استحکام استاتیک اتصال کامپوزیت RTM با فرآیند دوخت فیبر I
Abstract
1- Introduction
2- Test specimen fabrication
3- Test results
4- Conclusions
References
Abstract
Resin transfer molding (RTM) is a mass production process that can replace autoclave processes, and composite lap joints are extensively used in composite structures. When a tensile load is applied to a single-lap joint, both shear and tensile peel stresses are generated owing to the eccentric load effect. Reinforcing the composite joint in the thickness direction can reduce the shear and peel stresses generated in the joint, which can contribute considerably to the increase in the strength of the composite joint. Several reinforcing methods have been developed to improve the directional properties along the material’s thickness. Accordingly, a stitching process is typically used. However, the conventional stitching process has disadvantages because a) it requires complex equipment, and b) it cannot use highly elastic brittle fibers, such as carbon fibers. Recently, we proposed an I-fiber stitching process to minimize the bending of carbon fibers to prevent their fracture. In this study, composite, single-lap joint specimens were fabricated with RTM using an I-fiber stitching process, and their strengths were evaluated. The strengths of composite joint specimens fabricated at different stitching intervals and with the use of different patterns were compared with those of specimens fabricated without the use of the stitching process.
Introduction
Resin transfer molding (RTM) process is a mass-production process that can replace the autoclave process. In recent years, RTM processes have increasingly been applied to aircraft structures that are co-cured. Thick composite structures produced by co-curing have the disadvantage that their mechanical properties are weak in the thickness direction [1]. In order to compensate for this weakness, various methods have been developed for reinforcing the mechanical properties of the composite along the thickness direction. Some of these methods, including z-pinning and stitching, are being extensively used. The z-pinning process is a method for reinforcing the mechanical properties along the thickness direction by inserting pins made of various materials and shapes into the prepreg material. Son et al. [2] and Ko et al. [3] studied the fatigue characteristics of single-lap joint specimens reinforced with stainless steel and jagged pins exposed to various environmental conditions. Chang et al. [4] studied the tensile and fatigue characteristics of single-lap joint specimens reinforced with z-pins, and evaluated the optimization of the insertion pins. Park et al. [5] studied the tensile properties through pull-off tests of T-joint specimens reinforced with z-pins. The conventional stitching process is a method of reinforcing the mechanical properties in the thickness direction by intersecting the upper and lower fibers of the preform. Mouritz et al. [6] performed tensile, compressive, shear bending, and fatigue tests on the stitched composite specimens, and studied the characteristics of the stitching process. Beylergil et al. [7] studied the strength of the stitched composite, singlelap joint, and proved that the stitching process decreases the peel and shear stresses along the thickness direction and increases the joint strength. Aymerich [8] conducted fatigue testing on a single-lap joint specimen using a stitching process, and evaluated the stiffening effect of stitching.