BS 7270:2006
$142.49
Metallic materials. Constant amplitude strain controlled axial fatigue. Method of test
| Published By | Publication Date | Number of Pages |
| BSI | 2006 | 28 |
This British Standard describes a method of cyclically loading a metallic specimen under strain control between set strain limits to determine its fatigue resistance. The fatigue resistance is measured in terms of cycles to failure as a function of the applied strain range and the associated variations in stress range, mean stress and plastic strain range. The method is restricted to uniaxially loaded parallel section specimens tested in air at ambient temperature and to metals where time-dependent deformation can be ignored. The method is applicable to both high- and low-cycle fatigue tests.
NOTE 1 Advice on the generation of data sets from individual specimen results determined using this method is given in Annex A.
NOTE 2 Users should assure themselves that the test conditions used and the specimen orientation are relevant to their application.
PDF Catalog
| PDF Pages | PDF Title |
|---|---|
| 3 | Contents 1 Scope 1 2 Normative references 1 3 Terms and definitions 1 4 Symbols 2 5 Principle 4 6 Test equipment and environment 5 7 Specimen geometry 6 8 Alignment of test fixtures 9 9 Test procedure 10 10 Test report 12 Annexes Annex A (informative) Generation of data sets 14 Annex B (informative) Test fixtures 14 Annex C (normative) Dynamic verification of extensometry 20 Annex D (normative) Specimen preparation 20 Annex E (normative) Verification of alignment of the load train 21 Bibliography 23 List of figures Figure 1 – One cycle, defined for sinusoidal and triangular waveform strain histories 3 Figure 2 – Stress-strain hysteresis loop 4 Figure 3 – Test section profile for cylindrical specimens 7 Figure 4 – Alternative test section profile for cylindrical specimens 7 Figure 5 – Test section profile for plate specimens 8 Figure 6 – Plot of maximum force against cycles for a cyclically softening material 12 Figure B.1 – Schematic diagram of grips for a button end specimen 16 Figure B.2 – Schematic diagram of grips for a conical end specimen 17 Figure B.3 – Schematic diagram of grips for a threaded end specimen 18 Figure B.4 – Schematic diagram of hydraulically actuated grips for flat specimens 19 Figure E.1 – Strain-gauge locations for a cylindrical specimen 22 List of tables Table 1 – Cylindrical specimen geometry 8 Table 2 – Alternative cylindrical specimen geometry 9 |
| 4 | Foreword a) New Annex on measurement of specimen bending (see Annex E); b) Reference to the use of electromechanical recording systems was deleted and is no longer recommended (see 6.4); c) Recommended ambient temperature range is specified (see 6.5); d) New subclause on test commencement (see 9.3). |
| 5 | 1 Scope 2 Normative references 3 Terms and definitions 3.1 stress 3.2 cycle 3.3 maximum 3.4 maximum bending strain |
| 6 | 3.5 minimum 3.6 mean 3.7 range 3.8 amplitude 3.9 total strain 3.10 total strain range 3.11 plastic strain range 3.12 elastic strain range 3.13 frequency 3.14 half-life 3.15 fatigue life 4 Symbols |
| 7 | Figure 1 One cycle, defined for sinusoidal and triangular waveform strain histories |
| 8 | Figure 2 Stress-strain hysteresis loop 5 Principle |
| 9 | 6 Test equipment and environment 6.1 Test machine and test fixtures 6.2 Extensometry 6.3 Cycle counting |
| 10 | 6.4 Recording of hysteresis loops 6.5 Test environment 7 Specimen geometry a) buckling does not occur at the highest compressive forces in the test programme; and b) premature failure (cracking) does not occur at the transition with the parallel length or within the transition radii. |
| 11 | Figure 3 Test section profile for cylindrical specimens Figure 4 Alternative test section profile for cylindrical specimens |
| 12 | Figure 5 Test section profile for plate specimens Table 1 Cylindrical specimen geometry |
| 13 | Table 2 Alternative cylindrical specimen geometry Table 3 Plate specimen geometry 8 Alignment of test fixtures |
| 14 | 9 Test procedure 9.1 Specimen insertion 9.2 Extensometer attachment 9.3 Test commencement |
| 15 | 9.4 Data recording |
| 16 | 9.5 Test termination Figure 6 Plot of maximum force against cycles for a cyclically softening material 10 Test report 10.1 Essential information a) the number of this British Standard, i.e. BS 7270; b) specimen identity, type, dimensions and method of preparation; c) maximum and minimum values of ambient temperature and, if applicable, relative humidity; d) waveform and strain rate or testing frequency as appropriate; e) total strain range and mean strain; f) loading direction, i.e. tension or compression; |
| 17 | g) initial measured modulus of elasticity (over the first ¹ cycle); h) number of cycles to failure, Nf, (state the percentage force drop); i) the stress range and the mean stress at half-life ±10 %; j) the plastic strain range at half-life ±10 % (see Figure 2 for its derivation from the hysteresis loop of stress against strain); k) the approximate position of the major crack in relation to the specimen geometry and the extensometer location. 10.2 Additional information a) material specification; b) material composition, heat treatment and mechanical properties; c) product size and form (e.g. casting, plate); d) specimen orientation; e) testing machine and extensometer used; f) class and date of calibration of the test machine and of the extensometer. |
| 18 | Annex A (informative) Generation of data sets Annex B (informative) Test fixtures B.1 General B.2 Fixtures for cylindrical specimens B.2.1 Text fixture design a) a loading surface through which the compressive loads are transmitted; b) a surface ensuring alignment of the specimen axis with the grip axis; c) a second loading surface through which the tensile loads can be transmitted; d) an arrangement maintaining the loading surfaces in contact, whatever the state of loading, within the working range of the design. |
| 19 | B.2.2 Button end specimen B.2.3 Conical end specimen B.2.4 Threaded end specimen B.3 Fixtures for plate specimens |
| 20 | Figure B.1 Schematic diagram of grips for a button end specimen |
| 21 | Figure B.2 Schematic diagram of grips for a conical end specimen |
| 22 | Figure B.3 Schematic diagram of grips for a threaded end specimen |
| 23 | Figure B.4 Schematic diagram of hydraulically actuated grips for flat specimens |
| 24 | Annex C (normative) Dynamic verification of extensometry a) Insert a hardened steel specimen in a suitable test machine in accordance with 9.1; the specimen being produced from steel quenched and tempered to an elastic limit U 800 MPa. b) Attach the extensometer as described in 9.2. Cyclically extend and compress the specimen through a strain of ± 0.2 % using the same waveform as in the fatigue test. c) Ensure that the test frequency is the maximum at which the extensometer might be used. If electromechanical equipment is used to record the data, operate it at the maximum frequency at which it might be used. d) After 100, 200 and 300 cycles, record hysteresis loops as described in 6.4. Ensure that the plastic strain range recorded at zero mean stress is less than 0.01 %. Annex D (normative) Specimen preparation D.1 General D.2 Machining the specimen blank |
| 25 | D.3 Finish machining a) Turning/milling. Remove metal by cuts of progressively decreasing depth. b) Grinding. Use a suitable coolant to prevent heating of the surface. Remove metal by a succession of cuts of decreasing depth. D.4 Polishing of the gauge length Annex E (normative) Verification of alignment of the load train E.1 General E.2 Procedure |
| 26 | Figure E.1 Strain-gauge locations for a cylindrical specimen |
| 27 | Bibliography |
