NASA Technical Reports Server (NTRS) 20160007727: Effects of Damage on Long-Term Displacement Data of Woven Fabric Webbings Under Constant Load for Inflatable Structures

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by  NASA Technical Reports Server (NTRS)

National Aeronautics and
Space Administration
Effects of Damage on Long-term Displacement Data
of Woven Fabric Webbings Under Constant Load for
Inflatable Structures
Winfred S. Kenner
NASA LaRC
Structural Mechanics and Concepts Branch
AIAA SciTech 2016, January 3-8, 2016
San Diego, California
Outline
National Aeronautics and
Space Administration
•  Background

Inflatable Structures
§ 

Problem Statement
§ 

•  Approach
•  Hardware and Test Facility

•  Test Results

•  Summary
2
Inflatable Structures
National Aeronautics and
Space Administration
Research Materials:
Typical Inflatable Structures
Kevlar Webbing Vectran Webbing
1 2
Lightweight

Small
Storage
Volume
Fast Build
3
Typical Roll of Webbing Material
4
(Flexible Structural Restraint Layer)
4
Problem Statement
National Aeronautics and
Space Administration
Goal: Conduct an experimental creep study to identify effects of
damage on webbing performance over extended time period
Causation: Damage due to deployment and/or service
Definition: Damage is defined as vertical incisions of varying
length and number
Analytical analysis: Inaccurate for nonlinear materials over time
Time period: Study was conducted over an 18-month time period
Typical Inflatable Module Damaged Area
Interwoven

Webbings

Y-axis Y-axis
Incision

Orienta2ons

X-axis X-axis
5
Research Approach
National Aeronautics and
Space Administration
Goal: Generate long-term displacement data from webbings under load
Computer
system
Webbing
(damaged)
Test
Facility
Load
?∆
Test Facility Test Hardware Displacement Data

Measuring Acquisition
•  Large •  High load
•  Overhead crane capacity D evice •  Variable rate
•  Available for •  Quick
•  Accurate •  Continuous
multiple years assembly
•  Continuous recordings
measurements over multiple
years
5
Creep Test Facility
National Aeronautics and
Space Administration
Initial creep test, Feb 2012
Creep test hardware (3 rows)
I-beam structures
Concrete weights
Typical displacement sensor
Webbing
displacement
measuring and
support fixture
•  Webbing
material
•  Transducer
sensor
Applied load
6
Magnified Webbing Images
National Aeronautics and
Space Administration
Pristine Webbing Damaged Webbing
Fill
yarns
Yarn
cuts
Warp
yarns
Selvage
edge
yarns
Small
vertical
incision
Fibers
Damage categories: Small, Medium, Large
Eleven test groups defined by test material, applied load, and damage
Horizontal incision: Known to have an adverse effect on strength
proportional to length
7
Test Matrix
National Aeronautics and
Space Administration
Pristine Webbings Damaged Webbings
Group Webbing Webbing UTS W ebbing Length Group Webbing Webbing UTS W ebbing Length Incision
# materials # (%) length of test # materials # (%) length of test length
(months) (months) (inches)
1 6K 1 20 144 34 7 6K 1 20 60 18 5
Kevlar 2 20 144 34 Kevlar 2 20 60 16 5
2 6K 1 20 60 3 6K 1 6.7 60 14 1
8
Kevlar 2 20 60 3 Kevlar 2 6.7 60 14 1
3 6K 1 43 68 39 3 6.7 60 14 1
Kevlar 2 43 84 39 9 6K 1 20 62 3 5
3 50 82 35 Kevlar 2 20 62 3 5
4 50 80 35 3 20 62 3 5
4 6K 1 50 80 34 10 6K 1 20 60 18 5 (multiple)
Vectran 2 50 80 34 Vectran 2 20 60 18 5 (multiple)
3 50 80 34 3 20 60 18 5 (multiple)
5 12.5K 1 29 116 29 11 12.5K 1 29 48 18 1
Vectran 2 29 116 29 Vectran 2 29 41 18 1
3 29 43 18 1
3 29 116 22
6 6K 1 25 66 44
Vectran 2 25 66 44
3 25 66 44
4 25 66 44
5 20 66 44
*Ultimate tensile strength (UTS)
8
Environmental Influences on Displacement
Displacement Data
Temperature Data
105

0.455
)
F
˚
(

) e
s
r
e u
h t
c 0.385 a
n r
e
i
( p

t m
n ---External Temperature
e e ---Internal Temperature
m T 0
e 0.315
12/23/11 12/12/15
c
a
pl Time (date)
Webbing #1
s
i
D
Webbing #2
0.245
Webbing ?∆
2/5/13 1/14/14 12/23/14 12/1/15
Time (date)
Daily, seasonal, and yearly temperature and humidity effects
influence the creep displacement curve
Webbings exhibits negative coefficient of thermal expansion ( C T E)
9
National
Characteristics of Displacement Curve
Aeronautics
and
Space
Administration
6K Kevlar Webbings Loaded to 22% UTS
4.47
Material creep
Global wave
4

)
s pattern
e
h 1
c 4.39 Seasonal
n
i expansion/
(

t 3
n contraction
e
m
e
4.31 Local
c
a
2 wave
l
p
s pattern
i
D
4.23
8/11/12 9/24/13 11/7/14 12/21/15
Time (date)
3-year time period
Pristine
Four characteristic curve patterns
Webbing
Failure experienced above 50% UTS
10