Tailorable Structural Performance of 3D Printed Multi-Material Joints: A Combined Theoretical, Computational and Experimental Study

  • Alvaro Martinez Alvarez

Student thesis: Master's Thesis

Abstract

Structural adhesive joints are essential elements of aerospace vehicles and are increasingly being encountered in a wide array of fields. Innovative joint designs using a variety of material systems are inevitably needed to realize more efficient, cost-effective structural systems. The increased usage of advanced composites in primary and secondary aerospace structural components is a key driver for the development of robust, reliable and repeatable bonding procedures so as to ensure efficient joint load transfer, long term durability, and aerodynamic performance. In this study, firstly, a unified theoretical framework for determining the interfacial stresses in a multi-material single-lap joint subjected to monotonic tension is delineated within the purview of two-dimensional continuum elastostatics. The joint consists of similar/dissimilar geometrically graded isotropic adherends and a compliant homogeneous interlayer. The principle of minimum complementary energy in conjunction with a variational method is used to obtain the governing equations. Both essential and natural boundary conditions as well as continuity of interfacial stresses were exactly satisfied. Minimization of complementary energy in the assembly yields a system of coupled ordinary differential equations in terms of unknown stress functions. These governing equations were then solved numerically imposing traction and traction-free boundary conditions. Theoretical results indicate that the peak shear and peel stresses which appear at the ends of the overlap of a compliant interlayer can be significantly minimized by geometrically grading the adherends over the bond length. Secondly, geometrically graded joints were prototyped using a multi-material 3D printer and the mechanical response of these joints were experimentally evaluated. Furthermore, using the in situ optical technique known as digital image correlation (DIC), full-field quantitative strain maps of localization and evolution were also obtained in order to identify the onset of damage in the critical zones. Results obtained from the tensile tests affirm that the performance of the joints can be maximized by adopting an optimum graded profile. Finally, analytical and experimental predictions were corroborated by finite element calculations. Availability of multi-material 3D printing technology enables design of composite systems with tailorable structural performance and eliminates producibility constraints associated with conventional structural adhesive bonding.
Date of AwardMay 2015
Original languageAmerican English
SupervisorKumar Shanmugam (Supervisor)

Keywords

  • Structural Adhesive Joints
  • Aerospace Vehicles
  • Advanced Composites
  • Interfacial Stresses
  • Geometrically Graded Joints.

Cite this

'