hyonny kim assistant professor school of aeronautics and astronautics, purdue university
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Hyonny Kim Assistant Professor School of Aeronautics and Astronautics, Purdue University presented at the FAA Workshop on Key Characteristics for Advanced Material Control September 16-18, 2003, Chicago, IL Funding Acknowledgements: - PowerPoint PPT PresentationTRANSCRIPT
FAA Workshop Chicago 2003-09 1
Strength and Damage Tolerance ofAdhesively Bonded Joints:
Stress-Based and Fracture-Based Approaches
Hyonny KimAssistant Professor
School of Aeronautics and Astronautics,
Purdue University
presented at the
FAA Workshop on Key Characteristics for Advanced Material Control September 16-18, 2003, Chicago, IL
Funding Acknowledgements:
FAA, NASA AGATE, WSU/NIAR, NASA Langley Research Center, ASEE, Purdue Research Foundation
FAA Workshop Chicago 2003-09 2
Outline
Introduction Bonded Joint Stress Analyses
in-plane shear loading combined shear + tension loading plastic strain-based ultimate load variable bondline thickness tension loading in general unbalanced single lap joint
Damage Tolerance of Disbonded Joints – Buckling/Disbond Growth experiments models
New Directions
FAA Workshop Chicago 2003-09 3
Introduction – General Joint Loading
in-plane shear + tension produces adhesive shear stress
Nx
Nx
Ny
Ny
Nxy
Nxy
Tension Due toInternal Pressure
CompressionDue to Fuselage
Bending
Shear Due toFuselage Torsion
Segment of JointLoaded by Biaxial
Tension/Compressionand Shear
Bonded Doubler
FAA Workshop Chicago 2003-09 4
IntroductionDamage Tolerance: Buckling/Disbond Growth
compression causes buckling
subsequent disbond growth possible
FAA Workshop Chicago 2003-09 5
IntroductionDamage Tolerance: Buckling/Disbond Growth
Stringer-Stiffened Panel Wing Assembly
P
FAA Workshop Chicago 2003-09 6
Overarching Objectives
bridge knowledge gap between coupon data and full scale structural performance
provide engineering and scientific community with advancements in:
the mechanics of bonded joints
damage tolerance design and analysis philosophy
assist FAA and GA companies by providing research support
FAA Workshop Chicago 2003-09 7
In-Plane Shear Loaded Lap Joint
in-plane shear load transfer across joint produces
xz shear stress in adhesive
NxyNxy
Outer Adherend
Inner Adherend
z
x
y
-1 .0 -0.5 0.0 0.5 1.0y/c a t x = L /2
0
1
2
3
4
5
,
MP
a xza
Adhesive x-z Shearfor A lum inum Jo in t
FEA
SLBJ Theory
Kim, H. and Kedward, K.T., “Stress Analysis of Adhesive Bonded Joints Under In-Plane Shear Loading,” Journal of Adhesion, Vol. 76, No. 1, 2001, pp. 1-36.
FAA Workshop Chicago 2003-09 8
In-Plane Shear Loaded Doubler
inherently 2D problem
yz shear peaks along x = 0, a
xz shear peaks along y = 0, b (not shown)
x
yz
00
b
a
NxyNxy
Bonded Doubler- Outer Adherend
Base Structure- Inner Adherend
022 ooxy
oxy C
yt
oxy
oaxz
xt
oxy
oayz
Kim, H. and Kedward, K.T., “Stress Analysis of Adhesive Bonded Joints Under In-Plane Shear Loading,” Journal of Adhesion, Vol. 76, No. 1, 2001, pp. 1-36.
FAA Workshop Chicago 2003-09 9
Combined Loading: Shear + Tension
y
x y
0 200 400 600 800 1000 1200
|N | (lb /in )
0
200
400
600
800
|N |
(lb
/in) ta = 0 .01
Von-Mises Based Failure Envelope
NxyNxy
Outer Adherend
Inner Adherend
z
x
y
Ny
Ny
Kim, H. and Kedward, K.T., “The Design of In-Plane Shear and Tension Loaded Bonded Composite Lap Joints,” Journal of Composites Technology and Research, Vol. 24, No. 2, 2002, pp 297-307. Invited paper to special issue in honor of Don Oplinger.
FAA Workshop Chicago 2003-09 10
Plastic Strain-Based Ultimate Load
0 0.05 0.1 0.15 0.2 0.25 0.3 0.350
5
10
15
20
25
30
Shear Strain
Sh
ear
Str
ess
(MP
a)
DataFitting Curve
in-plane shear loading ductile adhesive joint carries greater
load than elastic-limit design more conservative than Hart-Smith
elastic-perfectly plastic model
adhesive test data from J. Tomblin, WSU
Kim, H. and Lee, J., “Adhesive Nonlinearity and the Prediction of Failure in Bonded Composite Lap Joints,” Joining and Repair of Composite Structures, ASTM Special Technical Publication STP1455, submitted January 2003.
FAA Workshop Chicago 2003-09 11
Failure Prediction vs. Test Data
box beam torsion lap shear coupon
experiments conducted by Wichita State University (John Tomblin)
Maximum Shear Flow
0
500
1000
1500
2000
2500
3000
0.00 0.05 0.10 0.15 0.20 0.25
Bondline Thickness (in)
Max
. Sh
ear
Flo
w (
lbf/
in)
Experimental Data
Purdue Analysis*
Constitutive behavior for 0.20 was not avail. Used 0.12 data, with reduced failure strain.
Tomblin, J., Seneviratne, W., Kim. H., and Lee, J., “Characterization of In-Plane Shear Loaded Adhesive Lap Joints: Experiments and Analysis,” FAA Final Report, DOT/FAA/AR-03/21, May 2003.
FAA Workshop Chicago 2003-09 12
Variable Bondline Thickness (VBT)
FAA Workshop Chicago 2003-09 13
VBT: Increased Stress Due to Bondline Thinning
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
t1 / tu n if
0
1
2
3
4
5
6
7
8
M in. f
M ax. f
f = 1
Kim, H. “The Influence of Adhesive Bondline Thickness Imperfections on Stresses in Composite Joints,” Journal of Adhesion, Vol. 79, No. 7, 2003, pp 621-642.
FAA Workshop Chicago 2003-09 14
Tension Loading of Unbalanced Single Lap
closed-form stress analysis of generalized unbalanced joint
Joint Specs: - glass/epoxy, - overlap 2c = 25.4 mm, - to = 2.49 mm, ti = 2to, ta = 0.33 mm
FAA Workshop Chicago 2003-09 15
Damage Tolerance of Disbonded Joints
damage tolerance is safety concern thin flanges
typically 1 mm (0.04 in.) susceptible to buckling + disbond growth
disbond not easily detectable adhesive properties affect growth critically
processing of joint very important
FAA Workshop Chicago 2003-09 16
Buckling/Debonding Experiments
Construction: glass/epoxy &
carbon/epoxy face sheets 6.3 mm foam core two halves secondarily
bonded with PTM&W ES6292 paste adhesive
FAA Workshop Chicago 2003-09 17
Experimental Measurements
Kim, H., Kwon, H., and Keune, J., “Buckling Initiation and Disbond Growth in Adhesively Bonded Composite Flanges,” 44th AIAA / ASME / ASCE / AHS / ASC Structures, Structural Dynamics, and Materials (SDM) Conference, April 7-10, 2003, Norfolk, VA
FAA Workshop Chicago 2003-09 18
Disbond Growth Model
one-edge free flanges
fracture-mechanics based compute strain energy
release rate assumed post-buckled mode
shape
33
2212
1 )by(c)by(c)by(c[)y,x(w
a
xmcos])by(c...)by(c n
n
214
4
m = 1:
m = 2:
FAA Workshop Chicago 2003-09 19
Comparison of Model and Experiments
0 50 100 150 200 250
D isb o n d L en g th , a (m m )
0.000
0.001
0.002
0.003
0.004
0.005
App
lied
Far
field
Str
ain
, o
Buckling - SS
Buckling - C
D isbonding - SS
D isbonding - C
Experim ent - Buckling
Experim ent - D isbond
G c = 578 J/m 2
Glass/Epoxy [0]4; b* = 25.4 mm – 0.8 mm Flanges
FAA Workshop Chicago 2003-09 20
Non-Uniform Disbond Growth Front
FAA Workshop Chicago 2003-09 21
Strain Energy Release Rate Profile
detailed view of G along disbond front
predicts corner disbond initiation
comparison with VCCT/FEA as programmed by R. Kreuger
0 0.2 0.4 0.6 0.8 1y/b *
0
100
200
300
400
500
G (
J/m
2)
FEA
M odel
o = 2,450
E xtrapo la ted G peak
FAA Workshop Chicago 2003-09 22
New Directions:Intrinsic Material Properties vs. Joint Behavior*
understand relationship between intrinsic material properties vs. “properties” inferred from structural (joint) behavior intrinsic material properties should
be independent of joint configuration, e.g., bondline thickness, mode of loading
resolve differences observed from different test methods: tensile test dogbone napkin ring Krieger Gage / ASTM 5656
use nonlinear analyses and correlation with tests to extract TRUE, consistent, description of intrinsic material behavior
0 0.05 0.1 0.15 0.2 0.25 0.3 0.350
5
10
15
20
25
30
Shear Strain
Shea
r Stre
ss (M
Pa) t
a= 2.0 8 mm
ta= 1.0 7 mm
ta= 0.3 3 mm
* this topic was raised at the ASTM
Symposium on Joining and Repair of
Composite Structures, March 2003,
Kansas City, MO
* Adhesive test data from J. Tomblin and W. Seneviratne, WSU
FAA Workshop Chicago 2003-09 23
New Directions: Bonded Joint Impact
(a)
(b)
(c)
Damage on 38.1 mm Overlap Joint Due to 40 J Impact;
(a) Impact Side; (b) Back Side, (c) C-Scan Showing Disbond Area
characterize damage modes
identify damage formation mechanisms
determine governing parameters
advanced: model
predictions
basic guidance studies needed:
FAA Workshop Chicago 2003-09 24
New Directions: Shear Buckling and Disbonding
investigate in-plane shear buckling and subsequent disbond growth
leads into combined compression + shear loading
Disbond in JointBetween FuselageHalves
N xy
o
A
B
FAA Workshop Chicago 2003-09 25
New Directions: Health Monitoring of Bonded Joints
real time (or time interval based) monitoring of joint health
existing: ultrasonic scanning common method for discrete
interval inspection real-time implementation
difficult electrical resistance external or embedded sensors /
crack gages / fiber optics acoustic waves
useful for internal, non-accessible locations correlate measurements with damage shape and location
input for damage tolerance prediction models
FAA Workshop Chicago 2003-09 26
New Directions: Full-Scale Behavior Prediction
Disbond in JointBetween FuselageHalves
N xyo
A
B
PDisbond
SandwichConstruction- Halves Bonded Along Top and Bottom C-L
Vertical Load
Side Load at25% Chord
Path to get from Coupons & Elements to Full Scale Component Level
UnderstandExperimental Data
Refined Models:Adhesive Plasticity, Peel StressFailure Under Multiaxial Stress,
Fracture Mechanics
???Other Factors
develop predictive models:maintain balance between simplicity and complexity