Improved method for determining rheological parameters of composite materials during creep under torsional deformation

This paper presents an improved method for determining rheological function parameters of viscoelastic-plastic materials, demonstrated through creep under torsional deformation. The approach is based on the heredity theory (Boltzmann’s principle), using curve fitting to identify parameters (A, α, and β). The improved method from previous studies uses precise graph construction via computational tools, with curve alignment performed using a least square–like approach. An extended database of theoretical rheological function graphs and tables, developed from complex mathematical models and prior research, was employed in the analysis. Importantly, the study highlights that modern aircraft structures, where a significant portion of elements are made of advanced composite materials, are exposed during flight to complex, time-dependent loading conditions. Under these conditions, creep phenomena may develop within structural components, leading to residual deformations and gradual degradation of mechanical properties over time. Even with initially high safety margins, such effects can eventually cause the failure of critical elements after prolonged operation. Therefore, the presented method provides a scientific and practical tool for assessing and predicting the long-term viscoelastic–plastic behavior of aviation composites, ensuring structural integrity, flight safety, and an extended operational lifetime of aircraft.