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GB/T 4337-2015 (GB/T4337-2015)

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GB/T 4337-2015: PDF in English (GBT 4337-2015)
GB/T 4337-2015
ICS 77.040.10
H 22
Replacing GB/T 4337-2008
Metallic materials - Fatigue testing - Rotating bar bending
(ISO 1143:2010, Metallic materials - Rotating bar bending fatigue testing,
Issued by: General Administration of Quality Supervision, Inspection and
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
1 Scope
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.
3.1 fatigue
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
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
7.1 General
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
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
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.
Annex A
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.2.1 General
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
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
A.4.4.1 Relative error of test machine force value including force sensor and force unit
(Above excerpt was released on 2022-06-04, modified on 2022-06-04, translated/reviewed by: Wayne Zheng et al.)
Source: https://www.chinesestandard.net/PDF.aspx/GBT4337-2015