Detailed explanation of the testing standards and methods of electro-hydraulic servo fatigue testing machine in the field of composite materials

1. The rigid need for fatigue testing under the wave of lightweight composite materials

As the process of lightweighting new energy vehicles accelerates, the application proportion of carbon fiber composite materials (CFRP) and glass fiber composite materials (GFRP) in body panels and structural parts continues to increase.The anisotropy and complex damage mechanism of composite materials make fatigue performance evaluation much more complex than that of metallic materials.Electro-hydraulic servo fatigue testing machineWith its large load, high precision and multi-mode loading capabilities, it has become the preferred equipment for fatigue testing of composite materials.

Shandong Huayan Intelligent Equipment Group Co., Ltd.Electro-hydraulic servo fatigue testing machineseries, supports multiple fatigue loading modes such as tension-tension, tension-compression, and compression-compression. It can complete fatigue performance testing of polymer-based composite materials in accordance with ASTM D3479, ISO 13003, GB/T 35465 and other standards, providing reliable data support for the research and development of automotive composite materials.

2. Common standards for fatigue testing of composite materials

2.1 International standards (ASTM series)

2.2 International standards (ISO series)

• ISO 13003: Fiber-reinforced plastic composites—Determination of fatigue properties under cyclic loading.
• ISO 12106: Metallic material fatigue testing—axial force control method (for composite-metal hybrid structures).

2.3 National standards (GB/T series)

• GB/T 35465-2022"Test Method for Fatigue Performance of Polymer Matrix Composite Materials": The core standard for fatigue testing of composite materials in China, covering tension-tension, tension-compression, and compression-compression cycle modes.
• GB/T 3354-2014"Test Method for Tensile Properties of Oriented Fiber Reinforced Polymer Matrix Composites": Static Tensile Benchmark Test.
• GB/T 1448-2005"Test Methods for Compression Properties of Fiber Reinforced Plastics": Static Compression Benchmark Test.
• GB/T 16779: Test method for tensile-tensile fatigue properties of fiber-reinforced plastic laminates.

2.4 Specific standards for the automotive industry

• T/CSAE"Performance Evaluation of Automotive Carbon Fiber Front Cabin Covers": It stipulates that the tensile strength of CFRP front cabin covers for vehicles is ≥500MPa, the tensile elastic modulus is ≥40GPa, and the bending strength is ≥400MPa.
• Corporate standards of various OEMs (BYD, SAIC, GAC, Geely, Great Wall, Tesla engineering specifications).

3. Sample requirements

3.1 Tensile fatigue specimen (ASTM D3479 / GB/T 35465)

• Sample form: A rectangular laminate spline with reinforcement sheets (usually aluminum alloy or fiberglass sheets) pasted on both ends.
• Size reference: Thickness 2-4mm; width 12.7mm (ASTM standard) or 15mm (GB standard); gauge length 100-150mm.
• Layer design: The layering sequence needs to be clear, such as [0/±45/90]ns symmetrical layering.

Preparation requirements:

• Low-speed diamond water-cooled cutting to avoid thermal damage
• Edges are water-polished to eliminate cutting defects
• The fiber direction must be parallel to the direction of stress
• There should be no glue overflow or layered micro-cracks in the gauge area.
• The thickness error of the same batch is controlled within ±0.1mm

3.2 Bending fatigue specimen

• For rectangular strip specimens, the four sides are chamfered after cutting to eliminate stress concentration.
• Do not over-sand the surface fibers.
• Sandwich specimens must be strictly prevented from debonding between the panel and the core material.

3.3 Delamination fatigue specimen (ASTM D6115)

• Double cantilever beam (DCB) specimen with a polytetrafluoroethylene film pre-placed in the middle as the initial layering.
• Unidirectional fiber reinforcement, the fiber direction is consistent with the crack propagation direction.

3.4 Automotive composite component specimens

• Subassembly fatigue testing can be performed using actual components (such as carbon fiber hoods, floors).
• The loading method and support boundary conditions need to be designed according to the actual stress conditions of the component.

4. Test method

4.1 Tensile-tensile fatigue (R>0)

• load pattern: Tension-tension cycle, stress ratio R=σmin/σmax>0, commonly used R=0.1.
• Control method: Stress control (Procedure A) constant amplitude stress cycle tests life; strain control (Procedure B) constant amplitude strain cycle is suitable for low cycle fatigue.
• frequency selection: Usually 1-10Hz, the sample temperature needs to be monitored to avoid changes in the properties of the resin matrix caused by self-heating.
• Termination condition: The specimen breaks completely, the stiffness drops beyond a threshold (usually 50% of the initial stiffness) or the predetermined number of cycles is reached.

4.2 Tension-compression fatigue (R<0)

• load pattern: Pull-compression complete reverse cycle, R=-1.
• Technical difficulties: During the compression stage, the specimen needs to be prevented from buckling, and a lateral support device needs to be configured.
• Advantages of electro-hydraulic servo fatigue testing machine: Strong bidirectional loading capability and high compression load control accuracy.

4.3 Compression-compression fatigue

• load pattern: Pressure-pressure cycle, R>1.
• Suitable for composite components mainly subjected to compressive loads (such as composite columns, floors).

4.4 Fatigue delamination initiation test (ASTM D6115)

• A cyclic expansion load was applied to the DCB specimen.
• Gradually reduce the load level and determine the starting threshold Gth for type I fatigue delamination.
• Evaluate the resistance of composite structures to delamination expansion.

4.5 Stiffness degradation monitoring

• The typical characteristic of fatigue damage in composite materials is the gradual decrease in stiffness with the number of cycles.
• The elastic modulus of the specimen is measured periodically during the test (such as every 10^4 cycles).
• Draw the stiffness degradation curve as an important indicator of fatigue damage evolution.

4.6 Environmental Coupling Fatigue Test

• It can be carried out in a high and low temperature environmental chamber to simulate the extreme operating temperatures of automobiles (-40℃~+85℃).
• The influence of the environment on the fatigue properties of composite materials can be studied in combination with the hot and humid environment (temperature + humidity).
• Shandong HuayanElectro-hydraulic servo fatigue testing machineIt can be equipped with an environmental chamber to achieve multi-field coupling fatigue testing.

5. Precautions for model selection

5.1 Load capacity

• Laboratory grade material sample testing: 10-50KN is sufficient.
• Automotive composite material components (cabin cover, floor) sub-assembly testing: 50-200KN.
• Large composite structural parts: above 200KN, multi-channel coordinated loading is required.

5.2 Bidirectional loading capability

• Composite material fatigue testing often requires tension-compression bidirectional loading, and the compressive load capacity of the equipment must be confirmed.
• Electro-hydraulic servo models are superior to electronic servo models in terms of bidirectional loading.

5.3 Waveform and frequency

• Waveforms such as sine waves and triangle waves must be supported.
• The frequency range is 0.1-50Hz, which can meet the fatigue testing needs of most composite materials.
• High-frequency testing requires attention to the heating problem of the sample, and it is recommended to equip it with temperature monitoring.

5.4 Fixture system

• Composite material specimens require special wedge clamps or hydraulic clamps to avoid premature fracture caused by stress concentration at the clamping end.
• Need to be equipped with reinforcement sheet pasting process guidance.
• Bending fatigue requires three-point/four-point bending tooling.

5.5 Strain measurement

• Composite material fatigue testing requires accurate strain measurement, and it is recommended to equip extensometers or strain gauges.
• Non-contact video extensometer is preferred to avoid damage to the specimen caused by contact extensometer.

5.6 Data processing software

• It is necessary to support S-N curve drawing, stiffness degradation curve, and fatigue limit calculation.
• Supports data export to common formats (Excel, CSV) to facilitate subsequent analysis.

6. Advantages of Shandong Huayan electro-hydraulic servo fatigue testing machine in the field of composite materials

Shandong Huayan Intelligent Equipment Group Co., Ltd.Electro-hydraulic servo fatigue testing machineHas the following characteristics:

1. Multiple load level coverage: From 10KN to 4000KN, meeting the testing needs from material level to component level.
2. High-precision closed-loop control: The force control accuracy is better than ±0.5%, and the displacement resolution is 0.01mm.
3. Multi-mode loading: Supports various fatigue modes such as tension-pull, tension-compression, compression-compression, and bending.
4. Can be equipped with environmental box: Achieve multi-field coupling fatigue testing such as high and low temperature, humidity and heat.
5. Customization capabilities: Special fixtures and tooling can be customized according to the shape of automotive composite components.
6. Own measurement and testing: Ensure the accuracy of the testing machine and the reliability of the data through its own measurement and testing company.

Electro-hydraulic servo fatigue testing machine directly supplied from the manufacturer, an overall solution for composite material fatigue testing.

Consultation hotline: 13465928815

Company official website: www.huayantest.cn