Material Qualification and Certification Determine Allowables by Means of Virtual Simulation Combined With Limited Testing

Issue #16 - October 20th, 2008

Software Suite for Durability, Damage Tolerance, Reliability & Life Prediction
Enhances FEA Solvers MSC Nastran*, ABAQUS, ANSYS, RADIOSS & LS-DYNA

* Best Performance and Verified Solutions with MSC Nastran

This Week's Feature Composite Example

Material Qualification and Certification Determine Allowables by Means of Virtual Simulation Combined With Limited Testing

(a) Top View (laminate)  (b) Top View (individual plies) (c) Iso-View (laminate) (d) Iso-View (individual plies) Figure 1 - Virtual Testing of an Open-hole Coupon with Progressive Failure Analysis

A-basis and B-basis strength values are critical to reduce risk in structural design of composite aircraft structures. A previous newsletter presented a novel approach to determine A- and B-basis allowables for composite materials (click here for previous newsletter). This newsletter provides additional details of the A and B-basis allowable generation and describes a link between virtual testing and design carpet plots. 

The calculation of allowables for polymer matrix composite for aerospace applications is governed by FAA and Military Handbook 17-E standards and rules. The process is costly and time consuming as large numbers of coupon tests are inevitable (example: the generation of allowables for the IM7 fiber and 5250 resin for the F22 program cost close to 100 million dollars). To accelerate the prediction of allowables and reduce the number of coupon tests, GENOA combines multi-scale composite modeling with progressive failure analysis (PFA), probabilistic analysis and minimum test data to determine A- and B-basis values. Figure 1 shows the multi-scale PFA. The PFA is used to produce virtual scatter data using probabilistic analysis. Figure 2 shows the process flowchart. The scatter in material strength is determined by iterating on coefficient of variations (COV) of random variables from single or multiple sources of uncertainties (i.e. fundamental material properties and fabrication variables). The iterative process replicates scatter in the strength value obtained from the test of one coupon of each material batch. If the scatter is unknown, then maximum of 10% coefficient of variation can be chosen as per the FAA regulations for composite materials. However, when test data variation is known, then a COV can be estimated, as shown in Figures 3 and 4. In Figure 3, a COV of 0.06 provides a good estimate of the test data and in Figure 4, a COV of 0.01 is used. The methodology is applicable to notched (Figure 5) and un-notched coupons and structures and has the potential of reducing the coupon count for testing by over 60%. 

It is important to have design envelopes before and after the A- and B-Basis values are generated. The design envelop is a graphical representation of the variation in material properties (stiffness, Poisson's ratio, and strength) with variation in ply angle [e.g., 0/+45/-45/90] distribution in the laminate. The graphical representation is referred to as a 'Carpet Plot' in industrial practice. A typical Carpet Plot is shown in Figure 5. The carpet plot is a powerful tool which can be used as a design reference. In GENOA, a carpet plot is generated automatically after virtually simulating ASTM standard or other chosen testing methods (Figure 1). First, the layup in the laminate is automatically varied and ASTM or user defined tests are virtually simulated for each laminate layup. This is an automated process, requiring minimal user interface. Next, the virtual test database is filtered for the carpet plot information desired and plotted graphically.  The carpet plots generated need not be limited to A and B-basis allowables. Other carpet plot options include laminate stiffnesses, first ply failure and final failure. If test data is available, then test results can be plotted on top of the virtually generated carpet plots for verification.

More focus on virtual testing and carpet plot utilization to reduce physical test matrix reduction will be shown in upcoming future newsletters.

 

Figure 2 - Flowchart for generating A-basis and B-Basis Allowables in GENOA using testing standards for ASTM and MIL-HDBK 17-E and FAA

Figure 3 - Cumulative Density Functions (CDFs) with assumed coefficients of Variation of 0.06, 0.075, 0.10 for compressive composites un-notched composite coupon  [1]

 

Figure 4 - Scatter from test and simulation for the strength of the open-hole coupon along with GENOA predicted A- and B-Basis values [2]

 

Figure 5 - Carpet plot for various percent of 45 deg plies is useful to reduce coupon testing

References:

1. G. Abumeri, M. Garg, and M. R. Talagani, A Computational Approach for Predicting A- and B-Basis Allowables for Polymer Composites, SAMPE Fall Conference, TN, 2008.
Click here to email us for the technical publication.

2. M. R. Talagani, Z. Gurdal, and F. Abdi, S. Verhoef ?Obtaining A-basis and B-basis Allowable Values for Open-Hole Specimens Using Virtual testing? AIAAC-2007-127, 4. Ankara International Aerospace Conference, 10-12 September, 2007 ? METU, Ankara.
Click here to email us for the technical publication.

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

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Predicting Post-Buckling Response and Ultimate Failure of Composite 2-Stringer Panels

Issue #15 - June 10th, 2008

Software Suite for Durability, Damage Tolerance, Reliability & Life Prediction
Enhances FEA Solvers MSC Nastran*, ABAQUS, ANSYS, RADIOSS & LS-DYNA

* Best Performance and Verified Solutions with MSC Nastran

This Week's Feature Composite Example

Predicting Post-Buckling Response and
Ultimate Failure of Composite 2-Stringer Panels

Figure 1 - Damage & Durability Analysis of a Composite 2-Stringer Panel Subjected to Post-Buckling Analysis

Predicting the failure load of composite panels with post-buckled regions is a complicated undertaking as it involves buckling and damage evolution (Figure 1). The difficulty is complicated further by the fact that the ultimate failure (structural collapse) is driven by localized failures produced by damage in fiber and matrix in the post-buckled area of the structure. Reliable assessment of these load limits requires the application of advanced computational simulation that integrates composite mechanics at the micro-scale of fiber and matrix with finite elements, buckling, damage tracking and fracture analysis. The technical approach must rely on physics-based composite failure criteria capable of detecting all types of damages including non-visible ones. If localized buckling takes place before damage, the buckling mode shape is superimposed on the structure's geometry. Inception of damage prior to buckling requires repeated buckling analysis with degraded stiffness to account for detected damage. This analysis capability, integrated in the GENOA Software, was applied successfully to a two-stiffener composite panel under shear loading. The test results were closely reproduced with the analysis simulation. Including post-buckling effect was instrumental to replicate the test, since otherwise we risk over-predicting the failure load. As shown next, this analytical approach can be very effective in guiding the design and in reducing the number of tests of post-buckled composite panels.
 

Problem Description

The two-stringer J-stiffened composite panel evaluated for durability with post-buckling consideration is presented in Figure 2. It was made of AS-4/3501-6 carbon/epoxy unidirectional fabric. The fabric consisted of a wide sheet of unidirectional tows of fibers based together with polyester thread to keep it from unraveling. Twelve plies of the skin were laid up to form a 1.83 mm (0.072 in.) thick quasi-isotropic [0,90,45,0,-45,90]s laminate. The "J" shaped stiffeners were constructed with the same lay-up except for the flanges that were only half the thickness of the basic laminate. The skin panel and the stiffeners were stitched together with Kevlar and fiberglass threads [1,2]. The experimental results were adopted from the literature [1].

 

Figure 2 - Geometry of Two-stiffener composite panel [1]

The panel was modeled with Mindlin-Reissner thick shell elements and loaded in tension in the diagonal direction at one corner of the panel while fixing the opposite corner [2]. Details of the technical approach are provided next followed by discussion of results.

Technical Approach

Using a representative finite element model with appropriate stiffness and strength limits of the various materials, the software assesses the performance of composite panels with post-buckling consideration by:

1. Determining the buckling mode shape of the panel (in this case skin buckling mode). Typically selects the buckling mode shape with the lowest eigenvalue.
2. Initiating durability analysis through the sequential application of incremented static loading till structural fracture takes place. During the load stepping process, the software checks and tracks damage resulting from: fiber failure in tension or compression, matrix cracking (transverse tension/compression and in-plane shear), and delamination (normal tension and transverse and longitudinal out-of-plane shear). The analysis strategy is described here: 

1. GENOA's progressive Failure Analysis (PFA) module starts with the full-scale finite element model and reduces the material properties down to the micro-scale of fiber and matrix. With every load step material properties are updated, reflecting any changes resulting from damage or cracks due to the applied loading. 
2. If the applied load reaches the skin buckling load, the buckled shape is superimposed onto the panel. In this way the panel is placed into its bifurcated and stable lower energy state. In a physical test it would naturally move to this state. 
3. If material damage is detected prior to local buckling, the code updates the stiffness and repeats the buckling analysis with reduced stiffness to extract a new buckling load. 
4. When material and structural equilibrium states are reached, the load is incremented to the next level. With every additional load step, buckling analysis is repeated to update the mode shape. As the load increases, damage in the panel will initiate, grow and accumulate leading to ultimate panel failure, as shown next in the simulation results. 

Results
For the considered two-stiffener composite panel, experimental data indicated that local buckling of the skin occurred prior to reaching the ultimate load. Figure 3 shows the analytical results illustrating damage in the panel at initiation stage in the post-buckled region and damage progression when the ultimate load is reached. The software was used first to perform a linear bifurcation buckling analysis. The Buckling analysis showed that the initial buckling load is 8.275 kips (36.81 kN), which is very close to the experimental results [2]. As the load was incremented during the progressive failure analysis, the software superimposed the buckling mode shape on the structure's geometry when the applied load reached the buckling load of 8.275 kips. From that forward, the buckling analysis was repeated every time the load was increased followed by update in the structure's geometry to include the mode shape effect. Structural damage was detected at a load higher than the buckling load. The PFA process allows for localized failures to occur in the panel that ultimately results in panel collapse. Delamination due to relative rotation of the plies is shown in Figure 4.

(a) Damage Initiation                                         (b) Damage Progression

Figure 3 - Net damage due to progressive failure for composite two-stringer panel under diagonal tension. (Red indicates areas where failures have occurred)  a) at initiation of post-buckled region and b) near ultimate load.

 

(a) Delamination Initiation                                         (b) Delamination Propagation

Figure 4 - Delamination location with respect to individual plies due to progressive failure analysis for composite two-stringer panel under diagonal tension. (Red indicates delamination locations)  a) at initiation of post-buckled region and b) near ultimate load.

Load deflection results obtained from the simulation are compared to test and shown in Figure 5. The technical approach employed here yielded excellent agreement between the simulation and experimental results when progressive failure technique is used in a post-buckling analysis; i.e., when the panel is allowed to go into its lower energy buckled state prior to performing the progressive failure analysis. Figure5 also shows the diagonal deflection versus applied load obtained via simulating the progressive failure analysis without any buckling and post-buckling effects. The simulation results for the unbuckled panel clearly indicates that the ultimate load is over-predicted by about 35% and the stiffness by about 7.6% [2]. The results presented here demonstrate the effectiveness of the methodology integrated in GENOA. It can be reliably used to perform iterative designs prior to committing to a large test program. Testing can be done once satisfactory performance is derived from the software.

 

Figure 5 - Comparison of experimental and analytical load deflection curves for composite two-stringer panel [2]

 

References:

1. Yeh, H-Y and Chen, V., 1996. Experimental Study and Simple Failure Analysis of Stitched J-Stiffened Composite Shear Panels. Journal of Reinforced Plastics and Composites, Vol. 15, pp. 1070-1087.  Click here to email us for the technical publication.

2. Minnetyan, L. and Huang, D., 2001. Progressive Fracture of Stitched Stiffened Composite Shear Panels in the Postbuckling Range. Journal of Reinforced Plastics and Composites, Vol. 20, pp. 1617-1632. Click here to email us for the technical publication.

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

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Composite Storage Module Joint Analysis and Test Verification

Issue #14 - April 28th, 2008

Software Suite for Durability, Damage Tolerance, Reliability & Life Prediction
Enhances FEA Solvers MSC Nastran*, ABAQUS, ANSYS, RADIOSS & LS-DYNA

* Best Performance and Verified Solutions with MSC Nastran

This Week's Feature Composite Example

Composite Storage Module Joint Analysis and Test Verification

Figure 1 -Multi-side Adhesive and Cohesive Failure of Joint and (Bottom) Composite Storage Module and Joint Geometry, Relatively Clean Ti Interface Indicates a Premature Adhesive Failure in this Location [1]

The premature failure of adhesively bonded composite joint tests, suggest adhesive failure as opposed to cohesive failure. This type of joint failure may be due to a) non-clean interface surfaces preparation, b) thick bond line, c) existence of voids in the adhesive bond line or a combination of all three

    In support of the ONR (Office of Naval Research) SBIR Phase II program, several Naval joint structures were studied. These joints included a General Dynamics designed joint for use on a composite storage module, and two test articles of a General Dynamics/Boeing designed joint attaching the walls of a director's room to the deck of a ship. During testing, the General Dynamics Composite Storage Module (CSM) joint failed prematurely and progressive failure analysis was employed to shed light on the possible causes of the premature failure.

    The General Dynamics Composite Storage Module (CSM) joint was a particularly useful example structure as a thorough analysis and testing program that accompanied the design and verification of the joint development. A significant portion of this program was developed into a paper [1]. The CSM joint version of interest was composed of a graphite/epoxy quasi-isotropic laminate adhesively bonded to a tapered titanium fitting. The CSM and joint details are shown in Figure 1. Details of the FE model and materials used in the analysis are shown in Figure 2. The tensile load on the joint bends the joint resulting in peel stresses in the adhesive EA9394 layer. The test indicated that the primary failure mode of the joint was adhesive failure within the EA9394 layer between the titanium and fiberglass.
 

Figure 2 -  FE Model Details and Materials for Progressive failure Analysis (PFA) [1]

    Several steps were taken before the final GENOA Progressive Failure Analysis (PFA) was performed in order to develop and demonstrate confidence in the software. For example, as a baseline check, linear analyses were performed using standard FEA software packages ANSYS and ABAQUS along with GENOA. General Dynamics performed the ABAQUS simulation. Stress results along the adhesive centerline of the EA9394 adhesive are shown in Figure 3 for all three codes. The validation of GENOA simulation to capture the nonlinear material behavior of the adhesive was achieved by duplicating the ABAQUS analysis performed by General Dynamics.

Figure 3 - Comparison of Centerline Peel Stress Predictions Within the (Linear) EA9394 [1]

    A full PFA with GENOA was then performed and compared to the test data. The predicted load deflection curve and associated damage mechanisms are shown in Figures 4a and b. While the failure mechanisms predicted by the analysis were very similar to those observed during the test, the analysis predicted a much higher strength for the joint as shown in Figure 4a. The tested joint may have failed at a much lower load (see blue curve in Figure 4a) because (1) the titanium surfaces were improperly prepared for the adhesive and/or (2) the maximum value of strain the adhesive could withstand was lower than that assumed from measurements of the adhesive done in 1995 and provided in reference 3. Without some relatively inexpensive coupon-level tests to establish a more relevant value of adhesive strength/strain limit, the failure strain criterion was not adjusted. However, improper surface preparation was investigated further.

    Subsequent review of the failure surfaces revealed a clean titanium surface indicating a premature interfacial failure of the adhesive to titanium bond (Figure 1). Analyses were performed to introduce the clean surface interfaces on the titanium fitting (test suggest adhesive failure as opposed to cohesive failure) using: 1) Virtual Crack Closure Technique (VCCT), and 2) using PFA and degrading the adhesive properties assuming using 20% void formation [2].

    VCCT required a predetermined crack path, and was modeled in two ways; a) multiple crack locations, and (b) single crack initiation point. For these simulations the crack path was determined from PFA (Figures 4b and 5a). The results obtained predicted higher strength value than predicted by PFA strain based analysis (blue curve in Figure 4a). Plane strain fracture toughness for peel and shear, (K1C and KIIC), values were required to run the analysis using the VCCT approach. The K1C and KIIC values for EA9394 adhesive were obtained from somewhere else [3]. Note that PFA predictions are usually close but are not considered very accurate when pre-cracked conditions exist in a simulation due to infinite stresses near a sharp crack tip.

 

Figure 4 - Load-deflection curve and associated damage events [2]

    Thereafter to capture the effect of improper bonding, the VCCT analysis was defined on limited node pairs as shown in Figure 5b. The trend of the results indicated that defining the partial bonding can simulate the effect of improper bonding, as shown in Figure 6.

    Similarly a void content of 20% was used to simulate the improper bonding in PFA. Again the results were found to be a close match with that of the test (see Figure 6).

Figure 5 - (a) Single VCCT approach. Note that the crack initiates from the right hand side and propagates to the left. (b) Partial Single VCCT approach to simulate partial (improper) bonding. The left hand side images are the initial setup and the right hand side is the final failure of the bonding [2].

 

Figure 6 - Comparison of the simulated load displacement curve with test data [2].

    In conclusion, if proper contact surface area information is available before the analysis, PFA and VCCT can be used judiciously to simulate the effect of improper bonding. Moreover, insight into potential improper bonding can can be achieved by varying the voids percentage in the adhesive to simulate the improper bonding scenario if surface area is not available.

References:

1. George F. Leon, Michael F. Trezza, Jeffrey C. Hall,1 and Kelli Bittick, "Evaluation of a Carbon Thermoplastic to Titanium Bonded Joint", ASTM-STP1455-11707.081503.  Click here to read technical publication.

2. Xie, D., Garg, M., Huang, D., and Abdi, F., "Cohesive Zone Model for Surface Cracks using Finite Element Analysis," AIAA-49SDM-106742-2008.  Click here to read technical publication.

3. T. R. Guess, E. D. Reedy, M. E. Stavig, 1995. "Mechanical Properties of Hysol EA-9394 Structural Adhesive," SANDIA REPORT, SAND95-0229. UC-704. Click here to read technical publication.

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

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GENOA 4.3 Release with A- and B-Basis Allowables

Issue #13 - February 25th, 2008

Software Suite for Durability, Damage Tolerance, and Life Prediction
Augments FEA Solvers MSC Nastran*, ABAQUS, ANSYS & LS-DYNA

* Best Performance and Verified Solutions with MSC Nastran

This Week's Feature Composite Example

GENOA 4.3 Release Now Available 

Figure 1 - Progressive Failure Analysis of T-Joint

    The latest 4.3 release contains significant improvements in its popular Progressive Failure Analysis (PFA) module and translation support for NASTRAN, ABAQUS and ANSYS. Included in this release are 50 Step-by-Step Tutorial examples that fulfill a diverse range of applications and engineering needs.

    4.3 also features the new A- & B- Basis Allowable module which may be viewed through GENOA's Web Demo.  Users who are interested in applying their own data in this module may try GENOA through the on-line CVT web service for 3 free months.  For more information, please contactsales@ascgenoa.com.

    GENOA is an engineering software suite that augments commercial Finite Element Analysis (FEA) packages by providing Progressive Failure Analysis (PFA) capability. It can investigate structural responses to material degradation from damage induced by static, cyclic (low and high cycle fatigue), impact, Power Spectrum Density (PSD) and thermal loading.
 

Figure 2 - Over 100 materials in the new Archived Material Databank (Includes a large selection of commonly used fiber/resin and lamina properties)

List of Significant Features and Updates

In response to the requests of our existing and potential customers, the following new features and improvements have been made in GENOA 4.3:

New Features

• A- & B-Basis Allowables
• Elliptic dome shapes
• Strain Gage feature extended to both element- and node-based FE models
• Thermal databank
• Low and high fidelity filament winding optimization
• Design envelope for Damage Plies % vs. Loading 
• Archived databank of 100+ materials

Other Improvements

GUI:
• Results Model panel displays the FE model volume, weight and current iteration number next to GENOA logo
• Importing of external models into Filament Winding module is made easier
• Fixed concerns of numerical translation problems in Element Material Coordinate card due to Regional Settings Differences (GUI)
• Windows VISTA support (Environment variables adjusted)
• Improved table editing fields in all tables
• Strain Gauge added for Stress and Strain panels (including Ply Stress and Strain panels)
• Added the out-of-plane ply properties entry fields 

PFA:

• NASTRAN Element 35 (C-Gap element) added to GUI
• Offset feature for shell elements added for both NASTRAN and ABAQUS
• Extended PFA's capability to account for Virtual Crack Closure Technique (VCCT) analysis when mixed ply properties are used
• Added *INCLUDE keyword to write user additional keywords for FE solvers used in GENOA
• Added material definition for temperature variations
• Evaluate inter-lamina strength for Ply Option
• Added out-of-plane material properties entries for ply properties in material databank file

Figure 3 - New A&B Module (Effectively Reduces Coupon Testing for Material Qualification)

Did You Know?

Trying GENOA with Your Own Models

Alpha Star Corporation's Collaborative Virtual Testing (CVT) is a web service that runs GENOA through the Internet.  If you are interested in trying GENOA for free through the web with your own models, please contact Alpha Star Corporation for a free trial.  For more information, contact sales@ascgenoa.com.

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

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A- and B-Basis Allowables for Composite Materials

Issue #12 - January 28th, 2008

Software Suite for Durability, Damage Tolerance, and Life Prediction
Augments FEA Solvers MSC Nastran*, ABAQUS, ANSYS & LS-DYNA

* Best Performance and Verified Solutions with MSC Nastran

This Week's Feature Composite Example

A Novel Approach to Determine A- and B-Basis Allowables for
Composite Materials 

Figure 1 - V-Notched Shear Test (Equivalent to ASTM D5379-Isopescu Test)

Many aircraft and spacecraft have advanced designs based on a well-matured and systematic testing technology; however, the manufacture and service life risks still remain. In production, testing to reduce risks due to manufacturing defects is performed at many steps up to and including the entire assembly / integration system levels. Even with all this testing, costly failures still occur and these are increasingly prone to public scrutiny. Table 1 shows the possible mission outcomes given a test prior to service. These tests could be at the part, sub-component, component, sub-assembly, assembly and product levels. As the system moves through production, the cost of executing the mitigation strategy increases due to the increased time and labor required for disassembly and reassembly. Composites are particularly vulnerable to increased risk from the execution of this mitigation strategy from both the additional testing that the adjacent structure will be subjected to and the risk of damage due to increased handling. Sometimes the additional damage done by repeated ground tests is not considered in the overall "remaining life" assessment of the system.

 

Table 1.  Possible Outcomes of the Item Tests [1]

A-Basis and B-Basis allowable values are of great importance in the engineering industries involving composite structures. In most cases, strength Allowables are defined using "design point strategy," meaning that Allowables will be obtained for certain predefined configurations, after which only these configurations are allowed for use in the design. In order to reduce cost, limited amount of configurations will be tested, reducing the choice in configurations and with that the optimization possibilities. A solution to this problem would be a "design space strategy" where few tests are needed to calibrate and validate a failure analysis method, after which analysis can be used to analyze a wide range of possible configurations.

The use of A-Basis and B-Basis allowable properties recognizes that material properties are statistical in nature. The two statistically based tolerance bounds are:

A-Basis or T99: At least 99% of the population of material values is expected to equal or exceed this tolerance bound [2-3] with 95% confidence (single point catastrophic failure with no-load redistribution)

B-Basis or T90: At least 90% of the population of material values is expected to equal or exceed this tolerance bound with 95% confidence (redundant load path with load redistribution)  

These allowable values are important for reducing risk in structural designs. Allowable determination is a time consuming and expensive process, since a large number of tests are required. In order to reduce cost and product lead-time, Virtual Testing is used to reduce necessary physical tests by replacing them with analysis. The objective is to reproduce scatter from multiple sources: manufacturing, material properties, and test. This is done analytically using combined multi-scale Progressive Failure Analysis and Probabilistic Analysis methods to generate reliably the scatter (variability) in material and coupon strength. To assure high accuracy, the multi-scale analysis is used based on a hierarchical analysis, where a combination of macro-mechanics and micro-mechanics are coupled with finite element analysis, damage tracking and fracture, and material degradation capability to analyze structures in great detail [4]: The procedure for predicting material Allowables is: 

1. Calibration of Constituents (fiber and matrix) to verify the lamina/laminate properties

2. Selection of Random Variables: appropriate variables are selected and reasonable assumptions are made to reproduce natural scatter in the material strength (i.e., void and fiber volume fractions). (See Reference 4 for further details.)

3. Use Virtual Simulation capability in GENOA Software to Predict Probabilistic Scatter in the Failure Load for Each Type of Test: combine progressive failure, as shown in Figure 1, analysis with probabilistic methods

4. Plot and Compare Generated Cumulative Distribution and Probability Density Functions for each test category, as shown in Figure 2.

5. Obtain A and B Basis Allowables from 0.01 and 0.1 Probabilities with 95% confidence, as shown in Figure 2. 

Figure 2. GENOA Results: Cumulative Distribution Function Vs. Test Data [3]

There are three distinct capabilities (options) for generating the A- and B-Basis Allowables using GENOA Software using:

1. User Provided Test Data - Approach combines deterministic and statistical methods as specified in: 

- MIL HDBK-17E: Military Handbook for Polymer Matrix Composites

- FAA CFR 14: Aeronautics and Space

2. Limited Test Data (1 coupon from each batch) - Approach combines progressive failure analysis with probabilistic methods. Reduce the number of tests for material qualification. 

3. Without Test Data - For trade study approach combines progressive failure analysis with probabilistic methods (assume scatter based on standard practices).

Figure 3. GENOA Probabilistic Sensitivities of Random Variables

Results & Discussions

Example of generating the A- and B-Basis Allowables using GENOA Virtual Simulation, based on limited test data [option 2] is shown in Figure 2. The material Allowables are generated and compared with published test data using 3 compressive fiber-resin woven composite coupon tests (1st coupon of the 1st panel of the 1st batch). In addition, the software generates the sensitivity of design parameters to the Allowables (Figure 3). The selected variables in simulation were: fiber longitudinal modulus, fiber compressive strength, matrix modulus, matrix compressive strength, fiber volume ratio and void volume ratio. The computational capability presented here results in three major benefits:

1. Reduction in the number of coupon tests for material qualification

2. Accelerate the trade-off studies in the down-selection process for certifying new materials

3. Identification of critical material and manufacturing variables to maximize material performance for a given application

References:

1. Frank Abdi, Tina Castillo, Edward Shroyer "Risk Management of Composite Structure" Book Chapter 45, CRC Handbook, January 2005. Click here to read technical publication. 

2. R. Rice, R. Randall, J. Bakuckas, S. Thompson., "Development of MMPDS Handbook Aircraft Design Allowables". Prepared for the 7th Joint DOD/FAA/NASA Conference on Aging Aircraft, September 8-11, 2003, New Orleans, LA. Click here to read technical publication.

3. 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 read technical publication.

4. M. R. Talagani, Z. Gurdal, and F. Abdi, S. Verhoef "Obtaining A-Basis and B-Basis Allowable Values for Open-Hole Specimens Using Virtual Testing" AIAAC-2007-127, 4. Ankara International Aerospace Conference, 10-12 September, 2007 - METU, Ankara. 
Click here to read technical publication.

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

This software feature will be available in our upcoming GENOA 4.3 release and utilized through our on-line web service.

This issue was brought to you by Alpha STAR Corporation.

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