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Fracture surfaces were studied using Scanning Electron Microscopy to investigate the mode of failures and completely different fracture surface morphologies for these two cases explain the observed difference in number of cycles to failure with the reversal of the load sequence .
 Fracture, Scanning Electron Microscopy, fracture, morphologies, failure
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 Fracture, Scanning Electron Microscopy, fracture, morphologies, failure