Investigation of UD hybrid basalt fibre/epoxy composite mechanical properties depending on length

A basalt micro-fibre bundle (yarn), slightly twisted and impregnated by polymeric matrix with uniformly distributed within the matrix volume microscopical particles of oil shale ash (OSA) is used in textile reinforcement of a composite structure. Oil shale ash (OSA) is a powder, obtained in the combustion process, during generation of electricity at electrical power plants in Estonia. Polymeric matrix is epoxy resin. Mechanical properties of the hybrid composite — epoxy matrix (with OSA) reinforced by continuous basalt fibres depend significantly on the stress transfer and failure mechanisms occurring at the micro-fibre-matrix interface. The present work experimentally investigates the strength of such basalt fibre/epoxy (with OSA) composite rod, emphasizing its dependence on length. Composite samples were experimentally fabricated with 10 wt.% of OSA in polymeric matrix impregnated basalt micro-fibre bundles forming rods with a diameter of 0.13cm. Experimentally fabricated rods are with the length 1, 10 and 82 cm. The rods were tested by tension till rupture and the stochastic Weibull approach was used for rod strength statistical evaluation. The results revealed a scale effect, where shorter rods exhibited higher tensile strengths compared to longer rods, attributed to the lower probability of critical flaws in smaller volumes. The experimental strength data were analysed using the two-parameter Weibull distribution. The shape parameter α ranged from 3.87 (82 cm) to 8.98 (10 cm), while the scale parameter β increased from 891 MPa (82 cm) to 1169 MPa (1 cm). These Weibull parameters quantify the length-dependent strength variability of the basalt fibre/epoxy composite rods, enabling stochastic modelling of the reinforcement fragmentation process when such rods are used in composite structures.