Linghui He

Measuring Mechanical Properties of the 3D Carbon/Carbon Composite Using Automated Grid Method

A precise measurement, which was based on the automated grid method, was developed to analyze the mechanical properties of a three-dimensional reinforced carbon/carbon composite under tensile and shear loading conditions. Young’s moduli and Poisson’s ratios of the carbon/carbon composites were studied by means of unidirectional tension testing, and the shear modulus was measured using the Iosipescu shear testing technique. The contact measurement method also was applied to test the tensile strain, and a more sophisticated method based on the digital image correlation technique was applied to test the shear strain. All the testing results obtained from the different methods agree well with one another, and the analysis indicates that the automated grid method is appropriate for testing the mechanical properties of carbon/carbon composites. Based on the stress state analysis, the Young’s modulus along the wrap or weft fiber orientations of the carbon/carbon composite can be obtained via the Iosipescu shear test.

Full-field analysis of notch effects of 3D carbon/carbon composites

Carbon fiber reinforced carbon matrix composites (C/Cs), as important candidate aviation and aerospace materials, have good prospects for application in extreme environments. However, notch effects of C/Cs have not been studied adequately. In this work, the notch effects of 3D-C/C composites were investigated by the full-field measurement digital image correlation method. Six kinds of specimens with different notch patterns including one central hole, multi-holes, and double edge notches, were examined to analyze their mechanical properties. The tests were carried out on MTS 809 testing machine and the deformations of specimens were monitored by a CCD camera. Using the full-field measurement, both the local mechanical properties (stress concentration, shear damage, and fracture behavior) and the globe properties (notch sensitivity and tensile behavior) were studied. The results indicated that the fracture stress on the net cross section was constant and it was independent on the material heterogeneity, notch patterns, and notch depth.

Effect of the meso-structure on the strain concentration of carbon-carbon composites with drilling hole

Abstract In this work, the influence of fiber/matrix meso-structure on the strain concentration of three-dimensional (3D) reinforced carbon-carbon composites with a drilling hole is discussed by experimental and numerical ways. The full-field digital image correlation (DIC) method is adopted to obtain the strain field of the experimental specimens, and the meso-FEM model with the consistent meso-structure of the experimental specimens is established to reveal the main deformation and damage mechanism. The results show that the strain concentration appeared off the location of ±90° hole tips, which is different with homogeneous material. Furthermore, the shear bands are observed and located on the region between the cut fiber yarn and the adjacent uncut one. The peculiarities are found connecting with the meso-structure. Moreover, the damage locations obtained from the meso-model show good agreements with the experimental fracture path, thereby, the analyses are verified.