13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- 25 mm gage length specimen, the Young’s modulus increases from 109 ± 11 GPa at a strain rate of 30 s-1 to 111 ± 10 and 128 ± 11 GPa at strain rates of 50 s-1, and 100 s-1 respectively. The tensile strength increases from 1622 ± 104 MPa at a strain rate of 30 s-1 to 1675 ± 51 and 1707 ± 82 MPa at strain rates of 50 s-1, and 100 s-1, respectively. Maximum strain increases from 0.0245 ± 0.003 mm/mm to 0.0253 ± 0.0017 mm/mm and then to 0.0282 ± 0.0022 mm/mm, and toughness increases from 20.1 ± 2.6 to 20.5 ± 1.4 MPa and to 26.0 ± 4.3 MPa when the strain rate increases from 30 to 50 and then to 100 s-1. For the 50 mm gage length specimen, the Young’s modulus increases marginally from 118 ± 28 to 121 ± 22 GPa when the strain rate increases from 20 to 60 s-1. While the tensile strength increases by as much as 23.5% from 1579 ± 100 to 1874 ± 110 MPa, the maximum strain increases about 15% from 0.0217 ± 0.003 mm/mm to 0.025 ± 0.0026 mm/mm, and toughness increases about 29 % from 18.8 ± 2.5 MPa to 24.3 ± 4.0 MPa. 0 40 80 120 160 Strain Rate, s-1 80 120 160 200 Young's Modulus, GPa L0 = 25 mm L0 = 50 mm (a) 0 40 80 120 160 Strain Rate, s-1 1200 1600 2000 2400 2800 Tensile Strength, MPa L0 = 25 mm L0 = 50 mm (b) 0 40 80 120 160 Strain Rate, s-1 0.01 0.02 0.03 0.04 0.05 Maximum Engineering Strain, mm/mm L0 = 50 mm L0 = 25 mm (c) 0 40 80 120 160 Strain Rate, s-1 10 20 30 40 50 Toughness, MPa L0 = 25 mm L0 = 50 mm (d) Figure 5. Strain rate effect on the dynamic material properties of Kevlar 49 fabric: (a) Young’s modulus, (b) tensile strength, (c) maximum strain, and (d) toughness. L0 is the gage length.
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