Multiscale modeling and formation analysis of technological interlaminar stresses in thick-walled gfrp rings

Thick-walled GFRP rings are widely used in high-loaded friction units of working elements of road-building machines as sliding bearings. They must endure high radial loads and work in the condition of a limited lubrication by using the lubricant which is located only in the open pores of the bushing. In large structures of sliding bearings (bearing elements of road-building machines) the thickness of a bushing might be dozens of millimeters. The reality is that it is necessary to use bushings with a rather big thickness to reduce the dynamic load for road-building machines. However, if the thickness of a composite ring increases, it often results in the inter-laminar failure which is caused by high technological (inter-layer) and stretching stresses due to the anisotropic thermal expansion and shrinkage of fabric composites. Furthermore, these stresses can also cause a significant distortion of a thick-walled GFRP ring after machining. In this work, it is assumed that the tension winding of the pre-impregnated fabric on a rigid mandrel leads to a heterogeneous compression of the internal layers and a distortion of the original composite woven structure through the thickness. The threads of the inner layers are curved more than the threads of the outer layers. For this reason, the coefficients of thermal expansion (CTE) of the inner layers happen to be larger than the CTE of the outer layers. Irregular distribution of the CTE gives rise to residual tensile stresses in the transverse (radial) direction. This paper presents the results of dilatometric studies of distributing of the CTE in the thickness of the hoop and axial directions. To determine the volume fraction of filaments and matrix into the threads of GFRP, we used the burn-out method. The observation of slices in the optical microscope allowed us to determine the degree of the curvature of fibres and the thickening of inner ring layers for further 3D modelling. The structure of the woven composite ring was modelled by using impregnated unidirectional (UD microplastic) threads and repeated unit cell. Modulus of elasticity, Poisson's ratios and coefficients of thermal expansion at microscale, macroscale and mesoscale were calculated by FEA (ANSYS Workbench). Thermomechanical properties were used to evaluate the residual technological interlayer stresses in the GFRP sliding bearing busing at the macroscale.