Structural mechanics of textile composites: Effect of braid construction and geometric parameters on composite performance.

摘要

Design equations are developed for the production of circular 4-step braided preforms. Equations are presented for calculating machine parameters, preform parameters (such as unit cell dimensions, actual and directional fiber volume fractions, braider/axial ratios, and fabric linear density), and material requirements. The equations are incorporated into a computer program utilizing readily available data to calculate these values. Equations and a second program are presented for thin structures.; A design methodology is presented for the production of complex shapes through near net shape manufacturing. Case studies show the procedures required for producing right angled and contoured parts, as well as the feasibility of producing such parts.; The performance of mechanically fastened 3-D braided carbonlepoxy composites is evaluated through a series of experiments. In addition, some properties of 2-D braided composites are assessed for comparison. Experimental results provide evidence that: (1) optimum values of width to diameter ratio (w/d), edge distance to diameter ratio (e/d), and diameter to thickness ratio (d/t) recommended for laminates are similar to those for 3-D braided composites; (2) the integrated nature of 3-D braided preforms improves the bearing behavior of their composites; (3) braid angle affects both bearing strength and failure mode of the joint; (4) variations in axial percentage affect bearing behavior, with optimum performance using 50% of the maximum number of axials; (5) provided optimum spacing is used, multiple fasteners do not affect bearing strength; (6) both tow size and hole formation technique affect bearing behavior—optimum bearing strength is achieved with molded holes if small tow sizes are used; and (7) the use of lateral constraint increases bearing strength of 3-D braided composites.