A predictive model for the effects of thermal history on the mechanical behavior of amorphous polymers

The effects of thermal history during formation on the mechanical behavior of amorphous polymer solids must be part of a constitutive description for polymers in order to enable efficient design of manufacturing processes. A nonlinear, thermoviscoelastic constitutive equation for amorphous polymers has been previously derived via the rational thermodynamics framework, where the dissipation is assumed to occur on a material timescale that is controlled by the non-equilibrium entropy, In this paper we report on the predictions of this constitutive equation for poly(vlnyl acetate). The material properties required by the constitutive model were determined for poly(vinyl acetate) from PVT and linear viscoelastic shear and bulk moduli measurements. Predictions of specific volumes during isobarfc cooling from the rubber and nonlinear uniaxial stress-strain curves just below Tg are in reasonable agreement with experimental data. The model predicts that samples cooled below Tg and then isothermally annealed for specified times will exhibit yield stresses that increase with Increasing annealing time, as well as the familiar effects of changes in temperature and strain rate on the uniaxial stress-strain and yield behavior. Shortcomings and potential improvements in the model are discussed.

[1]  A class of simple solids with fading memory , 1969 .

[2]  D. Plazek.  The Temperature Dependence of the Viscoelastic Behavior of Poly(vinyl acetate) , 1980 .

[3]  J. Sauer.  Deformation, yield and fracture of polymers at high pressure , 1977 .

[4]  P. M. Naghdi,et al.  A class of non-isothermal viscoelastic fluids , 1972 .

[5]  R. Simha,et al.  Use of a theoretical equation of state to interpret time-dependent free volume in polymer glasses , 1981 .

[6]  J. Ferry,et al.  Dynamic mechanical properties of polyvinyl acetate , 1954 .

[7]  R. Simha,et al.  Configurational Thermodynamic Properties of Polymer Liquids and Glasses. Poly(vinyl acetate). II , 1974 .

[8]  I. L. Hopkins.  Stress relaxation or creep of linear viscoelastic substances under varying temperature , 1958 .

[9]  S. Newman,et al.  Stress-Strain Behavior of Rubber-Reinforced Glassy Polymers , 1965 .

[10]  John E. McKinney,et al.  Dynamic Compressibility of Poly (Vinyl Acetate) and Its Relation to Free Volume , 1963, Journal of research of the National Bureau of Standards. Section A, Physics and chemistry.

[11]  K. C. Rusch,et al.  Yielding behavior of glassy polymers. I. Free-volume model , 1969 .

[12]  G. Adam,et al.  On the Temperature Dependence of Cooperative Relaxation Properties in Glass‐Forming Liquids , 1965 .

[13]  J. Ferry,et al.  VISCOELASTIC PROPERTIES OF POLYVINYL ACETATES. I. CREEP STUDIES OF FRACTIONS1 , 1963 .

[14]  Bernard D. Coleman,et al.  Thermodynamics of materials with memory , 1964 .

[15]  H. Kawai,et al.  Tensile stress relaxation behavior of partly to completely acetylated polyvinyl alcohol polymers , 1961 .

[16]  J. Caruthers,et al.  A New Nonlinear Viscoelastic Constitutive Equation for Predicting Yield in Amorphous Solid Polymers , 1986 .

[17]  R. Stratton,et al.  DYNAMIC MECHANICAL PROPERTIES OF POLYVINYL ACETATE IN SHEAR IN THE GLASS TRANSITION TEMPERATURE RANGE , 1963 .

[18]  Igor Emri,et al.  Volume change and the nonlinearly thermo‐viscoelastic constitution of polymers , 1987 .

[19]  M. Litt,et al.  Cold flow of glassy polymers. II: Ductility, impact resistance, and unoccupied volume , 1967 .

[20]  W. Knauss,et al.  Non-linear viscoelasticity based on free volume consideration , 1981 .

[21]  M. Goldstein,et al.  PVT Relationships for Liquid and Glassy Poly(vinyl acetate). , 1974, Journal of research of the National Bureau of Standards. Section A, Physics and chemistry.

[22]  Leslie Morland,et al.  Stress Analysis for Linear Viscoelastic Materials with Temperature Variation , 1960 .

[23]  K. C. Rusch.  Time-temperature superposition and relaxational behavior in polymeric glasses , 1968 .

[24]  L. Struik.  Physical aging in amorphous polymers and other materials , 1978 .