بررسي تجربي و شبيه‌سازي رفتار سازههاي مركب تقويت‌شده با پارچه‌هاي حلقوي پودي سه‌بعدي چندسلولي تحت ضربه با سرعت پايين

San‎dwich structures are among the lightweight, high-performance structures that are highly suitable for aerospace an‎d automotive applications. However, their closed-cell structure makes them prone to internal corrosion an‎d delamination, complicating inspection an‎d repair. With the emergence of composite structures reinforced with three-dimensional textiles, the search for better an‎d newer materials has entered a new an‎d special stage. In the composite material industry, despite the unique capabilities such as high design flexibility an‎d the possibility of producing integrated three-dimensional structures with complex geometries, the use of knitted fabrics, especially weft-knitted fabrics, is less common compared to other textiles due to their structural nature. Three-dimensional weft-knitted fabrics are fully integrated structures with both in-plane an‎d out-of-plane multi-axial alignment. Consequently, the composite structures produced from these fabrics, besides being lightweight, exhibit much more effective performance in terms of core-shell separation resistance an‎d mechanical properties such as impact resistance. This dissertation aims to produce three-dimensional multicellular weft-knitted fabrics to achieve structures similar to the final product shape an‎d model the mechanical behavior of the resulting composite structures. These emerging knitted structures are a new type of three-dimensional textile created using pyramid-shaped weft-knitting with various cubic, triangular, an‎d diamond geometries in the thickness an‎d core. The composite structures obtained from them were experimentally subjected to static compression an‎d low-velocity impact loading an‎d compared with composite structures reinforced with spacer weft-knitted fabrics to eva‎luate their mechanical behavior. The obtained results were ultimately used for finite element model simulation. Experimental tests were based on eva‎luating the effects of compressive an‎d low-velocity impact loading, considering structural factors such as the type of geometry, fiber volume fraction, an‎d structure height. The comparison of experimental results showed that pyramid-shaped composite structures exhibited a remarkable 50.47% increase in fiber volume fraction, 66.28% maximum compressive force, 52.25% maximum impact force, an‎d 90.57% improvement in compressive an‎d 14% improvement in impact energy absorption compared to spacer composite structures. Finally, the mechanical behavior prediction of the structures was carried out using a multi-scale finite element method designed as software, including microstructure, mesostructure, an‎d macrostructure scale analysis with Python programming, homogenization, an‎d localization steps, an‎d predicting damage initiation using modified Hashin failure criteria data in composite structures. The software also enabled the prediction of composite structure strength an‎d identification of critical areas at the mesostructure scale. The good agreement between the simulation model results an‎d experimental results indicates the high capability of the proposed software in predicting the behavior of the composite structures considered in this dissertation.

حسين حسني , حسين ديباجيان

هادي رزقي ملكي

سعيد آجلي , هوشنگ نصرتي , مهدي سلماني تهراني