Interfacial mechanical strength characterization in multilayered materials via nanoscale impact and nano mechanical Raman spectroscopy experiments

A composite materials strength can significantly depend on the constitutive description of interfaces. A computational model of composite deformation should, therefore, incorporate interface constitutive behavior. These interfaces poses several challenges in studying them due their length scales of micrometer to nanometer as well the coupling of other factors such as confinement during the loading. Thus, separating main phase constitutive behavior from interface constitutive behavior in mechanical property measurement experiments is an arduous task. In this work, an epoxy interface between glass plates is analyzed under quasistatic and dynamic loading conditions to obtain a description of interfacial constitutive response at strain rates from 10-2 to 103 s-1. The experiments were conducted with indenters of radius 1, 10 and 100 μm on the interfaces thicknesses of 1, 10 and 100 μms within the spatial error tolerance of less than 3 μms. The interface thickness was verified with the Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis. The approach relies on describing interfaces as a confined material phase between two unconfined phases. Dynamic microscale impact tests are used to obtain stress-strain response as a function of strain rate for the analyzed interfaces. The data was then subjected to statistical analysis to remove experimental errors. An analytical model was developed to find the confinement effect and the solution was verified by capturing stress maps with Nanomechanical Raman Spectroscopy (NRS) experiments pre and post experiments to analyze the change in the stress distribution around interfaces. Based on the analyses of confinement effects, a constitutive model is proposed to predict the interface deformation behavior with a dependence on both strain rate and confinement effect. This model is further used in the finite element simulations to predict and quantify the role of interfaces in multilayered materials