MTS Series 647 Hydraulic Wedge Grips - Manual (Page 79)

Description Item
Hydraulic Grip Supply 3
Determine Gripping Pressure
About Grip Pressure Determination
The output pressure of the hydraulic grip supply determines the gripping force applied to the specimen by
the wedges. The optimum gripping force is great enough to securely grip the specimen, yet low enough to
minimize specimen deformation or prevent specimen slippage during the test.
Warning:
Improper grip pressure can damage the grips.
Insufficient grip pressure can result in specimen slippage or wedge movement which can damage
the grips. Using a grip pressure that exceeds the pressure rating of the grip can result in damage
to the grips.
The minimum pressure level, calculated in the following procedures, ensures that the wedges
will be properly seated in the wedge chamber to prevent any movement of the wedges within the
chamber when a full axial or load is applied to the specimen.
Definition of terms
This section defines the parameters used in the gripping pressure formulas. The figure “Gripping Principles”
illustrates some of the parameters.
A = Area of the grip piston (cm
2
or in
2
)
A Model
2.54 in
2
16.38 cm
2
647.02
10.30 in
2
66.45 cm
2
647.10
7.84 in
2
50.58 cm
2
647.25
12.51 in
2
80.75 cm
2
647.50
26.95 in
2
173.96 cm
2
647.100
64.6 in
2
416.77 cm
2
647.250
Series 647 Hydraulic Wedge Grips Reference Manual 79
Operation