MTS Fracture Analyzer - Manual (Page 79)

• The function Pi() represents the mathematical constant, pi.
• The function SystemRate() represents the system data rate.
7.5.6.0 Modulus Calculation Functions
Modulus is calculated from the slope of the Least Squares Fit calculation of the Stress and Strain arrays
between the starting and ending indexes.
Loading Modulus
LoadingModulus(Stress, Strain[, startIndex, endIndex])
The loading modulus is the modulus of the portion of the curve where the load on the specimen increases.
This function calculates the loading modulus using the Stress and Strain arrays between the startIndex and
endIndex.
If the startIndex is set to -1, the optimum start index is the valley offset by 5 points. If variables represent this
box in the function and the original value is -1, the variable contains the calculated index at the completion
of the function.
If the endIndex is set to -1, you can calculate the optimum endpoint:
1. Locate a nominal end index at 25% of the stress range and within the linear modulus range.
2. Calculate a nominal modulus at the nominal end index.
3. Expand the nominal end index away from the start index until the new modulus value differs from the
nominal modulus by more than 2%.
4. The endIndex is set before the newly calculated modulus exceeds the nominal modulus.
If variables represent this box in the function and the original value is -1, the variable contains the calculated
index at the completion of the function.
UnLoading Modulus
UnLoadingModulus(Stress, Strain[, startIndex, endIndex])
The unloading modulus is the modulus of the portion of the curve where the load on the specimen decreases.
This function calculates the unloading modulus using the Stress and Strain arrays between the startIndex
and endIndex.
If the startIndex is set to -1, the optimum starting index is the peak offset by 5 points. If variables represent
this box in the function and the original value is -1, the variable contains the calculated index at completion
of the function.
If the endIndex is set to -1, you can calculate the optimum endpoint:
1. Locate a nominal end index at 25% of the stress range and within the linear modulus range.
2. Calculate a nominal modulus at the nominal end index.
3. Expand the nominal end index away from the start index until the new modulus value differs from the
nominal modulus by more than 2%.
4. The endIndex is set before the newly calculated modulus exceeds the nominal modulus.
If variables represent this box in the function and the original value is -1, the variable contains the calculated
index at the completion of the function.
MTS TestSuite™ Fracture Analyzer User Guide 79
7.0 Variable Analysis