Christos Kassapoglou

Stacking Sequence Blending of Multiple Composite Laminates Using Genetic Algorithms

Abstract This paper presents a methodology for designing any two-dimensional array of laminated composite panels with varying loads such that continuity of some or all of the plies is maintained across adjacent panels. This design process is commonly referred to as blending and is beneficial in helping to minimize the manufacturing effort and cost of the panels while meeting structural requirements at minimum weight. The methodology discussed here involves an automated 2-step optimization process using a commercial genetic algorithm software code called DARWIN . The methodology is tested using a 3×3 array of sandwich panels, and an 18-panel group arranged in a horseshoe pattern. Results for each design problem are generated using ADOPTECHs Java-based composite laminate design software called OLGA , which utilizes the DARWIN optimization engine. A comparison between the individually optimized panels designs and the blended designs for each design problem is also presented.

Determination of Interlaminar Stresses in Composite Laminates under Combined Loads

A method to determine the complete state of stress at free edges of com posite laminates under combined loads (uniaxial tension or compression, moment, and out-of-plane shear) is presented. Based on the principle of minimum complementary en ergy, two coupled ordinary differential equations are derived with use of calculus of varia tions. The stresses are determined in closed form and are in good agreement with other solutions published in the literature for uniaxial tension and applied moment. This solu tion is applicable to general laminates with straight free edges and is computationally very efficient.

Simultaneous cost and weight minimization of composite-stiffened panels under compression and shear

An approach is presented to determine the part configuration that minimizes the cost and weight of composite-stiffened panels under combined compression and shear loads. The stiffened panel is designed so that no overall, bay, or stiffener buckling occurs under the applied loads. Skin and stiffener material failure conditions and manufacturing constraints are also imposed. The stiffened panel cost and weight are minimized for a variety of stiffener cross-sectional shapes. A set of near-optimum (in a Pareto sense) configurations is determined. The final optimum configuration is selected from this set by minimizing a weight and cost penalty function.

Minimum cost and weight design of fuselage frames ☆: Part B: cost considerations, optimization, and results

Abstract An approach is presented to design fuselage frames for minimum weight, minimum cost, or a combination of the two. The approach combines structural requirements and manufacturing constraints into an optimization scheme that alters the geometry of the individual frame components until the objective function is minimized. In addition to the lowest weight and cost points, a near-optimal Pareto set of designs is found, out of which the design that minimizes both cost and weight is determined through a penalty function approach. Four different fabrication processes are considered: conventional sheet metal, high speed machined metal, hand laid-up composite, and resin transfer molded composite. For lightly loaded frames, an automated resin transfer molding process gives the lowest cost and weight designs. For highly loaded frames, high speed machining gives the lowest cost design but automated resin transfer molding gives the lowest weight design. The effects of fabrication process and some of the design and manufacturing constraints on cost and weight are examined.

Minimum cost and weight design of fuselage frames. Part A : design constraints and manufacturing process characteristics

Abstract As part of an approach to design fuselage frames for minimum weight, minimum cost, or a combination of the two, the design constraints and the effects of manufacturing process are discussed. Four different fabrication processes are considered: Conventional sheet metal, high speed machined metal, hand laid-up composite, and resin transfer molded composite. For each process, the limitations and applicability are translated to constraints for the geometry of the frame. In addition, the constraints arising from structural requirements are presented and discussed. These constraints are discussed as a necessary foundation for solving fuselage frame cost and weight optimization problems.

Calculation of stresses at skin-stiffener interfaces of composite stiffened panels under shear loads

Abstract A simple energy-based approach to calculate stresses at skin-stiffener interfaces of composite stiffened panels under shear loads is presented. Solutions to the governing partial differential equations are sought that satisfy boundary conditions and traction continuity. The stress functional forms are determined by minimizing the energy using a variational approach. The resulting closed form stress expressions are compared to finite element solutions and are shown to be in very good agreement.

Determination of the optimum implementation plan for manufacturing technologies — The case of a helicopter fuselage

Abstract This paper presents an approach to determine manufacturing technology implementation scenarios as a function of time. The optimum paths from the point of view of minimum investment or maximum recurring cost savings are determined, and their advantages and disadvantages are discussed. The logic and the results of a software code created to determine these paths are described. Hybrid scenarios that compromise between the two cases of minimum investment and maximum recurring cost savings are also presented. The approach is based on using a target optimum technology mix that yields the lowest recurring cost with a given probability. This target is determined assuming that all candidate technologies are available immediately and are applicable over the entire structure. Then, the applicability of the candidate technologies as a function of time is determined, and the non-recurring cost associated with process and product development is calculated as a function of time. The applicability and non-recurring cost are used to generate time-dependent implementation paths that reach the target technology mix with lowest investment or maximum yearly recurring cost savings.