Does An Appropriate Test Protocol Exists for Characterizing the Hail Ice Threat Environment in Support of the Damage Tolerance Requirements?

Transcription

1 Does An Appropriate Test Protocol Exists for Characterizing the Hail Ice Threat Environment in Support of the Damage Tolerance Requirements? Comparison of current test concepts and a recommendation. 13 Nov 2007 Halpin & H. Kim 1

2 Issue: Test Protocol Simulating Hail Ice Damage Real hail ice in its naturally occurring state is nearly impossible to test complex internal structure and shape typically oblate spheroid that is spherically layered or agglomerated dense frozen, porous, and liquid regions density (reported in literature) layers kg/m 3 overall observed kg/m 3 SIMULATED HAIL ICE (SHI) is manufactured in the lab: frozen water cast into spheres; density ~ 920 kg/m 3 unfilled ice monolithic, flat, and spherically layered cotton filled per ASTM F320 spec (windshield testing) Firing Orientation 50.8 mm Ball with 8 g Cotton Fill Objective of study: comparison of impact damage initiation to composite panels by cotton-filled and unfilled simulated hail ice (SHI) 13 Nov 2007 Halpin & H. Kim Cotton-Filled Ice 2

3 Comparison of Two Hail Ice Test Protocols: The Cotton Reinforced Ice Does Not Reproduce Typical Hail Induced Material-structural Damage (data by H Kim) ASTM F320 Fiber Rupture & Puncture P&W Hail Ice Test, INITIAL Delamination & Resin Cracking 13 Nov 2007 Halpin & H. Kim 3

4 Impact Damage Size vs. KE (data by H Kim) Delamination Circumf. or Crack Length (in.)16 Woven Carbon/Epoxy Panels: to in. Ice: 1.68 in. Unfilled 1.5 and 2.0 in. Cotton-Filled FTE - cotton Cotton-Filled - Penetration FTE - Ice Unfilled - No Damage Unfilled - Delamination Unfilled - Cracking Cotton-Filled - No Damage Cotton-Filled Cracking Clean Hole - Diameter Same as Ice 2.0 in. Ice 1.68 in. Ice 1.5 in. Ice Nov 2007 Halpin & H. Kim 4 Projectile Kinetic Energy (ft-lbf)

5 A Head-to-Head Diagnostic Test: Private Communication (The Nature of the Impactor Makes a Difference!) Simulated hail ice, no damage observed at 500 in-lbs Damage threshold ~380 ft-lbs (4567 in-lbs) ASTM F320 composite reinforced ice Damage threshold ~44 ft-lbs (528 in-lbs) Damage size estimate >1 inch FFA-2 lead ball simulated FOD & runway debris. Damage threshold ~10 to 18 ft-lbs (~180 to 220 in-lbs) 13 Nov 2007 Halpin & H. Kim 5

6 Comparison: Parametric Estimates and Diagnostic Test Conditions for the ASTM F Inch Diameter Ball, & Simulated Natural Ice using the P&W. ASTM 320 Test SHI Test, No Damage Natural Ice Test Prediction FFA-2 Lead Ball Simulated FOD & Runway Debris. 13 Nov 2007 Halpin & H. Kim 6

7 Illustration of the Influence of Test Simulation Methodology on the Thickness of a Typical Pressurized Structure: The ASTM F320 Cotton Composite Reinforced Test Ball Is Significantly More Damaging That Simulated Hail Ice. An Inappropriate Test Protocol, ASTM F320 Adds Weight but May Not Provide Improved Damage Tolerance (Reduced CAI & Fatigue Sensitivity). 13 Nov 2007 Halpin & H. Kim 7

8 In Early 1980 s Pooled Data From Falling Weight Testing Was Used to Correlate CAI Capability Resulting From a Combination of Delamination, Resin Cracking & Fiber Breaking Delamination & Resin Cracking Produces Lower CAI Capability Than Fiber Breaking 13 Nov 2007 Halpin & H. Kim 8

9 Different Damage Morphologies May Have Different CAI Strengths: Notional Illustration ASTM F320 Fiber Rupture & Puncture P&W Hail Ice Test, INITIAL Delamination & Resin Cracking 13 Nov 2007 Halpin & H. Kim 9

10 Cotton-Filled Ice Penetration Type V Damage Mode Clean Hole (data by H Kim) Target: 8-ply woven carbon/epoxy plate, quasi-isotropic, in. Thickness, held by pictureframe fixture having 11x11 in. Opening and providing clamped b.c. (With in-plane freedom) Projectile: 2.0 in. Dia. Ice with cotton fill per ASTM F320, v o = 283 ft/s, KE = ft-lbf Result: type V damage mode clean hole penetration of size roughly same as projectile dia. Impact-Side View Back-Side View Liberated Panel Fragments, Recovered Ice Ball 13 Nov 2007 Halpin & H. Kim 10

11 Cotton-Filled Ice Penetration Type IV Damage Mode Large Cracking (data by H Kim) Target: 8-ply woven carbon/epoxy plate, quasi-isotropic, in. Thickness, held by picture-frame fixture having 11x11 in. Opening and providing clamped b.c. (With in-plane freedom) Projectile: 2.0 in. Dia. Ice with cotton fill per ASTM F320, v o = 183 ft/s, KE = 77.1 ft-lbf Result: type IV damage mode thru penetration with large cracking patterns, ~ 13.1 total crack length Impact-Side View Back-Side View 13 Nov 2007 Halpin & H. Kim 11

12 Comparison: Cotton-Fill vs. Unfilled Damage at ~180 ft-lbf (data by H Kim) in. thick panel impacted by ASTM F320 Cotton-Filled Ice Ball, 2.0 in. Dia. v o = 283 ft/s, KE = ft-lbf Damage: clean hole penetration ~ 2 in. diameter in. thick panel impacted by Unfilled Ice Ball, 1.68 in. Dia. v o = 370 ft/s, KE = ft-lbf Damage: penetration with large cracking ~ 13 in. tot. crack length Both Images Panel Back-Side View 13 Nov 2007 Halpin & H. Kim 12

13 Fuel Tank - Tire Rupture Performance Requirements in AC (A Positive Example) 13 Nov 2007 Halpin & H. Kim 13

14 Compliance Testing Performed at a Structural Configuration Level. Properties of the Impacting Rubber Disk Comparable to Tire Tread Used for the Aircraft Per the Performance Requirement. 13 Nov 2007 Halpin & H. Kim 14

15 Structural Capacity for Impact Threats Characterized With Test Articles Representative of Aircraft Design and Impacting Objects Relevant to the Threat 13 Nov 2007 Halpin & H. Kim 15

16 Suggested Test Standard: Common Format - Performance Based & Relevant to Damage Tolerance Needs Bird Strike ASTM modified Far Part 25 (no airframe requirement?) Weight-Size - 90% Velocity, V C Performance Focus Bird carcass Gel Pack Document Threat Other Hail Strike ASTM modified Far Part 25 (no airframe requirement?) Weight-Size - 90% A/C Velocity, V C & Hail Terminal velocity Performance Focus Simulated Hail Ice Document Threat Other 13 Nov 2007 Halpin & H. Kim 16

17 Comparative Test Program Recommended 1960 through the 1980 for bird strike Bird carcass & Gel Pack calibration Competitive test & simulation model development EU investments 1990 s into 2005 AC good example; tire rupture performance requirement Lightning requirements - performance focus? Activity similar to birdstrike recommended for the hail ice threat Natural ice versus Simulated Hail Ice Competitive test & simulation model development Document in common location Requirements for airframe (fragmented) Characterization of threat environments Acceptable test protocol(s) 13 Nov 2007 Halpin & H. Kim 17

18 !Sandwich" Construction: Honeycomb Sandwich Construction Increases Vulnerability 13 Nov 2007 Halpin & H. Kim 18

19 Summary: Ice Impacts on Composites 13 Nov 2007 Halpin & H. Kim 19

20 SUMMARY 1. Damage Thresholds should be the bases for the dimensioning of laminates exposed to hail and other impact threats (the damage thresholds will depend on the nature of the threat, FOD is different that hail ice, than the ASTM ball, than the rubber puck for tire damage, The threat environments need to be quantified, agreed to, and kept up to date. They are independent of platforms. (Good data base for the US But need data for international locations.) JOINT INTERNATIONAL EFFORT? A data base need; hail & operational velocities, Defense of a design is the responsibility of the OEMs including test & analysis methods. (Realistic test protocols are available.) 4. Inspection for Cause; Hail example, triggered by extreme Rogue weather conditions, and a defined operating period allowing short term operations before repair, dependent upon severity of damage as defined by the Pxx internal load conditions or Allowable Damage Limits. This perspective would utilize a Self Evident Rogue Event instead of Self Evident Damage as a criteria condition. The dent has been a Self Evident Damage criteria condition BUT is not a sufficient basis for a preventive design & maintenance concept. 13 Nov 2007 Halpin & H. Kim 20