GENOA, MCQ-Composites to Join Altair Partner Alliance Composites Lineup

AlphaSTAR Corporation’s progressive failure analysis tools are now available to HyperWorks users 

TROY, Mich. – June 12, 2013 – The Altair Partner Alliance today announced the addition of its sixth composites partner, AlphaSTAR Corporation (ASC). HyperWorks users can now access its multi-scale progressive failure analysis (MS-PFA) software, GENOA, as well as the Material Characterization and Qualifications (MCQ) Composites Suite. GENOA and MCQ are applicable in many industries, including aerospace, automotive, wind energy and sporting goods.

“We are very pleased with the addition of AlphSTAR to the Altair Partner Alliance,” said Dr. Robert Yancey, Altair Sr. Director – Aerospace for Altair. “AlphaSTAR has been involved in composites analysis and design for many years, and it will add advanced technologies and expertise to our Partner Alliance. We have already worked with ASC for key customer projects in the past, and we look forward to more collaboration in the future.” 

GENOA is an engineering software suite that performs material characterization qualification, durability and damage tolerance (D&DT), and reliability prediction for structural design and analysis of composites structures. It augments the limitation of commercial finite element analysis (FEA) packages by providing multi-scale (micro-macro) PFA capability. GENOA was developed to cost effectively predict strength and time-dependent reliability and durability of structural components during the design stage, and to reduce experimental testing support. With the ability to predict damage and fracture evolution as well as end of life of many types of composites, GENOA takes laminated composites with either continuous or short fibers from micro-mechanics to the structural level, while considering the various operational and environmental conditions. 

MCQ-Composites, the second tool available from AlphaSTAR, predicts composite material properties, considering both fiber and matrix uncertainties. It is designed to characterize and qualify material properties that can be used as input for FEA of simple or complex structural components. MCQ allows the user to quickly generate relevant information for a given material, whether it is a composite, hybrid, or ceramic material system. MCQ provides a library of fiber, matrix and ply properties that can be easily expanded or modified for application to FE analysis. In addition, it can effectively predict fiber, matrix and composite/sandwich laminate properties, as well as stress-strain curves, ply behavior and more.

“GENOA and MCQ work together to provide users an accurate and powerful composites analysis solution,” said Dr. Anil Mehta, AlphaSTAR’s Vice President of Business Development. “HyperWorks customers will not only be able to harness the capabilities of AlphaSTAR’s software to address their questions about where, when and why their parts are failing, but also how to optimize their design to alleviate those occurrences. By utilizing advanced failure mechanisms, GENOA is able to investigate structural responses from material degradation, caused by damage induced from static, cyclic, impact, power spectrum density (PSD) and thermal loading. GENOA's PFA also is able to account for the effects of manufacturing defects, fiber waviness, springback, residual strength, moisture and temperature. By using GENOA, a wide range of material systems become available, including metals, ceramics, composites and nano composites. We look forward to working with the Altair Partner Alliance to provide the best composites solutions possible, to a broader audience.”

HyperWorks users can take advantage of the integration between GENOA and Altair’s RADIOSS solver, as well as the integration with OptiStruct, which is currently in process and will be available soon. 

Available for the last 12 years, Altair’s innovative unit-based licensing system allows HyperWorks users customizable access to a growing portfolio of applications, optimizing their return on investment (ROI) by making more than 28 in-house developed applications available by use of a single pool of recyclable HyperWorks units (HWUs). 

After experiencing this original licensing model’s success, Altair has offered the opportunity for third-party companies to run their own applications under this unit-based system, a collaboration now known as the Altair Partner Alliance. The overall flexibility of these HWUs empowers users and allows them access to the largest and most complete suite of CAE applications available, making the benefits to participating HyperWorks customers infinite. The ROI increases for users each time a new application is added to the offering, since any of the partner programs can be accessed using the same leased HWUs they are already using to run HyperWorks. This makes more than 55 additional applications available at no incremental cost or long-term commitment.

HyperWorks users can download GENOA and MCQ Composites atwww.altairalliance.com/alphastar. To learn more about AlphaSTAR, GENOA or MCQ, please attend one of the introductory webinars, being held on June 26, 2013, at 10 a.m. and 2 p.m. EDT. These webinars will be hosted by Altair and presented by AlphaSTAR.

AlphaSTAR Corporation
AlphaSTAR is a leading engineering services and software company that provides innovative physics-based simulation technologies for structural modeling and analysis of advanced composite structures in the aerospace, automotive, defense, and energy industries worldwide. Utilized in defense agencies, manufacturing companies, and universities, the company’s product line includes its core structural design and simulation software, GENOA, and also MCQ Composites, enabling customers to reduce their need for expensive physical testing by over 60%. AlphaSTAR is headquartered in Long Beach, California and is the recipient of esteemed industry and technology awards for R&D and software development. For more information, visit www.alphastarcorp.com.

About Altair
Altair empowers client innovation and decision-making through technology that optimizes the analysis, management and visualization of business and engineering information. Privately held, with 1,800 employees, Altair has offices throughout North America, South America, Europe and Asia/Pacific. With a 27-year track record for high-end software for engineering and computing, enterprise analytics solutions, and innovative product design and development, Altair consistently delivers a competitive advantage to customers in a broad range of industries. To learn more, please visit www.altair.com or www.simulatetoinnovate.com. 

About the Altair Partner Alliance
Altair’s HyperWorks platform applies a revolutionary subscription-based licensing model in which customers use floating licenses to access a broad suite of Altair-developed, as well as third-party, software applications on demand. The Altair Partner Alliance effectively extends the HyperWorks Platform from 28 internally developed solutions to more than 50 applications with the addition of new partner applications. Customers can invoke these third-party applications at no incremental cost using their existing HyperWorks licenses. Customers benefit from unmatched flexibility and access, resulting in maximum software utilization, productivity and ROI. For more information about the Altair Partner Alliance, visitwww.altairalliance.com.

Media Contacts:
Jennifer Korail
Airfoil for APA
+1 (248) 304-1429
korail@airfoilgroup.com
Dr. Anil Mehta
Vice President of Business Development, AlphaSTAR Corporation
+1 (714) 317-2523
amehta@alphastarcorp.com

Source of the news:
http://www.altair.com News release

COPV - Technical Brief - April 2013

Technical Brief
April 2013

Validation of Burst Pressure Analysis and Manufacturing Techniques for  Composite Over-wrapped Pressure Vessels

GENOA provides engineers with a validated computational approach to determine residual stresses in composite over-wrapped pressure vessels (COPV). It also identifies leakage and burst locations, as well as associated failure modes under service.

The Challenge:  To accurately determine the onset of crack formation, leakage, slippage of gas between dome and valve assembly, and rupture of COPVs.

Other challenges pertain to accurate determination of the following:

• Ply angle distribution
• Residual stresses due to winding and curing
• Tank reliability due to scatter in manufacturing parameters, defects, and material properties
• Strength allowables for risk reduction
• Rupture due to service load:  Proof, Auto-Frottage (load, unload),  Sustained Fatigue (short, high cycles) pressurization,
•  Slippage/Leakage prediction
• Damage and failure multi-site locations
• Reliability
• Addressing variability in tank  performance considering “As-designed” versus “As-built” and “As-is”
• Tank certification

Another challenge stems from the complexity of modeling and analysis of composite materials. Most finite element analysis (FEA) solvers assess damage at the lamina level whereby damage initiates at lower scale in the fiber, matrix, and interphase. These challenges can be addressed through an integrated capability that couples winding analysis with multi-scale progressive failure analysis, including modeling of defects and uncertainty analysis.

The Solution:  To utilize GENOA’s Filament Winding & Multi-Scale Progressive Failure Analysis

Residual stresses are calculated through GENOA’s Filament Winding (GENOA-FW) module. To calculate residual stresses, GENOA uses design parameters, such as tape tension, internal pressure, and curing effects. The tank finite element model is generated based on inputted tape thickness and width, winding angles, and wrapping circuite location during winding. The winding pattern can be optimized to reduce weight. Tanks with metallic and plastic liners or those without liner are modeled and analyzed with GENOA’s FW module. Residual stresses from autofrettage are also determined with the analysis. To ease the design of the tank, the FW module is capable of generating two distinct FEA models using:         

§         Low Fidelity: 3D thick shell elements that merges all plies into a single element thru thickness

§        High Fidelity: 3D solid where plies thru thickness are modeled with layers of solid elements

With generated FEA model and calculated residual stresses, GENOA’s multi-scale progressive failure analysis (MS-PFA) performs leakage and burst rupture analyses. The code integrates finite element analysis with multi-scale composite mechanics and damage tracking and fracture. Several FEA stress solvers are used within the GENOA environment for evaluating durability and damage tolerance of the tank. These solvers include NASTRAN, ABAQUS, ANSYS, and nodal based MHOST [1].

MS-PFA identifies all stages of damage evolution: damage/delamination initiation and growth, and probabilistic fiber stress rupture fracture initiation and growth to failure. It calculates micro-cracks, stiffness degradation in the matrix, delamination within the plies, and fiber failure in tension and compression including micro-buckling. The COPV tank can be evaluated with MS-PFA subject to static, fatigue, and impact loading conditions to accommodate tank certification process [2]. Reliability evaluation considers the uncertainties in geometry, material, fabrication process and loading [3].  It ranks the effect of considered random variables on leakage, delamination, and rupture of tank and determines the scatter in burst pressure. In addition to uncertainty analysis, a test reduction methodology for determining A- and B-basis allowable design loads is integrated. A-basis design allowables generation can be determined with reduced testing using B-basis values from accepted test methods or can be generated from lamina level uncertainties [4].

Validation: Figure 1 shows a failed composite tank that was modeled and analyzed with the software. Figure 2 shows typical filament winding input requirements supporting helical and hoop winding schemes. Data used as input includes winding schedule, tape width, and tape tension. The tanks analyzed include spherical, and cylindrical with geodesic domes. ASC validated its technical approach for both space and automotive applications and subject to extreme environmental conditions (elevated and cryogenic temperatures).  Typical analysis results are used to determine conditions for leakage, burst location, damage evolution through-the-thickness, and reliability. Filament wound composites over-wrapped tanks were considered in for the application of motor cases for solid rockets motor cases [3] Deterministic evaluation of durability and damage tolerance of tank using GENOA resulted in predicted burst pressures that are within 8.8% of the test for 4 groups of tank design. The pressurized tanks were also evaluated in presence of uncertainties in constituent stiffness and strength and manufacturing variables. The sensitivity analysis indicated that the fiber mis-alignment and ply thickness are the most influential variables that affect the burst pressure as indicated in Figure 3.  Scatter in burst pressure, A Basis Allowable as a result of considered uncertainty is shown in Figure 4. The results show that a reliability 0f 0.999 can be achieved if burst pressure is kept under 3033 psi.  When damage evolution through thickness is of concern, GENOA offers capability to generate high-fidelity solid element FE models. Figure 5 shows the snap shots from automated process to generate high-fidelity solid FE model from previously generated shell element FE model. The high-fidelity model helped account for the out-of-plane shear stresses, which results in delamination, more accurately. Figures 6 to 8 show the damage evolution at the laminate level, ply-by-ply level and final burst predictions compared to the test specimen in Figure 1.

Another validation of the capability done under the NASA space launch initiative effort [5] determines leakage in COPV at cryogenic temperatures. Analysis showed a large percentage of failure in composites initiate as matrix cracking. When matrix cracks it releases energy causing accumulation of additional cracks that continues till a saturation point. GENOA can track this initiation, accumulation and saturation process.

 Conclusion: GENOA provided a reliable and verifiable low as well as high fidelity simulation solution in determining residual stresses, identifying leakage, burst locations, and associated failure modes under service in COPV’s.

References:

1.       S. Nakazawa, “The Mhost Finite Element Program, 3-D Inelastic Method for Hot Structure Components”, Volume 1 Theoretical  Manual,  NASA Technical Contract Report CR-182205, March, 1991.

2.       C. Keddy , “Composite Overwrapped Pressure Vessel Modeling and Analysis”, White Sands Test Facility, Johnson Space Center, July 2008.  

3.       G. Abumeri, F. Abdi, M. Baker, M. Triplet and, J. Griffin “Reliability Based Design of Composite Over-Wrapped Tanks”.  SAE World Congress, 2007, 07M-312, Detroit Mi, April 2007.  

4.       G. Abumeri, F. Abdi, K.S. Raju, J. Housner, R. Bohner and A. McCloskey: “Cost Effective Computational Approach for Generation of Polymeric Composite Material Allowables for Reduced Testing”, Inetch Book publishing, in print for March 2011 (Co-authored with Northrop Grumman and NIAR).

5.       F. Abdi, X. Su “Composite Tank Permeation and Crack Density Prediction and Verification”.  ASME Paper No. IMECE2003-4439 November 2003.

About AlphaSTAR Corporation: AlphaSTAR Corporation is a leading engineering services and software company that provides innovative physics-based simulation technologies for structural modeling and analysis of advanced composite structures in the aerospace, automotive, defense, and energy industries worldwide. As a solution provider, AlphaSTAR partners with Siemens PLM, Altair, ANSYS, MSC Software, DS Simulia, and LSTC. AlphaSTAR is headquartered in Long Beach, California and is the recipient of esteemed industry and technology awards for R&D and software development. Contact marketing@alphastarcorp.com or www.alphastarcorp.com. 

GENOA 5 Press Release

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GENOA 5 Delivers Up to 10 Times Performance Gains while its Re-Designed Graphics User Interface Maximizes Productivity

LONG BEACH, CALIFORNIA (February 7, 2013) - AlphaSTAR Corporation (www.alphastarcorp.com) announces the launch of the newest release of their Multi-Scale Progressive Failure Analysis suite, GENOA 5. Designed to cost-effectively predict strength, time dependent reliability, and durability of composite structural components with reduced physical tests, GENOA 5 is packed full with added capabilities like Filament Winding, Material Modeling, Fatigue Life, Crush & Crash Analysis, and more. This latest version will enable companies to confidently and accurately predict the validity and reliability of their products in the real world.

Specifically, GENOA 5 includes the following key enhancements and features:

• Re-designed graphic user interface (GUI) for more user-friendliness and robustness
• New Progressive Failure Analysis Engine for increased speed and better accuracy
• Integration with MCQ (Material Characterization & Qualification) Suite, including Composites, Nano, Ceramics, Metals
• Enhanced interfaces with MSC Nastran, NX Nastran, ABAQUS, ANSYS, RADIOSS, and LS-DYNA
• Over 110 downloadable examples, including verified test validation cases and ASTM manual
• Improved project management and file system, and online help with the GUI

"Our focus in software product development is to extend and enhance GENOA's capabilities in order to improve the multi-scale and micro-mechanics analysis of composite structures," said Dr. Anil Mehta, AlphaSTAR's VP of Business Development. "For example, customers will find that the design interface is even more empowering, user-intuitive and responsive. GENOA 5 will enable our customers to continue to foster product innovation with reduced time and cost in working with new engineered material selections for robust designs."

About AlphaSTAR Corporation: AlphaSTAR Corporation is a leading engineering services and software company that provides innovative physics-based simulation technologies for structural modeling and analysis of advanced composite structures in the aerospace, automotive, defense, and energy industries worldwide. As a solution provider, AlphaSTAR partners with Siemens PLM, Altair, ANSYS, MSC Software, DS Simulia, and LSTC. AlphaSTAR is headquartered in Long Beach, California and is the recipient of esteemed industry and technology awards for R&D and software development. Contact marketing@alphastarcorp.com orwww.alphastarcorp.com.

Technical Brief: Managing Defects and End of Life Prediction/Validation in Composite Wind Turbine Blades

Technical Brief:   Managing Defects and End of Life Prediction/Validation in Composite Wind Turbine Blades

Under a research grant from the US Department of Energy (DOE), and collaborating with Sandia National Laboratories, AlphaStar Corporation was able to solve Durability and Reliability challenges of composite wind turbine blades.

The Challenge: Determine Why, Where and How Wind Turbine Blades Fail

In the operational environment, the blades designed and built by Sandia Labs and TPI Composites (the blade manufacturer) were continually breaking (Fig. 1). The blade failures were costing Sandia and TPI valuable time, costs and resources to continually replace broken blades without understanding the root cause of the problem inherent to composite materials.

                              

Figure1: Progressive failure analysis and test validation of Sandia?s BSDS blade under static loading

The Solution: GENOA & MCQ-Advance Multi-Scale Progressive Failure Analysis

AlphaStar with its flagship products GENOA and MCQ provided an Advanced Simulation Methodology based on Multi-Scale Progressive Failure Analysis (MS-PFA) to answer why, where and how blades fail. Also, MS-PFA assessed the durability, damage tolerance and reliability of blade structures in the presence of uncertainties in composite material properties, such as manufacturing defects. 

Why Blades Fail

Composite blade design does not consider scatter in composite material properties, manufacturing processes and resulting defects ?As-Build Vs. As-Designed?, but it relies on empirical methods to establish design allowables for sizing of composite blades. 

Where and How Blades Fail

Ply drop off due to manufacturing processes causes (Fig. 2) high local stress concentration and results in unstable crack and delamination propagation from root to tip (as shown in Figure 1).  This means that due to resin rich voids matrix has been degraded. 

MS-PFA narrowed the blade failure to the region of ply-drop off very common in composite wind turbines for material thickness transitions for inherent weaknesses created by the design; the results are supported and verified by the test. 

Figure 2.  Ply Drop off of Thick Laminates Under Tension Loading

The unique advantages of the MS-PFA approach are as follows (details in references below):

·         Material Characterization and Qualification

·         Scale up from material to structure using a building block validation strategy

·         Accurately identifies the contribution failure mechanisms during the failure evolution process

·         Conditions that cause the delamination of first ply (on-start of failure), its location as well as track progressive damage evaluation/failure of the composite blade within the plies

·         Accurately considers inter laminar material and geometric discontinuities at the ply drop offs

·         MF-PFA simulation results are in good agreement with the Physical Test Data on actual wind turbine blades; composite blade material is calibrated against available ASTM standard test data

·         Simulation reproduced strength and fatigue life as observed in the test, thus ensuring reliance and confidence in simulation in guiding the design of blades for improved performance (Fig. 3)

·         Modified design changes of key composite material in the blade resulted in weight reduction of more than  10% 

Figure 3: Progressive failure analysis and test validation of Sandia?s BSDS blade under static loading

  References:

1.        Wind-Laminate-Ply Drop: Frank Abdi, Joshua Paquette, Glenn Crans, Levon Minnetyan, Pier Marzocca,  ?Durability of Tapered Composite Laminates under Static and Fatigue Loading ?, AIAA-SDM 2011 conference, Denver Colorado

2.        Wind-Blade-Robust-Design: Galib Abumeri, Joshua Paquette, Frank Abdi,  ?Durability and Reliability of Wind Turbine Composite Blades Using Robust Design Approach?, AIAA-SDM 2011 conference, Denver Colorado, AIAA_SDM_945357reliability. 

3.         33 Meter Wind Blade OPTIM: Galib Abumeri and Frank Abdi, Joshua Paquette ?DURABILITY AND RELIABILITY OF LARGE WIND TURBINE COMPOSITE BLADES?.  SAMPE Journal  Nov/Dec 2012, Vol 48, No 6 WWW.Sampe.org. 

Let us talk Physics Based Simulation Technologies for Modeling and Analysis of Advanced Materials

Lets talk Physics Based Simulation Technologies for Modeling and Analysis of Advanced Materials

http://www.AlphaStarCorp.com
http://www.ASCGENOA.com

Software Suite for Material Qualification and FEA Based Durability, Damage Tolerance, Reliability & Life Prediction

Issue #20 - April 13th, 2010

Software Suite for Material Qualification and FEA Based Durability, Damage Tolerance, Reliability & Life Prediction

GENOA 4.4 Software Release News

GENOA's Material Qualification and Characterization (MCQ) Module

Figure 1 - MCQ Generated Ply Properties Features of MCQ: -          Laminate properties (mechanical-thermal/electrical) -          Load limits and damage/failure modes -          "As-built" and "as-is" material state -          Manufacturing defects and environmental effects   -          2D/3D composite architectures; Polymers  (Thermosets, Thermoplastic, and Chopped Fiber), Fiber-Metal-Laminate, Nano, and ceramics -          Allowables and carpet plots for test reduction -          Mesh-less unit cell simulation -          Accurate, robust, and user friendly -          Industry verified and endorsed

Alpha STAR released GENOA's MCQ forWindows 2000/XP/Vista/7 and Linux. It enables the ultra rapid modeling, design, and analysis of advanced polymer composites for aerospace, automotive, wind turbine, ship building, and infrastructure industries. MCQ uses a unit cell approach for assessing material behavior not requiring finite element modeling. It is applicable to all un-notched laminates where uniform state of stress persists. MCQ models all types of composite architectures including tape, 2-D /3-D woven and braided materials using simplistic multi-scale physics based micro-mechanics formulation. It accounts for "as built" and "as-is" state taking into consideration manufacturing defects and effect of uncertainties in material properties and specimen geometry.

MCQ is a one "stop shop" for:
(1) generating thermo-mechanical-electrical properties of laminated composites; (2) predicting laminate strength, damage and failure modes, and (3) generating material design envelope, carpet plots, and A- and B-Basis strength allowables. It relies on physics based multi-scale failure mechanisms to predict laminate behavior. Strength- and strain-based failure criteria accounting for matrix cracking, de-lamination, fiber failure and interaction between fiber and matrix are evaluated to determine conditions for damage initiation and growth and final failure.

Figure 2 - Design Failure Envelope Progression for a [0,90,45,-45] Symmetric Layup

Figure 3 - Virtual Generation of Allowables [1,2]: Cumulative Distribution Function Generated by Simulation Compared to Limited Test data for Polymer Composites at 180 F with 85% Relative Humidity (Aged Moisture)

MCQ is ideal for providing quick, simplistic, easy to use, and in-expensive guide to material selection. Accurate estimation of material properties plays a very important role in delivering a design that meets cost and production schedule requirements. MCQ comes with a dedicated data base of material properties for glass, carbon, ceramics and other systems. The code is designed for use by engineers and scientists who use micro-mechanics (fiber/matrix/interphase) type input and those who use macro-mechanics (ply level input). MCQ delivers accurate stiffness and strength properties as input to your Durability and Damage Tolerance (D&DT) evaluation.

 

Figure 4 - Material Performance Envelop Generated by the Software

MCQ Performs composite laminate analysis considering "as-built" and/or "as-is" material states: manufacturing anomalies (i.e., void size/shape, fiber waviness, interphase coating), design (i.e., ply orientation, thickness, 2D/3D architecture).

• Fiber, Matrix, and Lamina Calibration
  Reverse engineer effective linear fiber/matrix properties from lamina or laminate test data (strength and stiffness). The effective properties accounts for the thermal residual stresses and interface due to curing process. 
• Non-Linear Material Characterization Optimization (MCO)
  Reverse engineers effective fiber, matrix, ply non-linear properties (stress strain curves) from ply or from laminate test data.
• Ply Level Analysis
  Predicts equivalent ply properties (mechanical/thermal/electrical) using fiber matrix properties as input. Example of mechanical properties (Figure 1) is ply strength in 11, 22, 33, 12, 23, and 13 directions. Example of electrical properties is ply and laminate conductivity.
• Laminate Analysis
  Predict equivalent laminate properties using fiber/matrix or ply properties as input. The properties calculated include laminate strength and stiffness, and electrical and thermal properties as well.
• Design Failure Envelope
  Predicts design failure envelope for chosen failure criteria for laminates. Strength, strain, and interactive based failure mechanisms are available (Figure 2). Fiber failure under tension/compression including micro-buckling, matrix cracking under tension and compression and delamination (in-plane and out-of-plane) are determined for the ply and the laminate. Several Failure Criteria can be compared for better understanding and comparison against test data.
• Ply Characterization
  Graphically shows variation in strength as a function of ply orientation and fiber or void volume ratio
• A- & B- Basis Allowables
  Rapid and accurate prediction of A- and B-basis strength allowables for un-notched uniformly stressed coupons. This module provides the option of predicting allowables from a minimal number of test replicates. With a dedicated sensitivity analysis one can determine the influence of manufacturing parameters and material properties on the laminate strength. This helps reduce the scatter and improve the performance of the material (Figure 3 & 4).
• Parametric Carpet Plot
  Generate multiple carpet plots that show variation in thermo-mechanical properties, including strength, stiffness and thermal expansion, with variation in ply layup distributions (Figure 5). This capability is ideal for use at the beginning of a new program as it provides an accurate and a complete map of the material properties providing alternate design options rapidly and at low cost.

Figure 5 - Carpet Plot of Laminate Strength as Function of 0, 45, and 90 degrees Ply Angles (Red = Fiber Failure, Green = Matrix Failure, Blue = Matrix Shear Failure)

References: 
1. Galib Abumeri, Frank Abdi, and Mike Lee, "Verification of Virtual Generation of A- and B-Basis Allowables for Polymer Composites Subject to Various Environmental Conditions", SAMPE 2009 China Conference. Click here to email us for the technical publication.

2. DOT/FAA/AR-03/19, Final Report, "Material Qualification and Equivalency for Polymer Matrix Composite Material System: Updated Procedure" Office of Aviation Research, Washington, D.C. 20591, U.S. Department of Transportation Federal Aviation Administration, September, 2003.Click here to email us for the technical publication.

Visit us today and find out more about GENOA at www.ascgenoa.com.

Click here to read the full technical product data sheet of GENOA.

This issue was brought to you by Alpha STAR Corporation.

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Durability & Reliability Enhancement of Assembled Composite Structures by use of Parametric Robust Design (PRD) Concept

Issue #19 - November 17th, 2009

Software Suite for Material Qualification and FEA Based Durability, Damage Tolerance, Reliability & Life Prediction

This Week's Feature Composite Example

Durability & Reliability Enhancement of Assembled Composite Structures by use of Parametric Robust Design (PRD) Concept

Figure 1 - FEM of the panel-panel Joint Figure 2 - Test configuration

Parametric Robust Design (PRD) module is put to use to maximize durability and reliability of a complex assembled ceramic matrix composite (CMC) structure subjected to concentrated loads. PRD optimizes the geometry of the structure subject to prescribed constraints for the purpose of improving the durability. For the given structure, the ultimate load is increased by 6.5% after optimization. Additionally, the optimized structure exhibited higher reliability as the probability of failure is reduced from 0.08 (before optimization) to 0.02 (after optimization). Details of the technical approach and summary of results are discussed next.

Background: 

The durability and reliability of complex composite structures is affected by joint tolerances such as hole size and fitup, manufacturing discrepancies, environmental factors (temperature), fatigue (vibration), and loads due to assembly mismatch. Material properties as well as manufacturing scatter, such as voids, add to the complexity of evaluating assembled structures. The need exists to apply a comprehensive methodology to assess these effects on the structure's performance and assess its reliability without resorting to test every time. A computational approach integrating probabilistic methods with composite mechanics and finite element based Progressive Failure Analysis (PFA) is in order to assess durability and reliability of these complex structures. The approach applies parametric modeling and analysis to suggest competing designs to improve overall performance. This concept is demonstrated on a panel-to-panel joint structure made from ceramic matrix composites (CMC) [Ref 1-2].
The material candidate considered is carbon fiber reinforced silicon carbide (C/SiC) due to the stability of its properties through large temperature variations.

PRD is applied to X-37 joined components involving panel-to-panel configuration shown in Figure 1. The top row of bolts connects the two L-shaped plates made of 3D CMC laminate material with the two back-to-back vertical plates made of 2D CMC laminate material. The bottom row of bolts connects the back-to-back plates made of 2D laminate material. Fiber glass composite is used to support the specimen. Figure 2 shows the test configuration.

Progressive Failure Analysis of Existing Design:

PFA Results showed that damage initiates as interlaminar shear failure at the corner of the L-shaped angles (Figure 3). Then it propagates through the vertical and horizontal plates of the 2D laminates. Figure 4 shows damage initiation and propagation to failure.

 

Figure 3 - Damage initiation at lower L-shape corner

 

Figure 4 - Animation of Damage from initiation to fracture Simulation predicted failure load is 71,511 N compared to 79,178 N from test [Ref 1] (Failure modes are combined in-plane and interlamina shear)

Parametric Robust Design:

To improve the durability and damage tolerance of the assembled joint structure, the L-shape panels and corners were optimized by use of Parametric Robust Design capability in the GENOA software. This feature is founded on automatic update of geometric FEA model parameters. It also includes optional material properties and ply-manufacturing details parameters. A large number of designs can be generated in a very short time once the high and low bounds for each design variable are identified. This tool reduces the number of real designs by use of virtual simulation. It simply provides alternate designs that can enhance the part's performance. 

For the present case, four design variables were chosen from initial deterministic results (Figure 5):

• 2D Flange radius: flange_radius
   
• 2D Flange thickness: flange_t
   
• 3D Flange radius: top_flange_radius
   
• 3D Flange thickness: top_flange_t

Figure 5 - Design Variables

In addition, other variables representing material and fabrication uncertainties were integrated for more realistic performance:

• 2D & 3D Flange Fiber content: FVR
   
• 2D & 3D Flange Void content: VVR
   
• 2D & 3D Flange Fiber orientation: Angle
   
• 2D & 3D Flange Matrix shear strength: SmS
   
• 2D & 3D Flange Fiber shear modulus: Gf12 and Gf23

Technically, many more variables could be considered. Attention has to be paid to optimization constraints and dimensions of the part, volume, weight and eventually computer resources. The results of the parametric robust design analysis are shown in Table 1.

Table 1 - Improved design compared to initial one

With marginal increase in weight and volume, the ultimate load is improved by 6.5%. Figure 6 shows a bar chart of the load applied load versus the material damage volume percent for the initial and optimized models. With optimization, the structure became more damage tolerant as it sustained more damage before fracture.

Figure 6 - Material damage volume as a result of applied loading obtained from PFA (before and after optimization)

Reliability evaluation of the optimized joint was undertaken to determine the effect of the new design on the probability of failure. Random variables pertaining to geometry, fabrication parameters, and material properties were considered. Sensitivity analysis results are presented in Figure 7 showing the relative effect of random variables on the joint failure load. It ranks the random variables by order of importance. As noted in the same figure, the void content (VVR) in the 2D panels is the most influential parameter. Information from the sensitivity analysis can be used as a guide to reduce testing for design certification by eliminating variables from the test matrix that show no effect on desired response.

 

Figure 7 - Probabilistic Sensitivities of geometric, material and fabrication random variables

With prescribed uncertainties and distributions of the random variable, probabilistic analysis was performed before and after optimization. The cumulative probability is plotted before and after optimization in Figure 8. It is evident that a structure with enhanced durability subjected to the same uncertainties is bound to exhibit increased reliability. For example, if the design load is 60,000 N, the reliability before optimization is 0.92 (probability of failure of 0.08). After optimization, for the same design load, the reliability is 0.98. More information on the study can be found in reference 3.

Figure 8 - Cumulative probability for joint failure load

References: 
1. F. Abdi, X. Sue, J. Housner, "Durability Evaluation of NASA's X-37 2D/3D C/SiC CMC Assembled Sub-Elements". SAMPE Conference Paper, May 2008. Click here to email us for the technical publication.

2. F. Abdi, T. Castillo, D. Huang, V. Chen, A. Del Mundo "Virtual Testing of the X-37 Space Vehicle". SAMPE Conference Paper, 2002. Click here to email us for the technical publication.
 

3. F. Rognin, F, Abdi, J. Housner, and K. Nikbin, "Robust Design of Assembled Composite Joining Concepts, a Combined Durability-Reliability Evaluation", SAMPE Conference Paper, 2009. Click here to email us for the technical publication.

 

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