Evaluation of interface toughness of bi-material Ni/Al by molecular dynamics method

Bi-materials in submicron scale have been widely used in many industries, especially in the microelectronics industry. Due to the different deformation between the two material layers, damage usually occurs on the surface between the two material layers. In this paper, the Molecular dynamics (MD) method is used to investigate the mechanical properties of bi-material Ni/Al under the tensile strain. The examined Ni/Al structure has dimensions of 10.90 nm x 5.27 nm x 4.22 nm/10.93 nm x 5.26 nm x 4.21 nm, with strain rates of 1.83x108s-1, 5.48x108s-1, 1.83x109s-1 and 5.48x109s-1, respectively. The interactions between the atoms in the system are described by the EAM (Embedded Atom Method). The calculated results show that Young's modulus of bi-material Ni/Al does not change under the various strain rates, while the fracture strength of Ni/Al increases with increasing of the strain rates. In addition, the effects of load position and temperature on the fracture strength of Ni/Al are also investigated. With the strain rate of 1.83x108 s-1, the fracture strength of Ni/Al at 100oK and 700oK is 6.6 GPa and 4.3 GPa, respectively. The obtained results of the study are helpful in the design and fabrication of devices based on the bi-material Ni/Al.

Determining Interface Fracture Toughness in Multi Layered Environmental Barrier Coatings with Laser Textured Silicon Bond Coat

In the high temperature combustion atmosphere inside of aircraft turbines, the currently used ceramic matrix composites require a protective environmental barrier coating (EBC) to mitigate corrosion of the turbine parts. Besides thermomechanical and thermochemical properties like matching thermal expansion coefficient (CTE) and a high resistance against corrosive media, mechanical properties like a high adhesion strength are also necessary for a long lifetime of the EBC. In the present work, the adhesion between an air plasma sprayed silicon bond coat and a vacuum plasma sprayed ytterbium disilicate topcoat was aimed to be enhanced by a laser surface structuring of the Si bond coat. An increase in interface toughness was assumed, since the introduction of structures would lead to an increased mechanical interlocking at the rougher bond coat interface. The interface toughness was measured by a new testing method, which allows the testing of specific interfaces. The results demonstrate a clear increase of the toughness from an original bond coat/topcoat interface (8.6 J/m2) compared to a laser structured interface (14.7 J/m2). Observations in the crack propagation indicates that the laser structuring may have led to a strengthening of the upper bond coat area by sintering. Furthermore, in addition to cohesive failure components, adhesive components can also be observed, which could have influenced the determined toughness.

Dopamine/zinc oxide doped poly(N-hydroxyethyl acrylamide)/agar dual network hydrogel with super self-healing, antibacterial and tissue adhesion functions designed for transdermal patch

Dual network (DN) hydrogel has a unique advantage, that is, it has high interface toughness and strength for transdermal drug delivery systems. However, the current DN hydrogel matrix lacks good...

Quantitative Prediction of the Whole Peeling Process of an Elastic Film on a Rigid Substrate

The whole peeling behavior of thin films on substrates attract lots of research interests due to the wide application of film-substrate systems, which was well modeled theoretically by introducing Lennard–Jones (L-J) potential to describe the interface in Peng and Chen (2015, Effect of Bending Stiffness on the Peeling Behavior of an Elastic Thin Film on a Rigid Substrate,” Phys. Rev. E, 91(4), p. 042401). However, it is difficult for real applications because the parameters in the L-J potential are difficult to determine experimentally. In this paper, with the help of the peeling test and combining the constitutive relation of a cohesive zone model (CZM) with the L-J potential, we establish a new method to find the parameters in the L-J potential. The whole peeling process can then be analyzed quantitatively. Both the theoretical prediction and the experimental result agree well with each other. Finite element simulations of the whole peeling process are carried out subsequently. Quantitative agreements among the theoretical prediction, numerical calculation, and the experiment measurement further demonstrate the feasibility of the method. Effects of not only the interface strength but also the interface toughness on the whole peeling behavior are analyzed. It is found that the peeling force at a peeling angle of 90 deg during the steady-state stage is affected only by the interface toughness, while the peeling force before the steady-state stage would be influenced significantly by the interface toughness, interface strength, and bending stiffness of the film. All the present results should be helpful for deep understanding and theoretical prediction of the interface behavior of film-substrate systems in real applications.

Bond Characteristics of Macro Polypropylene Fiber in Cementitious Composites Containing Nanosilica and Styrene Butadiene Latex Polymer

This study evaluated the bond properties of polypropylene (PP) fiber in plain cementitious composites (PCCs) and styrene butadiene latex polymer cementitious composites (LCCs) at different nanosilica contents. The bond tests were evaluated according to JCI SF-8, in which the contents of nanosilica in the cement were 0, 2, 4, 6, 8, and 10 wt%, based on cement weight. The addition of nanosilica significantly affected the bond properties between macro PP fiber and cementitious composites. For PCCs, the addition of 0–2 wt% nanosilica enhanced bond strength and interface toughness, whereas the addition of 4 wt% or more reduced bond strength and interface toughness. The bond strength and interfacial toughness of LCCs also increased with the addition of up to 6% nanosilica. The analysis of the relative bond strength showed that the addition of nanosilica affects the bond properties of both PCC and LCC. This result was confirmed via microstructural analysis of the macro PP fiber surface after the bond tests, which revealed an increase in scratches due to frictional forces and fiber tearing.