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Spring Fatigue Test Result Evaluation

- May 29, 2018 -

Professional overview of methods for detecting spring fatigue performance and relaxation rate

one. Spring fatigue testing requirements

Springs subjected to variable loads must be tested for fatigue performance within the company's internal quality control, user inspection, new product identification, certification, industry sampling, and process adjustment. The test method can be used for fatigue life verification test or reliability assessment test. However, for product classification and certification, reliability assessment test must be used. Assess its reliability index.

The inspection organization, inspection report and inspection cycle required for different inspection purposes are shown in Table 1.
Detection mechanisms, reports, and cycles required for different testing purposes

 Purpose of inspection Testing organization Inspection report Inspection cycle Life cycle Screening of quality inspection organization recognized by the company or enterprise - Process adjustment at any time Enterprise or company recognized quality inspection organization - Synchronized with process adjustment cycle Internal quality control Enterprise or enterprise recognized quality inspection agency - at least Once every six months, the user submits the agreement to both parties - Synchronize with the inspection cycle. Industry sampling for new products. Formal identification. Government authorized or designated ministry (provincial) level or above. The third-party quality inspection agency designated by the accreditation committee shall have a measurement certification mark and laboratory certification mark when required.

For the fatigue life verification test, the number of specimens below 4 cylinders shall not be less than 5 sets; for engines of 4 or more cylinders, the number of specimens shall not be less than 3 sets;

For reliability assessment tests, the number of specimens is determined according to Table 6-6.

IV. Spring fatigue test frequency

1) The test frequency can be determined according to the frequency range of the tester and the actual operating frequency of the spring. In addition to the random load test, the test frequency should be kept constant throughout the test.

2) The test frequency γr shall be equal to the inherent natural frequency of a single test spring, satisfying (γ/γr) >10. Gamma is calculated according to formula (7-79).

Fives. Spring fatigue test amplitude amplitude is divided into displacement amplitude and stress amplitude. For the fatigue life verification test and reliability evaluation test of the coil spring, the displacement amplitude is generally used as the test amplitude.

VI. Spring Fatigue Test Procedure Refer to Section 6, Section 5 Spring Fatigue Test.

Seven. Selection of Spring Failure Modes During fatigue testing, the springs are divided into two types: fracture and loss of the prescribed function due to relaxation. Depending on the functional requirements of the spring, either one or two of them can be selected as failure modes for fatigue life.

Eight. Spring fatigue test result evaluation

1) Determination of fatigue life: Under a given failure condition, the maximum number of cycles reached by the tested spring is the fatigue life of the spring.
2) Verification of fatigue life: After a given number of cycles, if no failure occurs in the spring, the verification test passes.

3) Reliability verification: According to the given reliability target value, determine the appropriate sample number n according to Table 6-6, test under the specified test conditions and requirements, and judge according to the required failure mode. If the qualified number obtained is greater than the minimum qualified number r required in the table, the verification test passes and if not, it passes. Dongguan hardware spring

4) Spring relaxation rate: The relaxation rate ε of the spring is expressed as a percentage of the load loss after the spring test:

    Where F - the spring load measured before the test;
    Fi - The spring load measured after the test.

The relaxation rate after fatigue test should be within the range specified by the pattern.

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