Composites World – Simulation Saves

Posted on 9/1/2014

Source: Composites World

A look inside the increasingly well-equipped virtual toolbox for composite design, analysis, and manufacturing.

In the world of software, buzzwords are endemic. But if one buzzword trumps all, today, in the composite industry, it’s simulation. If there is an aspect of composites design, development or production that it would be advantageous to simulate digitally before facing the expensive proposition of producing the physical product, there’s a software product for it. Over the past few years, there’s been a big push to add or expand composite-focused simulation tools to existing software suites (signaled by Dassault Systèmes’ acquisition of Simulayt, Siemens PLM’s acquisition of Vistagy, and Autodesk’s numerous acquisitions of simulation software, including that created by Firehole Technologies). There is a strong drive to bring such software to maturity, providing more reliable validation of composite material systems, part design, structural analysis and manufacturing processes.


It’s a virtual world

It’s axiomatic: Money spent in the virtual world is much more money saved in the real world of product development. But there’s a catch: By nature, composites are far more complex and variable than the metals that preceded them. Yet, many software developers are rising to the challenge, and now, more than ever, the composites industry has a plethora of simulation software choices to add to its toolbox.

And none too soon. “When companies began working with composites, it was a very manual approach from design to analysis to manufacturing. Speed wasn’t necessarily as important as ensuring the part wasn’t over-designed or under-designed and met structural integrity,” says Rani Richardson, CATIA sales, North American market, Dassault Systèmes (Waltham, Mass.). “Today, there is a big push on the manufacturing side to streamline automation and produce high-quality parts faster. Machine throughput is critical. However, the design and simulation software used to feed the automated machine tools needs to be integrated and capable of producing numeric code to run the machine.”

The key from the developers’ side, says Richardson, is integration of software tools. “With integration from virtual design to virtual testing to virtual manufacturing, design engineers, stress analysts and manufacturing engineers have the ability to provide feedback to the other disciplines prior to sending the part to the shop floor. In the end, there is reduced lifecycle, improved part quality and an increase in the probability the part will be produced correctly the first time.”

Dassault Systèmes provides a variety of product development applications, including CATIA, SIMULIA finite element analysis (FEA) and DELMIA for manufacturability. Along with the company’s simulation software, these tools enable 3-D design, engineering, 3-D CAD, modeling, simulation, data management and process management. Earlier this year, the company announced Release 2014X of its 3DExperience platform’s on-site and on-the-cloud portfolio. Also of note is (Composites Design and Manufacturing Hub), which is hosted by Dr. Byron Pipes at Purdue University, and provides access to simulation tools, including Dassault’s. “The intent of this site is to recognize simulation software maturity level and assess gaps in the process while educating the composites community of what tools are available,” explains Richardson.


Better optimization

What drives the majority of composites simulation, for the user, is optimization. Leigh Hudson, Fibersim product manager, Siemens PLM Software (Waltham, Mass.), says, “People are finally getting to the point, especially in the aerospace and defense markets, where it’s not a question of ‘Can we build it?’ but ‘How can we optimize it?’” Today’s customers want it all: decreased weight, increased part quality and faster production rates.

Siemens PLM has a significant focus on automotive, according to Hudson, believing that the materials and processes developed for automakers will be adopted by other industries. “In high-volume automotive, lightweighting is creating demand for decision support as they attempt to find the right mix of materials and processes that meet demanding production cycle times. Therefore, automotive has the challenge of optimizing the use of composite materials while at the same time looking at different production techniques to meet one- to two-minute production cycles,” he adds.

Like Richardson, Hudson affirms that “there has to be a much closer integration, or at least interoperability, between the design tools that are performing material, part shape and manufacturing simulations and the tools that are being used for FEA.” With a more complex part, the optimization time between design and FEA can go on too long. “One way we’ve worked to speed the process is by working with the CAE community to develop common language that can be used by NX CAE, as well as other CAE solutions, and Fibersim, our composite design solution,” explains Hudson.

A second area of focus is on closing the loop between manufacturing, design, and analysis. “Optimized use of composite materials requires a tighter upstream exchange of information between manufacturing and development,” says Hudson. “In the past, analysts defined desired orientation based on load paths and used significant material property knockdowns. The method was employed because the effects of manufacturing processes were unknown to the analyst and fiber misalignment has a large impact on product strength and stiffness,” he explains. “Today, when we go through a manufacturing producibilty simulation process in Fibersim, in the CAD tool, and develop a flat pattern based on that simulation to pass to the layup technician, we also provide a ply book showing the flat pattern, its location on the 3-D part, and the layup process.” Hudson believes the next step is to supply similar information to laser projection systems to assist in hand layup. “Today, there’s still too much variability from one layup to the next, which can affect fiber orientation,” he says.

For automated manufacturing, says Hudson, the design engineer doesn’t have the same path planning tools as the manufacturing engineer. “As a result, the simulation that the design engineer uses and the layup strategy that a path-planning tool generates could result in very different fiber orientations,” he points out. “It’s a little bit like designing with blinders on. The solution is to ensure that the designer can validate that the path planning results in acceptable fiber orientation for part performance.” Fibersim is capable of bringing the path planning information into the world of the designer to ensure that functional requirements are met, he contends.

The current release of Fibersim (v13.0) has several must have features, Hudson adds. “Fibersim’s Multi-Ply design capability is making traditional ply-based design a thing of the past,” says Hudson. Multi-Ply is an additive ply design method that brings design change automation to traditional ply-based design. “This approach is yielding efficiencies in the development cycle of up to 80 percent over the traditional approach,” he reports. Also available is Fibersim’s Parametric Surface Offset technology, which derives an accurate inner mold line or intermediate surface at any point in the design that is modifiable and updatable. “Parametric Surface Offset is making final part definitions and tooling based off part designs easily achievable,” asserts Hudson.


Complete visualization

“The aerospace and auto-racing industries’ need for better composites design and analysis tools have been the primary drivers for the significant enhancements to software tools over the past five years,” contends Dr. Robert Yancey, VP, Aerospace Solutions, Altair (Troy, Mich.). But he agrees that, going forward, change will be driven by the unique requirements not only of the auto industry but also the wind energy industry, which, he says, “uses more mixed-material architectures that are creating the need to better model transition zones between different material types and configurations.”

In addition to its CAE software suite, HyperWorks, Altair offers a host of composites-centric tools. Yancey says the OptiStruct application, which is part of Altair’s HyperWorks, features a simulation-driven design-and-optimization solver and “has the ability to optimize laminated composite structures to produce the lightest weight laminate that meets design requirements.” He adds that the new application has made a positive impact in the aerospace, auto-racing and biking industries. In the past year, Altair added a ply drop-off rate constraint to OptiStruct and many enhancements for visualization of model setups and results in HyperWorks.

Currently, says Yancey, the must-have feature is the ability to visualize the model in multiple dimensions. With metals, visualizing overall part geometry was sufficient, he explains. For composites, however, the user must also see the ply geometry, the ply angles and laminate configurations for laminated composites, as well as the fiber orientations and distributions for short-fiber composites, the weave patterns for woven composites, and core configuration, such as honeycomb structures. These visualizations need to be available, he adds, “in both the model setup pre-processor and the results-reporting post-processor.”

Without robust visualization capabilities for composites, the process of design and analysis can be overly tedious, very inefficient and prone to errors,” he sums up, adding that “much progress has been made in just the last few years, which is making composites design and analysis more intuitive and efficient” (see “Editor’s Note,” at end of article).

Affordable manufacturing

Given the variety of resin, fiber, tooling and process options available for composites, the challenge is deciding which combination of material and process is both the best and the most cost-effective manufacturing option, says Craig Collier, president, Collier Research Corp. (Hampton, Va.). The company’s software tool, HyperSizer, which recently launched Version 7, is used with CAD, FE modelers and FEA programs to achieve a composite design that is fully optimized and manufacturable.

HyperSizer is used throughout the design process to quantify critical failure modes, reduce structural weight and sequence composite laminates for fabrication to avoid unexpected design problems and weight growth as the design matures. The first step is to import an FE model that is a single plane of shell elements or that discretely models the component. Four fundamental meshing techniques are supported. However, the more discretely meshed a model is, he says, the less opportunity for sizing optimization because variables become locked down by the mesh.

New in HyperSizer 7.0 are several tools designed to bring optimization to maturity, explains Collier. For example, composite designs — especially those that use automated fiber placement (AFP) or automated tape laying (ATL) — include many ply drops, that is, patches of carbon fiber fabric placed strategically to meet specific and often localized mechanical requirements. Ply drops, however, are time-consuming and expensive to apply. Version 7 attempts to move away from ply drops toward an overall design that has more consistent thickness, avoids the use of ply drops, minimizes material use, yet meets all required mechanical loads. This could be particularly applicable to wing or fuselage skins, which are famous for their patchy ply drops, he suggests.

HyperSizer 7.0 also allows for simultaneous optimization of stringers and skins. Historically, says Collier, these two structures are optimized separately, despite the fact that they function together in the application.

HyperSizer also has tools to optimize sandwich structures on space launch vehicles. He believes this will be particularly attractive in the commercial space  market, which has become very competitive, forcing OEMs to find ways to save more weight in composite structures. “The ability to find minimum weight is not good enough anymore,” he says. “It’s got to be something we can make.”


Micro-level modeling

Digimat, from e-Xstream engineering (Mount-Saint-Guibert, Belgium), focuses solely on modeling composite materials from the micro-level up, and might provide an answer for improved design- and analysis-driven manufacturing process control. The software predicts lamina properties, using a homogenization technique that also maintains matrix and fiber results individually when coupled with FEA software. (Digimat interfaces with most FEA structural analysis codes, including MSC, Nastran, Marc, Abaqus and ANSYS.)

“Accurate predictions of new materials is a big driver for us,” explains Bob Schmitz, e-Xstream’s business development manager. That includes “not only accurate simulations for the structural analysis of parts but accurate predictions of how a new material will perform, so that our customers can down-select to the best material for the application before testing physical samples.”

This is critical in a time when companies are evaluating many types of composites, not only traditional aerospace continuous fiber/epoxy systems or short fiber structural plastics, but also many alternatives and hybrids, such as over-molded components, reports Schmitz, noting that Digimat is not restricted to a specific type of composite.

“According to feedback from customers in the automotive industry using short fiber-reinforced polymers in composites, prototype testing has been reduced by 50 percent or more, using Digimat,” Schmitz reports. “Our software enables the inclusion of fiber orientation directly into the structural analysis,” he adds. “By doing this, users are able to more accurately simulate the true material performance and thus the true part performance before going to test.” In addition, users are able to identify high-risk areas, and capture stiffness and strength more accurately, he notes. “Generally, in the analysis process, geometric effects causing stress concentrations or localized strain increases can be identified,” he says. “With Digimat, we’re also able to evaluate how the processing of that part is affecting the stress contours and strain distribution throughout the part.”

Scheduled for release in August, Digimat-FE imbeds an FE solver directly into Digimat, enabling engineers to create and solve a detailed finite element model of a material microstructure, all in one tool. “The benefit is the ability to study detailed stresses and strains throughout a composite microstructure, such as how they are distributed between the fibers and matrix, and how adding additional fillers or voids impacts the materials behavior,” explains Schmitz.

“One of the trends we’re seeing is simulation being done by material suppliers,” he adds. “Material suppliers can use Digimat to develop their material models, and then deliver those validated material models to their customers for use in their simulations.”

Looking ahead, more advanced progressive failure models are planned for structural FEA applications, says Schmitz. The company is developing Digimat-VA, which will automate the process of creating virtual coupon testing — creating the coupon, running the simulation, testing it and delivering certain test results very rapidly.


Refining failure models

Autodesk’s (San Rafael, Calif.) portfolio of simulation software includes Autodesk Simulation Composite Design (ASCD) and Autodesk Simulation Composite Analysis (ASCA). Earlier this year, in a webinar hosted by CompositesWorld, Doug Kenik, product line manager, Autodesk Simulation Composite Products, discussed the need for simulating past first-ply failure in conventional implicit FEA tools, and how to achieve convergence using ASCA (see “Editor’s Note,” below).

Simulating ultimate failure in composite structures using traditional implicit FEA codes can be challenging. “The behaviors of composite materials are inherently nonlinear during failure cascades, and the FEA solvers can have difficulty converging on solutions during such events,” says Kenik.

Typical FEA programs integrate a variation of a Newton Raphson scheme, an iterative or nonlinear solver that updates stiffness, stress and strain at every increment, explains Kenik. This approach assumes that the response of the structure can be approximated as smooth. “However, composites have discrete failure modes in which the stiffness is lost instantaneously,” explains Kenik. FEA programmers have developed approaches to overcome convergence problems for highly nonlinear events, such as contact and unstable damage growth for composites. One method implemented to mitigate the effects of discontinuity in nonlinear analysis is the use of material viscosity, which allows the solution to dampen out the effects of damage evolution by providing a stiffness variable that is dependent on viscosity and time.

“Viscosity is great for converging on a solution, however,” warns Kenik, “you have to study how the viscosity affects the problem. Viscosity is just another variable that you have to tune to make sure that your finite element model is behaving correctly.”

To avoid uncertainty, Autodesk’s ASCA uses composite-specific proprietary methods to converge on a solution in nonlinear FEA, says Kenik. “It converges without relying on viscosity, and it is very efficient.” The robust convergence offered by ASCA dramatically reduces simulation times and helps to reduce testing of physical components. ASCA 2015 is embedded with traditional FEA packages — MSC Software, ANSYS, Abaqus, NEi Nastran — using multiple failure theories, including Tsai-Wu, Hashin, Puck and constituent-level MCT theory. ASCA also provides capabilities to simulate complex failure modes, such as coupled inter- and intra-laminar failure, as well as algorithms to reduce mesh sensitivity of progressive damage simulations. The software comes prepopulated with a database of multiple unidirectional and woven materials, which can be used in addition to standard material data.

ASCD 2015 is geared toward preliminary design. The tool is a standalone desktop application that combines a prepopulated materials database, a laminate module with capabilities for laminate stress, strain and failure simulation, and solutions for deformation, bending, vibration and compressive stability of laminate plates, sandwich panels, tubes and beams. The application allows composite engineers to quickly iterate early in the design process by using the closed-form solutions embedded within the product. The 2015 release has additional solutions for manufacturing considerations, such as spring-in of laminates from temperature or moisture changes as well as a new reporting utility.

During the past year, Autodesk also has sponsored two free technology previews — known as Project Cassidy and Project Sundance — to generate interest and gain feedback from the community for new and future directions of advanced materials simulation within Autodesk (see “Learn More”). “Both are helping to ease new users into composite simulation,” says Kenik. “One of the most difficult tasks in composite simulation is defining material orientations for the FEA analysis. Both technology previews provide easy and intuitive interfaces to help users include material orientations in their simulations and understand their impact on performance, which leads to lighter designs and a more efficient design process.”  (For more on materials database integration, see “Granta” item in “Learn More.”)


Closing the loop

CGTech (Irvine, Calif.) sees its suite of VERICUT composite applications as the first major steps for automated composite manufacturing processes toward closing the loop between design and manufacturing. For years, the company specialized in numerical control (NC/CNC) simulation, verification, optimization and analysis software technology for manufacturing. Recent additions to its products include VERICUT Composite Paths for Engineering (VCPe), VERICUT Composite Programming (VCP) and VERICUT Composite Simulation (VCS).

“Using software to do virtual layup experiments offers an effective tool for confirming that the part design is producible, and that the as-built part will match the design intent,” says CGTech’s product marketing manager Bill Hasenjaeger.

VCPe, he says, gives the user the ability to measure and evaluate the effects of automated fiber placement (AFP) and automated tape laying (ATL) path trajectory, material steering, surface curvature, course convergence and other process constraints as they would be applied in manufacturing. The software also provides producibility analysis of the fiber angle, based on the curvature of the part, and overlap and gaps needed for structural analysis. Tape course geometry can be written to various CAD formats for further evaluation by the user’s analysis methods and tools.

“It allows engineers to understand fiber orientation, not just through simulation on the design tool, but through simulation based on what the manufacturing engineer is going to use to actually produce the path planning,” explains Hasenjaeger.

VCS validates the layup process through simulation. The program reads CAD models and NC programs from VCP or any industry path-generation program and then simulates the sequence in a virtual CNC environment, applying simulated material, according to the NC layup instructions.

VERICUT is a standalone software package, but can be integrated with leading CAM systems, including Dassault’s CATIA and Siemens PLM’s NX. CGTech has a strategic partnership with Siemens PLM to provide rapid design and manufacturing iterations, thereby optimizing the development of composite structures produced via AFP and ATL.

Enabled to do “more iterations, with faster and better feedback earlier in the development process, firms are better able to evaluate the tradeoffs between manufacturing complexity and cost,” says Hasenjaeger. “It also allows engineers to design specifically for the manufacturing process and take advantage of innovative uses of composite materials.”

Looking ahead, Hasenjaeger points to the development of new AFP machine technologies, many using robots, to apply material over complex shapes at a lower cost than traditional gantry-style machines. “Today, many manufacturers are still struggling to apply current AFP technology to complex high-curvature part shapes,” he says. “Innovative NC programming approaches are needed to successfully and reliably fiber-place complex parts while achieving the structural requirements of the laminate.”


Optimizing RTM

ESI (Paris, France) offers a suite of applications designed to realistically simulate and fine-tune composites manufacturing processes. Focused on structures made of continuous fibers in a thermoset or thermoplastic matrix, ESI’s tools enable analysis and optimization of each manufacturing operation, while transferring material history (change in fiber orientations, curing degree, temperature distribution, etc.) from one operation to the next.

ESI’s composite simulation products include PAM-FORM for analysis of forming and preforming of dry textiles or prepreg materials; PAM-RTM for analysis of liquid composite molding and curing processes; and PAM-DISTORTION, which predicts manufacturing-induced residual stresses and shape distortion of composite parts. ESI also offers a CATIA V5 PLM-based composites portfolio that combines PAM-RTM and PAM-QUIK-FORM. The pair simulate unidirectional composite deformation during the draping process and can detect, early in the design process, whether or not a selected material is viable for manufacturing.

“ESI’s Composite Simulation Suite allows better understanding and control of the draping stage, the injection strategy and the distortion due to curing,” says Federico Martin de la Escalera, head of Research and Technology Dept., Aernnova Engineering Solutions Iberica SA (Madrid, Spain). Aernnova implemented the PAM-RTM software in its engineering process while applying RTM to two Airbus A350 XWB parts — the bearing rib and the leading edge of the horizontal stabilizer — as a means to better understand and control the injection process and to manage final part quality, according to ESI. Tests based on Aernnova engineers’ initial RTM mold design and injection strategy resulted in wrinkles and dry spots that affected the mechanical performance of the structural parts. According to ESI, PAM-RTM analysis led to the addition of new vent points that eliminated the dry spots.

Aernnova’s engineers also simulated the preforming stage using ESI’s composites forming application, PAM-FORM, to predict the fiber angle in the preform. These results were then used in PAM-RTM as a function of shear angle, which improved the prediction of resin flow pattern and filling time, says ESI.


Validation across industries

An assortment of maturing simulation tools is available to the composites industry. More importantly, software developers and composites engineers understand that by working together to validate simulation models and develop common languages, simulation methods can be strengthened across the board. Although there is still work to be done, the wheels are in motion and the gaps are getting smaller.