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Common issues with fatigue testing

This experiment is mainly used for torsional fatigue testing and static torsional stiffness strength testing of vehicle transmission shafts, half shafts, and various shaft components and materials. It is widely used in aerospace, military, ground vehicles, higher education, quality inspection and other fields. Implementing standard EN12663.1-2010 "Structural Requirements for Railway Vehicle Bodies in Railway Facilities Part 1 Selection Methods for Locomotives, Railway Passenger Vehicles, and Railway Freight Vehicles"

Fatigue testing of automotive components is the core means of evaluating the durability of parts under long-term alternating stress, which can help you accurately predict the life of parts, optimize design, and ensure safety and compliance. Here are the key points:

 

1、 Test purpose
Evaluate structural integrity: Verify the reliability of parts in long-term use by simulating cyclic loads.
Determine fatigue life: Identify the risk of crack initiation and propagation to avoid sudden failure.
Optimization design: providing data support for lightweighting or structural improvement.
Compliance verification: Meet international and industry standards such as ISO and SAE.
 

2、 Test type
Stress control test: Maintain a constant stress amplitude and measure fatigue life.
Strain control test: Evaluate low cycle fatigue performance.
Load spectrum test: Simulate based on measured road loads.
Rotation bending test: applicable to shaft components.
Torsion fatigue test: Evaluate the characteristics under torsional load.
Composite load test: Simulate multiple loads acting simultaneously.
 

3、 Testing process
Sample preparation: Randomly select 3-5 samples and inspect the surface for defects.
Plan formulation: Set the load type, amplitude, frequency, and number of cycles.
Installation adjustment: Customize specialized fixtures to ensure that the load direction is consistent with the actual working conditions.
Pre test: Determine the approximate fatigue limit.
Formal experiment: Follow the plan and monitor real-time data such as load and displacement.
Termination determination: Based on fracture, cycle count, or performance degradation.
Post test inspection: Analyze the fracture surface and measure the amount of deformation.
Data processing: Draw S-N curves and issue testing reports.
 

4、 Testing standards
International standards: ISO 12107:2012, ISO 11439.
National standards: GB/T 3075-2008, GB/T 15248-2008.
Industry standards: SAE J2380, QC/T 491.
 

5、 Testing equipment
Electro hydraulic servo fatigue testing machine: Simulate and measure the power spectral density function.
Electromagnetic resonance testing machine: suitable for high-frequency testing.
Multi axis loading system: simulating complex working conditions.
Crack monitoring devices: such as acoustic emission and strain gauges.
 

6、 Test conditions
Load type: sine wave, triangular wave, square wave, or actual load spectrum.
Stress/strain level: Set multi-level levels according to the working conditions.
Loading frequency: usually 1-200Hz.
Stress ratio (R value): -1 (symmetric cycle), 0 (pulsating cycle), or a specific value.
Environmental conditions: normal temperature, high temperature, low temperature, or corrosive environment.
Cycle times: 10 ⁴ -10 ⁷ times.

 

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