Unfolding Analysis of Composite Laminate T Profiles under

Unfolding Analysis of Composite Laminate T
Profiles under Pull-Off Loads
11/11/2015
XIX Reunión de Usuarios de
SIMULIA
INDEX

INTRODUCTION

PROBLEM DESCRIPTION

BASIC FINITE ELEMENT MODELS
•
Description
•
Damage Criteria
•
Sensitivity Analysis
•

−
Theoretical material properties
−
Curve F33 – Thickness
Results
−
Failure Load & Field Stress
−
Shear-Moment interaction diagram
COMPLEX JOINTS
•
Test & FE Model
•
Results
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TÍTULO
T and I profile components are widely used in aerospace composite structures, such as fuselage or
belly fairing stringers and beams, where pull-off loads are derived mainly from the differential
pressure:
ΔP
Main Failure:
Unfolding Failure in
Fillet radius
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PROBLEM DESCRIPTION – WHY … ?

Why a FE Model is needed to define the unfolding allowables in T-Profiles under pull through
loads?
•
Stress field is well know for tension L-Angle, but for T-Profile is not feasible to obtain accurately the interlaminar stress in the fillet radius area
•
Allowables for T-Profiles are usually defined through three-point bending test:
•
−
Tests are defined for a combination of shear - bending in the start of the fillet radius
−
Those combined allowables are used conservatively as a simple allowables, and a rectangular shearmoment interaction diagram is defined:
FE Model can be used to defined accurately the allowables for different combination of shear and
bending moment in the T-Profiles in order to avoid too conservative hypothesis
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PROBLEM DESCRIPTION – TEST

FE Model correlation has been defined for 5 configurations with different laminates and Tape
material.

Laminates, materials and test results are not presented for reasons of confidentiality

Typically failure in T-Profiles under pull-off loads:
Image Courtesy of Alestis Aerospace
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BASIC FE MODEL DESCRIPTION

FE Model Description
•
2D Plane Stress (plane strain condition also has been evaluated)
•
One element by lamina has been defined through laminate thickness
•
Delaminate behavior (crack scenario) has been defined in radius between ply and deltoid
•
For profiles with a high number of plies (≥ 30 plies) multiple crack scenarios (delaminate behavior) have
been defined between plies (4 plies nearest to deltoid) in order to study delamination between plies
+-45º
0º
90º
Deltoid
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BASIC FE MODEL DESCRIPTION

Damage Scenario
•
Crack scenarios are defined by means of cohesive surfaces:
Mono-crack scenario for laminates with < 30 plies
Multi-crack scenario for laminates with ≥ 30 plies
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BASIC FE MODEL DESCRIPTION

Damage Initiation
3
 3

 f3,t

2


    13

 f13,s






1
Quadratic nominal
stress criterion
For analysis:
K = 1. E6 N/mm2
2
1
3
1

Damage Evolution - Benzeggagh-Kenane criterion
G
GI ,C  GII,C  GI ,C  Shear
 GT
GShear  GII  GIII
GT  GShear  GI
n

  GT ,C

Where GC is the fracture toughness for interface opening
(mode I) and shear (mode II):
 GI,C = 0.4 J/m2
 GII,C = 1.0 J/m2
 n (BK constant) = 2.284
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SENSITIVITY ANALYSIS – DELTOID STIFFNESS

A sensitivity analysis to deltoid stiffness material has been carried out

2 parameters have been evaluated:

•
Failure load
•
Maximum vertical displacement
Deltoid
Conclusions:
•
Failure load is not affected by deltoid stiffness
•
For analysis EDELTOID is fixed to E3 (Tape), B-BasisFailure load
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SENSITIVITY ANALYSIS – σ3_t STRENGTH

σ3_t is the main parameter for T-Profile unfolding allowable

Following picture shows the results for the nominal material strength:

Conclusions:
•
Normal material strength (σ3_t) presents a strength increase with the thickness
•
A σ3_t curve depending from thickness is defined in order to tune FE Model to test
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SENSITIVITY ANALYSIS – σ3_t STRENGTH

Curve defined to adjust σ3_t to test behavior:
Similar behavior than
Composite L-Angle
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RESULTS – POST PROCESSING

Configuration 1 (Thickness = 2.208 mm). Failure Load
Ply - 03
Failure Load
NO Damage – F = 0.89
Ply - 04
Damage Initiation – F = 1.0
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RESULTS – POST PROCESSING

Configuration 1 (Thickness = 2.208 mm). Field Stress
σ3 [N/mm2]
2


    13

f

 13,s
3

f
 3,t
2

   30.68   91.92% Failure Contribution

 32.0 

  13

f
 13,s
σ13 [N/mm2]
2
3

f
 3,t

 1


2
2

  8.07% Failure Contribution


Conclusions:

Failure is produced mainly for normal stress derived
from bending moment in fill radius
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RESULTS – POST PROCESSING

Configuration 1 (Thickness = 2.208 mm). Delamination
σ3 [N/mm2]
Delamination
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RESULTS – SHEAR-MOMENT INTERACTION DIAGRAM

Shear-Moment interaction diagram – Unfolding Allowables
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COMPLEX JOINTS

A FE Model have defined to obtain the behavior of a composite laminate T_Profile specimen
subjected to a mechanical pull-off load and joined in base to sandwich panels:
Image Courtesy of Alestis Aerospace
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COMPLEX JOINTS – FE MODEL

Basic Assumptions:
•
•
A non-linear FE Model have been created with following non-linear behavior:
−
Large displacement condition
−
Contact between joint parts and test machine parts
Load = Failure Load from Test
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COMPLEX JOINTS – RESULTS

Results
•
Prying Effect
•
Load = Failure Load from Test
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COMPLEX JOINTS – RESULTS

Results – Shear and Bending Moment in Fillet Radius:
Shear and Bending Moment are referred to the
starting point of fillet radius
V
M
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Thank you for your attention
[email protected]
[email protected]
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