MTS Fatigue Template - Manual (Page 34)

Cycle 0 (zero)
The application collects data for each complete cycle. A cycle starts at mean level and ends at mean level.
In most cases, mean level is zero. For cases where mean level is not zero, a ramp initially occurs to mean
level before the test actually starts. The application stores the data collected during this initial ramp in cycle
count 0.
Stable cycle determination
The application identifies the stable cycle based on user-entered parameters.
Application-determined stable cycle
For an application-determined stable cycle, a consecutive number of cycles must remain within the stable-cycle
deviation factor to determine the reference cycle. Typical cycle counts are from 5 to 100 cycles.
Enter the percentage deviation that consecutive cycles must be within, as compared to an initial cycle. If a
cycle deviates beyond this percentage before the stabilizing factor amount is reached, that cycle becomes
the new cycle against which following cycles are compared. Typical stable cycle deviation factors are around
1%.
Test completion
The LCF test runs until it meets one of the termination criteria. Examples of test termination criteria include:
• Non-controlling failure threshold (%)
• Peak-valley deviation
Non-controlling failure threshold (%)
For tests run in strain control, you define a percentage of stable load amplitude to use for failure detection.
When the test reaches the stable cycle, the test compares the peak loads with this cycle to determine if the
test should be terminated due to specimen failure. For tests run in load control, enter the percentage of stable
displacement for failure detection. When the stability reference cycle is reached, the test compares the peak
displacements to this cycle to determine if the test should be terminated due to specimen failure.
Crack initiation determination
After a stable cycle is identified, each subsequent cycle is compared to the stable cycle. If the non-controlling
range (force range for a strain controlled test) deviates by the user-entered percentage, the application stores
the cycle number as the crack initiation cycle. Typical range drops are near 5%.
Peak-valley control failure
If the control value end levels are not met, the test stops.
Ramp to mean load
When the test is complete, the system changes to force control and ramps to mean load at a rate set by the
user.
5.3.3.0 Strain Test
In the LCFS test:
34 MTS TestSuite
5.0 ASTM Low-Cycle Fatigue (LCF) Strain Template