PSI - Issue 43

Elisaveta Kirilova et al. / Procedia Structural Integrity 43 (2023) 282–287 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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1. Introduction In the last decade, research on transition metal dichalcogenides (TMDs) has been rapidly increasing based on their interesting and unusual electronic, optical and mechanical properties. Tungsten disulphide (WS 2 ), as a typical example of TMDs, has considerable potential in applications such as strain engineered devices and the next generation multifunctional polymer nanocomposites. Lalwani et al. (2013) have investigated the efficacy of tungsten disulphide nanotubes as reinforcing agents to improve the mechanical properties of poly(propylene fumarate) (PPF) composites as a function of nanomaterial loading concentration. It results in a significant enhancement in the mechanical properties such as compressive modulus, compressive yield strength, flexural modulus and flexural yield strength of tungsten disulphide nanotubes- reinforced PPF nanocomposites compared to the neat PPF. Simić et al. (2019) reported a significant improvement in the tensile strength and toughness for the composite materials based on poly (vinyl butyral) (PVB) with the addition of very small quantity of WS 2 nanotubes. This reinforcement also results in increase of the absorbed energy of the knife stab and decrease of the deformation depth. Golan et al. (2021) have shown that addition of WS 2 nanotubes in the composite Poly(L-lactic acid) (PLLA) containing Hydroxyapatite (HA) results in improvement of its mechanical and thermal properties. Ghosh et al. (2021) reported that coupling of WS 2 nanotubes with poly(methyl methacrylate) (PMMA) results in nanocomposites with superior dynamic mechanical, flexural and tensile properties compared to the neat PMMA. These authors have conducted a series of experimental tests which have exhibited an increase in the composites material’s capability to absorb energy by enhancement of both the strength and strain and an improvement in the elastic domain and the impact resistance of the PMMA/WS 2 nanotubes composites. Lee et al. (2019) have investigated switching characteristics and the operating mechanisms of flexible resistive switching devices made from PMMA nanocomposites. They have been shown that dispersion of WS 2 nanosheets in the polymer matrix leads to low power consumption and great performance of the considered devices. Wang et al. (2020) have applied a combined photoluminescence (PL) spectroscopy and Raman spectroscopy for description of the strain distribution and stress transfer in WS 2 flakes. Falin et al. (2021) have performed both experimental study and theoretical calculations based on the finite element method (FEM) and density functional theory (DFT) for description of the elastic and strength behaviour of WS 2 . These authors have found that monolayer WS 2 has the highest volumetric Young’s modulus (302.4±24.1 GPa) and strength (47.0±8.6 GPa) compared to other inorganic polymer additives such as tungsten diselenide (WSe 2 ), and tungsten ditelluride (WTe 2 ). With the exception of the studies of Wang et al. (2020) and Falin et al. (2021), there are only few analytical models that can describe on macro level the behavior of the layered nanocomposites under combined loading. Most recently Kirilova et al. (2019) and Petrova et al. (2022a) have provided an analytical model and two solutions of the stresses transfer in the graphene/polymer nanocomposites, based on the application of two-dimensional (2D) stress-function method and minimization of complementary strain energy functional to the nanostructure. These studies include a procedure for the solution of governing ordinary differential equation of fourth order with constant coefficients for the axial stress in the first layer of the structure, for two different graphene-polymer nanocomposites. The other stresses in the structure’s layers are expressed and calculated as functions of this axial one and its derivatives. It has been established, that both abovementioned obtained solutions differ mathematically, which is due to the difference in layers’ geometry, following from the different thicknesses of the adhesive and polymer layers of the considered structures (Kirilova et al. (2019), Petrova et al. (2022a)). Both solutions have been validated recently (Petrova et al. 2022b) with shear-lag results for axial stress in WS 2 flakes (Wang et al. 2020). This study represents an implementation of the already developed theoretical 2D stress-function method for modelling of delamination in three-layer WS 2 /SU-8/PMMA nanocomposite structure subjected to static tension load and determination of factors which influence on it. Using two different geometries for the layer’s thicknesses and a parametric analysis, the influence of magnitude of applied load and of the length of the nanocomposite structure on the delamination, is modelled and investigated. The critical stress values of loading in which delamination is occurred in respect to the geometry of the structure (thickness and length), have been determined. 2. Problem statement and obtained analytical solutions Fig. 1 shows a representative volume element (RVE) of an adhesively bonded tungsten disulphide/poly(methyl methacrylate) nanocomposite structure. The axial tensile force P , (N.m) is applied to the PMMA layer. The coordinate