The main purpose of the experimental system is:

The fatigue loading test system is suitable for conducting static compression tests and unidirectional dynamic pulsation fatigue tests on various large components such as concrete structural components, sleepers, steel strands, anchorages, bridges, various trusses, automobile chassis, automobile front and rear axles, locomotive frames, various springs, and various large components. Due to the much lower energy consumption of open-loop pulse fatigue testing system compared to servo fatigue. The mechanical structure of the servo fatigue testing machine is more robust and aesthetically pleasing, and the working platform can be raised and lowered.

Combining the above two advantages, the fatigue testing machine designed by our company has an open-loop control system and a mechanical structure of a servo fatigue testing machine. Below are sketches and on-site photos of customers for this type of equipment

1、 System Introduction:

1.1 Composition and main functions of hydraulic pulse generator:

1.1.1 Host (Pulsator): The host is a mechanism that generates high-pressure pulsating oil, consisting of an excitation speed regulating motor, an adjustable eccentric crankshaft connecting rod mechanism, a pulsating oil cylinder, a load holding valve, a dedicated oil pump, and a lubrication system. Refer to Figure 3 for the appearance.

Figure 3: Photo of the Hydraulic Pulsator Main Unit

1.1.2 The main engine (pulsator) generates pulsating hydraulic oil in the system through the up and down reciprocating motion of the pneumatic cylinder piston with an adjustable eccentric crankshaft connecting rod mechanism, and its motion law conforms to a sine wave. The pressure of pulsating oil is adjusted through a load holding valve, and the magnitude of pulsation is achieved by adjusting the eccentricity of the eccentric crankshaft connecting rod mechanism. The working principle of the testing machine is that the motor simultaneously drives the crank connecting rod rocker mechanism and the hydraulic oil pump. The rotary motion of the motor is converted into linear reciprocating motion through the crank connecting rod rocker mechanism, causing the pulsating hydraulic oil cylinder to generate pulsating hydraulic oil, thereby driving the actuator to apply test force to the tested object. The motion law of the crank connecting rod rocker mechanism is a sine wave, and the output test waveform of the actuator is an asymmetric sine wave. The pressure of pulsating oil is adjusted through a load holding system, and the pulsation is achieved by adjusting the eccentricity of the crank connecting rod rocker mechanism. The testing force of the testing machine, the peak values of the testing force, and the continuous and stepless adjustable testing frequency.

The lubrication system mainly consists of a lubrication oil pump, dedicated relays, and pipelines. The pipeline of the lubrication system leads to various rotating joints and moving parts, and circulates lubrication to all moving parts to ensure that the testing machine can operate continuously for a long time. At the same time, the lubrication oil pump can also quickly fill the pulsator to make the actuator plug move quickly to the working position.

1.1.4 The machine is equipped with a dedicated oil pump to provide hydraulic oil for the pulsation system, which can fully meet the fatigue test requirements of different frequencies. The excess oil flows back to the oil tank through the overflow system of the load holding valve, and the dedicated oil pump can meet the long-term fatigue test requirements of the machine. The load holding system has the characteristics of sensitivity and reliability.

The rotating part of the host adopts specially developed needle roller bearings, which have the characteristics of large width, uniform load bearing, low friction force, and can withstand long-term alternating loads.

1.1.6 The testing machine has a complete lubrication mechanism. The lubrication system mainly consists of a dedicated lubrication oil pump, an electrical control system, and lubrication pipelines. It automatically controls the forced lubrication and cooling of various rotating and moving mechanisms to ensure that the testing machine can operate continuously for a long time. At the same time, the lubricating oil pump also has the function of quickly filling the pulsating oil cylinder, so that the actuator can quickly reach the working position.

During the testing process, if phenomena such as specimen damage, overload of testing force, failure to reach the set number of tests, lubrication system failure occur, the testing machine has automatic alarm and shutdown functions.

The testing machine adopts low-speed smooth start, flywheel energy storage and stabilization, and closed working oil chamber pulsation technology to reduce the power of the driving motor and effectively reduce the energy consumption of the test.

1.1.9 Configure fast unloading valve and fast oil filling valve to achieve fast unloading of the testing machine and fast oil filling of the actuator;

1.1.10 Suitable for installing multiple actuators of different specifications for multi-point synchronous loading tests. Up to 5 actuators can be connected simultaneously for synchronous loading testing.

1.2 Electrical control system:

1.2.1 The electrical control system realizes automatic control and manual adjustment of the testing machine; It has functions such as test force calibration, reset, dynamic and static measurement conversion, as well as test force setting, overload protection, and preset test times.

1.2.2 Equipped with alarm display devices for lubrication faults, sample fracture vibration protection, etc.

1.2.3 The pointer displays the test frequency and the working current of the main motor.

1.2.4 Configure electrical control and operation buttons for increasing and decreasing test force, rapid unloading, amplitude increase and decrease, rapid oil filling, increasing and decreasing operating frequency, main engine start and stop, main on and main off.

1.2.5 LCD displays static test force, dynamic test force peak, valley force value, test frequency and other functions.

Figure 4: Control Cabinet Photo Figure 5: Display Window Photo

1.3Actuator:

The actuator is the executing mechanism of the testing machine that applies the test force. Specially designed pulsating (unidirectional) loading actuator, suitable for simulating unidirectional alternating load scenarios. It is an independent kit with different specifications, which users can choose freely according to their experimental needs and can be installed and used in different forms and situations.

When the hydraulic oil of the pulsator enters the actuator cylinder, it pushes the piston to move, passes through the screw, and the pressure head to apply the test force on the specimen. By turning the handle, the extension of the screw can be adjusted. Different actuators are equipped with extension tubes of different specifications, which can be selected according to the needs of the experiment. A locking nut is installed on the adjusting screw to tighten the screw.

A steel ball is installed between the base and the oil cylinder for centering and alignment. When loosening the screw pressure plate (or nut), the oil cylinder can be rotated to connect the oil pipe, but applying test force requires all the loosened parts to be tightened. When conducting the test, loosen the air release screw above to eliminate air before tightening.

There are several tension springs installed around the actuator, mainly used to balance the weight of moving parts such as pistons. On moving parts such as pistons, there are weight markings and stiffness value markings on the tension spring. These values are used for dynamic error correction, and based on the weight balance, it is allowed to remove the tension spring symmetrically.

On the actuator base, there are four adjustment screws, adjustment nuts, springs, and indicator scales. The numbers 1, 2, and 3 are engraved on the scale, and the corresponding positions are adjusted according to the installation form of the actuator.

1.3.1 The specially designed pulsating (unidirectional) loading actuator outputs an asymmetric sine waveform, suitable for simulating unidirectional alternating load test conditions.

1.3.2 Configure actuators according to user requirements, with five specifications: 25KN, 50KN, 100KN, 250KN, and 500KN. Install them vertically on a dedicated force frame and work synchronously to apply pulsating test force to the sample.

1.3.3 The plunger mechanism is equipped with multiple springs that can adjust the pressure to balance the mass of the moving parts. The base and force plate are spherical hinge mechanisms, which can effectively counteract the lateral force during the test process.

1.3.4 Configure and adjust the screw and extension tube to meet the requirements of a large working space.

1.3.5 Installation, adjustment, indication devices, and specialized pipelines for oil discharge and reflux; Connect to the main pulsation generator through a dedicated pipeline.

Figure 6: Photo of the actuator

1.4 Computer control system:

1.4.1 The computer screen displays static test force, dynamic test force peak values, test waveforms, controls the printer to print test reports, and the control system has overload protection function.

1.4.2 The system has complete file operation functions for storing test curves and test data; At the same time, experimental data can be stored in text form for users to perform secondary data processing.

1.4.3 Use authentication and password login to set operational permissions.

1.4.4 The test software has a good human-machine interface, which is easy to operate and manage. The software can run on the Windows 98/2000/XP/NT Chinese operating system, and can complete the monitoring and management of the test process, as well as the processing of test data. The real-time displayed test data is consistent with the actual data unit and does not require secondary calculations.

Figure 7 Experimental Software Interface

1.5 Pipeline:

The pipeline adopts dedicated metal high-pressure pipes or high-pressure hoses, which facilitate the position adjustment of the actuator.

2、 Main technical indicators:

3、 Equipment configuration list:

3.1 One hydraulic pulse generator

3.2 One control cabinet

3.3 One 500KN actuator

3.4 One computer

3.5 HP A4 laser printer, one unit

3.6 Coarse pipeline and its sealing components (applicable to actuators above 100KN, pipeline of 20 meters), one set

3.7 One vibration protector

3.8 One set of specialized tools

3.9 Test specific accessories (designed according to user test requirements), one set