Time-Dependent Failure of Thin-Ply Composite Laminates

Citation

Ubamanyu, Kanthasamy (Uba) (2023) Time-Dependent Failure of Thin-Ply Composite Laminates. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/x286-g488. https://resolver.caltech.edu/CaltechTHESIS:05312023-210300139

Abstract

The demand for larger and lighter structures for next-generation space designs necessitates the use of deployable structures. Among the materials that hold promise for such applications, thin-laminate fiber composites with thicknesses less than 200 μm stand out due to their strength-to-weight ratio, packaging efficiency, and ability to deploy using stored strain energy. However, designing deployable structures with thin-laminate composites is challenging as they need to be stiff enough to withstand loads during deployment while also having a small volume in the packaged configuration. Complicating matters further, stress relaxation of the polymer matrix within the composite during long-term stowage in response to an imposed curvature can drastically impact both the deployment process and the performance of the structure in its deployed state, even leading to catastrophic failure in the stowed configuration.

This thesis presents a comprehensive study of the time-dependent failure behavior of thin-laminate fiber composites under bending, with a focus on a fundamental material-level understanding. The work is divided into three main parts. First, a novel test method called Flattening to Rupture (FTR) test was developed to effectively load composite coupons under long-term bending, enabling the measurement of time-dependent rupture and identification of the underlying failure mechanisms. Second, numerical simulations using the Abaqus/Standard finite element software were developed to understand the sequence of rupture events and the influence of several parameters that affect time-dependent rupture. Finally, a statistical approach was proposed to model the stochastic nature of the failure of thin composite laminates.

The contributions of this thesis extend the understanding of the microscale failure mechanisms involved in the time-dependent failure of fiber composites. These new insights pave the way for the efficient design of tightly and safely packaged deployable structures under long-term loading. The findings of this research can be utilized to optimize the design and performance of deployable space structures made of fiber composites, leading to new technologies that can advance space exploration.

Thesis Files