ISO 3928 pdf download,Sintered metal materials, excluding hardmetals — Fatigue test pieces
1 Scope
This International Standard specifies: – the die cavity dimensions used for making fatigue test pieces by pressing and sintering, together with certain dimensions of the test piece obtained from such a die; – the dimensions of the test pieces machined from sintered and powder forged materials. This International Standard is applicable to all sintered metals and alloys, excluding hardmetals.
2 Pressed and sintered test pieces for fatigue test by reverse bend and axial testing
2.1 General The pressed and sintered piece may also be subjected to further treatment, such as sizing, polishing or heat treatment. If such treatments are applied, they shall be stated in the test report. In a metallographically examined cross section of a test piece, in the gauge region, the piece shall show no micro-lamination greater than 0,25 mm in length. Corners shall be broken in the gauge area. 2.2 Test piece specification: unnotched Figure 1 a) shows a drawing of the unnotched test piece. The flatness and parallelism of 0,1 mm are mandatory. The other dimensions are advisory. Burrs shall be avoided. 2.3 Test piece specification: notched Figure 2 a) shows a drawing of the notched test piece. The flatness and parallelism of 0,1 mm are mandatory. The other dimensions are advisory. Burrs shall be avoided. The tooling radius 5,5 mm of the die is subject to wear, then the corresponding radius dimension of the test piece shall be reported.
3 Die specifications
3.1 General The die should preferably be of hardmetal and its surface finish shall be such as to allow compression of test pieces under normal conditions. The die may include a small exit taper to facilitate ejection and avoid cracks or microlaminations in the test pieces. Die cavity may be tapered 0,01 per side to aid ejection. Die bore may be enlarged by 0,5 % for tooling to be used for repressing. The die should be well supported with shrink rings (of internal diameter 0 0 01 + , 1 20 mm mm ), so as to minimize lateral expansion during compacting. Such support decreases the possibility of cracking of the specimen at ejection. To reduce the incidence of cracks in the specimen, it is recommended to use top punch hold down during ejection.
4 Machined test pieces
Many types of machined test piece may be used according to the different known procedures of fatigue testing (rotating beam, axial loading, reverse bending, etc.) except that it is not recommended to machine test pieces with square or rectangular cross sections. An example of the rotating beam piece, is given in Figure 3. Figure 4 shows an example of a test piece for axial loading fatigue testing. The machined test pieces shall be ground over their active length, using a diamond wheel, and lapped longitudinally in order to remove all traces of circumferential scratches. Final polishing should be in the longitudinal direction (no circumferential scratch lines should be visible); try to achieve a smooth blend with no undercut. Cold work and stresses from machining significantly increase the yield strength of austenitic stainless steel. Annealing or stress relieving may be required to duplicate the as-sintered structure. Any such heat treatment shall be reported. Practical experience with fatigue testing of carefully machined test pieces of circular cross section has shown that their endurance limits may be 20 % to 30 % higher than those obtained on unmachined, as-moulded test pieces with square or rectangular cross sections. Use progressively lighter machining passes to minimize residual stresses. Diameter in gauge length should be uniform within ± 0,025 mm.