ISO 12737:2010 pdf free download – Metallic materials一Determination of plane-strain fracture toughness.
7 Test specimen size, configuration and preparation
7.1 Specimen size
In order for a result to be considered valid according to this method, the specimen thickness (B), crack length (a) and ligament length (W —a) must all be not less than 2,5, where is the 0,2 % offset yield strength of the material in the environment and at the temperature of test. Meeting this requirement cannot be ensured in advance, thus specimen dimensions should be conservatively established for the first test in a series. If the form of the available material is such that it is not possible to obtain a test specimen with thickness, crack length and ligament length equal to or greater than 2,5, then it is not possible to make a valid Kk measurement according to this method.
7.2 Recommended specimen proportions
7.2.1 Recommended specimens
The recommended specimens are shown in Figures B.1 and C.1. Width (W) is nominally twice the
thickness (B). Crack length (a) is between 0,45 and 0,55 times the width.
7.2.2 Alternative proportions
In certain cases, it may be necessary or desirable to use specimens having Will ratios other than 2. and alternative proportions are allowed (see Annex B or C). Specimens having alternative proportions shall nevertheless have the same crack length-to-width (a/W) ratio as the recommended specimens.
7.2.3 Alternative specimen configurations
By prior agreement, alternative specimen configurations and their associated methods of analysis may be used, provided that they be accepted as national standards for Ki testing by an ISO member body, including those standards which have the multiple purpose of measuring Ki along with J or CTOD (crack tip opening displacement) properties, or both: e.g. ASTM E399-09 and References [1] and [2].
7.2.4 FatIgue-crack starter notch
Two fatigue-crack starter notch configurations are shown in Figures 2 a) and 2 b). The suggested root radius for the straight-through slot terminating in a V-notch is 0,10 mm or less. For the chevron form of notch, the suggested root radius is 0,25 mm or less. The method of notch preparation is discretionary. The starter notch (plus fatigue crack) must lie within the envelope shown in Figure 2 C) (see Annex A).
Two types of knife edges for attaching the displacement gauge are illustrated in Figure 3.
7.3 SpecImen preparation and fatigue precracking
7.3.1 Material condition
All specimens shall be tested in the final heat-treated, mechanically-worked and environmentally-conditioned state. Normally, specimens shall also be machined in this final state. However, for material that cannot be machined in the final condition, the final treatment may be carried out after machining, provided that the required dimensions and tolerances on specimen size, shape and overall surface finish are met (see Figures 8.1 and C.1), and that full account is taken of the effects of specimen size on metallurgical conditions induced by certain heat treatments, e.g. water quenching of steels.