Award Date

5-1-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Committee Member

Brendan O'Toole

Second Committee Member

Thomas Hartmann

Third Committee Member

Robert Boehm

Fourth Committee Member

Zhiyong Wang

Fifth Committee Member

Pradip Bhowmik

Number of Pages

129

Abstract

Fiber reinforced composites are light materials which exhibits great strength and stiffness. They also have good dimensional stability and impact resistance. They reduce mass and improve structural performance, so the demand for fiber reinforced composite materials increases day by day in various industries such as aeronautical, automobile and military. The analysis, design, and optimization of polymer composite materials under static loading conditions are mature fields of study. Many sources are available to find material properties and predict structural response. However, composite materials are often used in extreme environments where they are subject to shock, impact, and blast loading. Efficient computational analysis methods are still needed and the effect of loading rate on material properties is not fully documented in the literature.

The overall objective of this study is to understand dynamic tensile properties of composite materials and to improve the experimental procedure for determination of these properties. A new testing procedure for measuring the tensile properties of laminated composites under low and moderate strain rates has been optimized.

After studying the known properties of several different materials, a total of four types of fiberglass composites were manufactured and tested for this study. They are S2-glass/epoxy, E-glass/vinylester, S2-glass/vinylester and E-glass/epoxy materials. Testing of these materials allowed to do comparison between a high cost material system and a lower cost one and helped to quantify the differences between lower strength fibers (E-glass) and higher strength fibers (S2-glass) under dynamic strain rate loading.

Materials were tested at strain rates ranging from quasi-static to moderate strain rates that exist during a wide range of impact events. Quasi-static tensile testing and the dynamic tensile testing of the fiberglass composite materials were conducted with a method based on ASTM testing standard D3039. Quasi-static tensile testing was completed with the MTS testing system with a 0.0001 s-1 strain rate. Longitudinal, transverse and ±45º fiber orientations were tested to failure for each type of composite materials. Instantaneous force, strain data was recorded which was analyzed to obtain axial, transverse and shear material properties. Dynamic tensile testing was completed with the Instron Dynatup drop weight impact tower with a strain rate of 25 s-1. Samples were tested to determine appropriate properties in the longitudinal, transverse, and shear material directions. During each of the completed test, instantaneous force data was recorded. Upon completion of testing, the data was reduced to determine similar properties as were determined for the quasi-static testing.

Quantitative comparisons were drawn between the material systems regarding their respective behaviors at the different strain rates. Study was conducted to compare material system’s strength at different strain rate. Additional experimental data was obtained from a previous research where the exact same experimental setup was used. By combining the additional data, research was conducted to show the variation of strength in longitudinal, transverse and shear from-quasi static to 20, 25 and 100 s-1 rates.

As a cornerstone of this thesis, a test fixture was developed to allow for testing at higher strain rate. Comprehensive study was completed on experimental variables that affect the test and limitation of our current design. Few changes to the current design were made to improve test system as well as to ensure the capability of testing at intermediate strain rate region.

Keywords

Fiber reinforced composites; Dynamic tensile properties; Quasi-static to moderate strain rates

Disciplines

Mechanical Engineering

File Format

pdf

File Size

2.7 MB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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