Nonlinearly Viscoelastic Behavior of Polycarbonate. I. Response under Pure Shear

The nonlinearly thermo-mechanical creep behavior of (bisphenol A)polycarbonate was investigated at different temperatures (0 to 140°C) under pure shear loading. The shear creep in the linearlyviscoelastic range was measured with a torsiometer for referencepurposes and a master curve, along with a shift factor curve, wasconstructed. While the master curve is well defined with no detectabledeviation, the shift factor can be represented by essentially twostraight lines and offset at the β transition temperature ofpolycarbonate. The shear creep tests in the nonlinearly viscoelasticrange were conducted on an Arcan specimen geometry at differenttemperatures and under different stress levels, utilizing digital imagecorrelation for recording the creep strains. The difference between thenominal stress and the actual stress distribution in the Arcan specimenwas explored via numerical simulations (ABAQUS) by assuming linearlyquasi-elastic and quasi-plastic analyses in place of the as yetuncertain material characterization. Isochronal plots were created fromthe creep data. Nonlinearly viscoelastic behavior starts to take effectnear 1% strain at the temperatures considered. The applicability of thestress-clock representation for material characterization has beenexplored and is found, at best, to be dubious for this material. The`yield-like' behavior of polycarbonate has been examined in terms of theisochronal stress-strain response and a corresponding `yield-like shearstress' has been determined to be a monotonically decreasing function ofthe temperature, but again with an interruption or `jog' at the βtransition temperature. Time-temperature trade-off as practiced for`time-temperature shifting' at small strains does not apply in thenonlinear domain. The results are generally in agreement with thosefound for Poly(Methyl Methacrylate), thus fostering the idea that thepresent results can be generalized – with additional work – to other amorphous polymers.

[1]  G. McKenna,et al.  On the Physics Required for Prediction of Long Term Performance of Polymers and Their Composites , 1994, Journal of research of the National Institute of Standards and Technology.

[2]  David Turnbull,et al.  Molecular Transport in Liquids and Glasses , 1959 .

[3]  W. Knauss,et al.  Strain inhomogeneity and discontinuous crack growth in a particulate composite , 1998 .

[4]  W. Knauss,et al.  A reconciliation of dynamic crack velocity and Rayleigh wave speed in isotropic brittle solids , 1994, International Journal of Fracture.

[5]  N. Tschoegl,et al.  Effect of pressure on the mechanical properties of polymers. 2. Expansivity and compressibility measurements , 1983 .

[6]  Wolfgang G. Knauss,et al.  On the hygrothermomechanical characterization of polyvinyl acetate , 1980 .

[7]  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.

[8]  Richard Schapery.  An engineering theory of nonlinear viscoelasticity with applications , 1966 .

[9]  L. Brinson,et al.  Effects of physical aging on long term creep of polymers and polymer matrix composites , 1995 .

[10]  G. McKenna,et al.  Volume recovery in epoxy glasses subjected to torsional deformations: the question of rejuvenation , 1991 .

[11]  K. Liechti,et al.  An evaluation of the arcan specimen for determining the shear moduli of fiber-reinforced composites , 1997 .

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

[13]  Hongbing Lu,et al.  Surface deformation measurements of a cylindrical specimen by digital image correlation , 1997 .

[14]  K. Liechti,et al.  Finite Element Analysis of the Arcan Specimen for Fiber Reinforced Composites under Pure Shear and Biaxial Loading , 1999 .

[15]  The Temperature and Frequency Dependence of the Bulk Compliance of Poly(Vinyl Acetate). A Re-Examination , 1997 .

[16]  Hongbing Lu.  Nonlinear thermo-mechanical behavior of polymers under multiaxial loading , 1997 .

[17]  W. Peters,et al.  Digital Imaging Techniques In Experimental Stress Analysis , 1982 .

[18]  Henry Eyring,et al.  Mechanical Properties of Polymeric Materials , 1943 .

[19]  Arthur K. Doolittle,et al.  Studies in Newtonian Flow. II. The Dependence of the Viscosity of Liquids on Free‐Space , 1951 .

[20]  James M. Caruthers,et al.  Thermodynamic constitutive equations for materials with memory on a material time scale , 1996 .

[21]  Wolfgang G. Knauss,et al.  Nonlinearly Viscoelastic Behavior of Polycarbonate. II. The Role of Volumetric Strain , 2002 .

[22]  Mircea Arcan,et al.  The iosipescu shear test as applied to composite materials , 1984 .

[23]  Y. Liang,et al.  On the large deformation and localization behavior of an epoxy resin under multiaxial stress states , 1996 .

[24]  K. J. Saunders.  Organic Polymer Chemistry: An Introduction to the Organic Chemistry of Adhesives, Fibres, Paints, Plastics, and Rubbers , 1973 .

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

[26]  J. Ferry,et al.  Mathematical Structure of the Theories of Viscoelasticity , 1955 .

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

[28]  Z. Hashin,et al.  A method to produce uniform plane-stress states with applications to fiber-reinforced materials , 1978 .

[29]  R. Landel,et al.  The Temperature Dependence of Relaxation Mechanisms in Amorphous Polymers and Other Glass-Forming Liquids , 1955 .

[30]  Thomas S. Gates,et al.  Comparison of Physical Aging Effects on the Tension and Compression Creep of the IM7/K3B Composite , 1996, Aerospace.

[31]  Hongbing Lu,et al.  The Role of Dilatation in the Nonlinearly Viscoelastic Behavior of PMMA under Multiaxial Stress States , 1998 .

[32]  R. S. Rivlin,et al.  The mechanics of non-linear materials with memory , 1957 .

[33]  M. Boyce,et al.  A constitutive model for the nonlinear viscoelastic viscoplastic behavior of glassy polymers , 1995 .

[34]  Ronald S. Rivlin,et al.  The mechanics of non-linear materials with memory , 1959 .

[35]  W. Knauss,et al.  A simple creep torsiometer and its use in the thermorheological characterization of a structural adhesive , 1982 .

[36]  G. Vendroux,et al.  Submicron deformation field measurements: Part 2. Improved digital image correlation , 1998 .

[37]  R. Christensen.  Theory of viscoelasticity : an introduction , 1971 .

[38]  B. Bernstein,et al.  A Study of Stress Relaxation with Finite Strain , 1963 .

[39]  Wolfgang G. Knauss,et al.  A Note on the Determination of Relaxation and Creep Data from Ramp Tests , 2000 .

[40]  W. Knauss,et al.  The Time-Dependent Bulk Response of Poly (Methyl Methacrylate) , 2001 .

[41]  J. Ferry.  Viscoelastic properties of polymers , 1961 .

[42]  Herbert Leaderman,et al.  Elastic and creep properties of filamentous materials and other high polymers , 1943 .