Dynamic shear fracture behaviors and "pseudo-plastic" constitutive model of carbon/carbon composite pins.

• The shear failure stress of C/C composites increases with increasing strain rate. • Under quasi-static loading, the C/C composites damage with fibers fracture successively and the shear stress-strain curve shows a "pseudo-plastic" characteristic, while brittle fracture features subjected to dynamic loading. • A viscoelastic constitutive model incorporated with a damage model based on the Weibull distribution function is proposed. To understand the strain rate sensitivity of carbon/carbon (C/C) composite pins' shear behaviors, quasi-static and dynamic experiments are conducted using an electric universal testing machine and a drop weight impact testing machine. A scanning electron microscope (SEM) is used to observe the shear fracture surfaces. The results show that the shear failure stress increases with increasing strain rate. Under quasi-static loading, the C/C composites damage with fibers fracture successively, and the shear stress-strain curve shows a "pseudo-plastic" characteristic, while brittle fracture features subjected to dynamic loading. In order to explain such differences, a viscoelastic constitutive model incorporated with a damage model based on the Weibull distribution function is proposed. Parameters of the constitutive model are estimated based on the experimental data. After that, the theoretical shear failure stresses are obtained by calculating the maximum shear stress of the constitutive model for different shear strain rates. The fitted model and theoretical failure stress match well with the experimental data. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]