Theoretical a spects of some mechanical properties of composites

Dissertant

Nashat, Mustafa Hamid

University

University of Technology

Faculty

-

Department

Department of Electromechanical Engineering

University Country

Iraq

Degree

Ph.D.

Degree Date

2007

English Abstract

In the present wok, two mathematical models are constructed in order to define the detailed nature of composite.

The first one is based on the classical Rule of Mixtures, (ROM) which is normally rotted from the ordinary strength of materials.

The second model is based on the theory of elasticity, which deals with the detailed response of the internal] macrostructure of the composite.

A virtual composite was assumed to be formed of a number of matrices (Epoxy resin and Nickel) containing various inclusions (Carbon fibers and powder, E-glass fibers and powder, and Kevlar fibers) in sequential permutations, and various volume fractions up to 45 %.

Individual combinations are then presumed to generate an overall view with which heterogeneity in the bulk or the target may affect its response to an external impact.

Furthermore, the Hertzilia contact mode! is modified to serve in deducing the response of a composite material to a low velocity impact.

The mechanical properties of various composites, (fibers enforced and powder dispersed), are deduced from the above first two models, and then used in the third mathematical model to investigate the impact behavior of the material in question.

Throughout mos : of this work, the response of the material to the impact events is analytically divided into three stress components (compressive, bending, and shearing forces) propagating through a target, which is in accordance to the model (closed form approximation).

Moreover, an adjacent computation is made to investigate the state of bonding of the fiber-matrix interface in a preliminary attempt to understand the mechanism of force transfer across this interface.

The results derived from the above mentioned basic models are found most of the time in very good agreement with the published experimental work.

However, the departures of the computed Ell values from this agreement are within ± 5 % in the case of the elasticity model.

On the other hand, those departures exhibited by RNM model are also nearly in the range of i 5%, throughout this world the individual computed values deduced from the elasticity model exhibited various degrees of superiority over the ROM model.

In addition to what has been mentioned above, this work is complimented by demonstrating the capability of the above mentioned modified model, to distinguish between composite heterogeneity with different geometries.

Peak force values deduced from impact results are used in a finite element calculation [code-ANSYS).

The values of deflection under load (U,) and Von - Misses stresses are calculated.

The results are found to confirm the above suggested distinguishing capabilities of the modified models.

Finally, it is thought that that such computations would allow the prediction of ultimate limitations of composites ability to withstand an impact, thus may provide an additional material design tool.

Main Subjects

Mechanical Engineering

Topics

• Mathematical models
• Composite materials
• Mechanical properties

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305500