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Copyright 2001 by StressWave, Inc. All rights reserved.
Technical Report ST-01Fatigue Testing of 4340 SteelJuly 1,
2001
OBJECTIVE
The objective of this test program was to determine the fatigue
life improvement due toStressWave processing in a steel alloy.
INTRODUCTION
Alloy steels often require fatigue life improvement, in
aerospace and other applications.
This program was designed to determine if fatigue life
improvement in a steel alloy waspossible with the StressWave
process. The program used a baseline indenter designand application
parameters to process test specimens of AISI 4340 steel.
Testing was performed with open hole, zero load transfer
specimens under constantamplitude load conditions. Various test
stress levels were used to facilitatedevelopment of an S-N
curve.
TEST SPECIMEN PREPARATION
Test specimen blanks were machined from the same lot of 0.25
inch thick AISI 4340plate per AMS 6359 (Figure 1). After machining,
the specimen blanks were heat treatedto Rockwell hardness of 36-40
(160-180 KSI tensile strength) on the C scale.
Baseline specimens were prepared by drilling and reaming a
central 0.250 inch hole.StressWave specimens were prepared by
processing with a baseline indenter, thendrilling and reaming.
TEST PROGRAM
Test conditions are shown in Table 1. Testing was performed at
constant amplitudeload conditions, at a stress ratio (R) equal to
.05. Test frequency was 20 Hz.Specimens were cycled to two-piece
failure. All testing was performed in closed-loop,electro-hydraulic
fatigue test machines, calibrated periodically using standards
traceableto the National Institute of Standards and Technology
(NIST).
TEST RESULTS
Test results are listed in Table 1, and graphed in Figure 2 as
an S-N curve. At 60 KSImaximum stress level, the StressWave
specimens demonstrated better than 5:1 life
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SW TR ST-01, 4340 Steel
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improvement (treated life:non-treated life), as compared to the
baseline specimens. At50 KSI, the StressWave specimens demonstrated
better than 12:1 life improvement.
CONCLUSIONS
The StressWave process is effective for providing fatigue life
improvement in 4340steel, for the conditions tested.
Table 1. Test Conditions and Results
AISI 4340 plate per AMS 63590.375 inch thickZero load
transfer0.375 inch diameter open straight hole
Constant amplitude fatigue, cycle to failureR=.05, 20 Hz maximum
frequency
Maximumconstant amplitude Cycles to failurestress level (KSI)
Baseline StressWave
50.0 271,343 3,000,000NF101,516 1,268,027
60.0 78,000 592,32871,559 805,242
411,571
Figure 1. Test specimen blanks(4340/AMS 6359)
