Study on techniques to analyse striation profiles in aero-engine samples

• Main Author: Tan, Pei Yi
• Other Authors: Pang Hock Lye, John
• Format: Final Year Project
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/72266
• Institution: Nanyang Technological University

Fatigue is a failure process developed by the effect of the cyclic loadings which occurs at the stress levels below the monotonic yield strength of the material. Fatigue accounts for the most common mode of the failures in metals with an estimation of 90%. Fatigue striations, which are described as characteristic ripple markings on fatigue fracture surfaces, is an useful indicator for post-failure analysis. It has been shown that there is a strong correlation between the striation spacing and crack growth rate, which is only valid at medium crack growth rates, in the Paris regime. In the first part of the project, comparison of the microscopy techniques is done between the Laser Scanning Confocal Microscope (LSCM) and Scanning Electron Microscope (SEM). An area of interest was selected on each of the failed aero-engine specimens and microscopic images taken by the LSCM and SEM were compared. The comparisons drawn between LSCM and SEM techniques are in terms of the measurements, 2-D and 3- D imaging capability, image contrast, sample preparation, speed of image acquisition, ease of operation and its portability. In the second part of the project, it is essential to understand the effects of the frequency on the formation of the striations. Another set of specimens were wire cut from the annulus fillers and subjected to a high and low frequency respectively to investigate the difference in striations formation. It was found that the higher the applied frequency was, the smaller the striations spacing were formed. It was also discovered that application of lower frequency resulted in a larger fatigue region.