An investigation of polysulfone-Al/Li alloy interaction involved single lap shear joints and wedge samples following an FPL etch, sulfuric acid anodization (SAA) and phosphoric acid anodization (PAA). The study of the Al/Li surfaces involved the determination of the elemental composition and morphological features of the pretreated adherend before bonding and following failure. When thermoplastic polysulfone (PSF) was either thermally pressed or primed onto the microporous surface, the PSF indeed penetrated into the porous oxide and thereby provided a mechanical means of adhesion. The wedge test results for the adherend pretreated by PAA and SAA were superior to those for the FPL etched adherend. The failure path for the FPL etched samples was at the adhesive/oxide interface whereas the failure path for the SAA and PAA samples was within the adhesive but with occasional divergence of the crack into the oxide. The porous oxides on Al/Li alloy formed after PAA and SAA treatment were shown to undergo dramatic changes in morphology on short term (<90 hrs) exposure to 71 C and 100% R.H. environment. The mechanism of failure was due to moisture which caused slight hydration of the Al/Li oxide and subsequent debonding of the PSF from the oxide layer. Lithium was not concentrated at the surface in the PAA treated Al/Li alloy as shown by AES depth profiling. The effect of lithium on the durability of the bonded alloy is considered minimal. Along these lines, cyclic loading, use of primers, and infrared spectroscopy studies have been carried out. The mode of moisture intrusion into the polysulfone-Al/Li oxide interphase region is discussed. Specifically, water molecules diffuse into the polysulfone rather than transporting along the interface. Moisture then attacks the oxide interface. Thin polysulfone coatings on pretreated aluminum surfaces were characterized utilizing dynamic mechanical thermal analysis (DMTA), and dielectric thermal analysis (DETA) to detect changes in the molecular motions and structural transitions in the polysulfone-aluminum interphase. The order of the loss peak temperature of the polysulfone is, PSF coating on a porous Al > PSF coating on a smooth Al > neat PSF film. The activation energy of relaxation is also lower for neat PSF when compared to the thin film cast onto a smooth Al or a porous PAA Al substrate. The loss peak temperature shift and the higher activation energy associated with the coated films can be explained by the entropy being reduced when the chains are laid down in two dimensions. Thus studies of polymer properties in the interphase region will contribute to the understanding of the adhesive-adherend interaction. / Ph. D.

A set of experimental tests were performed at Virginia Tech to investigate transverse joints and blockouts on full depth concrete bridge deck panels. The joints were designed on a deck replacement project for a rural three span continuous steel girder bridge in Virginia. Two cast-in-place and four post-tensioned joints were designed and tested in cyclical loading. Each joint was tested on a full scale two girder setup in negative bending with a simulated HS-20 vehicle. The blockouts were built as hollow concrete rings filled with grout and left to shrink under ambient conditions. Thirteen combinations of different surface conditions and grouts were designed to test the bond strength between the materials. The strain profile, cracking patterns, and ponding results were measured for all specimens. A finite element analysis was performed and calibrated with the laboratory results. The cast-in-place joints and the two post-tensioned joints with 1.15 MPa (167 psi) of initial stress experienced cracking and leaked water by the end of the tests. The two post-tensioned joints with 2.34 MPa (340 psi) initial stress kept the deck near a tensile stress of 1.5√(𝑓'c) and performed the best. These transverse joints did not leak water, did not have full depth cracking, and maintained a nearly linear strain distribution throughout the design life. Full depth deck panel may be effectively used on continuous bridges if a sufficient amount of post-tensioning force is applied to the transverse joints. The finite element model provides a design tool to estimate the post-tensioning force needed to keep the tensile stresses below the cracking limit. The blockouts with a roughened surface or an epoxy and a grout equivalent to Five Star Highway Patch grout had the highest bond stresses, did not leak water, and had smaller cracks at the grout-concrete interface than the control samples. A minimum bond strength of 2.5√(𝑓'c) was maintained for all of the specimens with a grout equivalent to Five Star Highway Patch. A pea gravel additive in the grout reduced shrinkage and reduced the bond strength. The finite element model provides a design tool to estimate cracking at the grout-surface interface. / Ph. D.

This thesis was prepared as a result of the growing interest in and the increasing importance of electric welding as applied to many types of manufactured products. Although the art of electric welding is comparatively new, great steps have been taken in its adaptation to industry. As yet the process is underdeveloped, and no information is available whereby one may know with certainty the behavior to expect from a welded joint. The composition of the metal to be welded, the composition of the welding rod, and the method used in welding are but a few of the factors which determine the ultimate strength and behavior of an electrically welded specimen. Far from claiming the credit for a comprehensive report on electric welding, the authors of this thesis admit that it of necessity is limited in its treatment of the subject. Both steel and wrought iron specimens were tested, the steel specimens ranging from 0.2 to 0.5 per cent carbon content. At first the investigation embraced lap-welded and butt-welded joints, but because of the fact that properly made lap-welds never break in the weld, and hence give no indication as to the strength of the weld, this type was abandoned, and all V-type butt-welds were used. All of the welds, with a few exceptions which will be mentioned later, were tested in tension, their tensile strength being used as an indication of their ultimate strength. The Tinius Olsen strain gage was used in obtaining the elongations of the specimens. In the tables which follow, the values in the deformation column will be expressed in Tinius Olsen units, each unit being 0.0003333 of an inch. If the value in the deformation column were 2.3 and this value were desired in inches, the conversion factor 0.0003333 should be multiplied by 2.3, giving 0.00076659 inches as a result. The welding was done with a Lincoln Stable Arc Welder. During the welding operations the voltage was kept at 60 and the amperage was about 150. / M.S.

A high frequency impedance-based qualitative non-destructive evaluation (NDE) technique has been successfully applied for structural health monitoring at the Center for Intelligent Material Systems and Structures (CIMSS) [1-3]. This new technique uses piezoceramic (PZT) patches as actuator-sensors to provide a low-power driven constant voltage dynamic excitation, and to record the modulated current flow through the structure. Therefore, it relies on tracking the electrical point impedance to identify incipient level damage. The high frequency excitation provided by the PZT, ensures the detection of minor changes in the monitored structure. It also limits the sensing area to a region close to the PZT source, therefore only changes in the near field of the PZT are detected, enhancing the ability of this technique to localize incipient damage. The phenomena of the PZT's sensing region localization has been the driving motivation for this research. More fundamental analytical research should be performed before full application of this technique is possible. Thereby, a wave propagation continuum mechanics based approach has been applied to model the high frequency vibrations of one dimensional structures. Energy dissipation mechanisms, such as bolted connections and internal friction, are considered to have a major role in the attenuation of the PZT's induced wave, therefore these mechanisms has been extensively studied. To analyzed bolted connections, linear and nonlinear joint models have been used to describe the wave interaction with such nonconservative discontinuities. Also, with the use of an impedance based model, the electromechanical coupling of the PZT and the host structure is added into the formulation. The wave interaction and energy dissipated at the bolted discontinuity has been assessed with energy flux computations of the incident, transmitted, and reflected waves. The effect of loosening the bolted joint has been also analyzed by reducing the spring stiffness and increasing the damping in the dash pots for the linear joint model, and reducing the Coulomb stiffness and shearing force at the interface for the nonlinear case. A scheme based on the correspondence principle has been applied to calculate the specific damping capacity of a system, at any given frequency, as a quantification of the energy dissipated through the system. The material damping was added into the formulation assuming the modulus to have a complex representation, and therefore the corresponding loss factors were found with active measurement of the material properties of the specimen via a wave propagation method, that monitories the wave's speed at two locations. Once the bases of the analytical model have been set up and corroborated with experiments, a parametric study has been developed to account for the various factors that can affect the sensing range of the PZT’s induced wave, and therefore to have a “rule of thumb on how to go about” when bonding PZTs to structures to monitor them. Apart from the energy dissipation mechanisms, other parameters responsible for the reflection of the incoming wave, and its consequent attenuation, has also been reconstructed. With the extensive analysis of these parameters, an impedance damage metric, based on the undamaged and damaged impedance, has been developed for various factors that can be the source of incipient damage. An attenuation metric has also been introduced to identify the degree of transmission of the propagating wave at certain discontinuities. The analysis of the case scenarios reproduced in this parametric study will aid in the knowledge about the number of PZTs needed to be placed in the monitored structure, the most critical locations, and when a monitored member in a system need to be replaced. / Ph. D.

This study addresses the issue of adjusting the proportion of load transmitted by each hole in a multiplehole joint so that the joint capacity is a maximum. Specifically two-hole-in-series joints are examined. The results indicate that when each hole reacts 50% of the total load, the joint capacity is not a maximum. One hole generally is understressed at joint failure. The algorithm developed to determine the load proportion at each hole which results in maximum capacity is discussed. The algorithm includes two-dimensional finite-element stress analysis and a failure criteria. The algorithm is used to study the effects of joint width, hole spacing, and hole to joint-end distance on load proportioning and capacity. To study hole size effects, two hole diameters are considered. Three laminates are considered: a quasi-isotropic laminate; a cross-ply laminate; and a 45 degree angle-ply laminate. By proportioning the load, capacity can be increased generally from 5 to 10%. In some cases a greater increase is possible. / M.S.

Articular cartilage is a material with the appearance of simplicity and uniformity, but the chemical and biological structure of this material is very complex and not yet known in every detail. Our knowledge of cartilage wear behavior is limited and needs to be enlarged. Knowledge in this area could be important for the prevention and treatment of degenerative joint diseases. Within the framework of this thesis. a literature search focused on the key words joint lubrication and cartilage wear was conducted. The result of this search was that almost all studies and experiments which have been carried out to investigate tribilogical processes in synovial joints focused on friction behavior. Only a few tests dealing with cartilage wear were conducted. Most of the cartilage wear studies were carried out under exaggerated conditions which might change the wear mechanisms. Two studies were undertaken under conditions close to normal conditions occurring in natural joints; one in entire joints with a pendulum device, the other one with a cartilage-on-cartilage test system. The test devices used in these tests offered no or limited opportunities for the variation of the test parameters. Test parameters are, for example, the type of motion, applied load, velocity, variation of the velocity during each cycle, type of specimen, and test fluid composition. In consideration of the findings of the literature search, it was decided to design a new test device providing the capability of measuring friction, wear, and displacement due to wear and/or cartilage deformation. Furthermore, the new test device for cartilage wear studies, allows the variation of the above mentioned test parameters. / Master of Science

Fiber optic sensors fabricated from standard silica fibers have many advantages over conventional sensors like small size, portability, durability and immunity to electromagnetic fields. Unfortunately, these sensors are not suitable for use in harsh environments where the temperatures are greater than 700°C and large working stresses are involved. Sapphire fiber-based sensors present an attractive alternative for use in such environments. The material properties of sapphire like high melting point, extreme hardness and relative imperviousness to chemical reactions, coupled with the advantages of optical fiber sensing, enhance the performance of these sensors for rugged use. Unfortunately, commercial sapphire fiber that is currently available has higher optical attenuation than silica fiber and is costlier. 0, it is prudent to use a small length of sapphire fiber as a sensor head, which is then spliced to a standard singlen10de silica fiber which acts a lead-in/lead-out fiber to the sapphire sensor head. This thesis investigates possible splicing techniques to fabricate such a sensor set-up. Comparative results from experiments performed on splices that have been obtained by each of these techniques, are presented. Furthermore, two different sensor configurations using a sapphire fiber, spliced to a silica fiber, are developed, and the results of preliminary tests are presented. / Master of Science

This paper presents the results of testing to determine the appropriateness of the seismic load duration factor and to investigate the possible effect of previous load history from cyclic loading on connection reserve capacity and ductility. The single shear nail and bolt connection types tested represent common connection geometries used in wood construction in the United States. The results of two methods of fully reversing cyclic loading of connections are presented. The first method was a load-controlled test with the applied cyclic loads acting at specified percentages above current nominal design values. The sets of specimens were then ramped to failure and the results were compared to a monotonic control set of specimens to determine if any reduction in connection capacity or ductility had occurred as a result of the cyclic loading. From the load-controlled cyclic testing, it was found that previous cyclic loading at load levels as high as twice current nominal design loads did not adversely affect connection capacity. The second cyclic loading method was a displacement-controlled test that involved successive phases at increasing displacement levels. Each phase consisted of a peak displacement, followed by a series of three decay cycles, then by a series of three cycles at the original peak displacement, the third of which is used to determine the stabilized system. The process is repeated at increasing incremental levels of displacement. The phased displacement stabilized load-displacement curve was fit to an equivalent energy elastic-plastic system for determination of connection parameters. Results from the two cyclic test methods, and from monotonic testing, indicate that the current load duration factor for wind and seismic loading is justified. / Master of Science / incomplete_metadata

periments and predictions was found to be excellent around the net-section region. Although predictions for other strains were not as good, they were within the range of experimental data. Distribution of contact stresses between the pins and the hole edges was also studied. Numerical analysis suggests that the prevalent assumption of radial cosine distribution of contact stress between the pin and hole edge is in substantial error. It can also be concluded that the strength of the joint is for the most part, independent of its width, though for narrower specimens, the holes were quite highly loaded. / Master of Science

Design procedures are developed that combine both the finite element method and the transfer matrix method in design. These procedures were drawn up as a result of the analysis of a large continuous mining machine to be produced by Fairchild International. Combining the methods allowed the analysis to be split into smaller jobs. Two examples are given. The first example divides the machine into a number of separate finite element analyses where the internal loads on each component are determined by the transfer matrix method. The second example analyzes the transition region between each of the separate finite element analysis. Utilizing both methods in design reduced computer usage costs. / Master of Science