BS EN 843-6-2009 pdf download.Advanced technical ceramics Mechanical properties of monolithic ceramics at room temperature Part 6: Guidance for fractographic investigation.
The sequence of steps in undertaking fractography on a specimen is outlined in Figure 1. It should be noted that not all the steps will be necessary on every occasion; for example, if only a check on approximate position of failure is needed. SEM examination is not generally necessary. Thus, the following series of paragraphs should be used as appropriate to the task, defined by the type of Investigation needed.
6.2 SpecImen storage and cleaning of fracture surfaces
Fracture surfaces are rough and are prone to contamination in handling and storage. Contamination can lead to misinterpretation of observed features, especially in the SEM. Where possible, store fractured fragments separately in clean, dry, conditions In which the fracture surfaces cannot contact foreign bodies,
NOTE Storage in paper or plastic containers can lead to pick-up of contamination. Glass vials minimise risks, but can damage surfaces If the specimen is loose in the vial. It is recommended to avoid the use of tape or mouldable compounds as the adhesive is difficult to remove once contaminating the fracture surface.
Avoid handling with naked hands: use tweezers or surgical gloves to avoid contamination from body oils.
Cleaning facilities are required to allow removal of such contamination without damaging further the fracture surface. It is recommended that solvents such as acetone or ethyl alcohol are used in conjunction with a laboratory ultrasonic bath to remove soluble or loose contamination.
Dry the specimens using compressed air.
6.3 Visual inspection
6.3.1 Examine visually all the available fragments using a good light source and a hand lens as appropriate.
6.3.2 Label all fragments with an indelible marker at positions that are remote from the surfaces of interest. Make a sketch of the labelled fragments for future reference.
6.3.3 Where there are several fragments, use the pattern of cracks to identify the originating fracture surface (the primary fracture):
NOTE I Annex A contains some examples of crack patterns in test-pieces and components.
NOTE 2 It is recommended not to attempt to fit the fracture pieces tightly together since this may induce
further damage on the fracture surfaces which will impede subsequent investigations
6.3.4 Examine the primary fracture surface for evidence of an origin of the fracture. This may be
Identified by tracing back any radiating ridges or grooves.
NOTE I Annex B shows some examples of fracture surface patterns which may aid this step However, it should be noted that:
1) to place a height-adjustable light barrier parallel to the fracture surface to shield the side of the specimen;
2) if appropriate, to rotate the specimen so that a clear impression is obtained of the fracture markings under illumination from all directions;
3) if appropriate, to coat the fracture surface with a thin layer of an opaque substance, such as a metal, e.g. gold. However, coating should be used with discretion if subsequent SEM!EDX analysis is to be performed.
NOTE 2 It can be helpful to the identification of the fracture orion if the two mating halves of the fracture surface are placed side by side with the respective halves of the fracture origin adjacent. It is sometimes easier to see the radial pattern of marks in this way.
6.4.2 If appropriate, sketch or record the images photographically.
6.4.3 Increase the magnification in stages and examine the suspected origin. If possible. identify any feature at the origin, including the detailed pattern of local marks, or any marks or damage on the external surface which may have caused the failure. Take photomicrographs if appropriate.
NOTE 1 At magnifications above about x200 fracture surfaces are generally too non-planar for effective optical microscope examination, and are difficult to illuminate adequately from the side. In some cases, mixed normal and oblique lighting can reveal important features.
NOTE 2 The radiating pattern of fracture marks can often be traced back to the origin, but only if these are deaily identifiable.
6.5 IdentIfication of major fracture surface features
Identify the major features of the fracture surface in terms of fracture lines (3.4.1) emanating from a focal point in an equivalent manner on the two fracture surfaces. Identify strongly hackled regions, and any mirror and mist regions. Identify the position and tentative nature of the fracture ongin in relation to the component or test-piece geometry and likely stressing. Correlate these observations with any ancillary observations of the surface condition.
NOTE 1 The interpretation of the visual observations may not necessarily be straightforward, and optical microscopy may not have adequate resolution or clarity of image to allow positive identifation of the cause of failure. If higher magnification is required, or confirmation of the chemical nature of the origin, SEMIEDX examination should be employed (6.6, 6.8). However, a number of possible types of feature can be identified (not all In every case), which will provide evidence for the report
NOTE 2 The radius of the mirror, If present, is linked to the fracture stress at the point of failure through an empirical fracture mechanics relationship. lithe fracture stress and the mirror constant are known (see Annex D), the mirror size can be calculated, which is a guide to interpretation of a fracture origin. Alternatively, if the mirror radius and mirror constant are known, the fracture stress can be estimated.
NOTE 3 PartIcularly with regard to optical observations, It Is important to describe the origin In terms of its physical form, and not how it appears under particular observational conditions.BS EN 843-6-2009 pdf download.
BS EN 843-6-2009 pdf download
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