Influence of Molding Methods on Defects in AFM Carbon Fiber Samples under Static Loading

Static tests of AFM carbon fiber samples made by autoclave and vacuum molding methods were carried out. Acoustic (acoustic emission and ultrasonic) methods, strain gauging, and microanalysis of thin sections were used to test for defects. The location of acoustic emission signals in the area of stress raisers made it possible to establish that the number of defects in autoclave molding is ten times less than under vacuum molding. Ultrasonic and acoustic emission methods, strain gauging, and microanalysis allowed determining the structure of AFM carbon fiber, the coordinates of defects, and their type. During the testing of unloaded samples made by vacuum molding, manufacturing defects were found that grew in size during static stretching and led to the occurrence of new destructions. No manufacturing defects were found in the samples produced by autoclave molding. Microanalysis of samples produced by the vacuum method revealed defects associated with fiber destruction, matrix cracking, and delamination. Tests of samples prepared by autoclave molding have shown that there are practically no defects in them.