The viscosity of a soda‐lime silica glass was measured at high strain rates. The data show non‐Newtonian viscous flow in this inorganic oxide glass with the viscosity values below the expected Newtonian value. Following the imposition of large, steady strain rates, the observed stress increases with time to a maximum and then decreases to a time‐independent value. A comparison of the viscosity behavior of this glass with the molecular dynamics results in a ’’Lennard‐Jones’’ glass shows a number of points of correspondence and suggests the interpretation of the non‐Newtonian behavior as resulting from structural rearrangements in the material. The combined data show that the sustained, steady‐state stress asymptotically approaches a maximum at very high strain rates. This limiting stress is interpreted as the actual cohesive strength of the material and is calculated to be 1.4×108N/m2 (20,000 psi) for the glass under study.

Non‐Newtonian viscous flow in glass

Stress optical studies of oriented poly(methyl methacrylate)

The microscopic infrared dichroism measurement is made on a quenched iPP thin film during the stepwise elongation to obtain the molecular orientation functions, fam and fc, in the amorphous and the crystalline phases, respectively. Results reveal that the pseudo-affine deformation of the amorphous phase occurs for fam < 0.45 with fc = 1.85fam, and concurrent structure alternation of a small portion of crystallites is evidenced from a limited change in the degree of crystallinity Vc. The true stress−strain relationship on the mesoscale is discussed on the basis of an interpenetrating network model, in which thin threadlike strands composed of crystallites firmly connected through intercrystalline links (C network) penetrate through an elastic network composed of amorphous chains interconnected to each other with lamellae at cross-linking sites (CEAM network). Combining the Matsuoka viscoelastic constitutive equation and the Takayanagi model for the C network below and above the yielding point, respectively...

Molecular Orientations and True Stress-Strain Relationship in Isotactic Polypropylene Film†

Cold-drawn uniplanar-axially oriented sheets of nylon 6 have been annealed at 195°C, hot-rolled at 130°C, and then chemically treated with phenol to form the α crystalline phase. The morphology is parallel-lamellar, with the molecular chains at right angles to the lamellar plane. The long period is 96.7 ± 0.7 A. The extensional compliances S33 (parallel to the draw direction) and S11 (the transverse direction in the sheet) and the shear compliances S44, S55, and S66 have been measured at 20.0 ± 0.3°C by dead-loading creep and torsional methods, in two relative humidity ranges, 0–10% and 61–69% RH. Dependence upon time (creep), strain, and humidity have also been determined. The extensional compliances show the cross-over of S33 above S11 when the αa transition or Tg is reduced to below room temperature by increasing the relative humidity from zero to 65%. The results are explained by using Takayanagi models for the extensional compliances and interlamellar shear or crystallite shear for the shear...

Anisotropic mechanical properties of drawn nylon 6. I. The α phase

The role of individual chains in polymer deformation

Two aspects of the mechanical behaviour of solid polymers are reviewed: (i) anisotropic mechanical behaviour of oriented polymers, and (ii) nonlinear viscoelastic behaviour. In the case of anisotropic behaviour, the discussion includes a comprehensive account of progress to date in obtaining experimental data, together with recent attempts at understanding the behaviour in structural terms. The discussion of nonlinear viscoelastic behaviour, on the other hand, is almost entirely at a phenomenological level. Here it is attempted to bring together the many different approaches and to show their common relationships, particularly between the engineering formulations and those based on continuum mechanics.

https://iopscience.iop.org/article/10.1088/0034-4885/38/10/001/pdf

I M Ward

Papers

Anisotropic and nonlinear viscoelastic behaviour in solid polymers