Longitudinal and Transverse Moduli and Strengths of Low Angle 3-D Braided Composites

Abstract

This paper presents the results of an experimental study conducted on a class of three-dimensional braided graphite-epoxy composites as well as the results of a modeling study to relate the microstructural variables such as volume fraction of fibers and braid angles to the anisotropic elastic moduli and strengths of these composites. In the experimental program, composite samples with a range of volume fractions (0.2-0.45) and a range of braid angles (0°-30°) were produced and tested in simple compression in both longitudinal and transverse directions. Such data is currently unavailable in literature on a single material system. Extreme care was taken in processing to minimize porosity and non-homogenieties in microstructure, and in proper strain gaging to ensure the reliability and reproducibility of our measurements. In the modeling study, the measured elastic moduli were compared against the currently employed isotrain and isostress models for these materials. At the present time, it is widely reported in literature that the predictions of isostrain model are fairly accurate. This study revealed that the isostrain model predictions can be in significant error and that a weighted average of the isostrain and isostress model predictions yielded the best comparisons against the experiments. For the strength of the composite in the longitudinal and transverse directions, correlations expressing these properties as a function of volume fraction and braid angle were motivated by micromechanics and experimental observations. The predictive capability of these correlations for the selected class of 3-D braided composites was found to be reasonable.

Statistical model of the 3-D braided composites strength

“…[6], we validate the method mentioned above to calculate the In Ref. [6], the composites are composed of Thornel T-300 3 K carbon fiber/imide-IV epoxy, and the mechanical capability parameters of fiber and matrix is not repeated. But in Ref.…”

“…But in Ref. [6] the statistical parameters about the longitudinal tensile strength calculation of 3-D braided composites are not considered, so these parameters are determined according to the method in previous section.…”

“…The 3D of 4 directional fiber structure of 3-D braided composites [6] is shown in Fig.1(a), and in the research the unit cell shown in Fig.1(b) can be used. In this unit cell, 4 bundles of braiding yarn (1-4) are located on the diagonal of unit cell, where the axial braiding yarn is parallel to x axis, and they intersect at the center of unit cell.…”

Nonlinear bending behavior of 3D braided rectangular plates subjected to transverse loads in thermal environments

“…T is temperature rise from some reference temperature at which there are no thermal strains, and ⎡ (15) in which α 11 and α 22 are the thermal expansion coefficients measured in the fiber and transverse directions, respectively, and defined by [27] …”

“…Chen et al [5] have studied the microstructure of three dimensional braided preforms. Chou [6], Du and Ko [7], Pandey and Hahn [8], Mohajerjasbi [9], Chen et al [10] and Kalidindi and Abusafieh [11] studied mesostructures and yarn interlacing patterns of braided composites, analyzed the microstructures of braided fabrics through analysis of braiding carrier motion, computer graphics simulation, computer solid modeling, and experimental observations, etc. Based on these studies [2][3][4][5][6][7][8][9][10][11], a unit cell of the model for the 3D 4-step 1 × 1 rectangular braided composite is established.…”