Experimental Mechanics

, Volume 14, Issue 1, pp 10–18 | Cite as

Mechanical and optical characterization of an anelastic polymer at large strain rates and large strains

Two empirical constitutive relations have been determined which characterize, respectively, the uniaxial and photomechanical behavior of a polyester-styrene copolymer for strain rates from 10−5 to 3×103 in./in./s and strains up to 40 percent
  • K. W. Chase
  • W. Goldsmith
Article

Abstract

Two constitutive relations have been determined from test results that characterize, respectively, the uniaxial and photomechanical behavior of a polyester-styrene copolymer for strain rates from 10−5 to 3×103 in./in./s and strains up to 40 percent. The high-strain-rate data were obtained by means of a split-Hopkinson-bar apparatus. Intermediate-strain-rate tests, performed with the aid of a drop tower, were reported in an earlier paper. Quasi-static experiments were conducted on a standard testing machine.

A nonlinear, four-parameter, elastic-viscoplastic model was constructed which describes the mechanical behavior. The parameters were determined by a least-mean-squares curve-fitting procedure. The viscoplastic parameters were found to obey a power law in strain rate. The photomechanical model was found to be linear with strain well into the plastic-deformation region, while the slope of the strain-birefringence curve for each strain rate also varied by strain rate to a power.

Keywords

Polymer Mechanical Engineer Fluid Dynamics Mechanical Behavior Testing Machine 

List of Symbols

σ

uniaxial stress (psi)

y

yield stress (psi)

s

static stress (psi)

ε

uniaxial engineering strain (in./in.)

e

uniaxial Lagrangian strain (in./in.)

E0,E1

elastic moduli (psi)

E

asymptotic slope of stress-strain curve (psi)

η,\(\bar \eta \)

viscous moduli (psi-s)

τ,\(\bar \tau \)

relaxation time (s)

\(\eta _{O, } \bar \eta _O \)

coefficients of nonlinear viscous moduli (psi-s)

\(\tau _{O, } \bar \tau _O \)

coefficient of nonlinear relaxation times (s)

\(\bar \sigma _y \)

coefficient of rate-dependent yield stress (psi)

Ē1

coefficient of rate-dependent elastic modulus (psi)

q

power-law exponent

c0

rod-wave velocity (ft/s)

σ1, σ2, γ

empirically determined parameters

t

instantaneous specimen thickness (in.)

t0

initial specimen thickness (in.)

m

birefringence parametern/t (fringes/in.)

\(\dot m\)

rate of birefringence parameter (fringes/in./s)

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References

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Copyright information

© Society for Experimental Mechanics, Inc. 1974

Authors and Affiliations

  • K. W. Chase
    • 1
  • W. Goldsmith
    • 2
  1. 1.Department of Mechanical EngineeringBrigham Young UniversityProvo
  2. 2.Department of Mechanical EngineeringUniversity of CaliformiaBerkeley

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