MTS Series 609 Alignment Fixture - Manual (Page 44)

Series 609 Alignment Fixture Product Information 44
Notched Round Thin Diameter Specimens
Specimen Preparation
Where: ε
1
through ε
8
are the strain readings from gages 1 through 8
Au is the average strain of the upper gages
Al is the average strain of the lower gages
4. Calculate the percent bending strain for each level.
Use this formula to find the percent bending strain (PBS):
Where:
Bu is the bending strain of the upper gages
Bl is the bending strain of the lower gages
Au is the average strain of the upper gages
Al is the average strain of the lower gages
5. Calculate the direction of the maximum strain for each level.
Use this formula to find the direction ( φ) of the maximum (most tensile)
bending strain:
Where: ( φ) is measured from the highest reading (most tensile) strain
gage toward the second highest reading strain gage
Bu
x
is the highest strain of the x axis of the upper gages
Bl
x
is the highest strain of the x axis of the lower gages
Bu
y
is the highest strain of the y axis of the upper gages
Bl
y
is the highest strain of the y axis of the lower gages
The bending strain directions for all levels should generally agree if you
have satisfactorily removed the “S” bend.
Notched Round Thin Diameter Specimens
A typical gaged specimen has two levels of strain gages. The gages allow you to
determine bending strains at each level. Analysis of the strain readings produce a
profile of the grip alignment.
Gage placement
On small diameter specimens where you can not use four gages at each level, use
three gages at each level. Attach and number the six gages as shown here.
Au
ε
1
ε
2
ε
3
ε
4
+ + +
4
--------------------------------------- = Al
ε
5
ε
6
ε
7
ε
8
+ + +
4
--------------------------------------- =
Upper Gages Lower Gages
PBSu
Bu
Au
------- 100 × = PBSl
Bl
Al
----- 100 × =
Upper Gages Lower Gages
φ arc
Bu
x
Bu
y
--------- tan = φ arc
Bl
x
Bl
y
------- tan =
Upper Gages Lower Gages