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Servo Linear Actuators for Hydraulic Dynamic Testing

Hydraulic Servo Actuators

Model: UTHA

Servo Linear Actuators for Hydraulic Dynamic Testing

High-precision, high-frequency linear actuators engineered for fatigue testing, structural dynamics, and multi-channel servo-hydraulic test systems.

UnitedTest is a leading manufacturer of electro-hydraulic servo test equipment. Our servo linear actuators are the core power source of dynamic test systems—converting hydraulic energy into precisely controlled mechanical motion for materials, components, and full-scale structures.


UnitedTest manufactures high-performance hydraulic servo linear actuators for dynamic mechanical testing, fatigue, seismic simulation, multi-channel synchronized loading. Full compliance with ASTM, ISO, GB/T standards, force range ±1kN~±2000kN, customized stroke & frequency, widely used in automotive, aerospace, medical implant, construction lab dynamic test.

General introduction

Hydraulic Servo Linear Actuator for Dynamic Mechanical Test | UnitedTest Manufacturer

UnitedTest's hydraulic servo linear actuator (servo cylinder) is the core actuator of an electro-hydraulic servo dynamic mechanical testing system. It's designed specifically for high-frequency cyclic fatigue, dynamic loading, earthquake simulation, reciprocating impact, and both dynamic and static strength testing. Using closed-loop electro-hydraulic servo control technology, it provides high-precision linear push-pull loads, supports independent single-channel loading, multi-channel synchronous coordinated loading, and is suitable for testing dynamic mechanical properties of materials, components, and structural parts. It's a key standard component for fatigue testing machines, dynamic loading test benches, seismic simulation systems, and endurance testing platforms for components.


UnitedTest has been focusing on mechanical testing equipment for over ten years and independently develops a full range of dynamic servo linear actuators. Thrust ranges from ±1kN to ±2000kN, stroke can be customized from 50mm to 500mm, working frequency is 0.01~100Hz, and multiple structures like hydrostatic bearings or dual rod ends are available. It fully meets global mainstream dynamic testing standards like ISO, ASTM, and GB/T, and is exported to universities and industrial testing centers in Europe, America, Southeast Asia, and the Middle East.


What Is a Servo Linear Actuator?

A servo linear actuator is a hydraulic execution mechanism that converts hydraulic energy supplied by the system into mechanical energy to perform work on a load. It works together with a servo valve, servo controller, and sensors to deliver very high precision and dynamic performance. It can be used either as a standalone actuator or integrated into standard test machines and complex multi-axis, multi-channel test rigs, and is widely applied in test systems for materials, parts, structural components, and complete structures.


According to its motion form, it is divided into linear actuators and rotary actuators. The linear type is the dominant choice for hydraulic dynamic testing.

Key Features

  • Test principle
  • Key Design Features of UnitedTest Servo Linear Actuators
  • Core Functions & Capabilities
  • How to - Standard Usage Process
  • Application
  • Standard
  • Keywords
  • UnitedTest Brand Core Advantages
  • How to Select the Right Actuator

Hydraulic Power Source: Equipped with UnitedTest constant pressure servo hydraulic pump station, outputs high-pressure clean hydraulic oil to power the actuators; 


Servo Valve Closed-Loop Control: The servo controller sends analog/digital signals to drive the servo valve, precisely adjusting the flow and pressure of oil in and out; 


Double-Acting Linear Cylinder: The piston inside the cylinder moves the piston rod for bidirectional linear push and pull, and the double rod, equal area design eliminates off-center loads and improves dynamic response consistency; 


Triple Real-Time Feedback Closed-Loop:

- Built-in Coaxial LVDT Displacement Sensor: Collects piston rod stroke in real-time for position closed-loop control;

- High-Precision Front-End Load Sensor: Collects dynamic push/pull force in real-time for force closed-loop;

- Servo Valve with Built-in Flow Feedback: For speed closed-loop control;


Dynamic Waveform Reproduction: The control system can output any dynamic load waveform like sine, triangle, square, random, seismic, and road spectra, perfectly simulating real operating alternating loads, completing fatigue, durability, impact, and dynamic stiffness tests.


1, Sealing & Guidance — Two Technology Tiers

TechnologyTechnologyTechnology
Conventional sealing (O-ring, guide tape, Hirch seal, Stripe seal)Simple structure, low cost, higher friction, lower frequency response, shorter lifespanStatic loading & low-cycle fatigue
Hydrostatic bearing support (no seals, special coated journal, oil-film lubrication)Near frictionless linear reciprocating motion, high sensitivity, long life, frequency response up to 1000 HzHigh-frequency fatigue, vibration testing

2, Structural Forms

Single-ended rod, double-acting — shorter overall length, lower cost, ideal for static and low-speed tests

Double-ended rod, double-acting — higher loading speeds, preferred for dynamic fatigue testing


3, Integrated Sensor Suite

Built-in non-contact high-frequency LVDT displacement sensor — infinite resolution, no frictional wear

High-response electro-hydraulic servo valve (external mount) — e.g., Moog or domestic aerospace-grade valves

Load cell mounted at piston rod tip for real-time force measurement


4, Anti-Lateral-Force Design

UnitedTest actuators feature spherical joint bearings at both ends (similar to MTS 249 Swivel Base), minimizing damage from lateral forces of the specimen. The modular joint design allows conversion to rear-flange mounting and adjustable bearing clearance.




1) Core Functions of Dynamic Testing (Key Product Selling Points)

High-Frequency Alternating Fatigue Loading

Continuous cyclic tension and compression with up to 10⁷ cycles; measures fatigue limit, S-N curves, and durability life; supports low-cycle and high-cycle fatigue, thermo-mechanical fatigue testing, complies with ASTM E606 and ISO 12106 fatigue standards.

Multi-Waveform Dynamic Simulation

Replicates road bump loads, seismic acceleration waveforms, periodic impacts, and alternating stress; random spectrum loading simulates real service conditions.

Dynamic Stiffness / Damping Testing

Real-time acquisition of load-displacement hysteresis curves, calculates dynamic elastic modulus and damping coefficient for components; key tests for rubber bearings, shock absorbers, and composite materials.

Coordinated Multi-Channel Loading

2~16 actuator channels linked, phase synchronization error <0.1°, enables multi-point synchronized dynamic loading tests for vehicle frames, car bodies, bridge joints, and prefabricated structures.

Dynamic Crack Growth Monitoring

Captures tiny crack growth rates in real time under high-frequency cycles, specialized for fracture mechanics of metals and composites.


2) Static Auxiliary Functions

Static monotonic tension, compression, bending, creep under constant load, and relaxation testing; integrates dynamic and static functions, one actuator covers all testing needs.


3) Intelligent Control & Supporting Functions (UnitedTest Exclusive Software Advantages)

Free switching between force / displacement / strain in a three-closed-loop system with one-click mode change;

Multiple safety protections including overload, overstroke, and low hydraulic pressure, with automatic shutdown;

Automatic full-process data storage, curve export, and standard test report generation;

Remote parameter adjustment, program updates, and remote technical support for overseas clients.

Step 1: System Integration Assembly

Select the UnitedTest servo linear actuator based on test force and stroke range;

Pair with the matching flow servo valve, hydraulic accumulator, and constant-pressure servo oil source;

Mount the actuator using one of three options: trunnion, flange, or ball joint; the ball joint eliminates lateral offset loads;

Connect LVDT displacement sensors and load sensors to a multi-channel servo controller.


Step 2: Hydraulic System Debugging

Fill with special anti-wear hydraulic oil, start the cooling system, and adjust the system working pressure; purge air from the pipelines and check seals for leaks (in line with GB/T 32216 general test requirements for hydraulic servo cylinders).


Step 3: Sensor Calibration

Use the built-in software calibration program to zero the force and displacement, ensuring measurement accuracy meets ISO 7500-1 testing machine standards.


Step 4: Test Program Editing

In UnitedTest dynamic testing software, set control mode (force/displacement), waveform type, frequency, amplitude, number of cycles, and protection thresholds.


Step 5: Dynamic Test Running

Run 100 cycles without load to confirm system stability, then install the test sample and start dynamic loading; monitor load, displacement, and temperature curves in real time, and automatically export data reports when the test is done.


Step 6: Shutdown and Maintenance

Release pressure and clean the piston rod after the test, regularly replace seals and hydraulic oil to extend the actuator's dynamic service life.


1. Automotive Industry (Largest Application Market)

Chassis Components: Suspension, thrust rods, stabilizer bars, leaf springs - dynamic fatigue and reciprocating durability tests;

Body Structure: Frames, subframes, welded joints - multi-channel synchronous road spectrum loading;

Rubber Shock Absorbers: Bushings, shock absorbers - dynamic stiffness and alternating damping tests;

Standards: SAE J1049, ISO 16750, GB/T 30036.


2. Aerospace

Aircraft structural components, wing connectors, hydraulic pipelines - cyclic fatigue;

Aircraft mounts - dynamic impact and high/low temperature coupled dynamic loading;

Compliance Standards: ISO 18387 General Specification for Aerospace Hydraulic Actuators.


3. Medical Devices & Implants (UnitedTest's Advantage Track)

Orthopedic Implants: Artificial joints, spinal supports - dynamic physiological cycle fatigue (ASTM F3067, YY/T 0641);

Cardiovascular Devices: Vascular stents, balloon catheters - cyclic stretching and pulsatile dynamic simulation;

Polymer Medical Materials: PEEK, silicone membranes - alternating mechanical testing.


4. Civil Engineering & Seismic Applications

Reinforced concrete beams, columns, walls - low-cycle repeated seismic loading (ASTM E2126, ASTM E519);

Bridge bearings, seismic isolation rubber - dynamic hysteresis testing;

Geotechnical Engineering: Cyclic triaxial tests, horizontal dynamic load tests for pile foundations (ASTM D5311).


5. New Materials Industry

Metals / Composites: Carbon fiber, aluminum alloy - high/low cycle fatigue, crack propagation tests (ASTM E466, ISO 12106);

Polymer Materials: Plastics, films, rubber - high-frequency dynamic tension and impact testing;

Adhesives & Composite Joints - dynamic shear and peel fatigue testing.


6. Rail Transportation

Rails, sleepers, shock-absorbing fasteners - cyclic dynamic loading;

Train body and bogie components - durability testing, in line with TB/T 3122 industry standards.


7. Universities / Research Labs

General dynamic loading equipment for materials mechanics labs, seismic research institutes, biomechanics labs - supports project R&D and academic paper data collection.

(1) International ISO Standards

ISO 8626: Specifications for the characteristics of servo-hydraulic vibration test equipment (general for dynamic actuators)

ISO 7500-1: Accuracy requirements for static/dynamic testing machine force measurement systems

ISO 12106: Axial force control method for fatigue testing of metallic materials

ISO 18387: General specifications for aerospace hydraulic linear actuators

ISO 11343: Test standards for dynamic peel and cyclic loading of adhesives


(2) US ASTM Standards (high-frequency needs for overseas testing agencies)

ASTM E606: Standard for high- and low-cycle fatigue testing of metallic materials

ASTM E2126: Low-cycle repeated loading test for structural components under seismic conditions

ASTM E466: Axial cyclic fatigue mechanical testing

ASTM F3067: Dynamic fatigue testing for spinal implants (specific for medical implants)

ASTM D5379: Dynamic shear testing of V-notched composite materials


(3) Chinese National/Industry Standards (for domestic clients and export domestic certifications)

GB/T 32216-2015: Hydraulic transmission - Test methods for servo/proportional control hydraulic cylinders (actuator factory inspection)

GB/T 2611: General technical conditions for testing machines

GB/T 14452: Dynamic mechanical testing of bending for metallic materials

YY/T 0641: Industry standard for dynamic fatigue testing of orthopedic implants

GB/T 3766: General safety specifications for hydraulic systems

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Full Range of Self-Developed Customization

Thrust from 1kN to 2000kN, stroke, frequency, and mounting interfaces can be customized as needed; options include hydrostatic bearings, double-rod, mini high-frequency multi-structures, suitable for all dynamic testing scenarios.


Ultra-High Dynamic Performance

Dynamic force retention ≥85%, displacement accuracy ±0.001mm, force control accuracy ±0.5%, maximum operating frequency 100Hz, millions of cycles with low decay.


Global Standard One-Stop Matching

Factory equipment meets ISO/ASTM/GB/T full series dynamic test standards, provides calibration reports recognized by overseas labs, supports CNAS and ILAC certification.


Self-Developed Multi-Channel Coordinated Control System

Equipped with UnitedTest multi-channel servo controllers, up to 16 channels can load simultaneously with minimal phase sync error, software comes with industry-standard test program templates.


Durable, Low-Maintenance Structure

Piston rod coated with Diamalloy wear-resistant layer, imported high-temperature seals, hydrostatic bearings with zero friction loss, annual maintenance cost reduced by 60%; IP65 protection, dustproof and resistant to hydraulic oil contamination.


Global Localized Service

7 service points in China, overseas after-sales teams in Europe, America, and Southeast Asia, offering full equipment installation, calibration, remote debugging, and fast spare parts delivery.


Complete Supporting Ecosystem

Integrated procurement of servo hydraulic power units, accumulators, various test fixtures, high/low-temperature environmental chambers, and dynamic testing software—no need for third-party compatibility adjustments.


When configuring a servo linear actuator, consider these five factors:

Load requirements — determine max./min. load and variation range

Speed requirements — define speed range and variability

Control precision — select appropriate grade based on test standards

Energy efficiency — choose designs with accumulators to reduce flow pulsation

Maintenance convenience — modular design for easy seal replacement

Installation Configurations.


UnitedTest actuators support multiple mounting options:

✅ Front & rear flange

✅ Front & rear spherical joint (articulated)

✅ Foot mounting

✅ Single/Double clevis

Main Technical Specification

Rated force10 kN – 10,000 kN (customizable)
Amplitude±75 mm to ±200 mm
Frequency0.01 Hz – 100 Hz
Force control accuracy±0.5% FS
Displacement accuracy±0.5% FS
Max. operating pressure21 – 28 MPa
Peak frequency responseup to 1000 Hz (hydrostatic bearing type)


FAQ

Q1: What’s the difference between hydraulic servo linear actuators and electric servo cylinders in dynamic testing?

A: Hydraulic servo actuators handle high thrust, high frequency, and are shock-resistant. They are the first choice for heavy-duty dynamic fatigue testing in the thousands of Newtons range and long-cycle operations. Electric servo cylinders are only suitable for low-load, low-frequency static tests. High-frequency heavy loads can cause overheating and damage, so they can’t meet dynamic durability standards for automotive, construction, or aerospace applications.


Q2: Can UnitedTest servo actuators do multi-channel synchronized loading?

A: Yes, they support 2~16 channel linkage. With our self-developed multi-channel servo controller, phase synchronization error is less than 0.1°. This allows multi-point dynamic coordinated loading tests for car bodies, bridges, and prefabricated structures, meeting full-vehicle road simulation requirements.


Q3: Do the actuators meet the ASTM F3067 dynamic fatigue standard for medical implants?

A: The hydrostatic bearing high-frequency servo actuators are designed specifically for implant testing. Their force and displacement accuracy fully match ASTM F3067 and YY/T 0641, can simulate physiological cycle loads, and support medical device registration testing.


Q4: What’s the maximum frequency for dynamic testing?

A: The micro high-frequency series can reach up to 100Hz; the standard general-purpose model is 0~30Hz; the heavy-duty, large-tonnage models are 0~15Hz. High-frequency upgrade options can be customized according to testing needs.


Q5: Can the exported equipment come with international standard calibration certificates?

A: Every actuator comes with a third-party CNAS-accredited calibration report. The data meets ILAC international recognition standards, so labs in Europe, the US, and Southeast Asia can use it directly for standard testing.


Q6: How do servo actuators reduce dynamic cyclic wear?

A: Prefer UnitedTest hydrostatic bearing structures—no metal-on-metal friction. Combined with wear-resistant Diamalloy piston rod coatings and imported high-temperature fluororubber seals, they can handle millions of fatigue cycles without leaks or accuracy drift.

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Beijing United Test Co., Ltd.