Research On The Debonding Behavior Of Composite Structures With Functionally Graded Interphase And The Mechanical Properties Of Nano-Springs

The van der Waals(vdW) interaction have a great effect on structures in nano scale.Recently many kinds of nano-composite structures(such as coated films, coated nanospheres,coated nanolines and CNTs reinforced composites) have been prepared using physical and chemical methods. Besides many research about nano-composite structures in physical and chemical filds are reported. The interfaces of coated films, coated spheres and carbon nanotube(CNT)-reinforced composites have a large effect on their mechanical properties due to the large interface area per unit volume at these structures. The description of the interface strength and debonding of these structures has been a challenge in the continuum modeling.In view of the van der waals interactions between the interface of coated spheres,coated films and carbon nanotube(CNT)-reinforced composites with functionally graded interphase(FGI),we derive closed-form expressions of the interface strength through continuum mechanics and establish a novel nonlinear cohesive law. The cohesive law can be used to accurately describe the debonding behavior of the coated sphere subjected to radial tensile loading with FGI. The established analytical solutions should be of great help for understanding the mechanical properties of the composite structures, designing novel sphere-reinforced composites.Besides, in nano scale the vdW interaction plays rule in helical structures. Hooke’s law is a principle of physics that states that the force needed to extend a spring by some distance is proportional to that distance. The law is always valid for an initial portion of the elastic range for nearly all helical macrosprings. Here we report the sharply nonlinear force-displacement relation of tightly wound helical carbon nanotubes at even small displacement via a molecular mechanics model. We demonstrate that the van der Waals interaction between the intertube walls dominates the nonlinear relation based on our analytical expressions. This paper the mechanical properties of tightly wound helical carbon nanotubes considering the effect of vdW on two parallel CNTs is studied. This study provides physical insights into the origins of huge nonlinearity of the helical nanosprings.