Detail of GB/T 41155-2021

Introduction of GB/T 41155-2021

1 Scope This document specifies the dimensions of the die cavities used for the preparation of fatigue specimens by pressing and sintering, the dimensions of specimens prepared using the die and the dimensions of specimens machined from sintered and powder forged materials. This document applies to all sintered metals and alloys (excluding cemented carbides). 2 Normative references There are no normative references in this document. 3 Terminology and definitions There are no terms or definitions in this document that need to be defined. 4 Pressed and sintered specimens for reverse bending and axial fatigue testing 4.1 General rules Pressed and sintered specimens may be further processed, e.g. by dimensional finishing, polishing or heat treatment. If these treatments are carried out, they shall be indicated in the test report. In the metallographic examination of specimen sections, there should be no microcracks exceeding 0.25 mm in length in the test area. The pressing die should be kept in good condition to avoid burrs. The edges of the test area of the sintered specimen shall be polished to remove burrs produced during pressing. 4.2 Requirements for unnotched specimens The unnotched specimen is shown in Figure 2a). Flatness and parallelism shall be 0.1 mm. other dimensions are recommended. 4.3 Requirements for notched specimens Notched specimens are shown in Figure 3a). Flatness and parallelism should be 0.1 mm. other dimensions are recommended. As the 5.5 mm radius of the mould is prone to wear, the corresponding radius of the specimen should be reported. 4.4 Direction of load for the bending fatigue test If not otherwise stated, the specimen shall be oriented so that the direction of loading during pressing is parallel to the direction of pressing (see Figure 1). 5 Provisions for moulds 5.1 General rules Moulds should be of carbide with a surface roughness that allows the specimen to be pressed properly. The moulds may include a small draft slope to facilitate release and to avoid cracks or microlaminations in the specimen. The negative cavity can have a 0.01 draw slope on each side to facilitate release. The cavity can be enlarged by 0.5% to facilitate pressing and moulding. A good fit of the negative film to the die sleeve (120 + 0.01 0 mm internal diameter) is desirable to reduce the elastic after-effects during pressing and thus the possibility of cracking of the specimen during demoulding. It is recommended that the upper indenter is used to compress the release during demoulding to reduce specimen cracking. 5.2 Mould provisions for unnotched specimens The recommended cavities are shown in Figure 2b). Although expressed as "unnotched", the specimen still has a stress concentration factor (Kt), which should be in accordance with Table 1. 5.3 Mould provisions for notched specimens The recommended cavities are shown in Figure 3b). The stress concentration factor (Kt) depends on the radius (r) and shall be in accordance with the provisions of Table 1. 6 Machined specimens Depending on the fatigue test method (e.g. rotational bending, axial loading, reverse bending, etc.), various types of machined specimens can be used, but machined specimens with square or rectangular cross-sections are not recommended. See Appendix A and references [1] to [4] for details. Axially loaded specimens are shown in Fig. 5. See Appendix A and references [1] to [4] for details. Machined specimens should be ground with a diamond wheel in the working section and mechanically polished longitudinally to remove all circumferential scratches. The final polishing should be carried out in the longitudinal direction (without visible annular scratches) in order to achieve a smooth and dent-free specimen arc. Cold working and machining stresses can significantly increase the yield strength of austenitic stainless steels. Annealing or stress relieving can be used to restore the sintered structure. Such heat treatments should be specified in the report. Fatigue test practical experience shows that the fatigue limit of a mechanically finished circular cross-section specimen is 20% to 30% higher than that of a square or rectangular cross-section specimen after compaction without mechanical machining. The residual stresses are minimised by gradually reducing the amount of machining. The diameter should be consistent over the length of the scale, with a deviation of ±0.025 mm. 7 Identification of the specimen In order to identify the specimen, the following should be stated: a) The number of this document; b) the type of material; c) The density of the specimen; d) the dimensions of the specimen (thickness); e) When pressing and sintering specimens in accordance with Chapter 4, the state of all finishes shall be indicated and the material and surface finish of the pressing tool shall also be indicated; f) the form of the specimen, i.e. the number of the drawing; g) the material of the tool, i.e. tool steel or carbide; h) the sintered or heat treated condition; i) Hardness of the specimen after heat treatment; j) Radius of the bottom of the notched specimen, as shown in Figure 3.

Contents of GB/T 41155-2021

Forword 1 Scope 2 Normative references 3 Terminology and definitions 4 Pressed and sintered specimens for reverse bending and axial fatigue testing 5 Provisions for moulds 6 Machined specimens 7 Identification of the specimen