Modeling of IC Debonding of FRP-Strengthened Concrete Flexural Members
The presence of a fiber-reinforced polymer (FRP) strengthening material bonded to the tension face of a reinforced concrete beam will restrict but not prevent the opening of intermediate flexural cracks due to applied loading. Test results indicate that displacements at the toe of flexural cracks create stress concentrations at the interface of the FRP laminate and the beam, leading to the development of localized interface cracks that, typically, propagate, under the effect of the load, to join the original flexural cracks and cause delamination of the FRP system. This type of FRP delamination is commonly termed intermediate crack (IC) debonding. In this paper the analytical models published in the literature are reviewed and it was found that these models do not correlate well with measured experimental results. This paper proposes an analytical model that characterizes the interface shear stress based on two distinct sources: (1) the change in the applied moments along the length of the member and (2) ...
Bond Failure of Concrete Fiber Reinforced Polymer Plates at Inclined Cracks—Experiments and Fracture Mechanics Model
Bond failure is mostly brittle and often occurs a few millimeters deep in the concrete. A fracture mechanics-based engineering model of bond strength for this failure type, derived from pure bond tests exists. In a beam vertical shear crack, mouth displacements can reduce bond strength by reducing the total fracture energy required to destroy the local bond. To quantify this effect, the shear crack mouth displacements have to be calculated, dependent on the acting forces, the geometry, the reinforcement and the material parameters of the beam. Then a mixed mode fracture mechanics approach is used to quantify the of bond strength due to simultaneous action of bending and shear. In most cases, bond strength reduction due to vertical shear crack displacement will range around 5-10%. In CFRP-plates another type of debonding failure, specific to fiber reinforced plastics was observed. Interlaminar failure in the plate, preferably occurring with higher-strength concrete is considered a mixed mode fracture problem and was investigated by simultaneous measurements of the Mode I and mode II displacements of the bond crack with electronic speckle pattern interferometry (ESPI). A fracture mechanics approach to a criterion for interlaminar plate failure was derived. According to this, a surface tensile strength of the concrete of more than 3,0 MPa cannot be taken advantage of in design, since interlaminar plate failure will then govern bond failure.
New approach to vision-based BGA package inspection
Ball grid array (BGA) techniques have developed very fast due to the advantages of more I/O ports, small size, and so on. In this paper, a vision-based algorithm for BGA package inspection is proposed to accurately estimate center and diameters of solder-balls of BGA packages, so that defects of BGA packages, such as missing or extra balls, oversize or undersize balls, over-height or under-height balls, and pitch can be detected for ensuring the quality of BGA packages.