View
218
Download
4
Category
Tags:
Preview:
Citation preview
1
Crack Shape Evolution Studies with NASGRO 3.0
Elizabeth Watts and Chris Wilson
Mechanical Engineering
Tennessee Tech University Cookeville, TN
2
Outline• Problem Statement
• Background
• Analysis Approach
• Results
• Conclusions
(Newman and Raju, NASA TR-1578)
3
Problem Statement• Purpose and Goals of Analysis
– To predict crack shape evolution (CSE) and preferred path propagation (PPP) using NASGRO 3.0
– To check for self-consistency within NASGRO 3.0
– To compare NASGRO 3.0 with closed-form estimates of CSE and PPP
4
Background• Equations
– Newman-Raju K-solution– Paris vs. NASGRO, da/dN-ΔK– dc/dN – has correction for width based on closure
(McClung and Russell, NASA CR-4318)
5
Determining PPP• Crack Shape Evolution using Paris equation ratio
• Assuming that the PPP is equilibrium,
c
a
c
a
c
a
cc
aa
KC
KC
c
an
c
na
6
Tension PPP Equations• Newman-Raju coupled with Paris Equation with Crack
Closure Factor
• ASTM E740
• Irwin’s Solution
2
2.01
t
a
c
a
09.0
01.02.09.0
35.01.135.01.1
42
2122
R
RRR
t
a
c
a
t
a
c
a
c
a
R
nn
R
n
R
1c
a
7
Newman-Raju/Paris Estimate
n=3.75
8
NASGRO 3.0 Background• General purpose Fracture Mechanics software
from NASA JSC
• Version 3.0.4 released March 2000
• Crack growth rate
where C, n, p, and q are fitting constants and
q
c
p
thn
KK
KK
KR
fC
dN
da
max1
1
1
1
)(max
RgK
Kf open
9
Analysis Approach• Two Materials
– 2024-T351– A533B, C11 & C12
• Three Geometries– Surface Cracks – SC01, SC02, and SC04 (with both
internal and external cracks)• Constant Amplitude Loading• Three Load Ratios
– R = -1, 0.1, 0.7• Varying Loads
– Tension, Bending, Combined Tension and Bending– Internal Pressure, Calculated Internal Pressure, and a
Nonlinear Pressure Gradient
10
Material Properties• 2024-T351
• A533B, C11 & C12
(kpsi, in./cycles, and kpsi(in)1/2)
UTS YS KIc C n p q
68.0 54.0 34.0 .922e-08 3.353 .50 1.0
UTS YS KIc C n p q
100.0 70.0 150.0 .1e-08 2.7 .50 .50
11
da/dN – ΔK Plots for A533B0.01
1e-9
0.01
1e-9ΔK ΔK
da/d
N
da/d
N
12
Plate Geometries
tWM
M
S 0
S 0
a2c
S = 6 M
W t21
<<0.05 1.2ac
<2c
W0 < 1
S C 0 1 S C 0 2
a
Y
2c
x
tW
S (X) i
= 0, 1, 2, 3i
X = x/t
S (X) i
0.05 1.2c
< < a
2cW
0 < 1<
Surface Crack in Tension or Bending
Surface Crack with Nonlinear Stress
t t
13
Cylinder Geometry
S C 0 3
S0
S0
R(sphere)
S = p4 (internal pressure)
2c
a
M
M
t
W t2
6 MS =
1
<<0.05 1.2ac
internal or external crack
S C 0 4
pD
2c
a
internal or external crack
S (X) = Stresses due to internal pressure, pS (X) = Other stresses
0
i
S (X)i
i = 1, 2 ,3
X = x/t(from inner wall)
x
a<<0.05 1.2c
>D 4 t
t
Longitudinal Surface Crack in a Hollow Cylinder with Nonlinear Stress
14
Geometries• Flat Plates
– Width = 6 in.– Thickness = .5 in.
• Cylinder– Outer Diameter = 4 in.– Thickness = .5 in.
– ri/t = 3 Implies a thick-walled cylinder
15
Load Ratios• Expected similar results for R = -1.0 and
R = 0.1 because of closure
• Expected results for R = 0.7 to be different because of little closure
• An intermediate value of R = 0.4 used for 2024-T351 plate in tension
16
Outline• Problem Statement
• Background
• Analysis Approach
• Results• Conclusions
-72 NASGRO runs
-Show sample CSE
-Compare geometries
-Compare width effects
-Compare Paris and NASGRO
-Show sample PPP
-Compare PPP solutions
17
Typical Crack Shape Evolution
18
Geometry Comparison in NASGRO
19
Width Effects Comparison in NASGRO
20
Paris vs. NASGRO
Example of inconsistency
tWM
M
S 0
S 0
a2c
S = 6 M
W t21
<<0.05 1.2ac
<2c
W0 < 1
S C 0 1 S C 0 2
a
Y
2c
x
tW
S (X) i
= 0, 1, 2, 3i
X = x/t
S (X) i
0.05 1.2c
< < a
2cW
0 < 1<
21
Sample PPP
PPP
22
Comparison of PPP for Tension
ASTM E740 Solution
Newman-Raju/Paris with Closure Factor, n=2
Irwin’s Solution (a/c=1)
Newman-Raju/Paris with Closure Factor, n=3.75
NASGRO
tWM
M
S 0
S 0
a2c
S = 6 M
W t21
<<0.05 1.2ac
<2c
W0 < 1
S C 0 1 S C 0 2
a
Y
2c
x
tW
S (X) i
= 0, 1, 2, 3i
X = x/t
S (X) i
0.05 1.2c
< < a
2cW
0 < 1<
23
PPP Equations for Flat Plate in Tension
• ASTM E740
• Best Fit Equation from Excel
12.02
t
a
c
a
1.0047 0.0124 - 0.1544- =
0.9324 0.0797 - 0.1568- =
0.976 0.043 - 0.2001- =
0037.10124.02153.0
2
2
2
2
t
a
t
a
c
a
t
a
t
a
c
a
t
a
t
a
c
a
t
a
t
a
c
a(2024-T351,Tension, R=.1)
(2024-T351,Tension, R=.4)
(2024-T351,Tension, R=.7)
(A533B ,Tension, R=.1)
tWM
M
S 0
S 0
a2c
S = 6 M
W t21
<<0.05 1.2ac
<2c
W0 < 1
S C 0 1 S C 0 2
a
Y
2c
x
tW
S (X) i
= 0, 1, 2, 3i
X = x/t
S (X) i
0.05 1.2c
< < a
2cW
0 < 1<
24
PPP Comparison for Different R Values
tWM
M
S 0
S 0
a2c
S = 6 M
W t21
<<0.05 1.2ac
<2c
W0 < 1
S C 0 1 S C 0 2
a
Y
2c
x
tW
S (X) i
= 0, 1, 2, 3i
X = x/t
S (X) i
0.05 1.2c
< < a
2cW
0 < 1<
25
PPP Comparison with Different R Values
R=0.7
R=0.1
R=0.4
PPP for plate in tension, R=0.1
for Internal Pressure
26
SC04 Results• Consistent in SC04 geometry also• Best fit lines
0.9077 t
a0.1315 -
t
a0.143- =
c
a2
(2024-T351, Internal
Pressure, R=0.7)
0.9898 + t
a0.1471 -
t
a0.0933- =
c
a2
0.9615 t
a0.1741 -
t
a0.0726- =
c
a2
(2024-T351, Internal
Pressure, R=0.4)
(2024-T351, Internal Pressure, R=0.1)
27
Conclusions• K-solution between SC01 and SC02 self-
consistent
• Each of the NASGRO runs converged towards a PPP
• NASGRO PPPs are a function of R, unlike PPP equation in E740
• Width effects are small if a/t < 0.4
28
Acknowledgements• Kristen Batey, Jeff Foote, and
Sai Kishore Racha for NASGRO analysis
29
Questions?
30
End Conditions Encountered
• Net section stress > yield
• Unstable crack growth
• Crack depth + yield zone > thickness
• Broke through (transition to through crack)
• Crack outside geometric bounds (2c > W)
31
Recommendations• Check consistency with more challenging
stress gradients and weight functions
• Check the effects of an overloading – still consistent?
Recommended