Date of Award

2003

Degree Type

Thesis

Degree Name

Master of Applied Science (MASc)

Department

Mechanical Engineering

First Advisor

Zouheir Fawaz

Second Advisor

Kamran Behdinan

Abstract

Many studies were directed toward understanding damage patterns in composite

laminates and determining the damage development sequence upon high velocity impact. Damage accumulation depends on projectile velocity and on a number of other

parameters, so that it is not possible to set strict limits between the different regimes.

However, experiments show that, for a given set of experimental conditions where the

impact speed is the only variable, there is a certain threshold velocity below which no

detectable damage occurs. Above the threshold velocity, no surface damage is observed except for a small indentation at the contact point, but significant internal damage

consisting of delaminating and matrix cracks is introduced. As the impact velocity

increases further, surface damage due mainly to fiber breakage is introduced. For very

high speeds, the target does not have time to deform, and perforation occurs, leaving a

clean hole in the sample.

The objective of this study is to develop a mathematical model that corresponds to the deformed geometry under high velocity impact applications for composite laminates. A total of 100 tests were conducted on composite laminates, struck by cylindrohemispherical projectiles at normal incidents with velocities up to about 100 mls. The types of materials, used this study, are AS4/3051, IM7/5250 CarbonlEpoxy and TI003

Glass/Epoxy. The strain energy was obtained by derivation of the proposed deflection

function. The strain energy was plotted with respect to the deflection of the mid-plane

and, then correlated through dynamic correlation factors to actual kinetic energy

during the impact. The dynamic correlation factors were determined using a genetic

algorithm regression analysis. Two types of materials were tested, namely plain graphite

composites and hybrid composites. The growth of the delamination and also the effect of varying the stacking sequence were investigated for the different type of materials and various orientations.

The mathematical model appears to provide a reasonable representation of the deformation of composite laminates during the penetration by a cylindro-hemispherical projectile. Furthermore, hybrid composites appear to provide more resistance to the impact, whereas plain composites have less resistance with respect to the higher velocities. It was concluded that, the change of the material in a hybrid composite affects the growth of the damaged area and also reduces the impact penetration resistance. Hence, IM7/E-Glass hybrid has a higher resistance to the penetration. Measurements of

the energy levels of the hybrid composites indicated that they offer the highest resistance

to ballistic perforation. The hybrid composites perforated at velocities between 77 mls

and 83 (mls), whereas the graphite composites perforated at velocities between 48 m/s

and 59 (mls). The higher perforation resistance is attributed to the reduced level of

delamination generated during the impact, and also the addition of the E-Glass, which

was capable of absorbing more energy during the impact.

In studying the graphite composites, the best orientation in terms of the stacking sequence was found to be [(45, -45, 0, 90) 2 ] S , which indicates that this stacking sequence withstand higher velocity and hence absorbs more energy during the impact. Therefore, the quasi-isotropi corientation [(45, -45, 0, 90) 2 ] S is best for impact resistance if a laminate is not combined with E-Glass. The ballistic-limit velocity prior to perforation for the Quasi-isotropic laminate was measured as 58.9 m/s. This is a significant increase compared to the other plain graphite samples. The energy required for the complete perforation is approximately 48% higher in this stacking sequence as compared to other plain Graphite specimens. It was also found that the energy absorption capability is reduced significantly in the cross-ply laminates. The penetration resistance of the [(0,90,0,90) 2 ] S laminate and the energy required for perforation are approximately 50% less than the other plain graphite specimens.


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