IMPLICATION OF INITIAL OBSERVATIONS

The initial fractographic observations allow the investigator to draw some conclusions regarding the cracking mechanisms for the attachment bolt and the saddle clamp bracket. If a fatigue crack exists, there is a prima facie case for pursuing litigation against the service company that performed the rebuild. The corrosion product enables us to determine, qualitatively, whether a crack existed in the component for an extended period of time, and may provide evidence to support a accusation of negligence or lack of due care.

The relevant pictures are shown below as thumbnail images, which can be clicked on to download a larger image.
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Figure 3 Inboard attachment bolt
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Figure 4 Saddle clamp fracture - undercarriage leg side at top of picture
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Figure 6 Higher magnification view of saddle clamp
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Figure 7 SEM view
The following observations can be made from these pictures;
  • The inboard attachment bolt has failed by a cup-and-cone mechanism (refer to the Fractography resource).
  • The saddle clamp has a much flatter fracture surface with three distinctly different regions apparent.
  • These three regions are shown in the optical fractograph given as Figure 5 - in the top light grey region, some ridges are present (see Fractography Resource)
  • This light grey region is shown at higher magnification in the SEM fractograph of Fig. 6, and some parallel lines which outline a semi-elliptic shape are apparent.  Some irregular holes can also be seen in this region, particularly at the left in the middle of the three bands of crack growth.

  • This information can be assembled to provide some initial ideas regarding the mechanism and causes of the failure.

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