Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Schneider, Judy A.

Committee Member

Lavoie, J. Andre

Committee Member

Sullivan, Rani W.

Committee Member

Lacy, Thomas E.

Date of Degree

5-12-2012

Document Type

Dissertation - Open Access

Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Department of Mechanical Engineering

Abstract

The industrial demand for high strength-to-weight ratio materials is increasing due to the need for high performance components. Epoxy polymers, although often used in fiber-reinforced polymeric composites, have an inherent low toughness that further decreases with decreasing temperatures. Second-phase additives have been effective in increasing the toughness of epoxies at room temperature; however, the mechanisms at low temperatures are still not understood. In this study, the deformation mechanisms of a DGEBA epoxy modified with MX960 core-shell rubber (CSR) particles were investigated under quasi-static tensile and impact loads at room temperature (RT) and liquid nitrogen (LN2) temperature. Overall, the CSR had little effect on the tensile properties at RT and LN2 temperature. The impact strength decreased from neat to 3 wt% but increased from neat to 5 wt% at RT and LN2 temperature, with a higher impact strength at RT at all CSR loadings. The CSR particles debonded in front of the crack tip, inducing voids into the matrix. It was found that an increase in shear deformation and void growth likely accounted for the higher impact strength at 5 wt% CSR loading at RT while the thermal stress fields due to the coefficient of thermal expansion mismatch between rubber and epoxy and an increase in secondary cracking is likely responsible for the higher impact strength at 5 wt% tested at LN2 temperature. While a large toughening effect was not seen in this study, the mechanisms analyzed herein will likely be of use for further material investigations at cryogenic temperatures.

URI

https://hdl.handle.net/11668/17923

Comments

toughening||cryogenic||epoxy||CSR||core-shell rubber

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