Detection of spring fatigue and relaxation rate

1. Requirements for spring fatigue detection
All springs subjected to variable loads must be tested for fatigue in the process of internal quality control, user inspection, new product approval, certification, industry sampling and process adjustment. 999 new full news. Test methods can be used for fatigue life test or reliability assessment test, 999 new full news. But for the classification and certification of products, reliability assessment exams must be used to assess their reliability indicators.
See Table 1 for the testing institutions, testing notifications and testing cycles required for different testing purposes.
Testing institutions, notifications and cycles required for different testing purposes
Inspection of inspection target inspection organization inspection report inspection period
Life selection company or quality inspection agency recognized by the company-held at any time
Process adjustment enterprise or quality inspection agency recognized by the enterprise-synchronized with the process adjustment cycle
Internal quality control company or quality inspection agency recognized by the company-at most once every six months
The agreement between the two parties for the user’s inspection-synchronized with the inspection cycle
Industry sampling inspection of new products, finalization and appraisal of government-authorized or designated quality inspection agencies at or above the ministry (provincial) level, complete measurement certification marks are held when needed
The third-party quality inspection agency authorized by the certification country, approved by the National Laboratory Accreditation Committee, and designated by the certification committee, 999 Xin Quanxun. Complete measurement certification marks and laboratory certification marks are held when needed
For different testing purposes and product types, the minimum required number of test cycles is shown in Table 2. 999 new full news.
Table 2 Minimum number of test cycles (times) specified by spring product type and test purpose
Product Type Industry Sampling Verification Type Verification Certification
Valve spring
Regulating spring
Plunger spring 1×10
Hydraulic spring
Suspension springs are selected according to classification standards
After the fatigue test for the specified number of cycles, the spring relaxation rate tolerance is specified in accordance with the corresponding standards. When the standard does not stipulate, the mandatory inspection shall be determined by the inspection unit, and the non-mandatory inspection shall be practiced as required by the user or the inspected unit.
For the reliability evaluation test, the qualified crystal, first-class and first-class products of the spring should reach the reliability level specified in Table 3 after the specified test conditions and cycle times. Sunny The reliability of the fatigue life of the product to be certified must reach the reliability index of the first-class product. 999 new full news website.
Table 3 Reliability index of product grade and fatigue life
Product grade reliability R (%)
Class A
First grade
Qualified product 99.99
2. Spring fatigue test sample
1) The sample should be manufactured in accordance with the technical documents approved by the prescribed procedures and inspected to be qualified.
2) Samples should be randomly and independently selected from the same batch of products, and the distinction between inspection batches should be in accordance with JB/T practice.
3) Number of samples:
For the fatigue life test, the number of samples should be no less than 5 sets for the mobilization machine with 4 cylinders or less; the mobilization machine with 4 cylinders or more, the new full news. The sample size is not less than 3 sets;
For the reliability evaluation test, the number of samples is determined according to Table 6-6.
3. Spring fatigue test machine
1. Using mechanical, electromagnetic resonance or electro-hydraulic servo test machine, 50 Xin Quanxun Network. A supporting host is also available. When using electromagnetic resonance test machine, the test amplitude should not be too large.
2) The error of the test machine should be in accordance with relevant regulations.
3) The frequency of the test machine should be adjustable within a certain range to meet different test requirements.
4) The test machine should generally have a complete function: test time or frequency preset function; (hardware spring) active timing or counting function; test amplitude emergence or control function; active shutdown function.
4. Spring fatigue test frequency
1) The test frequency can be determined according to the frequency range of the test machine and the actual professional frequency of the spring. In addition to the random load test, Sunny The examination frequency should be kept constant throughout the examination process.
2) The examination frequency γr should be the same as the natural natural frequency of a single examination spring, satisfying (γ/γr)>10.50 γ is calculated according to formula (7-79).
5. Spring fatigue test amplitude The amplitude is divided into displacement amplitude and stress amplitude. Generally, the displacement amplitude is used as the test amplitude for the fatigue life test and reliability evaluation test of the coil spring. 999 new full news.
6. Spring fatigue test procedure Refer to Chapter 6 Section 5 Spring fatigue test.
7. Selection of spring effective mode When the spring is exhausted, the effective mode is divided into two types: fracture and loss of specified effectiveness due to relaxation. Detection of spring fatigue and relaxation rate. Following the effectiveness requirements of the spring, one or two of them can be selected as the effective mode of fatigue life.
8. Evaluation of spring fatigue test results
1) Judgment of fatigue life: the maximum number of cycles of the tested spring under the given effective conditions, the spring. It is the fatigue life of the spring.
2) Verification of fatigue life: After a given number of cycles of the test, if the spring does not take effect, the verification test is passed.
3) Reliability verification: According to the given reliability target value, fatigue. According to Table 6-6, determine the appropriate sample number n, and perform the test under the specified test conditions and requirements. Judge by the effective mode requested. If the number of passes obtained is greater than the minimum required number r in the table, the examination will pass, otherwise it will fail.
4) Spring relaxation rate: the spring relaxation rate ε is expressed as the percentage of load loss after the spring test: relaxation.
Where F-spring load measured before the test;
Fi-spring load measured after the exam.