Composite structural sizing software improves with new design and manufacturing features

HyperSizer v6 structural sizing and analysis software can help reduce structure weight while maintaining strength and improving manufacturability, especially for complex composite and metallic designs. Developed and proven at NASA, the software—the first commercialized by the agency—has a track record of 20% weight reduction in high-profile government and commercial aerospace projects.

Composites have gained wide acceptance and validation in aerospace applications while accelerating growth in a variety of industries. Their weight-to-strength properties promote fuel efficiency and allows hitting energy targets without impacting durability. “One of the biggest roadblocks to effective composite design is the inability of engineers to adequately explore optimized layups simultaneously with other design variables,” says Collier Research President Craig Collier. “This results in design inefficiencies and compromises.”

To address the issues, HyperSizer works with FEA solvers in a continuous, iterative loop, conducting trade studies and examining millions of potential design candidates down to the ply, even element level. The software ensures structural integrity through an extensive suite of failure analysis predictions that are validated to test data. The tool also enhances manufacturability by minimizing ply drops, identifying and controlling laminate transition drop/add boundaries, and defining best ply shapes and patterns. Hypersizer can be used from preliminary design to final analysis.

New features in HyperSizer v6 include:

• Manufacturability optimization – To help design for efficient manufacturing, the software can now identify, define, and control ply-count compatibility, laminate sequencing, interleaving, and ply-drop minimization. This results in fewer processing steps, cost-effective layups, and a faster turnaround in the mold.
• Post-buckling analyses – Automated compression, shear, and compression-shear post-buckling analyses have been added. These are based on complex NASA-developed methods that serve as the foundation for metal aircraft design. Integrated with flexural-torsional buckling, these let engineers cut weight in aluminum skin airframes. Such analyses, difficult to perform with nonlinear FEA alone, have been extended to composite material systems as well.
• Panel Concepts – Two novel, damage-tolerant composite architectures are now available, providing more structural sizing variables and optimization flexibility: Prseus is a Boeing, NASA, and Air Force Research Lab-developed dry-fabric woven material poltruded rod structure, while “reinforced core sandwich” is an alternative sandwich panel similar to foam sandwich. Specialized analyses for both these panel concepts have been implemented and correlated to test data established for accurate strength predictions.

Serving as the analysis hub and automating data transfer during design and manufacturing cycles, HyperSizer integrates with FEA software, such as Nastran and Abaqus, and with composite CAD tools, such as Catia and FiberSIM. HyperSizer ensures that design and analysis departments are kept current and working with the same design data.

“Given the increasing emphasis on more complex materials, engineers must improve and automate their design processes to reach higher levels of efficiency,” says Collier. “It’s no longer good enough to spot-check. Each part must be examined as a system. HyperSizer lets engineers more fully explore the entire design space.”

“It’s challenging to cut weight while maintaining strength and controlling cost,” says Tom Ashwill, technical leader in Sandia National Laboratories Wind Energy Technology Department. “HyperSizer has the capability to systematically optimize placement of a variety of different materials throughout the blade to maximize load resistance and minimize weight and thus cost.”

Collier Research Corporation
www.hypersizer.com

Building a better turbine blade

Craig Collier/President, Collier Research Corp./Hampton Roads, Va./ hypersizer.com

A first objective on most any large design project is to get to the lightest weight possible. At NASA Langley Research Center, where I helped develop the code that later became HyperSizer, designs for spacecraft that include composites also have a zero failure-tolerance. Those projects must strike a critical balance between low weight and high strength. The same is true in the wind-power industry. Weight is of tremendous importance when designing wind-turbine blades because a lighter blade uses less material, it is easier to manufacture and transport, and has lower fatigue loads.
With failure rates still high for turbine blades (a Sandia survey of wind energy plants documented rates as high as 20%) and down-time costly and bad for business, blade designers and manufacturers must turn to the best practices for designing composites.
HyperSizer software, for example, is a composite optimization and structural sizing tool that works out-of- the-box with a wide variety of finite-element analysis (FEA) solvers. The tool couples with FEA in a feedback loop, searching for solutions that minimize weight while at the same time maximizing structural integrity and manufacturability. The software analyzes complex composite structures (it works with metals and other materials as well) by quickly evaluating designs in a ply-by-ply, and even finite element-by-element, manner. Optimizing all possible permutations for a composite laminate design gives engineers control of most every design detail.

Design improvements to wind-turbine blades should increase their efficiency and performance, trim the cost of harvesting the wind, and keep it competitive with fossil fuels. To increase the power generating capacity of a turbine, blades must grow in length (power captured by a turbine is proportional to the square of blade length). As they grow, blades must be kept as light as possible. Lighter weight means better performance, longer life, lower manufacturing costs, and shortened manufacturing cycles, all factors that enhance competitiveness in energy markets. With a legacy in aerospace, the software has helped users such as NASA, Lockheed Martin, Boeing, and Bombardier, trim at least 20% of the weight from structures. The same can be true for wind-turbine blades.
Current utility-scale turbines are equipped with blades that range from
40 m (130 ft) to 90-m (300 ft) diameters. But there are prototype and concept blades on drawing boards that approach a staggering 145-m (475 ft) diameters. Design engineering issues such as structural strength, fatigue performance, buckling stability, blade stiffness, wing-tip deflection, and twist limits become increasingly important as turbine blades get longer. In simple terms, a blade must be as light as possible but stiff enough to maintain its aerodynamic shape and durable enough to carry wind loads without material failure. Furthermore, large blades must have a proper distribution of weight and stiffness to avoid instabilities produced by aeroelastic loads.

To optimize a blade’s design, the software begins where traditional FEA ends. Starting with a finite-element model and coupling seamlessly with FEA solvers, the software verifies structural integrity, predicts failure modes for all aeroelastic load cases, and identifies failure locations and loads, thereby achieving required safety factors. To resolve unacceptable safety factors, or simply to find a lighter weight design, it sizes (optimizes) a design by surveying millions of design-candidate dimensions and laminates. Setup, run time, and interpretation of results and initial redesign are typically accomplished in as little as four hours.
To evaluate what-if scenarios, trade studies, and sensitivities of a blade design, the software takes internal unit loads computed by FEA and determines an optimal combination of panel-and-beam concepts, cross-sectional dimensions, materials, and layups. To do so, it analyzes hundreds of different failure modes, achieving positive margins of safety (safety factor =1) for all analyses, all blade areas, and all load cases. The software also does panel trades. For example, a honeycomb or foam sandwich might be good for the shear web while a solid laminate might work best on a blade’s leading edge. The software can examine different layup stacks, as well as panel cross-section shapes.
The software eliminates manual calculations, offline spreadsheets, model re-meshing, and long running batch jobs. It also evaluates ply drop-off and ply-add patterns to help find the lightest laminate that meets strength requirements and with the fewest transitional regions.

HyperSizer includes features to evaluate blade areas with bolts (between blade sections) and adhesive joints (between the shear web and skin, for example). Analyses of bolt areas can prevent the common problem of overbuilding with heavier construction by optimizing padup thickness. Advanced analysis of adhesive joints looks at interlaminar shear and peel stress, delamination, and crack initiation.
A built-in library of materials can manage temperature and moisture-dependent properties, and can be customized with proprietary company and project data. The database includes metallics (isotropics), graphite and glass-fiber systems, sandwich cores (honeycomb, foam, syntactic), and hybrid laminates (plies of tape, fabric, and metallic foil). This extensive material list lets users analyze over 100 non-FEA based failure modes for all load cases. In addition, Sandia National Laboratories’ MSU/DOE Fatigue Database with 10,000 results on about 150 materials, can be imported to provide further capability.
In one application of the software, by NASA, it was the preliminary and final design tool (for flight certification) for projects such as the Ares V rocket and the astronaut’s composite crew module.
The economic and political climate is primed for growth in wind energy, but turbine performance, blade design, advanced materials, and quality in the field must reach the highest standards to help propel the industry forward. HyperSizer, with its composite analysis capabilities, has delivered great value to the aerospace industry and is ready to provide the same design assistance to the wind industry. It’s time for the wind industry to share in the benefits of the aerospace community’s accumulated expertise, without having to reinvent a composite wheel.