On Strain-rate Independent Fracture Toughness and Relaxation in Cyclic Tensile Behavior: A Case Study for Toughened Biobased Polyamide 410 Blends

Abstract

The equivalence in strain-rate dependent fracture toughness of toughened biobased polyamide 410 blends under high-strain conditions as in Izod impact toughness and low strain conditions as in essential work of fracture (EWF) assessment is discussed in this work. An escalation of ∼57% in resistance to crack initiation (we) (EWF parameter) and an increase of ∼356% Izod impact strength confirms the semi-ductile to ductile transition in the range of 10-15 wt.% of elastomer loading. The isotropic responses, i.e., strain-rate independent fracture-toughness of the blends, have indicated three factors (a) toughness originating from shear yielding/banding or craze bridging of dispersed elastomer domain, (b) gradual reduction in matrix stiffness and strength with greater extent of plastic deformation and (c) crack tip-blunting based fracture work to be responsible behind toughening of the blends. The crack opening displacement (COD) has indicated out-of-plane, i.e., vertical extension of advancing crack tip to be exceeding the in-plane crack extension in the composition range of 10-15 wt.% of the blends. The uniaxial cyclic-loading till twenty cycles with a 10 N increment (in every next cycle) showed the plastic-strain contribution to net deformation of the material. The phase-lag in the loading and unloading cycle (work loss hysteresis) increased with the number of cycles and plastic strain owing to viscosity-controlled energy dissipation in the form of cyclic plastic deformation showing elasto-viscoplastic nature of the PA 410 blend system.