Fracture tests were conducted on middle crack tension (M(T)) and compact tension (C(T)) specimens of 7.6 mm-thick 2324-T39 aluminum in the L-T orientation. The configurations tested included 102 mm-wide M(T), 305 mm-wide M(T), 152 mm-wide C(T), and 102 mm-wide C(T) specimens. The measured critical crack-tip opening angle (CTOA) for the 102 mm-wide M(T) tests, the 305 mm-wide M(T) tests, and the 152 mm-wide C(T) tests, after a small amount of crack extension, were 4.4, 4.9, 5.1 degrees, respectively. The scatter involved with these measurements was about +/- 1 degree

Dawicke, David S.

English

NASA Technical Reports Server

Fracture Testing of 2324-T39 Aluminum Alloy
D. S. Dawicke
Analytical Services and Materials, Inc.
ABSTRACT
Fracture tests were conducted on middle crack tension (M(T)) and compact
tension (C(T)) specimens of 7.6mm-thick 2324-T39 aluminum in the L-T
orientation.  The configurations tested included 102mm-wide M(T), 305mm-wide
M(T), 152mm-wide compact tension C(T), and 102mm-wide C(T) specimens.
The measured critical crack-tip opening angle (CTOA) for the 102mm-wide M(T)
tests, 305mm-wide M(T) tests, and 152mm-wide C(T) tests, after a small amount
of crack extension, were 4.4°, 4.9°, and 5.1° respectively.  The scatter involved
with these measurements was about ±1°.
NOMENCLATURE
a crack length
W specimen width
B specimen thickness
S applied stress
P applied load
∆a crack extension
COD total crack opening displacement
PD total pin displacement
INTRODUCTION
The critical crack-tip opening angle (CTOA) concept has been used successfully
to predict the fracture behavior of thin-sheet aluminum alloys [1-6].  These
studies have shown that for the thin-sheet aluminum alloy: the critical CTOA is
https://ntrs.nasa.gov/search.jsp?R=19960008158 2020-06-16T05:24:16+00:00Z
constant after an initial transient period [2], significant crack tunneling is present
during the transient period [2], compact tension (C(T)) and middle crack tension
(M(T)) fracture tests have the same critical CTOA [3], differences in the critical
CTOA and fracture behavior were observed in different crack orientations (L-T
and T-L) [4], the critical CTOA fracture criterion (obtained from small specimens)
was able to predict the fracture behavior of larger specimens with and without
multiple site damage (MSD) [5], and the critical CTOA during fracture is not
constant through-the-thickness during the initial transient period, CTOA reaches
a constant value [6].
An experimental fracture study was conducted on 7.6mm-thick, 2324-T39
aluminum alloy to access the applicability of the CTOA criterion to thicker
specimens.  The configurations tested included C(T) and M(T) specimens.
Measurements of load, crack extension, crack opening displacement and critical
CTOA were made during the tests.
EXPERIMENTAL PROCEDURE
Fracture tests were conducted on M(T) and C(T) specimens of 7.6mm-thick
2324-T39 aluminum in the L-T orientation (i.e., the load was applied in the
longitudinal or rolling direction and the crack was in the transverse direction or
perpendicular to the longitudinal direction).  The configurations tested included
102mm-wide M(T), 305mm-wide M(T), 152mm-wide compact tension C(T), and
102mm-wide C(T) specimens.  Some of the 102mm-wide M(T) specimens had a
9.5mm-diameter hole in the center of the crack and the 102mm-wide C(T)
specimens had a 10% side groove on each side.  All specimens were fatigue
precracked at loads that resulted in a final stress-intensity factor of about 8
MPa m.  The tests were conducted under displacement control and
measurements of load, crack extension, and crack opening displacement were
made as the crack grew.  For the M(T) specimens, the center-line crack opening
displacement was measured 10mm above and below the crack.  For the C(T)
specimens, the crack opening displacement was measured at the edge of the
specimen, 10mm above and below the crack.  The CTOA measurements were
made using the optical microscopy (OM) technique [2].
Crack tunneling behavior was investigated with the 102mm-wide, side grooved
C(T) specimens.  The specimens were fatigue precracked, then loaded under
displacement control until the crack began to stably tear.  The loading was
stopped and the specimen was fatigue cycled, until failure, at a stress ratio of
R=0.8 and a maximum load that was 80% of the maximum load during the stable
tearing portion of the test.  The macroscopic and microscopic appearance of the
stable tearing region was different than both the fatigue precracking and high-R
fatigue regions.  The interface between the regions denotes the crack front profile
at the end of the fatigue precracking and the end of stable tearing.
EXPERIMENTAL RESULTS
A summary of the M(T) and C(T) fracture tests is given in Tables 1-4 and a
tabular listing of all of the experimental measurements is given in Appendix A.
Fracture Results
The 102mm-wide M(T) fracture tests are summarized in Table 1.  Two of the
102mm-wide M(T) specimens were  supplied with a 9.5mm diameter center hole
and a 8mm-long saw cut was made on both sides of the hole.  Fatigue
precracking was used to develop a sharp crack tip.  Two additional M(T)
specimens were machined from the fractured halves of the 305mm-wide M(T)
specimens (these specimens did not have the center holes).  The crack
extension (measured on one side of the specimen) during fracture is plotted as a
function of applied stress in Figure 1.  Crack opening displacement
measurements were made for tests MT4-03 and MT4-04, and plotted as a
function of stress in Figure 2.  The displacement measurements were made, on
both sides, along the center line of the specimen and 10 mm above and below
the crack plane.  The values shown in Figure 2 are the average of the front and
back displacement measurements.
The 305mm-wide M(T) fracture tests are summarized in Table 2.  The crack
extension (measured on one side of the specimen) during fracture is plotted as a
function of applied stress in Figure 3.  Crack opening displacement
measurements were made and plotted as a function of stress in Figure 4.  The
displacement measurements were made, on both sides, along the center line of
the specimen and 10 mm above and below the crack plane.  The values shown
in Figure 4 are the average of the front and back displacement measurements.
The crack opening displacement measurements were used to obtain crack length
through the unloading compliance technique [7].  The compliance crack length
measurements are shown along with the optical surface crack measurements in
Figure 3.  The compliance indicated crack extensions were greater than visual
apparently because of crack tunneling.
The 152mm-wide C(T) fracture tests are summarized in Table 3.  The crack
extension (measured on one side of the specimen) during fracture is plotted as a
function of applied load in Figure 5.  The crack grew straight in only one test
(CT6-02), in the other two tests the crack immediately turned and grew at an
angle of about 45° to the plane of the fatigue precrack.  Crack opening
displacement measurements were made and plotted as a function of load in
Figure 6.  The displacement measurements were made on the edge of the
specimen, 10 mm above and below the crack plane.  Pin displacement (PD) were
made and plotted as a function of load in Figure 7.
The 102mm-wide C(T) fractures tests are summarized in Table 4.  These
specimens had a 10% side groove, running along the crack plane, on both sides
of the specimen.  One specimen was loaded until failure and the other five were
used to characterize crack tunneling.  Crack opening displacement
measurements were made and plotted as a function of load in Figure 8.  The
displacement measurements were made on the edge of the specimen, 10 mm
above and below the crack plane.  Pin displacement (or stroke) were made and
are also plotted as a function of load in Figure 8.
CTOA Results
Critical crack tip opening angle (CTOA) measurements were made for the
102mm-wide M(T), 305mm-wide M(T), and 152mm-wide C(T) fracture tests.  The
CTOA measurements are reported in Tables 5-7 and plotted as a function of
surface crack extension in Figure 9.  The average CTOA values (after 2mm of
surface crack extension) were 4.4°, 4.9°, and 5.1° for the 102mm-wide M(T),
305mm-wide M(T), and 152mm-wide C(T), respectively.  The 102mm-wide M(T)
fracture tests had a very small amount of stable tearing prior to specimen failure.
This resulted in only a few CTOA measurements per test and making
measurements difficult.  The 305mm-wide M(T) and 152mm-wide C(T) had
significantly more crack extension, thus more CTOA measurements.
SUMMARY
Fracture tests were conducted on M(T) and C(T) specimens of 7.6mm-thick
2324-T39 aluminum in the L-T orientation.  The configurations tested included
102mm-wide M(T), 305mm-wide M(T), 152mm-wide compact tension C(T), and
102mm-wide C(T) specimens.  Some of the 102mm-wide M(T) specimens had a
9.5mm-diameter hole in the center of the crack.  The 102mm-wide C(T)
specimens had a 10% side groove.  The measured CTOA for the 305mm-wide
M(T) tests and 152mm-wide C(T) tests were 4.9° and 5.1°, respectively.  The
scatter involved with these measurements was about ±1°.  The measured CTOA
for the 102mm-wide M(T) tests was 4.4°, however, very little stable crack growth
occurred before the specimen failed, making CTOA measurements difficult.
REFERENCES
1 Newman, J. C., Jr., Dawicke, D. S., and Bigelow, C. A., "Finite-Element
Analyses and Fracture Simulation in Thin-Sheet Aluminum Alloy," NASA TM-
107662, August 1992.
2 Dawicke, D. S. and Sutton, M. A., "Crack-Tip Opening Angle
Measurements and Crack Tunneling Under Stable Tearing in a Thin Sheet 2024-
T3 Aluminum Alloy, NASA-CR 191523, September 1993.
3 Dawicke, D. S., Sutton, M. A., Newman, J. C., Jr., and Bigelow, C. A.,
"Measurement and Analysis of Critical CTOA for an Aluminum Alloy Sheet,"
NASA TM-109024, September 1993.
4 Sutton, M. A., Dawicke, D. S., and Newman, J. C., Jr., "Orientation Effects
on the Measurement and Analysis of Critical CTOA in an Aluminum Alloy Sheet,"
NASA TM-109153, September 1994.
5 Dawicke, D. S., Newman, J. C., Jr., Sutton, M. A., and Amstutz, B. E.,
"Stable Tearing Behavior of a Thin-Sheet Material with Multiple Cracks," NASA
TM-109131, June 1994.
6 Dawicke, D. S., Newman, J. C., Jr., and Bigelow, C. A., "Three-
Dimensional CTOA and Constraint Effects During Stable Tearing in a Thin-Sheet
Material," NASA TM-109183, February 1995.
7 "1994 Annual Book of ASTM Standards, Section 3: Metal Test Methods
and Analytical Procedures," ASTM PCN 01-030191-23, p. E647.
Table 1
Summary of the 102mm-wide M(T) Fracture Tests
ID
Crack
Length,
a
(mm)
Max
Stress,
S
(MPa)
Comments
MT4-03 29.7 264.9 9.5mm center hole
MT4-04 30.2 256.8 9.5mm center hole
MT4-05 33.0 273.2 Cut from MT12-01, crack tunneling test
MT4-06 33.0 277.5 Cut from MT12-02
Table 2
Summary of the 305mm-wide M(T) Fracture Tests
ID
Crack
Length,
a
(mm)
Max
Stress,
S
(MPa)
Comments
MT12-01 114.3 205.3
MT12-02 119.4 203.4
Table 3
Summary of the 152mm-wide C(T) Fracture Tests
ID
Crack
Length,
a
(mm)
Max
Load,
P
(KN)
Comments
CT6-01 64.6 32.2 Crack turned and grew at 45°
CT6-02 62.0 29.8 Crack grew straight
CT6-03 64.9 34.2 Crack turned and grew at 45°
Table 4
Summary of the 102mm-wide Side-Grooved C(T) Fracture Tests
ID
Crack
Length,
a
(mm)
Max
Load,
P
(KN)
Comments
CT4-01 40.6 15.6 only compliance crack length measurements
CT4-02 41.9 12.0 crack tunneling test (limited stable tearing)
CT4-03 41.5 15.6 crack tunneling test (limited stable tearing)
CT4-04 41.7 14.4 crack tunneling test (limited stable tearing)
CT4-05 41.8 14.0 crack tunneling test (limited stable tearing)
CT4-06 40.8 14.7 crack tunneling test (limited stable tearing)
Table 5
CTOA Measurements for the 102mm-wide M(T) Fracture Tests
Crack Extension,
∆a
(mm)
CTOD
(degree)
0.02 6.9
0.38 6.3
0.74 4.9
1.09 4.6
1.40 4.6
2.41 3.3
2.67 3.8
3.25 4.3
3.40 4.9
5.05 4.4
5.11 4.4
Table 6
CTOA Measurements for the 305mm-wide M(T) Fracture Tests
Crack Extension,
∆a
(mm)
CTOD
(degree)
0.25 11.5
0.51 11.4
0.64 11.3
1.68 6.2
2.26 5.3
3.30 3.8
3.68 4.2
4.32 4.7
4.83 4.5
5.66 5.0
7.11 5.2
7.87 5.5
7.92 5.6
9.96 4.6
12.27 4.5
13.28 4.7
15.19 5.1
15.75 5.1
16.26 5.3
Table 7
CTOA Measurements for the 152mm-wide C(T) Fracture Tests
Crack Extension,
∆a
(mm)
CTOD
(degree)
0.33 8.4
0.66 8.6
1.52 6.6
4.32 5.9
6.43 5.4
7.92 4.7
9.07 4.8
10.52 5.4
12.04 3.7
15.42 5.7
17.83 5.8
23.88 4.4
39.47 5.1
43.43 5.3
0
50
100
150
200
250
300
0 1 2 3 4 5 6
MT4-03
MT4-04
MT4-06
S
(MPa)
∆a
(mm)
Figure 1 Crack extension data for the 102mm-wide M(T) fracture tests.
MT4-03
MT4-04
S
(MPa)
COD
(mm)
0
50
100
150
200
250
300
0 0.1 0.2 0.3 0.4
Figure 2 Crack opening displacement measurements for the 102mm-wide
M(T) fracture tests.
∆a
(mm)
S
(MPa)
MT12-01
MT12-02
Optical
Compliance
Optical
Compliance
0
50
100
150
200
250
0 5 10 15 20 25
Figure 3 Crack extension data for the 305mm-wide M(T) fracture tests.
S
(MPa)
COD
(mm)
0
50
100
150
200
250
0 0.5 1 1.5 2
MT12-01
MT12-02
Figure 4 Crack opening displacement measurements for the 305mm-wide
M(T) fracture tests.
05
10
15
20
25
30
35
0 10 20 30 40 50
CT6-01
CT6-02
CT6-03
∆a
(mm)
P
(KN)
Figure 5 Crack extension data for the 152mm-wide C(T) fracture tests.
05
10
15
20
25
30
35
0 1 2 3 4 5 6
CT6-01
CT6-02
CT6-03
P
(KN)
COD
(mm)
Figure 6 Crack opening displacements measurements for the 152mm-wide
C(T) fracture tests.
05
10
15
20
25
30
35
0 2 4 6 8 10 12
CT6-01
CT6-02
CT6-03P(KN)
PD
(mm)
Figure 7 Pin displacement (or stroke) measurements for the 152mm-wide
C(T) fracture tests.
05
10
15
20
0 1 2 3 4 5
COD
PD
P
(KN)
Displacement
(mm)
Figure 8 Crack opening and pin displacement measurements for the
102mm-wide (side groove) C(T) fracture tests.
05
10
15
0 10 20 30 40 50
102mm-wide M(T)
305mm-wide M(T)
152mm-wide C(T)
∆a
(mm)
CTOA
(degree)
Figure 9 Critical crack tip opening angle (CTOA) measurements for the
102mm-wide M(T), 305mm-wide M(T), and 152mm-wide C(T)
fracture tests.
APPENDIX A
Test Data Summary
Table 1
Crack Extension Data for Test MT4-03
Crack Extension,
∆a
(mm)
Stress,
S
(MPa)
0.00 0.0
0.15 178.1
0.53 229.8
1.91 258.0
2.66 262.6
3.40 264.9
5.11 264.3
Table 2
Crack Opening Displacement Data for Test MT4-03
COD
(mm)
Stress,
S
(MPa)
0.0 0.0
0.025 35.0
0.046 69.2
0.068 103.6
0.088 138.2
0.114 171.0
0.154 207.0
0.187 229.6
0.224 247.8
0.266 255.8
0.298 263.3
0.338 263.3
0.397 259.4
Table 3
Crack Extension Data for Test MT4-04
Crack Extension,
∆a
(mm)
Stress,
S
(MPa)
0.00 0.0
0.25 201.1
0.38 216.0
0.69 232.1
1.22 245.9
2.41 255.1
3.25 256.8
5.05 256.8
Table 4
Crack Opening Displacement Data for Test MT4-04
COD
(mm)
Stress,
S
(MPa)
0.0 0.0
0.026 45.9
0.045 69.1
0.064 103.6
0.084 138.1
0.112 172.1
0.146 200.3
0.167 215.1
0.193 230.3
0.235 244.6
0.275 251.7
0.317 252.9
0.366 251.4
Table 5
Crack Extension Data for Test MT4-06
Crack Extension,
∆a
(mm)
Stress,
S
(MPa)
0.00 0.0
1.04 274.1
1.68 277.5
Table 6
Crack Extension Data for Test MT12-01
Crack Extension,
∆a
(mm)
Stress,
S
(MPa)
0.00 0.0
0.25 114.9
0.51 134.1
0.79 153.2
2.26 172.4
5.16 178.9
7.11 184.8
7.92 190.6
9.96 192.7
13.3 199.6
15.2 201.9
16.3 204.9
19.7 205.3
22.0 202.6
Table 7
Crack Opening Displacement Data for Test MT12-01
COD
(mm)
Stress,
S
(MPa)
0.000 0.0
0.073 20.1
0.152 40.0
0.235 60.4
0.316 80.1
0.403 100.3
0.497 120.0
0.599 140.2
0.746 160.1
0.817 170.2
0.914 180.1
1.049 190.2
1.165 198.9
1.235 201.2
1.368 204.7
1.493 201.9
1.610 199.3
Table 8
Compliance Crack Extension Data for Test MT12-01
Crack Extension,
∆a
(mm)
Stress,
S
(MPa)
0.00 40.5
0.02 57.4
0.49 76.5
0.49 95.6
0.68 114.6
1.46 133.8
1.98 152.8
3.73 171.5
5.36 178.4
7.29 184.3
7.98 190.1
9.20 191.4
11.99 198.9
14.12 201.2
15.45 204.5
19.18 204.7
21.94 201.9
Table 9
Crack Extension Data for Test MT12-02
Crack Extension,
∆a
(mm)
Stress,
S
(MPa)
0.00 0.0
0.51 153.2
1.68 172.4
3.68 179.7
5.66 187.9
7.26 192.5
10.0 196.7
12.3 200.9
15.1 203.4
17.5 203.2
Table 10
Compliance Crack Extension Data for Test MT12-02
Crack Extension,
∆a
(mm)
Stress,
S
(MPa)
0.00 38.3
0.03 55.9
0.11 76.6
0.21 95.8
0.71 114.9
1.29 133.7
1.82 153.0
3.47 169.2
5.80 178.7
7.63 185.5
8.63 191.7
10.86 194.8
12.60 199.2
15.56 202.4
17.71 202.3
Table 11
Crack Opening Displacement Data for Test MT12-02
COD
(mm)
Stress,
S
(MPa)
0.000 0.0
0.071 20.0
0.155 41.1
0.234 60.5
0.318 80.9
0.402 100.1
0.501 120.9
0.600 140.3
0.734 160.7
0.804 170.1
0.919 181.6
1.037 191.2
1.100 195.8
1.209 199.6
1.290 202.4
1.388 202.3
1.508 200.7
Table 12
Crack Extension Data for Test CT6-01
Crack Extension,
∆a
(mm)
Load,
P
(KN)
0.00 0.0
0.46 24.1
1.68 29.1
3.51 29.9
4.57 31.1
5.41 31.8
7.14 32.2
8.81 32.1
12.34 31.4
13.49 31.0
14.94 30.8
16.71 30.2
18.31 29.5
20.30 28.1
23.32 26.9
25.83 25.1
27.41 23.4
29.11 22.3
30.61 21.2
32.44 20.1
Table 13
Crack Opening Displacement Data for Test CT6-01
COD
(mm)
PD
(mm)
Load,
P
(KN)
0.000 0.000 0.0
0.203 0.190 2.7
0.338 0.313 4.5
0.497 0.455 6.6
0.717 0.649 9.4
1.028 0.922 13.4
1.443 1.276 18.2
1.870 1.632 22.7
2.327 2.007 26.9
2.616 2.238 29.1
3.130 2.634 31.2
3.249 2.725 31.7
3.327 2.788 32.2
Table 13 (cont.)
Crack Opening Displacement Data for Test CT6-01
COD
(mm)
PD
(mm)
Load,
P
(KN)
3.431 2.861 32.1
3.621 2.995 31.7
4.427 3.579 30.5
4.885 3.894 29.0
5.608 4.400 26.7
5.907 4.787 24.9
4.901 23.4
5.748 17.9
6.449 13.1
7.641 9.0
9.458 4.7
11.886 2.1
Table 14
Crack Extension Data for Test CT6-02
Crack Extension,
∆a
(mm)
Load,
P
(KN)
0.00 0.0
0.46 23.0
2.03 26.8
6.55 29.6
7.65 29.8
11.00 29.8
12.57 29.2
16.36 28.0
21.18 24.7
22.68 23.1
25.12 22.5
30.48 21.0
Table 15
Crack Opening Displacement Data for Test CT6-02
COD
(mm)
PD
(mm)
Load,
P
(KN)
0.000 0.000 0.0
0.351 0.313 4.5
0.700 0.621 9.1
1.045 0.921 13.4
1.434 1.252 17.9
1.890 1.629 22.3
2.437 2.072 26.8
2.857 2.401 29.0
3.160 2.627 29.6
3.426 2.824 29.7
3.582 2.934 29.2
3.832 3.108 27.8
3.959 3.190 26.4
4.094 3.285 25.7
4.306 3.427 23.8
4.353 3.449 22.2
4.573 3.601 20.8
4.731 3.716 20.5
4.861 3.796 18.3
5.149 3.993 15.8
5.426 4.187 14.3
5.642 4.342 13.1
4.703 7.8
5.298 5.3
6.407 2.8
7.858 1.4
Table 16
Crack Extension Data for Test CT6-03
Crack Extension,
∆a
(mm)
Load,
P
(KN)
0.00 0.0
0.66 28.3
1.52 31.8
3.12 32.3
4.32 33.1
6.43 34.1
7.92 31.2
Table 16 (cont.)
Crack Extension Data for Test CT6-03
Crack Extension,
∆a
(mm)
Load,
P
(KN)
9.07 34.0
10.52 33.9
12.04 33.8
13.74 33.6
15.42 33.3
17.83 33.2
20.80 31.8
22.28 30.1
23.88 28.6
25.35 28.2
26.59 27.5
27.84 26.9
29.44 26.3
30.81 25.1
32.21 24.2
33.53 23.4
36.00 21.1
37.77 20.3
39.47 18.9
43.43 16.7
Table 17
Crack Opening Displacement Data for Test CT6-03
COD
(mm)
PD
(mm)
Load,
P
(KN)
0.000 0.000 0.0
0.157 0.158 2.4
0.307 0.300 4.5
0.619 0.586 8.9
0.953 0.883 13.5
1.278 1.169 17.8
1.655 1.491 22.3
2.073 1.843 26.8
2.567 2.252 31.1
3.005 2.594 32.9
3.692 3.096 34.2
4.574 3.717 31.4
Table 17 (cont.)
Crack Opening Displacement Data for Test CT6-03
COD
(mm)
PD
(mm)
Load,
P
(KN)
5.735 4.524 26.7
5.904 4.641 26.0
5.148 22.3
5.863 18.5
6.678 12.9
7.564 9.2
9.484 4.4
11.801 2.4
Table 18
Crack Opening Displacement Data for Test CT4-01
COD
(mm)
PD
(mm)
Load,
P
(KN)
0.000 0.000 0.0
0.160 0.167 2.2
0.327 0.348 4.6
0.479 0.508 6.7
0.643 0.676 8.9
0.814 0.851 11.1
1.011 1.041 13.4
1.173 1.181 14.5
1.448 1.404 15.6
1.650 1.547 15.5
1.755 1.573 13.0
1.881 1.646 12.0
2.133 1.810 11.1
2.287 1.865 8.1
2.671 2.099 5.5
3.024 2.333 3.9
3.512 2.672 2.5


Fracture testing of 2324-T39 aluminum alloy

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