Novel data obtained through experimental investigation into the fatigue response of 350WT steel, subjected to semi-random loading, comprised of various combinations of intermittent tensile overloads and compressive underloads are presented. An effective model for predicting the fatigue response is also introduced. For that, the capabilities of some of the currently available models are investigated and then an exponential delay model, being capable of accounting for the effects of not only overload ratio, but also stress ratio and overload/underload ratio is introduced. Since most variable amplitude models are based on a constant amplitude model, efforts were also expended to identify a constant amplitude fatigue crack growth model that would be easy to use, requiring the calibration of few (if any) empirical curve-fitting parameters. The integrity of a selected model is examined and results are presented.

1.
Broek
,
D.
, 1988,
The Practical Use of Fracture Mechanics
,
Kluwer Academic
,
Dordrecht
.
2.
Zheng
,
X.
, and
Hirt
,
M. A.
, 1994, “
Fatigue Crack Propagation in Steels
,”
Eng. Fract. Mech.
0013-7944,
48
(
3
), pp.
965
973
.
3.
Hammouda
,
M.
,
Ahmad
,
S.
,
Seleem
,
M.
, and
Sallam
,
H.
, 1998, “
Fatigue Crack Growth Due to Two Successive Single Overloads
,”
Fatigue Fract. Eng. Mater. Struct.
8756-758X,
21
, pp.
1537
1547
.
4.
Trask
,
D.
, 1998 “
Experimental and Numerical Investigation Into Fatigue Crack Propagation Models for 350WT Steel
.” MASc. thesis, Technical University of Nova Scotia.
5.
Taheri
,
F.
,
Trask
,
D.
, and
Pegg
,
N.
, 2003, “
Experimental and Analytical Investigation of Fatigue Characteristics of 350WT Steel Under Constant and Variable Amplitude Loadings
,”
Mar. Struct.
0951-8339,
16
, pp.
69
91
.
6.
Barsom
,
J. M.
, and
Rolfe
,
S. T.
, 1987,
Fracture and Fatigue Control in Structures: Applications of Fracture Mechanics
,
2nd ed.
,
Prentice Hall
,
Englewood Cliffs, NJ
.
7.
Hudson
,
C. M.
, 1981, “
A Root-Mean-Square Approach for Predicting Fatigue Crack Growth under Random Loading
,”
Methods and Models for Predicting Fatigue Crack Growth under Random Loading
, ASTM STP 748,
J. B.
Chang
and
C. M.
Hudson
, eds.,
American Society for Testing Materials
,
Philadelphia
, pp.
41
52
.
8.
Wheeler
,
O. E.
, 1972, “
Spectrum Loading and Crack Growth
,”
J. Basic Eng.
0021-9223,
94
, No. 1, pp.
181
186
.
9.
Sheu
,
B. C.
,
Song
,
P. S.
, and
Hwang
,
S.
, 1995, “
Shaping Exponent in Wheeler Model Under a Single Overload
,”
Eng. Fract. Mech.
0013-7944,
51
(
1
), pp.
135
143
.
10.
Yuen
,
B. K.
, and
Taheri
,
F.
, 2006, “
Proposed Modifications to The Wheeler Retardation Model For Multiple Overloading Fatigue Life Prediction
,”
Int. J. Fatigue
0142-1123,
28
, No. 12, Sep. 21, pp.
1803
-
1819.
11.
Willenborg
,
J. D.
,
Engle
,
R. M.
, and
Wood
,
H. A.
, 1971, “
A Crack Growth Retardation Model Using an Effective Stress Concept
,” Report AFFDL-TM-71-1-FBR,
Air Force Flight Dynamics Laboratory
, Wright-Patterson Air Force Base, Dayton, Ohio, January.
12.
Johnson
,
W. S.
, 1981 “
Multi-Parameter Yield Zone Model for Predicting Spectrum Crack Growth
,”
Methods and Models for Predicting Fatigue Crack Growth Under Random Loading
,
ASTM STP 748
,
J. B.
Chang
and
C. M.
Hudson
, eds.,
American Society for Testing and Materials
,
Philadelphia
, pp.
85
102
.
13.
Forman
,
R. G.
,
Kearney
,
V. E.
, and
Engle
,
R. M.
, 1967, “
Numerical Analysis of Crack Propagation in a Cyclic-Loaded Structure
,” Transactions of the American Society of Mechanical Engineers. Series D;
J. Basic Eng.
0021-9223,
89
(
3
), pp.
459
465
.
14.
Zheng
,
X.
, 1987, “
A Simple Formula for Fatigue Crack Propagation and a New Method for the Determination of ΔKth
,”
Eng. Fract. Mech.
0013-7944,
27
(
4
), pp.
465
475
.
15.
Wasen
,
J.
, and
Heier
,
E.
, 1998, “
Fatigue Crack Growth Thresholds—The Influence of Young’s Modulus and Fracture Surface Roughness
,”
Int. J. Fatigue
0142-1123,
20
(
10
), pp.
737
742
.
16.
ASTM E647-00
, 2000, “
Standard Test Method for Measurement of Fatigue Crack Growth Rates
,”
American Society for Testing Materials
, West Conshohocken, PA.
17.
Irwin
,
G. R.
, 1957, “
Analysis of Stresses and Strains Near the End of a Crack Traversing a Plate
,”
ASME J. Appl. Mech.
0021-8936,
24
, pp.
361
364
.
18.
Rushton
,
P. A.
, and
Taheri
,
F.
, 2003, “
Prediction of Variable Amplitude Crack Growth in 350WT Steel Using a Modified Wheeler Approach
,”
Mar. Struct.
0951-8339,
16
(
7
), pp.
517
539
.
19.
Rudd
,
J. L.
, and
Engle
,
R. M.
, Jr.
, 1981, “
Crack Growth Behavior of Center-Cracked Panels Under Random Spectrum Loading
,”
Methods and Models for Predicting Fatigue Crack Growth under Random Loading
,
ASTM STP 748
,
J. B.
Chang
and
C. M.
Hudson
, eds.,
American Society for Testing Materials
,
Philadelphia
, pp.
103
114
.
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