Influence of Mesostructure and Notch Parameters on the Finite Elements Size in Numerical Simulations of Composite Structures Failure

Numerical modelling of the mechanical behaviour of products and structures always includes a number of assumptions and simplifications. When designing structures made from composites, such simplifications include, first, homogenisation of the composite structure within a finite element. At the same time, it is necessary to understand how the assumptions affect the final result for a correct application of such models during strength analysis. This work considered the influence of the fabric mesostructure on composite strength in the presence of stress concentrators and on the finite elements size assignment when modelling structures with holes. During the work, rectangular composite specimens with holes diameters of 2 mm, 6 mm and 10 mm were subjected to tensile tests. Three different fabrics with the weave unit cell sizes from 3 mm to 8 mm were considered. The effect of holes on material strength was evaluated using the effective stress concentration factor. The tests were also simulated in ANSYS Mechanical using a custom material model implemented through UPF. The size of the finite element was selected based on the tensile tests results of specimens with the 6 mm hole. Verification was performed based on the results of testing specimens with other concentrator sizes. Analysis of the calculated and experimental results showed the presence of a region of nonlinear variation in the effective stress concentration coefficient depending on the hole diameter. In this area, using a unified finite element size to evaluate the strength of a composite with used concentrator sizes can lead to 30% errors.