Experimental and Numerical Study on Fracture Characteristics of Interface between In Situ Engineered Cementitious Composites and Steel Deck

In this study, engineered cementitious composite (ECC) is used as the pavement of orthotropic steel deck bridge and an epoxy adhesive is used to achieve wet-bonding between the steel deck and cast-in-place ECC. To investigate the fracture properties of bimaterial interface, the double cantilever beam (DCB) and 4-point end notched flexure (4ENF) specimens were used to obtain the fracture toughness, and virtual crack closure technology (VCCT) was used to calculate the energy release rates. A mixed fracture criterion was also established based on the blister test in this study. In addition, for the phenomena of water accumulation in the interface cracks, the hydrodynamic pressure under load was evaluated with a two-way fluid-solid coupling model and the propagation mechanism of cracks at the water-bearing interface was explored. The results showed that the energy release rates at the crack front showed obvious nonuniform distribution characteristics. The blister test indicated that a mixed fracture was in good agreement with the linear fracture criterion. The fracture effect produced by the hydrodynamic pressure of the interfacial water-bearing crack was far less than the fracture toughness of the interface, which indicated that the hydrodynamic pressure could hardly destroy the interface at one time but might cause the erosion fatigue damage of the interface.

Closed-Form Solution and Experimental Verification for the Axisymmetric Deformation Problem of Blistering Circular Thin Polymer Films under Uniformly Distributed Gas Pressure

The existing studies indicate that the measurement formulas used in blister test techniques, which are used to measure the mechanical properties of thin-film/substrate systems, are usually given based on an approximation—that is, the applied direction of the uniformly distributed transverse load is always vertical, while the applied direction of the uniformly distributed gas pressure is always perpendicular to the surface of the thin film. This approximation will lead to a large measurement error. In this study, we obtained the analytical solution to the problem of axisymmetric deformation of blistering circular thin polymer films under the action of uniformly distributed gas pressure via the power series method. An example is given to illustrate the error caused by the approximation mentioned above, and the validity of the solution presented here is verified. The result shows that the chance of error caused by the approximation increases with the increase in the applied load, and it far exceeds the allowable error of measurement when the applied load is relatively large. In addition, the related experiments of the blistering circular thin polymer film under uniformly distributed gas pressure are carried out, and the experimental results are compared with the theoretical results. The comparison results show that the analytical solution given in this paper is correct. The solution presented here is of great significance to improve the measurement accuracy of the blister test technique.

Blister Test as Method of Measuring Adhesion of Solids on a Flat Surface

The adhesion between coating and a flat metal surface hasbeen investigated by measurements. The setup is based on theformation of a blister by injecting nitrogen gas under pressurebetween the coating and the substrate. The adhesion energy isdetermined by recording the pressure as a function of therecorded blister radius development. A laser is moved over theblister in 2D with two programmable step engines to measurethe blister profile and thereby the radius of the blister betweensuccessive pressure increases. The design and operation of theinstrument are described and an evaluation of its performanceand limitations is given. The method could be useful for accuratemeasurement of adhesion of many types of surface coatings tometal and, possibly, to other substrates, as well as for studies ofthe various factors that influence adhesion. A better accuracy ofthe laser for measuring the blister profile would improve thesetup.We treated aluminium surfaces in different manners (sandpaper, polishing and blowing using glass particles) but found nosignificant impact on the adhesion energy between the x-linkedcoating layer and the metal. The adhesion energy measurementshowever have a large scatter. The coating layer that was not xlinkedhad a much lower adhesion energy.

A Mock Gas Molecules Model for Accurately Simulating Pressure Load at Micro- and Nanoscales

At micro- and nanoscales, the gas pressure load is generally simulated by the thermal motion of gas molecules. However, the pressure load can hardly be produced or controlled accurately, because the effects of the wall thickness and the atomic weight of the gas molecules are not taken into account. In this paper, we propose a universal gas molecules model for simulating the pressure load accurately at micro- and nanoscales, named mock gas molecules model. Six scale-independent parameters are established in this model, thus the model is applicable at both micro- and nanoscales. To present the validity and accuracy of the model, the proposed model is applied into the coarse-grained molecular dynamics simulation of graphene blister, and the simulation results agree well with experimental observations from the graphene blister test, indicating that the model can produce and control the pressure load accurately. Furthermore, the model can be easily implemented into many simulators for problems about the solid–gas interaction, especially for membrane gas systems.