The effect of strain rate on fracture behavior of poly(methyl methacrylate) was investigated.The uniaxial tensile rupture tests for the poly(methyl methacrylate) samples were carried out at different strain rates at ambient temperature.It is found that the elastic modulus of the material increases with increasing strain rate,while the elongation is reversal with strain rate.Simultaneously,there exists a critical strain rate within which the stress-strain curves overlap one another,and beyond which the curves depart from each other.The amount of energy added to the system due to work done by the imposed load was calculated,and the strain energy stored in the material at each strain rate was calculated by the current stress integral with respect to strain.The complementary strain energy,which is the difference between the work and the strain energy,was obtained and was considered to supply the surface energy to create a new crack surface in the polymeric material.It is found that the work done by the imposed load,which is needed for the fracture of poly(methyl methacrylate) sample,decreases with increasing strain rate,and the strain energy decreases with strain rate as well,which demonstrates that the polymeric material at high strain rate is easier to fracture than that at low strain rate.As the strain rate increases,the fracture mode changes from ductile,semi-ductile to brittle mode.The complementary strain energy almost sustains a constant at any strain rate.The density of surface energy,which characterizes the energy per unit area needed for creating crack surface,is a strain rate-independent material constant.
PA6/PTFE blends with varying polytetrafluoroethylene content from 3% to 15%(mass fraction) were irradiated by 60Co gamma-ray with various doses(20,50 and 100 kGy) under ambient conditions.Moisture absorption test,U-notched Charpy impact test and quasi-static tension and bending were conducted to investigate the effect of irradiation on moisture absorption and mechanical properties of the blends.It is shown that the exposure of the blend to 60Co irradiation improves the tensile modulus,tensile strength and flexural modulus due to irradiation induced cross-linking in PA6 phase.However,the Charpy impact strength of the blends is much lower than that of the original PA6 and it decreases slightly with the increase of irradiation dose.Moreover,the flexural modulus increases to a maximum value and then decreases with further increasing the PTFE content,and the moisture absorption decreases with the increase of the PTFE content and irradiation dose.
