Delamination/Disbond Arrest Fasteners in Aircraft Composite Structures

Transcription

1 Delamination/Disbond Arrest Fasteners in Aircraft Composite Structures Presented to Next Generation Transport Aircraft Workshop By Kuen Y. Lin, Eric Cheung, Luke Richard and Wenjing Liu William E. Boeing Department of Aeronautics and Astronautics University of Washington March 29, 2013

2 Acknowledgements This study was sponsored by the FAA through the AMTAS (Advanced Material for Transport Aircraft Structures), The Boeing Company and Toray. The authors wish to thank Marc Piehl, Eric Cregger, Gerald Mabson and Matthew Dilligan of Boeing and Kenich Yoshioka and Don Lee of Toray for their support and invaluable discussions. 2

3 Sponsored Project Information Principal Investigator: Dr. Kuen Y. Lin, Aeronautics and Astronautics, UW Research Assistants: Eric Cheung, Luke Richard, Wenjing Liu FAA Technical Monitor: Lynn Pham Other FAA Personnel: Curtis Davies, Larry Ilcewicz Industry Participants: Boeing: Marc Piehl, Gerald Mabson, Eric Cregger, Matthew Dilligan Toray: Kenichi Yoshioka, Dongyeon Lee, Felix Nguyen Industry Sponsors: Boeing and Toray The Joint Advanced Materials and Structures Center of Excellence 3

4 Crack Arrest Mechanism by Fastener

5 Objective and Approach Objectives - To understand the effectiveness of delamination/disbond arrest features - To develop analysis tools for design and optimization Technical Approach 1). Establish Finite Element models in ABAQUS/VCCT 2). Develop analytical capabilities for fast calculations 3). Verify analysis results with experiments 4). Conduct sensitivity studies on fastener effectiveness 5). Provide tools for design and optimization The Joint Advanced Materials and Structures Center of Excellence 5

6 Analytical Model Model is composed of a beam-column part and a truss part Fastener is modeled by a tension spring which works with the beam-columns in bending; and a joint flexibility spring which works with the trusses Crack tip Energy Release Rate (ERR) is obtained using VCCT Friction and joint/hole clearance is also modeled

7 Method of Solution Total energy = Π = U W Differentiate Π w.r.t. each degree of freedom δπ= δu δw =0 Results in a set of linear equations; solve linear system Obtain displacement solution Forces and crack tip ERR are derived from the displacement solution Crack propagation behavior and arrest effectiveness are analyzed

8 Beam-Column Polynomial shape function i ( ) β, w x j= 0 Beam-Column energy n = i j x j Truss Polynomial shape function n m j i( ) = αi, j + αi, k j= 0 k= n+ 1 u x x e Truss energy c k ( x L) L dw 1 L dw 2 dx 2 dx 2 2 i i Ubc, i = EI L 2 dx+ N dx 1 L i Utruss, i = AE dx L 1 L du dx 2 Fastener/Contact/Bond Springs 1 U = k u u 2 ( ) 2 i j

9 G II from VCCT Computes G II from crack tip shear force and crack tip sliding displacement G II 1 u F 2 bd 1,6 u,2,5 =

10 Mode Decomposition with Fastener: Applied Moment Only SERR Components vs. Crack Lenth - Moment SERR Components (N/mm) % - GI 50% - GII 50% w/ fastener - GI 50% w/ fastener - GII Crack Length (mm) 10

11 Mode Decomposition: Applied Tension Only SERR Components vs. Crack Lenth - Tension SERR Components (N/mm) % - GI 50% - GII 50% w/ fastener - GI 50% w/ fastener - GII Crack Length (mm) 11

12 2-Plate Specimen Description BMS (T800H/#3900-2) unidirectional pre-preg tape BMS peel ply Titanium Fasteners (0/45/90/-45) 3S (0/-45/02/90/45/02/-45/90/45/0) S

13 2-Plate Specimen

14 ATP 2

15 ATP 3

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17 Summary of Test Results Propagation arrestment and stable propagation thereafter demonstrated. Fastener install torque (friction) is a major driver of crack arrest capability. High-stiffness lay-up experience more increase in arrest capability for the same fastener size and torque. Fabrication of thick specimens is difficult. Crack front is not symmetric across the width of the specimen, especially near the fastener.

18 Analytical Solution vs. Experiment Properties used E 1 E 2 G 12 t = psi = psi = psi = in G IIC = 12 in-lb/in 2 Layups (0/45/90/-45) 3S /crack/(0/45/90/-45) 3S (0/-45/0 2 /90/45/0 2 /-45/90/45/0) S /crack/ (0/-45/0 2 /90/45/0 2 /-45/90/45/0) S Fastener Stiffness 30% of Huth s Equation

19 (0/45/90/-45) 3S /crack/(0/45/90/-45) 3S CLT E x = psi Plain Strain E x = psi Strain Gauge E x = psi

20 (0/-45/0 2 /90/45/0 2 /-45/90/45/0) S /crack/ (0/-45/0 2 /90/45/0 2 /-45/90/45/0) S CLT E x = psi Plain Strain E x = psi Strain Gauge E x = psi

21 Future Research Conduct Parametric Studies on Crack Arrest by a Single Fastener Develop Analytical Tool to Study Crack Arrest by Multiple Fasteners Conduct Experiments to Determine the Fastener Arrest Effectiveness using Resin Systems with Different G IC :G IIC Ratios Experimental Investigation of Delamination Propagation with Two Fasteners in Series

22 Delamination Arrest by One and Two Fasteners

23 Simulation of Varying G IC /G IIc Ratios G IC G IIC Ra'o

24 Single Axial Load Vs. Crack Tip Location

25 Summary Technical approach to disbond/delamination arrest features in aircraft composite structures have been presented. Analytical and experimental results on delamination arrest by fastener has been presented. Future research on the delamination arrest by fasteners has been identified.

26 Thanks for Attending Questions? Suggestions? Comments?

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29 Mode II Test Specimen in 3-D 29

30 Analytical Model Crack length pass the fastener Original crack length 30

31 Model Description 16-ply CFRP ( t = x 16 = 0.12 ) Lay-ups Percentage of 0-deg: 25% / 37.5% / 50% / 62.5% Fastener Ti-Al6-V4 (E = 16.5x10 6 psi) d = 0.25 in Fastener Flexibility (H. Huth, 1986) C a t1+ t2 b = d n t1e1 nt2e2 nt1e3 2nt2E3 The Joint Advanced Materials and Structures Center of Excellence

32 Discrepancies and Unknowns Discrepancies CLT E x /Plain Strain E x does not correspond to strain gauge E x Fastener joint has only 30% of the stiffness as predicted by Huth s model Fastener hole begins to crush, and fastener rotates as load increases Unknowns G IIC Contact Friction as a result of install torque

33 Results: Applied Moment Only Crack Length vs. Load - Moment Crack Length (mm) % 0-deg 25% 0-deg w/ fastener 37.5% 0-deg 37.5% 0-deg w/ fastener % 0-deg % 0-deg w/ fastener 62.5% 0-deg Moment (N-m) 62.5% 0-deg w/ fastener 33

34 Results: Applied Tension Only Crack Length vs. Load - Tension Crack Length (mm) % 0-deg 25% 0-deg w/ fastener 37.5% 0-deg 37.5% 0-deg w/ fastener 50% 0-deg 50% 0-deg w/ fastener 62.5% 0-deg 62.5% 0-deg w/ fastener Tension (N) 34

35 Friction and Fastener Preload DCB - Equal and Opposite Axial Load Effect of Fastener Preload and Friction 40 Crack Location (mm) No Preload 25% Preload 50% Preload 75% Preload No Preload w/ friction 25% Preload w/ Friction 50% Preload w/ friction 75% Preload w/ friction Normalized Load 35

36 Mode II Test Specimen Preliminary Findings Mode II Test Specimen Crack Location (mm) Mode II Test Specimen Load (N) 1 GI GII 0.8 SERR (N/mm) Crack Tip Location (mm) 36