Semester

Spring

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Nithi Ti Sivaneri

Committee Co-Chair

Hota Gangarao

Committee Member

Bruce Kang

Abstract

Composite π-joints are valued for their potential to reduce component weight, lower manufacturing costs, and simplify assembly. In aerospace applications, these qualities become even more valuable; however, these advantages must be carefully balanced with the safety requirements. Given the complexity of the π-joint geometry, it is crucial to determine and optimize the mechanical properties to ensure quality, performance, and safety throughout the lifetime of the part.

This thesis aims to investigate the effects of various factors on the mechanical properties of a composite π-joint manufactured using vacuum-assisted resin transfer molding (VARTM) processes. The discussion focuses on the effects of fabric stitch orientation, laminate layup, fabric material, π-joint fillet radius, π-joint core material, π-joint skin thickness, and fiber volume fraction. Through a combination of ASTM standardized tensile loading and three-point flexural experiments, in addition to ANSYS simulation, this thesis provides valuable insights into the manufacturing processes and design optimization of composite π-joints for aerospace applications.

Coupon testing demonstrated that prioritizing a longitudinal stitch bias and an optimized [90/0]12 laminate layup increased the tensile strength by 10.1% while enhancing modulus of elasticity and load-displacement slope. ANSYS simulations indicated the optimal fillet radius to be 3.75 in. (outer) and 0.5 in. (inner), which were scaled down to 0.5 in. and 0.125 in. for mold design based on manufacturing constraints. In π-joint testing, increasing skin plies improved flexural and tensile load-displacement slope but reduced flexural strength and modulus of elasticity. Carbon-fabric specimens exhibited superior load-displacement slope, modulus, and tensile strength compared to glass-fabric specimens but reduced flexural strength.

Overall, this thesis provides insights into optimizing composite π-joint design and fabrication; however, with some observations require further study to achieve a comprehensive understanding.

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