GB/T 4337-2015 English PDF (GBT4337-2015)
GB/T 4337-2015 English PDF (GBT4337-2015)
GB/T 4337-2015: Metallic materials -- Fatigue testing -- Rotating bar bending method
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
Replacing GB/T 4337-2008
Metallic materials - Fatigue testing - Rotating bar bending
(ISO 1143:2010, Metallic materials - Rotating bar bending fatigue testing, MOD)
ISSUED ON: SEPTEMBER 11, 2015
IMPLEMENTED ON: JUNE 01, 2016
Issued by: General Administration of Quality Supervision, Inspection and Quarantine;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 5
4 Symbols and designations ... 6
5 Test principle ... 7
6 Shape and size of specimen... 7
7 Preparation of specimens ... 8
8 Accuracy of test equipment ... 11
9 Heating and temperature measuring devices ... 11
10 Test procedures ... 11
11 Presentation of test results ... 14
12 Test report ... 15
Annex A (normative) Verification of bending distance of rotary bending fatigue testing machine ... 22
Metallic materials - Fatigue testing - Rotating bar bending
This Standard specifies the rotational bending fatigue test method for metallic materials. This Standard applies to the fatigue test of metallic materials under the condition of rotating and bending of specimens at room temperature and high temperature in air. Rotational bending fatigue tests in other environments (such as corrosion) can also be performed with reference to this Standard.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. GB/T 3075, Metallic materials - Fatigue testing - Axial force-controlled method (GB/T 3075-2008, ISO 1099:2006, MOD)
GB/T 10623, Metallic material - Mechanical testing - Vocabulary (GB/T 10623- 2008, ISO 23718:2007, MOD)
GB/T 13634, Metallic materials - Calibration of force-proving instruments used for the verification of uniaxial testing machines (GB/T 13634-2008, ISO 376:1999, IDT) GB/T 24176, Metallic materials - Fatigue testing - Statistical planning and analysis of data (GB/T 24176-2009, ISO 12107:2003, IDT)
GB/T 26077, Metallic materials - Fatigue testing - Axial-strain-controlled method (GB/T 26077-2010, ISO 12106:2003, MOD)
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in GB/T 3075, GB/T 10623, GB/T 24176 and GB/T 26077 as well as the followings apply.
process of changes in properties which can occur in a metallic material due to the test medium shall be indicated in the report.
6.2 Dimensions of specimens
Specimens used in the same batch of fatigue tests shall have the same diameter, the same shape and dimensional tolerances.
To accurately calculate the applied force, the measurement of the actual minimum diameter of each specimen shall be accurate to 0.01mm. Before the test, it shall be ensured that the surface of the specimen is not damaged when measuring the size of the specimen.
For cylindrical specimens subjected to constant bending (see Figures 4 and 5), the parallelism of the test section shall be guaranteed to be within 0.025mm. For other shapes of cylindrical specimens (see Figure 1), the parallelism of the test part shall be ensured within 0.05mm. The radius of the transition arc between the specimen holding part and the experimental part shall not be less than 3d. For funnel-shaped specimens, the arc radius of the test section shall not be less than 5d.
Figure 8 shows the shape and dimensions of the cylindrical specimen. Recommended diameters d are 6mm, 7.5mm and 9.5mm. The deviation of diameter d shall not be greater than 0.005d. Figure 9 shows the recommended high temperature fatigue test circular arc smooth specimen (hazardous section).
Since the shape and size of notched specimens are not standardized, this Standard does not cover notched fatigue tests. However, the fatigue testing procedures described in this Standard can be applied to notched fatigue specimens.
7 Preparation of specimens
When determining the rotating bar bending fatigue properties of the material, the following requirements for specimen preparation shall be noted. If the test procedure is designed to determine the effect of a factor (surface treatment, oxidation and so on) that is not in line with the sample preparation requirements, it is possible to deviate from the specimen preparation requirements. Any deviation in each case shall be noted in the report.
7.2 Sampling and marking
Sampling location, sampling direction and sample type shall be in accordance with the relevant product standards or mutual agreement.
Sampling from semi-finished products or parts can affect the test results. It is therefore necessary to take samples under fully informed conditions.
Sampling drawings shall be attached to the test report. It shall be clearly stated of: - Location of each specimen;
- Characteristic direction of semi-finished product processing (rolling direction, extrusion direction and so on);
- Identification of each sample.
Specimens shall be identified at each stage of processing. Reliable methods shall be taken to ensure that the marking will not disappear during processing or affect the results of the test. Each specimen needs to be engraved with unique marks on both ends of the specimen when the final machining is completed. It is ensured that each half of the specimen can be clearly identified after fracture of the specimen fatigue test. 7.3 Processing
7.3.1 Heat treatment of test materials
If heat treatment is performed after rough machining, it is recommended that final polishing be performed after heat treatment. Otherwise, heat treatment shall be carried out under vacuum or inert gas to prevent oxidation of the specimen. Heat treatment shall not alter the microstructural properties of the material under study. Details of heat treatment and machining procedures shall be noted in the test results.
7.3.2 Machining requirements
Machining may generate residual stresses on the surface of the specimen. These residual stresses may be caused by thermal gradients during the machining phase or by material deformation or changes in the microstructure. The effect of residual stress does not need to be considered in high temperature fatigue test. This is because the residual stress has been fully or partially released during the specimen holding process. However, suitable machining methods shall be adopted to reduce residual stress, especially in the final polishing stage. For harder materials, it is better to select the grinding process. - Grinding: The machining allowance of the specimen before grinding is +0.1mm. Grinding is carried out at a grinding speed not exceeding 0.005mm/r.
- Polishing: Remove the final 0.025mm machining allowance with different sandpapers with progressively smaller grains. It is recommended that the final polishing direction shall be along the axis of the specimen.
Changes in material microstructure may be caused by temperature increase and strain hardening during machining. It may undergo a phase change or in more cases recrystallization of the surface. The test is invalid because the tested material is no longer the original material. Some materials affect mechanical properties due to the presence of certain elements or compounds. A typical example is the effect of chloride ions on steel and titanium alloys. Contact with these elements shall be avoided during 8 Accuracy of test equipment
Different types of rotary bending fatigue testing machines are available. Figures 1 to 7 illustrate the principles of several main types of testing machines. Figure 11 shows the test principle of a rotary bending fatigue machine. The operation of the testing machine shall meet the following requirements: the maximum allowable value of the bending moment error is ??1% (see Annex A).
9 Heating and temperature measuring devices
9.1 The specimen is heated with a heating device such as a resistance furnace. 9.2 Furnace temperature shall be kept uniform. The working part of the specimen shall be within the length of the furnace. The temperature gradient is not more than 15??C. 9.3 Thermocouples, compensating wires, temperature control and temperature measuring instruments used for measuring or recording temperature shall be checked regularly. The verification period shall conform to product standards, customer requirements and good measurement practices.
9.4 The resolution of the temperature indicating device is at least 0.5??C. The minimum resolution of the temperature measuring device is 0.5??C. The maximum allowable error is ??1??C.
10 Test procedures
10.1 Mounting the specimen
Mount each specimen so that the test portion is not subjected to stresses other than the applied force.
To avoid vibration during the test, the coaxiality of the specimen and the drive shaft of the testing machine shall be kept within close limits. The maximum radial runout of the spindle is ??0.025mm. The radial maximum runout of the free end of the cantilever testing machine for single-point or two-point loading is ??0.013mm. For other types of rotating bending fatigue testing machines, the radial runout at both ends of the actual working part shall not be greater than ??0.013mm. The required concentricity shall be met before force is applied.
10.2 Application of force
The leverage ratio shall be calibrated in accordance with Annex A of this Standard. The test stress is calculated according to Table 2.
11.2 Graphical presentation
The most common graphical representation of fatigue test data is the S-N diagram, as shown in Figure 10. The abscissa represents the fatigue life Nf. Indicate the maximum stress, stress range or stress amplitude on the ordinate. A linear scale is generally used, but a logarithmic scale can also be used. Fit each data point with a straight line or curve to get the S-N curve diagram. The S-N diagram described by the above procedure has a 50% survival rate when the log life is normally distributed. However, a similar procedure can be used for other S-N curve diagrams of survival.
The S-N curve diagram shall at least include the material grade, material grade and tensile properties, surface condition of the specimen, stress concentration factor of the notched specimen (if required), type of fatigue test, test frequency, environment and test temperature.
12 Test report
In the fatigue test report, the test conditions shall be clearly stated and shall include the following information:
a) Reference to this Standard;
b) Metallurgical properties of tested materials and materials. The standard to which the material is manufactured;
c) Method of afterburning and type of testing machine used;
d) Type, size and surface condition of the specimen, number of points of application; e) Frequency of stress cycles;
f) Test temperature. If the self-heating temperature of the sample exceeds 35??C, the specimen temperature shall be indicated;
g) Maximum and minimum daily room temperature and humidity (according to negotiation);
h) Criteria for the end of the test, such as 2 ?? 106 or complete failure of the specimen or other criteria;
i) Any deviation from the required conditions during the test;
j) Test results.
Verification of bending distance of rotary bending fatigue testing machine A.1 General
There are two verification methods for the rotary bending fatigue testing machine. Both methods can be used and can give comparable results. The first method is dimension measurement and subsequent calculation methods. The second method is the strain gauge specimen method. Both methods can be used and can give comparable results. This appendix lists verification equipment, pre-verification inspections, verification procedures (dimensional measurement or strain gage test method), evaluation of verification data and acceptance criteria.
A.2 Equipment to be verified
A range of equipment is used for the calibration of rotary bending fatigue testing machines. Traceable force values are guaranteed by calibrated weights or force sensors. If the testing machine includes levers and calipers, calibrated weights and force transducers shall be used at the same time when calibrating the machine. The length measurement of the lever arm requires the use of a calibrated micrometer or caliper. A.2.2 Weight mass
The accuracy of the mass of the added weight during the verification process shall be better than or equal to ??0.1%. And at least every 5 years to be traceable to the national benchmark.
A.2.3 Force sensor
The dynamometer or force application unit used to verify the force value shall be calibrated in accordance with GB/T 13634. The dynamometer level shall be equal to or better than level 1.
A.2.4 Dimensional measurement
The micrometer(s) or measuring Caliper(s) used to establish dimensional measurements from the rotating bend test machine shall have a resolution of at least 0.01mm. The measurement error shall be within ??0.03mm.
A.3 Inspection of the test machine prior to verification
Prior to verification, the component parts of the machine shall be inspected for wear and replaced if necessary. Any such replacement shall be recorded in the machine maintenance record.
A.4 Verification steps for dimensional measurement
Rotary bending fatigue testing machines can be calibrated by a combination of dimensional and force measurements. Various lever arms convert the force into a bending moment applied to the specimen and require very precise measurement of the length of the force arm (see A.4.2). The method for verifying the force system depends on the source of the force value system used - from a series of weights, levers and vernier systems or force systems using load cells. The applied force is verified during verification using a special device such as Figure A.1.
A.4.1 Temperature stabilization
Place the verification device in the calibration environment long enough to achieve temperature equilibrium and stability. Record the temperature at the beginning and end of the verification.
A.4.2 Measurement of the average moment arm
Use a micrometer or caliper on both sides of the lever arm to measure the bending distance L (L1 and L2 for a four-point bending tester). Repeat the measurement three times (see Figures 1 to 7 and A.2). Calculate the average of each measurement. Record it as the average bending moment arm length . The difference between each measurement shall not be greater than 5%. For a four-point bending test machine, the difference between the measured mean values of L1 and L2 shall be within 1%. The average moment arm is used in the formula in Table 2 to calculate the force value that produces the required test stress.
A.4.3 Measurement of loading leverage
Machines that incorporate lever mechanisms are designed to amplify the payload or convert an inverted force value to an upright force value. The lever system is part of the testing machine, so it is required to measure the lever ratio. Calibrate the machine by accurately measuring the distance between the lever arm and the fulcrum or using a load cell and calibrated weights. The lever magnification ratio shall be recorded and used in the calculation of the test load.
NOTE Refer to ISO 7500-2 standard for lever ratio measurement using force sensor. A.4.4 Calculation of calibration parameters - Relative error q of test machine force value
A.4.4.1 Relative error of test machine force value including force sensor and force unit