Chapt. 7 Mechanics Properties of polymers 7.1 Basic physical quantities Stress, strain, modulus 7.2 Mechanics properties of rubber elasticity Theory of rubber elasticity 7.3 Fracture Mechanics of Brittle materials Griffith Theory 7.4 Fracture properties of polymer in glassy and crystalline state Yield(屈服), Craze(银纹, Fracture(断裂)
Chapt. 7 Mechanics Properties of Polymers 7.1 Basic physical quantities 7.3 Fracture Mechanics of Brittle Materials Stress, strain, modulus Theory of rubber elasticity 7.4 Fracture properties of polymer in glassy and crystalline state Yield(ቸᴽ), Craze(䬦㓩), Fracture(ᯝ㻲) 1 7.2 Mechanics properties of rubber elasticity Griffith Theory
Mechanical properties of polymer Bulk polymers combine elastic and viscous properties in both the fluid and the solid state. Therefore they are generally addressed as“ viscoelastic”(.弹)and,in fact, polymers are the main representatives of this special class of materials. Different fields of polymer application are concerned and they all need their own approaches: the properties under moderate loads, where deformations and velocities of viscous flow remain small the case of large reversible deformations realized in rubbers and the rheological properties of polymer melts at higher strain rates, both representing non-linear behavior and finally, of special importance for applications, yielding (h 服) and fracture(断裂)
Mechanical properties of polymer: Bulk polymers combine elastic and viscous properties in both the fluid and the solid state. Therefore, they are generally addressed as “viscoelastic” (㋈ᕩ) and, in fact, polymers are the main representatives of this special class of materials. ¾ Different fields of polymer application are concerned and they all need their own approaches: ¾ the properties under moderate loads, where deformations and velocities of viscous flow remain small ¾ the case of large reversible deformations realized in rubbers and the rheological properties of polymer melts at higher strain rates, both representing non-linear behavior ¾ and finally, of special importance for applications, yielding (ቸ ᴽ) and fracture (ᯝ㻲)DŽ 2
7.1 Stress strain and modulus ensue shear bulk F
7.1 Stress, strain and Modulus F F l0 l A0 T A0 F tensile shear bulk 3
Characterization of viscous flow 复杂流动方式的分解:三种最基本的流动变形)方式 a剪切流动(形变) shear viscosity n、b拉伸流动(形变) tensile viscosity n velocity gradient→ c.压缩流动(形变)- bulk viscosity for incompressible fluids nb)00
Characterization of viscous flow ༽ᵲ⍱ࣘᯩᔿⲴ࠶䀓˖й⿽ᴰสᵜⲴ⍱ࣘ)ਈᖒ)ᯩᔿ a.࠷࢚⍱ࣘ)ᖒਈ)-shear viscosity Ks b.ը⍱ࣘ)ᖒਈ)-tensile viscosity Kt c. 㕙⍱ࣘ)ᖒਈ)-bulk viscosity for incompresible fluids Kbof velocity gradient 2 dv dx 4
7.1 Stress strain and modulus tensile shear bulk F b F △F t-I A 2-1E tan≈0 B=o/4 e=oE Young's Modulus G=o/y Shear Modulus Bulk Modulus 5
7.1 Stress, strain and Modulus 0 tan s F A l l V J TT ' | ,N 0 0 0 1 t F A l l l V H O F F l0 l A0 T A0 F 0 , 0 ln t t l l F A dl l l l V H ³ G=Vs E=V /J t /H 0 b P V V V ' ' B=Vb /' tensile shear bulk Young’s Modulus Shear Modulus Bulk Modulus 5