Date of Award

2016-01-01

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Advisor(s)

Pavana Prabhakar

Abstract

Fiber-reinforced composite materials are widely used in the aerospace and automobile industries. Their strength-to-weight and stiffness-to-weight ratios make them suitable to be used in spacecraft, especially as cryogenic tank materials. One of the focus of this dissertation is to investigate the application of woven carbon and Kevlar® fiber composites as cryogenic tank materials. Tensile, bending and short beam shear tests are performed on rectangular specimens at room temperature and after cryogenic exposure (-196°C). It is found that the mechanical properties of these composite materials do not degrade significantly due to cryogenic exposure. It is observed that the failure mode took place before and after the cryogenic exposure is identical, which implies that the carbon and Kevlar® fiber composite can be used as a cryogenic tank materials. Hybridization of this two types of composites (carbon and Kevlar® fiber) is also studied. A computational study is conducted to reduce the number of experiments, and to find the optimum combination of carbon and Kevlar ® fiber reinforcements. Thirty different combinations of hybrid composites are studied computationally and six of these combinations are found suitable based on minimum number of peak stress and minimum peak stress value. This six optimum combinations along with some other combinations are manufactured by using the Vacuum Assisted Resin Transfer Molding (VARTM) process to facilitate comparative study. Comparison of mechanical test results performed on full cryogenic exposure, gradient exposure and pristine materials shows that the hybrid composites can be used as cryogenic tank materials.

Another important aspect of this dissertation is to study the inter-laminar reinforcement of multi-directional laminates by using additive manufacturing technology. Under thermos-mechanical loading, very high stress can be developed at the interfaces due to property mismatch between different plies leading to premature failure. In order to reinforce those interfaces, it is very important to identify these delamination prone interfaces. A novel semi-analytical model is developed to find the delamination prone interfaces in a multidirectional laminates under thermo-mechanical loading and the results of this model is compared with previously published results. Very thin lines of polylactic acid (PLA) are printed on the critical interfaces in multi-directional laminate by using MakerBot Replicator Desktop 3D printer and it is found that, inter-laminar shear strength (ILSS) is increased by approximately 28%. So, the additive manufacturing technology can be used to increase inter-laminar strength of multi-directional laminate.

Language

en

Provenance

Received from ProQuest

File Size

131 pages

File Format

application/pdf

Rights Holder

Md Shariful Islam

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