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<p> This thesis is a study of the adhesive behaviour of HeLa cells using a novel instrument designed for measuring both the shearing and compression force applied to the cells. For these experiments a micropipette forged as a double cantilever is used to grasp and manoeuvre a cell onto a silicon or Poly-L-Lysine (PLL) coated substrate. The substrate is then moved perpendicularly with respect to the micropipette tip thereby sliding and shearing the cell across the surface. The perpendicular and parallel deflection of the cantilever enables us to directly measure the friction and normal force. A new approach for calibrating both sections of the cantilever has been developped and will also be presented in this work. As a proof of concept, the experiment is also performed with a polystyrene bead. The polystyrene bead, a simpler system, manifests some of the typical results expected from friction experiments. </p> / Thesis / Master of Science (MSc)

<p> The high-throughput micro-adhesion tester (HMAT) was constructed to test the adhesive strength of polymers. The design criteria included the ability to rapidly test many different samples in a serial format, and a probe design that would compliment this objective by being easy to place and pull from the samples and easy to mass produce. The HMAT was able to perform 48 adhesion tests at about 30s per test for a total of 24 min. The final probes were made from a capillary tube with a small metal cap on the top for ease of lifting. They are easy to make and easy to place and pull from the custom probe box. The probe box was designed to hold the probes upright while the polymer is drying and during the test while not interfering with the test itself. Tests on PDMS show reasonable repeatability with the standard deviation being about 20% of the mean value. Since the HMAT is meant to be used for primary screening, the accuracy of the measurements is not as critical as it would be for later tests. </p> / Thesis / Master of Applied Science (MASc)

Adhesives and adhesively bonded structures are being considered as a viable alternative to conventional fastening methods. In order to gain wider acceptance, it is essential to address the issue of the mechanical characterization of adhesive materials and its implementation in the design of bonded joints. While measuring the in-situ properties of the adhesive in a joint is a difficult task, characterizing its bulk properties is a relatively simpler undertaking. The objective of this study was to propose and verify an experimental procedure that would allow the analytical prediction of the viscoelastic behaviour of a bonded joint, using bulk adhesive properties. The Arcan joint geometry was chosen because of the simple state of stress within the adhesive. / Master of Science

There have been successful techniques developed to measure resin distribution of phenol-formaldehyde adhesive on several types of wood surfaces. However, a technique that quantitatively measures UF resin on wood surfaces has been a problem because UF resin is colorless on wood fiber. The first objective of this study was to develop a technique to quantitatively measure surface area coverage and statistical distribution of urea-formaldehyde (UF) resin on medium density fiberboard (MDF) fiber. Two techniques were evaluated to quantitatively measure UF resin. One technique treated the resinated fiber with a reactive stain, such that the resin and wood could be distinguished and separated using digital image analysis. An epi-fluorescence microscope, color video camera, A/D image capture board, and image analysis software were used to measure the percent of resin coverage on the wood surface. The measured resin coverage of the treated fibers did not correlate with the target resin loading level. The other technique added ultraviolet dye to the resin and measured the distribution of resin with an image analysis system. The results of a mill trial confirmed the accuracy of the technique. This system has potential to be incorporated into a mill setting, which will provide MDF mills with a method of determining how resin is being distributed on their fiber. The second objective of this study was to identify factors that would influence the technique's acceptance among MDF mills. A questionnaire was developed, pretested, and sent to every MDF mill in the United States. The method of adding UV dye into the resin was favorable to most mills and could be tested either on-site or by a third-party company. This allows MDF mills to determine potential problems with their blending process. This method saves time and money since it is a proactive measure rather than a reactive measure. It should also lead to a more uniform and consistent product, which is the goal of every MDF mill. / Master of Science

The strengthening of steel bridges using CFRP laminates has become a commonly used technique because of its numerous advantages compared to conventional repairs which involve welding or bolting of new steel plates. These structures will experience some sort of irregular cyclic loading during their lifetime and to analyze these complex loading cases, small scale testing is used to evaluate the fatigue performance between the steel substrate, adhesive layer and the CFRP laminate. In this research, double-strap joints (DSJ) were fabricated consisting of two high-modulus CFRP laminates and ASTM A36 steel plates bonded using a two-part epoxy adhesive. Two types of steel surface conditions were considered to evaluate the fatigue behavior under constant force amplitudes. Roughness on the steel substrate was achieved by ½ in (13 mm) diameter pits approximately 1/8 in (3.18 mm) deep to simulate an irregular surface. The results show that the surface condition has marginal influence on the total life of the specimens. To assess the damage accumulation in the DSJ, phenomenological methods like the nonlinear strength wearout Model (NLSW) and stiffness degradation were used. It was found that residual strength and stiffness decreased in a non-linear fashion. A non-linear model was used that agrees well with the experimental results and can be used to predict the residual strength of the specimens under variable amplitude fatigue (VAF). / Master of Science / With an aging and deteriorating infrastructure potentially being subjected to heavier loads than initially designed for, bridge engineers are increasingly looking for innovative, yet cost-effective solutions for repairing and maintaining the existing bridge inventory with sufficient capacity to carry legal loads. One alternative is to enhance the flexural strength of deteriorated steel members using carbon fiber-reinforced polymers (CFRP). This research project will investigate whether the use of CFRP retrofits is feasible for fatigue strengthening. The research will serve as insight to help guide bridge engineers or researchers on when and where the use of CFRP retrofits is suitable for the strengthening of steel bridges.

Present stress analysis of adhesively bonded joints suffers from inadequate adhesive material characterization. The lack of correlation between bulk adhesive properties and the corresponding in-situ behavior has led to numerous adhesive test geometries. The current study was an attempt to predict the nonlinear viscoelastic response of an adhesive in-situ using properties obtained from a pure shear test geometry. Four candidate adhesive test geometries were studied both analytically and experimentally in terms of accurate shear property determination and realistic adhesive bond simulation. The thick adherend joint was chosen as the experimental reference of actual viscoelastic response in-situ; the Arcan specimen provided a pure shear stress state for material viscoelastic characterization. Results of finite element analysis and extensive experimental evidence suggest that residual thermal stresses alter the in-situ adhesive properties compared to the bulk adhesive: Furthermore, preliminary results indicate that the free volume nonlinear viscoelastic theory accounts for the effect of residual strains on the in-situ adhesive mechanical response. / M.S.

Poly(vinylidene fluoride) (PVDF) films can be easily etched into sensor devices. Since these sensors are relatively inexpensive, thin and light-weight, they can be attached to adhesively bonded joints permanently to measure bond integrity. The present study shows the different steps to design such sensors and proper techniques to attach them near the adhesive bondline. PVDF sensors have been successfully used as NDT transducers in pulse-echo, through-transmission, and acousto-ultrasonic techniques to monitor curing, to detect porosity and crack propagation in different model joint geometries. The potential of using these techniques for practical bonded structures has then been evaluated. / Master of Science

Spacecraft structures rely on honeycomb panels to provide a light weight means to support the vehicle. Honeycomb panels can carry significant load but are most vulnerable to structural failure at their joints where panels connect. This research shows that predicting sandwich panel joint capability using finite element analysis (FEA) is possible. This allows for the potential elimination of coupon testing early in a spacecraft design program to determine joint capability. Linear finite element analysis (FEA) in NX Nastran was used to show that adhesive failure can be predicted with reasonable accuracy by including a fillet model on the edge of the fitting. Predicting the ultimate failure of a joint using linear FEA requires that engineering judgment be used to determine whether failure of certain bonds in a fitting will lead to ultimate joint failure or if other bonds will continue to carry the joint's load. The linear FEA model is also able to predict when the initiation of core failure will begin. This has the limitation that the joint will still be able to continue to carry significantly more load prior to joint ultimate failure even after the core has begun to buckle. A nonlinear analysis is performed using modified Riks' method in Abaqus FEA to show that this failure mode is predictable. The modified Riks' analysis showed that nonlinear post-buckling analysis of a honeycomb coupon can predict ultimate core failure with good accuracy. This solution requires a very high quality mesh in order to continue to run after buckling has begun and requires imperfections based on linear buckling mode shapes and thickness tolerance on the honeycomb core to be applied. / Master of Science / Spacecraft structures rely on honeycomb panels to provide a light weight means to support the vehicle. Honeycomb panels consist of two thin metal sheets separated by a light weight honeycomb grid. The panels operate in a similar way to how an I-Beam works on a bridge. These panels can carry significant load but are susceptible to failure because the panels must be glued together when they are built. This research shows that predicting honeycomb panel joint capability using finite element analysis (FEA) is possible. FEA allows the engineer to model and predict failure in complex structures by mathematically combining many small shapes called elements which have known behaviors and properties into the shape of the actual tested article. The elements deflect in a known manner based on the load applied to the model. The honeycomb panel joint is predicted to break when the deflection in a particular element is higher than the element’s material capability. Obtaining the load where the panel breaks is critical information to have during the design of a spacecraft structure. Using the techniques presented in this thesis allows for the potential elimination of coupon testing early in a spacecraft design program to determine joint capability. Coupon testing is where honeycomb panels are built and tested to failure. This testing is very expensive in terms of both cost and program schedule and therefore using analysis to eliminate its need or to reduce its scope provides significant benefit to the spacecraft program.