Yarn Architecture Analysis of Two-step 3D Braided Composites

A comprehensive study of yarn architecture of two-step rectangle 3D braided composites is presented. Firstly, the braided surface, the shapes of yarns and the intertwining between braider yams and axial yams are analyzed from experimentation. With the microstructure being defined, three levels of unit cell structure are identified, i.e. large unit cell, second unit cell and minimal unit cell. Secondly, based on the minimal unit cell in the interior and on the boundary of the entire cross-section, the deformations of axial yams squashed by braider yams contribute to the increase of the fiber packing factors of axial yams. Finally, the predicted fiber volume fraction of the composites decreases with the increase of linear density of the braider yam and the pitch length. Favorable correlations between the predicted and the experimental results arc found for six groups of the composites.

北川震裂带柳杉林地土壤功能特性试验分析

汶川地震形成了大面积的震裂带,震裂带内水土流失严重。本文重点从土壤结构体分形维数、有机质含量、土壤抗冲性三个方面探讨了北川震裂带柳杉林地土壤结构功能特性,分析了地震裂隙程度对土壤结构体分形维数、有机质含量、土壤抗冲性的影响及其与土壤深度的相关性。结果表明地震裂隙程度对土壤结构体分形维数影响不显著,而地震3 a后强度裂隙样地土壤有机质含量、抗冲性大于中度裂隙或弱度裂隙样地;各样地土壤有机质含量、抗冲性与土壤深度显著负相关,有机质含量与土壤抗冲性存在显著的正相关关系。