Road administrators have to make decisions regarding the maintenance and rehabilitation of many existing jointed Portland Cement Concrete (PCC) pavements in the road network. Since these pavements are in general expensive to rehabilitate, agencies often opt for overlaying the deteriorated PCC pavement with Hot Mix Asphalt (HMA), resulting in a composite pavement. Unfortunately, the tensile stresses and strains at the bottom of the overlay developed from the movement of the joints, which are caused by the traffic and the changes in temperature, will create cracks on the surface known as reflective cracking. Reflective cracking can reduce the life of a pavement by allowing water or other particles to get into the underlying layers, which causes the pavement structure to lose strength. To improve the performance of the composite pavement, road agencies have studied mitigations techniques to delay the initiation and propagation of those cracks reflected from the PCC joints and cracks. Traditionally, these studies have relied only on laboratory testing or nondestructive tests. This dissertation expands the traditional approach by adding full-scale Accelerate Pavement Testing (APT) to a laboratory effort to investigate enhanced asphalt overlays that delay the initiation and propagation of cracks reflected from the PCC joints. The study was organized into three complementary experiments. The first experiment included the first reflective cracking study of hot-mix asphalt (HMA) overlays over jointed Portland cement concrete pavements (PCCP) conducted at the Virginia APT facility. A Heavy Vehicle Simulator (HVS) was used to compare the reflective cracking performance of a Stone Matrix Asphalt (SMA) control mix with a modified mix with a synthetic fiber. The discussion includes the characterization of the asphalt mixes, the pavement structure, construction layout, the equipment used, the instrumentation installed, and lessons learned. Results showed that the fiber-modified mix had a higher resistance to fracture, which increases the pavement life by approximately 50%. The second experiment compared the cracking resistance of the same control and modified mixes in the laboratory. Four cracking resistance tests were performed on each mix. These four tests are: (1) Indirect Tensile Asphalt Cracking Test (IDEAL-CT), which measures the Cracking Test index (CTindex); (2) Semicircular Bend Test-Illinois (SCB-IL), which measures the critical strain energy release rate (Jc); (3) Semicircular Bend-Louisiana Transportation Research Center (SCB-LTRC), which measures the Flexibility Index (FI); and (4) Overlay Test (OT), which measures the Cracking Propagation Rate (CPR). The results from the four tests showed that the fiber-modified mix had a better resistance to cracking, confirming the APT test results. The laboratory assessment also suggested that the IDEAL-CT and SCB-IL test appear to be the most practical for implementation. The third phase evaluated the performance of mixes designed with a high content of Reclaimed Asphalt Pavement (RAP) and an enhanced asphalt-rubber extender, which comprises three primary components: plain soft bitumen, fine crumb rubber and an Activated Mineral Binder Stabilizer (AMBS). The experiment evaluated the fracture resistance of nine mixes designed with different rates of recycled asphalt pavement (RAP) and asphalt-rubber, compare them with a traditional mix, and propose an optimized mixture for use in overlays of concrete pavements. The mixes were designed with different rates of RAP (15, 30, 45%) and asphalt-rubber extender (0, 30, and 45%) following generally, the design requirements for an SMA mix in Virginia. The laboratory test recommended in the second experiment, IDEAL-CT and SCB-IL, were used to determine the fracture resistance of the mixes. The results showed that the addition of RAP decreases fracture resistance, but the asphalt-rubber extender improves it. A mix designed that replaced 30% of the binder with asphalt-rubber extender and 15% RAP had the highest resistance to fracture according to both. Also, as expected, all the mixed had a low susceptibility to rutting. / Doctor of Philosophy / Reflective cracking can reduce the life of a pavement by allowing water or other particles to get into the underlying layers, which causes the pavement structure to lose strength. To improve the performance of the composite pavement, road agencies have studied mitigations techniques that will delay the initiation and propagation of those cracks reflected from the PCC joints. Traditionally, these studies rely only on laboratory testing or nondestructive tests that will assist in the decision-making stage in a short time manner. This dissertation focusses on a reflective cracking study conducted through Accelerate Pavement Testing (APT) using a Heavy Vehicle Simulator (HVS) and laboratory testing. The first task used an HVS to evaluate reflective cracking of a Stone Matrix Asphalt (SMA) control mix and a modified mix with synthetic fiber. One lane was constructed with two layers of 1.5-inches of a control Stone Matrix Asphalt (SMA) mix and the second lane with an SMA mix modified with the synthetic fiber. Results from APT demonstrated that the modified SMA has a higher resistance to fracture which increases the pavement life by approximately 50%. The second task estimated the fracture resistance of the mixes studied in task one following the laboratory test: Indirect Tension Asphalt Cracking Test (IDEAL-CT), Texas Overlay Test (OT), Semi-Circular Bend-Louisiana Transportation Research Center (SCB-LTRC) and Semi-Circular Bend-Illinois (SCB-IL) to estimate the Cracking Test Index (CTindex), Cracking Propagation Rate (CPR), critical strain energy release rate (Jc) and Flexibility Index (FI), respectively. Results showed that the modified mix had a better resistance to cracking, confirming the APT test results. Specifically, CTindex results showed that the modified mix is more resistant than the control, with indices of 268.72 and 67.86. The estimated Jc indicated that less energy is required to initiate a crack for the control mix that achieved 0.48 kJ/m2 compared to the modified mix with synthetic fibers 0.54 kJ/m2. FI results for the control and fibers were 2.16 and 10.71, respectively. The calculated CPR showed that the control mix propagates a crack at a higher rate of 0.188 compared to the modified mix with a CPR of 0.152. The third phase evaluated the performance of mixes designed with a high content of Reclaimed Asphalt Pavement (RAP) and an enhanced asphalt-rubber extender, which comprises three primary components: plain soft bitumen, fine crumb rubber and an Activated Mineral Binder Stabilizer (AMBS). The experiment evaluated the fracture resistance of nine mixes designed with different rates of recycled asphalt pavement (RAP) and asphalt-rubber, compare them with a traditional mix, and propose an optimized mixture for use in overlays of concrete pavements. The mixes were designed with different rates of RAP (15, 30, 45%) and asphalt-rubber extender (0, 30, and 45%) following generally, the design requirements for an SMA mix in Virginia. The laboratory test recommended in the second experiment, IDEAL-CT and SCB-IL, were used to determine the fracture resistance of the mixes. The results showed that the addition of RAP decreases fracture resistance, but the asphalt-rubber extender improves it. A mix designed that replaced 30% of the binder with asphalt-rubber extender and 15% RAP had the highest resistance to fracture according to both. Also, as expected, all the mixed had a low susceptibility to rutting.

Multi-layered electronic packages increase in complexity with demands for functionality. Interfacial delamination remains a prominent failure mechanism due to mismatch of coefficient of thermal expansion (CTE). Numerous studies have investigated interfacial cracking in microelectronic packages using fracture mechanics, which requires knowledge of starter crack locations and crack propagation paths. Cohesive zone theory has been identified as an alternative method for modeling crack propagation and delamination without the need for a pre-existing crack. In a cohesive zone approach, traction forces between surfaces are related to the crack tip opening displacement and are governed by a traction-separation law. Unlike traditional fracture mechanics approaches, cohesive zone analyses can predict starter crack locations and directions or simulate complex geometries with more than one type of interface. In a cohesive zone model, cohesive zone elements are placed along material interfaces. Parameters that define cohesive zone behavior must be experimentally determined to be able to predict delamination propagation in a microelectronic package. The objective of this work is to study delamination propagation in a copper/mold compound interface through cohesive zone modeling. Mold compound and copper samples are fabricated, and such samples are used in experiments such as four-point bend test and double cantilever beam test to obtain the cohesive zone model parameters for a range of mode mixity. The developed cohesive zone elements are then placed in a small-outline integrated circuit package model at the interface between an epoxy mold compound and a copper lead frame. The package is simulated to go through thermal profiles associated with the fabrication of the package, and the potential locations for delamination are determined. Design guidelines are developed to reduce mold compound/copper lead frame interfacial delamination.

Due to their ability to confer enhanced surface properties without compromising the properties of the substrate, coatings have become ubiquitous in heavy industrial applications for corrosion, wear, and thermal protection, among others. Kinetic Metallization (KM), a solid-state impact consolidation and coating process, is well-suited for depositing industrial coatings due to its versatility, low substrate heat input, and low cost. The ability of KM coatings to adhere to the substrate is determined by the quality of the interface. The purpose of this study is to develop a model to predict the interfacial quality of KM coatings using known coating and substrate properties. Of the various contributions to adhesion of KM coatings, research suggests that the thermodynamic Work of Adhesion (WAD) is the most fundamental. It is useful to define interfacial quality in terms of the critical strain energy release rate (GC) at which coating delamination occurs. Studies show that GC for a given interface is related to WAD. This study attempts to develop a theoretical model for calculating WAD and understand the relationship between GC and WAD. For a bimetallic interface between two transition metals, WAD can be theoretically calculated using known electronic and physical properties of each metal: the molar volume, V, the surface energy, γ, and the enthalpy of alloy formation, ΔHinterface; ΔHinterface is a function of the molar volume, V, the work function, φ, and the electron density at the boundary of the Wigner-Seitz cell, nWS.WAD for Ni-Cu and Ni-Ti interfaces were 3.51 J/m2 and 4.55 J/m2, respectively. A modified Four-point bend testing technique was used to experimentally measure GC for Ni-Cu and Ni-Ti specimens produced by KM. These tests yielded mean G­C values of 50.92 J/m2 and 132.68 J/m2 for Ni-Cu and Ni-Ti specimens, respectively. Plastic deformation and surface roughness are likely the main reasons for the large discrepancy between GC and WAD. At the 95% confidence level, the mean GC of the Ni-Ti interface is significantly higher than that of the Ni-Cu interface. Further testing is recommended to better understand the relationship between WAD and GC.