Thesis (M.E.)--University of Canterbury, 2006. / Typescript (photocopy). "31st May 2006." Includes bibliographical references (leaves 126-133). Also available via the World Wide Web.

This thesis addresses the issues surrounding the application of the finite element method to analyse composite structure repairs with an emphasis on aircraft applications. A comprehensive literature survey has been carried out for this purpose and the results are presented. A preliminary study and a comparative study of different modelling approaches have been completed. These studies aim to explore and identify the problems in modelling repairso n simplec ompositep anelsw ith speciala ttention given to adhesivem odelling. Three modelling approaches have been considered: Siener's model which is an extension of the traditional plane strain 2D model used for adhesively bonded joints, Bait's model which is a promising new approach and a full 3D model. These studies have shown that these methods are complementary providing a different insight into bonded repairs. They have also highlighted the need for a new modelling approach which will provide an overall view of bonded repairs. Improved modelling approachesh ave been developedf or externallyb onded patch and flush repairs. These models enable the study of adhesive failure as well as composite adherendf ailures.T hesea pproachesh aveb eena ppliedt o real repairs and the predicted results compared to experimental data. Four case studies have been conducted: external bonded patch repairs to composite plates, a scarf joint for bonded repairs, a flat panel repaired with a scarfed patch and a repaired curved panel. These case studies have shown that bonded repairs to composite structures can be analyseds uccessfullyu sing PC-basedc ommercialf inite elementc odes.

This thesis addresses the issues surrounding the application of the finite element method to analyse composite structure repairs with an emphasis on aircraft applications. A comprehensive literature survey has been carried out for this purpose and the results are presented. A preliminary study and a comparative study of different modelling approaches have been completed. These studies aim to explore and identify the problems in modelling repairso n simplec ompositep anelsw ith speciala ttention given to adhesivem odelling. Three modelling approaches have been considered: Siener's model which is an extension of the traditional plane strain 2D model used for adhesively bonded joints, Bait's model which is a promising new approach and a full 3D model. These studies have shown that these methods are complementary providing a different insight into bonded repairs. They have also highlighted the need for a new modelling approach which will provide an overall view of bonded repairs. Improved modelling approachesh ave been developedf or externallyb onded patch and flush repairs. These models enable the study of adhesive failure as well as composite adherendf ailures.T hesea pproachesh aveb eena ppliedt o real repairs and the predicted results compared to experimental data. Four case studies have been conducted: external bonded patch repairs to composite plates, a scarf joint for bonded repairs, a flat panel repaired with a scarfed patch and a repaired curved panel. These case studies have shown that bonded repairs to composite structures can be analyseds uccessfullyu sing PC-basedc ommercialf inite elementc odes.

No description available.

The purpose of this study was to gain a better understanding of the parameters affecting crack growth direction in unidirectional comµosite materials. To achieve this, the effect of anisotropy and biaxial loading on the direction of crack growth in unidirectional off-axis composite materials were investigated. Specific emphasis was placed on defining the crack tip stress field and finding a consistent criterion for predicting the direction of crack growth. Two models are presented to predict the crack tip stress field, an anisotropic elasticity solution and a singular isoparametric finite element formulation. After defining the crack tip stress field, three crack extension direction criteria, the Normal Stress Ratio, the Tensor Polynomial and the Strain Energy Density Criterion, were applied to predict the direction of crack extension. The theoretically predicted crack extension directions were then compared with experimental results. After comparison, it was determined that only the Normal Stress Ratio Criterion correctly predicts the direction of crack extension. / Master of Science

A process for fabricating particulate reinforced composites from dry powder-powder blends was developed. The process was designed to exploit the nature of fine powder constituent materials, such that the energy input during the molding process could be reduced. Polymer and reinforcement materials were chosen, characterized, and molded into composite plaques. These composites were characterized in terms of mechanical and thermo-mechanical properties. Stiffness, coefficient of thermal expansion, and overall dimensional stability were found to improve; and strength, strain-to-failure, and toughness were found to decrease to varying degrees. The results of these predictions were compared with simple micromechanics models to gain a better understanding of their physical behavior. / M.S.

published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

No description available.

The work in this thesis concerns the estimation of the electromagnetic, elastodynamic and piezoelectric properties of homogenized composite materials (HCMs). A composite may be considered homogeneous if wavelengths are suficiently large in comparison to the size of the particles of each component material. This thesis examines HCMs constructed from two component materials and several methods of estimating the HCMs constitutive properties. Firstly, the Maxwell Garnett estimates and Bergman-Milton bounds on the electromagnetic properties of HCMs are examined. While both are widely used, we re-examine them, for isotropic dielectric HCMs, in light of recent advancements in material manufacture. Secondly, we examine the strong-property-fluctuation theory (SPFT). The SPFT estimate is calculated using iterations upon an initial ansatz, these iterations being dependent on statistical cumulants of the spatial distribution of the particles of the component materials. The zeroth-order SPFT estimate is identical to the first-order and both are taken to be identical to a comparison material. For the second-order estimate a two-point correlation function along with its associated correlation length are used to characterize the component materials' particle distribution. The general framework for the elastodynamic SPFT was established in 1999 by Zhuck and Lakhtakia. Here we further develop the elastodynamic SPFT for orthotropic HCMs, in order to undertake numerical studies. We simplify certain integrals in order to make them amenable to numerical computation. Also, we establish the piezoelectric SPFT for orthorhombic mm2 materials. The general theory is developed first in a manner analogous to the elastodynamic SPFT. We then implement a two-point covariance function, perform similar integral simplifications to those done in the elastodynamic SPFT and carry out numerical experiments. From the numerical studies it is clear that, for both the elastodynamic and piezoelectric HCMs, the lowest-order SPFT estimate is similar to that provided by the corresponding Mori-Tanaka formalism. It is also apparent that the second-order SPFT estimate provides a significant correction to the lowest-order estimate, which reflects dissipative losses due to scattering.