Finite element study of the microdroplet test for interfacial shear strength: Effects of geometric parameters for a carbon fibre/epoxy system

Abstract

A 3D finite element model has been developed to identify the main causes of variability in the microdroplet test, which is commonly used to characterise the interfacial shear strength between polymer matrices and single filaments. A more realistic droplet shape and test configuration, including meniscus details and prismatic shear blades, have been modelled for a carbon fibre/epoxy system to simulate a more representative set up than is commonly used in the literature. The interfacial behaviour has been modelled using a cohesive surface contact and fibre breakage has been captured using a maximum stress criterion. A statistical study has been performed to systematically evaluate the influence of key geometrical test parameters on the variability in the measured interfacial shear strength values and the likelihood of fibre breakage. Parameters studied are fibre embedded length, fibre diameter, shear blade radial opening distance and shear blade axial misalignment. Results of the studied carbon fibre /epoxy system suggest that fibre embedded length and the combined effects of the shear blade radial distance and the shear blade axial misalignment are the most significant sources of variability for the measured interfacial shear strength. However, fibre embedded length and the shear blade radial distance are the most significant variables contributing to fibre breakage.

The Role of Typha angustifilia Fiber–Matrix Bonding Parameters on Interfacial Shear Strength Analysis

“…Similar results have also been reported, wherein it was found that the larger the fiber diameter, the higher the IFSS value for Typha fiber/epoxy resin [26]. This is due to the proportional relationship between fiber diameter, average peak force, and IFSS [11].…”

“…Larger fiber diameter led to higher IFSS value Reference [26] IFSS decreased with increasing embedded length Reference [27] Larger fiber diameter led to higher average peak force Reference [11] The force increased as the distance between the vise and the specimen grew Reference [31] Limitations…”

“…The microbond test method developed by Miller et al [8] is one of the most widely used test methods for the examination of the IFSS of a fiber-matrix bond [9]. These tests are difficult to conduct experimentally [10] for several reasons, such as the difficulty in accurately measuring the length of the fiber embedded in the matrix due to the formation of the meniscus at both ends of the matrix as well as difficulty in measuring the failure mechanism at the microscale level due to the very small size of the microdroplet [11]. On the other hand, it is often found that the fibers break before debonding occurs, requiring high accuracy and producing scattered results.…”

Longitudinal debonding in unidirectional fibre-reinforced composites: Numerical analysis of the effect of interfacial properties

“…An energy-based damage evolution with a linear softening law (see Fig. 3a) is considered for the debond propagation, as this is found to be more appropriate for brittle materials [46]. In fibre-reinforced composites, due to the higher Poisson and thermal contraction of the matrix, the debond crack surfaces are continuously in contact and the debond propagation is purely in mode II [22][47,48], under axial tensile loading and ∆𝑇 < 0.…”

Determination of cohesive parameters for fibre-reinforced composite interfaces based on finite element analysis and machine learning

“…1 Some experimental methods based on single fibres have been developed to measure IFSS, such as the single-fibre pull-out test, 2 microdebond test, 3 fragmentation test 4 and microdroplet test. 1,[5][6][7][8][9][10][11][12] Regarding the microdroplet test, numerical simulation, such as finite element analysis (FEA), is an important method to study the process of interfacial damage. In the FEA simulations, cohesive elements were usually adopted at the surface between fibre and resin.…”