Composite Material Qualification Process

© 2003, P. Joyce Composite Material Qualification Process ¾ Analysis alone is generally not considered adequate for substantiation of composite struc...
Author: Melvin Walsh
80 downloads 0 Views 279KB Size
© 2003, P. Joyce

Composite Material Qualification Process ¾ Analysis alone is generally not considered adequate for substantiation of composite structural designs. ¾ Instead the “building block approach” to design development testing is used in concert with analysis (first applied to aircraft qualification in the 1950s.) ¾ This approach is often considered essential to the qualification/certification of composite structures due to the sensitivity of composites to out-of-plane loads, the multiplicity of composite failure modes and the lack of standard analytical methods. © 2003, P. Joyce

1

Composite Material Qualification Process ¾Design substantiation is often called qualification in DoD applications and certification in civilian applications including FAA.

© 2003, P. Joyce

Composite Materials Qualification Process ¾ Design with structural metals is a mature technology (too comfortable?) ¾ The designer can take materials properties from a handbook, specify the alloy and heat treatment and, with little or no testing, move on to initial designs for the metallic component. ¾ Tests are performed to verify that the alloy, process and resulting material properties are as specified; design, manufacture and qualification of the prototype component follow.

¾ The Building block approach has evolved for composites because of their unique characteristics. © 2003, P. Joyce

2

Composite Material Qualification Process ¾ Building Block Approach ¾ Generate material basis values and preliminary design allowables. ¾ Based on the design/analysis of the structure, select critical areas for subsequent test verification. ¾ Determine the most strength-critical failure mode for each design feature. ¾ Select the test environment that will produce the strength-critical failure mode. ¾ Matrix-sensitive failure modes (compression, out-of-plane shear, and bondlines) ¾ Potential “hot-spots” caused by out-of-plane loads © 2003, P. Joyce

Composite Material Qualification Process ¾ Building Block Approach ¾ Design and test a series of test specimens, each one of which simulates a single selected loading condition and failure mode, compare to analytical predictions, and adjust analytical models or design allowables as necessary. ¾ Design and conduct increasingly more complicated tests that evaluate more complicated loading situations with the possibility of failure from several potential failure modes. Compare to analytical predictions and adjust models as necessary. © 2003, P. Joyce

3

Composite Material Qualification Process ¾Building Block Approach ¾Design and conduct, as required, full-scale component static and fatigue testing for final validation of internal loads. Compare to analysis. Component qualification is often complicated by the fact that critical design conditions include hot, wet environments. This is often accomplished by overloading a test article that is in ambient conditions, or by analysis of failure modes coupled with strain measurements related back to subcomponent hot/wet tests. © 2003, P. Joyce

Composite Material Qualification Process

© 2003, P. Joyce

Schematic of building block approach

4

Composite Material Qualification Process ¾Building Block Approach ¾Major purpose of this approach is to reduce program cost and risk while meeting technical, regulatory and customer requirements. ¾Cost-efficiency is achieved by ¾testing greater numbers of less-expensive small specimens, (each level involves fewer test articles than the one below.) ¾assessing technology risks early in the program and ¾using analyses in place of tests where possible.

© 2003, P. Joyce

Composite Material Qualification Process ¾Test levels can be defined in two basic ways: ¾Structural Complexity Level ¾Data Application Category

© 2003, P. Joyce

5

Composite Material Qualification Process ¾Five levels of Structural Complexity (each geometry or form-based) ¾Constituent ¾Lamina ¾Laminate ¾Structural element ¾Structural subcomponent

© 2003, P. Joyce

Composite Material Qualification Process ¾ The material form(s) to be tested, and the relative emphasis to be placed on each level, should be determined early in the material data development planning process and will likely depend upon many factors: ¾ Manufacturing process ¾ Structural application ¾ Corporate practices ¾ Procurement or certification agency © 2003, P. Joyce

6

Composite Material Qualification Process ¾ ¾ ¾ ¾

Most applications require at least two levels It is common to use all five levels A single level may suffice in rare instances Regardless of the level selected, physical and chemical property characterization of the prepreg (or the matrix if RTM) is necessary to support physical and mechanical property test results.

© 2003, P. Joyce

Composite Material Qualification Process ¾Constituent testing ¾Evaluates the individual properties of fibers, fiber forms, matrix materials, and fiber-matrix preforms. ¾Key properties, for example, include fiber and matrix density, and fiber tensile strength and tensile modulus

© 2003, P. Joyce

7

Composite Material Qualification Process ¾ Lamina testing ¾ Evaluates the properties of the fiber and matrix together in the composite material form. ¾ Prepreg properties are often included in this level, sometimes broken out in a separate level. ¾ Key properties include fiber areal weight, matrix content, void content, cured ply thickness, lamina tensile strengths and moduli, lamina compressive strengths and moduli, and lamina shear strengths and moduli. © 2003, P. Joyce

Composite Material Qualification Process ¾Laminate testing ¾Characterizes the response of the composite material in a given laminate design. ¾Key properties include tensile strengths and moduli, compressive strengths and moduli, shear strengths and moduli, interlaminar fracture toughness and fatigue resistance.

© 2003, P. Joyce

8

Composite Material Qualification Process ¾Structural element testing ¾Evaluates the ability of the material to withstand common laminate discontinuities. ¾Key properties include open and filled hole tensile strengths, open and filled hole compressive strengths, compression after impact strength, joint bearing and bearing bypass strengths. © 2003, P. Joyce

Composite Material Qualification Process ¾Subcomponent testing ¾Evaluates the behavior and failure mode of increasingly more complex structural assemblies (application specific.)

© 2003, P. Joyce

9

Composite Material Qualification Process ¾Material property testing can also be grouped by data application into one or more of the following categories: ¾Screening ¾Qualification ¾Acceptance ¾Equivalence ¾Structural substantiation © 2003, P. Joyce

Reproduction

Full Scale

Verification

Laboratory EMD Aircraft

Material/Process and Design Development

Certification Tests

Components

Elements/ Subcomponents Material Properties Manufacturing Process

Material Selection

© 2003, P. Joyce

Building Block Test Program

10

Composite Material Qualification Process ¾Material and Process Selection ¾Must look at both material and process together ¾Need to evaluate part requirements and cost goals ¾Material and process maturity are a factor ¾ Material allowables and process reproducibility will be required ¾ Experience from other programs can be used

Outcome: Candidate Materials and Processes © 2003, P. Joyce

Composite Material Qualification Process ¾Process Development ¾Define process limits ¾Develop mechanical properties at upper/lower limits

¾Demonstrate reproducibility within limits ¾Define critical steps/tools/equipment ¾Develop necessary inspection/QC tools/process Outcome: Process Specifications © 2003, P. Joyce

11

Composite Material Qualification Process ¾ Process Development ¾ Often composite materials must receive limited “requalification” every time a process parameter s altered – at least to show equivalency. ¾ Due to the statistical variability inherent in composites, even relatively smal changes during manufacturing can alter the load path or failure mode and produce statistically significant changes in composite properties.

© 2003, P. Joyce

Composite Material Qualification Process ¾ Currently “qualified” processes ¾ Hand lay-up ¾ Filament winding ¾ Resin transfer molding ¾ Fiber placement

¾ Potential processes ¾ Resin film infusion ¾ Vacuum assisted RTM ¾ Sheet Forming ¾ Pultrusion © 2003, P. Joyce

12

Composite Material Qualification Process ¾ Material Properties ¾ Physical and Chemical property determination ¾ Density ¾ Viscosity ¾ Cure kinetics ¾ Out time ¾ Tack ¾ Glass transition temperature

¾ Environmental sensitivity ¾ Moisture resistance ¾ Solvent attack ¾ Upper use temperature © 2003, P. Joyce

Composite Material Qualification Process ¾Material Properties ¾Mechanical Properties ¾Strength, Modulus, Notch Sensitivity, Fatigue Resistance, Damage Tolerance, etc.

¾Examine all critical modes and environments ¾Develop design allowables ¾B basis confidence

Outcome: Material Specifications, Design Allowables © 2003, P. Joyce

13

Composite Material Qualification Process ¾ Material Properties ¾ Defect/Damage Sensitivity ¾ Mechanical effect of defects ¾ Voids ¾ Delamination ¾ Wrinkles

¾ “Damage” tolerance ¾ Low velocity impact ¾ FOD

¾ Repair ¾ Develop repair materials and processes ¾ Demonstrate utility

Outcome: Repair Procedures and Specifications © 2003, P. Joyce

Composite Material Qualification Process ¾ Currently Qualified Materials (partial list) ¾ Carbon fibers: AS4, IM6, IM7, both uni and woven ¾ Glass fibers: E and S ¾ Resins: 3501-6, 977, 8552, 8551, E773 ¾ Core materials: Korex

¾ Potential Material Systems ¾ Resins: PR-500, 5250-4 ¾ Core: Syncore, Rohacell ¾ Adhesives © 2003, P. Joyce

14

Composite Material Qualification Process ¾Elements and Subcomponents ¾Fabrication of design details ¾Validation of analysis ¾Refined definition of inspection and repair requirements ¾Risk reduction for manufacturing and assembly

Outcome: Reduced Risk, Selection of Final M&P © 2003, P. Joyce

Composite Material Qualification Process ¾ Components ¾ Fabrication of actual components ¾ Manufacturing demonstration ¾ Destructive evaluation

¾ Demonstration of repairs ¾ Demonstration of componentlevel mechanical performance ¾ Validation of analysis ¾ Demonstration of systems interfaces ¾ Demonstration of damage tolerance

Outcome: Low risk materials, process design, and manufacturing process © 2003, P. Joyce

15

Composite Material Qualification Process ¾Certification Tests ¾Static ¾Dynamic ¾Fatigue

¾Flight Test ¾Flight clearance given based on data package of building block test results.

© 2003, P. Joyce

Rotorcraft ¾ The building block approach for rotorcraft differs from that for fixed-wing aircraft in several ways. ¾ Limited NDE – must accommodate larger defect sizes ¾ Must consider complex set of dynamic components ¾ Static fatigue and damage-tolerance requirements are addressed separately in rotorcraft. ¾ As with fixed-wing aircraft, design allowables usu. generated at the coupon level ¾ As with military aircraft the number and types of tests dependent upon component criticality. ¾ Damage-tolerance requirements for the rotor and drive systems are handled only at the full-scale level. ¾ Tailboom and roof beams/pylon support are fatigue critical and require full-scale testing and qualification, as a results these components undergo less coupon and subcomponent testing. ¾ Airframe testing is similar to that for fixed wing aircraft, except that fatigue is of more concern and thus receives more compete characterization at a lower level. © 2003, P. Joyce

16

General Aviation ¾ The situation for general aviation is very different from that of the large aerospace contractors. ¾ Take kit aircraft, they have already designed, built and flown their aircraft; now they want FAA certification. ¾ General aviation in general is equipped to produce aircraft quickly, in perhaps one year from project inception to production. As a result, large subcomponents can be produced sooner and much more economically – argues for “inverted building block” approach. ¾ The concept is that one should test the largest structure that is economically viable, allows such concerns as manufacturing induced defects to be addressed early in the design process. . . © 2003, P. Joyce

General Aviation ¾ Large scale articles should be used to identify the areas of critical concern and to develop element or subcomponent test plans for determining design allowables for the critical conditions. ¾ Coupon tests would be used primarily to establish the equivalency of the material to existing data, for environmental evaluation and for QA. ¾ Except in the case of truly new materials with no pre-existing data, the test matrix for coupon testing should be limited in scope. . . ¾ Changes in processing should only be accepted if equivalency of properties can be established (approach taken in qualifying RTMprocessed parts for the F-22.) ¾ AGATE program for sharing design allowables changes the landscape for GA in a very positive manner. . . © 2003, P. Joyce

17

References ¾ Composite Material Qualification Process, Roland Cochran ¾ “Quantifying qualification: the building block approach to designing composite structures,” High-Performance Composites, July/August 1999, pp. 20-24. ¾ Mil-Hdbk-17 Composite Materials Handbook, 1997. ¾ “Material Qualification and Equivalency for Polymer Matrix Material Systems,” FAA Technical Report, Tomblin, J.S., Ng, C.Y. and Raju, K.S., 2000.

© 2003, P. Joyce

18

Suggest Documents