Effective elastic, thermoelastic, and piezoelectric properties of braided composites using equivalent laminate modeling

Abstract

As the number of demands in composite materials grows, the need for automated composite manufacturing processes also increases. Composite braiding technique offers excellent production rate, low manufacturing cost, and high design flexibility, combined with low material waste. Compared to traditional laminated composites, braided composites generally offer better out-of-plane stiffness, strength, and toughness properties. However, due to their rather complex architecture, braided composites bring up another challenge for scientists and engineers, more specifically, in regards to the numerical or analytical characterizations.

Unlike laminated composites, braided composites consist of interlacing yarns, which have undulating profile in mesoscopic scale. To accurately model braided composites, either analytically or numerically, this mesoscopic profile has to be accommodated since it influences the overall effective properties of the braided composites in macroscopic scale. However, it is not a rather simple job, as it often requires a sophisticated modeling procedure and a considerably complicated analytical interpretation. On the other hand, modeling composite laminates is significantly simpler and straightforward using the well-established composite Classical Lamination Theory (CLT). Therefore, a mean to determine the effective properties of braided composites by correlating braided architecture into a corresponding equivalent laminate configuration is studied.

This thesis presents a feasibility study of using Equivalent Laminate Modeling (ELM) approximation to predict the effective elastic, thermoelastic, and piezoelectric properties of braided composites. Here, two braided composite configurations are considered: biaxial and triaxial. An analytical unit cell modeling of braided composites is presented as the reference to investigate the ELM feasibility. As importantly, a technique to practically introduce yarn undulation into ELM using constant undulation angle is proposed. It was found that ELM is able to provide a practical and efficient way to approximate the effective properties of braided composites predicted by considerably more sophisticated methods. It was also discovered that the proposed ELM with undulation effect was able to provide an excellent approximation of unit cell analysis results.