Advisor(s)

Ashkan A. Vaziri

Contributor(s)

Hamid Nayeb-Hashemi

Date of Award

2011

Date Accepted

8-2011

Degree Grantor

Northeastern University

Degree Level

M.S.

Degree Name

Master of Science

Department or Academic Unit

College of Engineering, Department of Mechanical and Industrial Engineering

Keywords

mechanical engineering, materials science, adhesively-bonded joints, foam sealants, mechanical properties, WPC

Disciplines

Mechanical Engineering

Abstract

A series of detailed experimental and finite element investigations were carried out to study the response of selected objects which are currently utilized for load carrying. These investigations were later applied to optimize the mechanical performance of the studied structures and materials. First, a number of experiments and detailed finite element simulations were carried out to study the response and failure of single lap joints with non-flat interface under uniaxial tension. The adherents were made from fiber reinforced epoxy composite and the custom-made mold allowed the fibers to follow the profile of the bonded joint interface. The experiments showed that the interface shape has significant effect on the mechanical behavior and strength of the bonded joints. Finite element simulations were performed to estimate the distribution of shear and peeling stresses along the bonded joints and the results were linked to the experimental investigations. Additional parametric calculations were also carried out to highlight the role of interface shape on the distribution of stresses, and inherently the overall strength and behavior of the bonded joints. In addition, the role of a central void on the distribution of the stresses in a bonded joint with flat and non-flat sinusoidal interfaces was investigated.

The second topic concerns Wood Plastic Composites (WPC) which are widely used in the industry due to its durability, low cost, and anti-moisture properties in comparison with the natural wood. In this research, we have produced flout shaped WPC samples using African black wood powder and Phenolic resin in a hot compression molding set-up. Initial WPC composites were produced by systematically changing the wood volume fraction. Based on these results the optimum temperature, pressure and wood volume fraction for developing WPC in a form of a flute is developed. A series of experimental procedures were performed to improve mechanical properties of WPC samples by studying the effect short fiber-glass addition to the wood matrix prior to hot pressing. The results showed that the addition of short fiber did not improve the strength of WPC but rather than it reduced its strength compared to unreinforced composite. In contrast encapsulated wood particle composite in an E-glass/epoxy composite sheet before hot pressing showed the mechanical properties of wood composite are enhanced.

Finally, a very simple and effective method for in situ retrofitting of existing structural parts, and the strengthening and healing of damaged materials and structures based on the application of foam sealants is presented. In this method, a viscous foam sealant is injected within the enclosed spaces of the structure to enhance its structural performance. This method is specifically effective for light-weight structures. After injection, the foam sealant expands and fills out the internal space of the structure and then solidifies in few hours. The solid foam enhances the load carrying capacity of the structure by direct contribution to the overall strength, and also by retarding the bending and buckling of the original structural parts. During expansion, the foam could return the deformed and damaged parts close to the original undeformed shape. A simple demonstration of the proposed technique is provided by crushing empty soda cans and aluminum honeycombs filled with commercially-available polyurethanes insulating foam sealant. After solidification, the foam-filled structures' peak load and energy absorption increased significantly in comparison with the amount of weight added due to the foam injection.

Document Type

Master's Thesis

Rights Information

copyright 2011

Rights Holder

Mahdi Ashrafi


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