MTS Landmark Tabletop - Manual (Page 33)

Functional Description
The load unit is a stand-alone testing structure. It consists of the following components:
• Load frame
• Crosshead lifts
• Manifold
• Actuators
• Servovalves
• Accumulators
• Two or more transducers
Load frame
The load frame is the basic structure. Two columns allow a crosshead to be moved up or down to accommodate
different size specimens and fixtures. The crosshead is one of the two reaction masses in the force train and
the base of the load frame is the other. A control panel lets you perform specimen installation procedures.
Crosshead
The crosshead has the actuator, servovalve, manifold, and accumulators mounted to it. It usually has a grip
or special fixtures attached to the actuator of the crosshead to install one end of the test specimen.
The crosshead can be positioned anywhere along the load frame columns. This lets you test specimens of
different lengths. It can be moved along the column manually or with hydraulic lifts. When the crosshead is
in an appropriate test position, it is manually clamped to that position.
Manifold
The actuator manifold acts as the hydraulic interface between the HPU and the components mounted to the
manifold (actuator, servovalves, and accumulators) of the load unit. It contains the required hydraulic porting
and plumbing to accommodate the various hydraulically controlled components. The manifold can also control
the hydraulic pressure to the load unit.
• Actuator: The linear actuator is located in the middle of the crosshead. It is a hydraulically powered piston
that applies displacement of (or force into) a specimen. It can apply equal power in tension and compression.
One end of the test specimen is installed into a fixture mounted to the end of the actuator rod.
The rotary actuator is coupled to the linear actuator. It is a hydraulically powered piston that applies angular
displacement of (or torsional force into) a specimen.
• Servovalves: The servovalve regulates the rate and direction of hydraulic fluid flow to and from a hydraulic
actuator. The load unit usually includes a Series 252 Servovalve. Each actuator requires a servovalve.
• Accumulators: The accumulators suppress line-pressure fluctuations. The load unit includes a pressure-line
accumulator to provide fluid storage so that a constant line pressure can be maintained at the servovalves
for maximum performance. The return-line accumulator minimizes return-line pressure fluctuations.
Pressure control
The load unit can be configured for several pressure configurations:
MTS Landmark™ Tabletop Load Units Product Information 33
Introduction