in the main console with the most recent best designs.

The Laminate Characteristics window allows the user to set the number of plies in the stacking sequence, the possible ply orientation angles, and the ply material types.

The radio buttons denoting the choice between fixed/variable number of plies control the text boxes that are used to specify the limits. For the Fixed number of plies option, the desired number of total plies is required and all designs use this value. When Variable number of plies is selected, both the lower and upper limits are required and the optimizer will determine the number of plies for each particular design. If the two-ply stack option is chosen, the number of plies is constrained to be a factor of four.

The balancing condition of the laminates can also be specified through the use of radio buttons. As a default choice, laminates are required to be balanced, which means that for each ply oriented at +45° there must exist another ply oriented at -45°. For the Balanced case, there is no requirement for the +45° ply to be adjacent to the -45° layer, they can be separated from one another by plies with other orientations. If the user selects the Two-ply stacks radio button, DARWIN will create laminates using 0₂°, ±45°, and 90₂° ply stacks, thereby automatically satisfying the balance constraint.

The Ply Angles checkboxes specify which ply orientation angles are available for design. In general, all of the angles should be checked, though some users may want to investigate panels that are only constructed of cross-ply laminates. At least one ply angle must be selected. Similarly, Ply Materials may be selected using the appropriate box. At least one material must always be selected, while up to three can be used (for this version of the software) during the design process.

OLGA has many options for controlling the optimization algorithm. Multiple genetic operators, convergence criteria, and population parameters may be modified to suit your problem.

One of the most unique and powerful features of OLGA is the ability to design blended laminates. Structures containing multiple composite panels must be able to transfer loads between the individual panels. One of the best ways to transfer these loads is to blend adjacent panels such that they share layers of the same material and fiber orientation. Blending results in more easily manufactured composite structures with minimum weight penalty.

In addition to traditional straight fiber laminates, OLGA will also design steered fiber laminates. Fiber steering is a method of construction for fiber-reinforced composites that allows the unidirectional fibers to be aligned along curvilinear paths. Fiber steering is performed by an advanced tow placement machine, such as Cincinnati Milacron’s VIPER™, which is able to steer the fibers along the desired paths through computer controlled trajectories. The shapes of the fiber paths are determined from software programs developed by ADOPTECH personnel. Research has shown that optimal fiber paths exist which can improve the performance of laminates under basic loadings. For more information about fiber steering, click here.

Whether you are an expert composites designer or are just learning, the OLGA Help set will ensure that you get the most from this powerful software.