Strain Controlled Fatigue Testing Request
Example:
3RD Party Vendor:
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Data Reporting:
Note that all fatigue data is to be reported in the Standard
SAE Format as per J2409.
e.g.: http://fde.uwaterloo.ca/Fde/Materials/Steel/Hsla/millerB55XF.html
(Click on "View Source" in your web browser and download source)
Similarly all Stress-Strain data for Tensile curves or cyclic
curves should be reported in the proposed SAE format:
e.g.: http://fde.uwaterloo.ca/Fde/fde_strain_stress.txt
Tensile test required for each material: report digitally and graph.
All periodic overload data should be reported via the standard SAE format
J2649: e.g.: http://fde.uwaterloo.ca/Fde/periodic_ol.html
All data recorded to 3 significant figure accuracy.
eg.: strain= 0.00312, stress= 401.mpa, modulus= 29700. ksi or 205000. mpa
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Fatigue testing process:
(Change if required, subject to approval )
Originator: A. Conle, Oct 28, 1992, Revised 2006
Re.: Strain controlled fatigue testing of Crankshaft material
The testing for the crankshaft material will include the following:
(B) Standard Strain-life Tests.
Before starting each tensile or fatigue test, the elastic
modulus shall be measured by applying a small load (below yield)
and recording the stress and strain.
Axial strain control for low cycle tests. A switch to load
control is allowed after 100K cycles if the hysteresis loop
shape has stabilized. Hysteresis loops to be recorded in
logarithmic cycle increments: 1,2,4,8,16,... or some form
thereof, such that the cyclic softening/hardening behavior may
be observed, and 1/2 life loop shape defined. The first few
cycles may be plotted on one graph. The loops should be of
sufficient size, on the graph paper, to obtain 3 significant figure
accuracy when reading the stress or strain. Subsequent loops should be
plotted on graph paper by a shift of the X axis zero on the
X-Y plotter. Full sized copies of graphs will be submitted.
Tests can be stopped by a 10% load drop (from the stable load) or
full seperation, and initial modulus slopes (1st cycle) should be
graphed or recorded.
Use ASTM-E606 standards.
Standard Strain Life Tests
APPROXIMATE!!
Test No. Strain Amp Expected Life
-------- ------- --- Range ---
S0 +- 0.010 500 cycles (at least 2pts with
S1 0.008 750 plastic strain if possible)
S2 0.007 2000
S3 0.005 5000
S4 * 10,000 (We need 3 Samples
S5 * 10,000 around 10K cycles)
S6 * 10,000
S7 * 50K
S7b * 50K
S8 * 100K
S9 * 100K - 1Million
S10 * 100K - 1M
S10b * 100K - 1M
S11 * 1M to 10M (We need about 3
S12 * 1M to 10M samples in this
S13 * 1M to 10M range)
S14 * 1M to 10M
* Strain level selected by tester.
For report or data files report Strain in strain units, NOT in %
If the expected strain levels are above +/-0.01 or +/-0.02 (axial
specimen buckling limits depend on quality of test machine aligment)
the test should be done using Diametral specimens and Diametral
extensometers. Further info on request.
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page 3 of attachment
(C) Periodic Overload Tests (Load Control )as suggested by
Prof. T.H.Topper Univ. of Waterloo:
1. Observe the "10K" cycle test's stress level from
the constant amplitude results in (B).: +-S_10K
2. Observe the Fatigue limit level from (B). : ^S_fl
(@ 10**6 cycles)
3. Run the following tests:
Wave form:
Smax= +S_10k
/\ /\ /\ /\ /\
\ / \ / | | \ / \
\ / \ / | | \ / \
\ / \ / \ / \ / \ /
\/ \/ | | \/ \/
| | Smin (see Tabl.)
\ /
| |
| |
| |
\/ Smin=-S_10k
overload cycle
The overload cycle is +- S_10k
For the regular cycle, between overloads, set Smax to the same
Smax as found in the "10K" overload cycle. Set Smin such that
the stress range corresponds to the following table:
Test ^ S No. of cycles
between overloads
--------- ------------- -----------------
OL1 100% ^ S_fl 200
OL2 95% ^ S_fl 200
OL3 90% ^ S_fl 300
OL4 85% ^ S_fl 300
OL5 ~85% ^ S_fl *
OL6 80% ^ S_fl 500
OL7 75% ^ S_fl 1000 This may reach 10**7
OL8 70% ^ S_fl 5000 "
Stop any test after 10**7 cycles. Repeat the 10**7 test, if it
also goes to 10**7 do not go to any lower levels, but repeat or
fill in some of the higher range tests. In general a typical
test should have between 2000 to 5000 overload cycles in it
(i.e. between 0.2 to 0.5 of the "10K" test damage).
The tester can adjust the numbers of cycles between overloads to
achieve this as the overload testing series develops. Once a cycle
ratio is selected for a given test, however, it should not be changed
during the test.
The overload tests attempt to find the periodic overload fatigue
limit curve. For this steel it is expected to be around 0.75
of the regular fatigue limit.