Abstract
A normal-incidence reflective polariscope, together with some auxiliary instrumentation, is described. The instrument consists of eight unit polariscopes, relatively oriented, which are indexed into position within a short period of time to obtain a set of eight data. These data provide sufficient information to separate the principal strains obtained at different time intervals. The primary experimental objective was to design an inflated-cylinder test, analogous to the loading experienced in a solid-propellant rocket, that would enable reasonable measurements of the triaxial surfacelayer strains of a viscoelastic material as a function of time. The stress geometry imposed on the viscoelastic material was that of an unrestricted, biaxially pressurized, thick-walled tubular cylinder. The material investigated was polyurethane solid propellant. Two different methods to reduce the biaxial strains in a low-modulus birefringent polyurethane coating are also described.
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Abbreviations
- C :
-
stress-optic constant, psi−1
- E :
-
Young's modulus, psi
- e 33 :
-
thickness strain of the coating
- n :
-
number of points being investigated
- n 11 :
-
refractive index in the 11 privileged direction
- n 22 :
-
refractive index in the 22 privileged direction
- t :
-
coating thickness at any state of strain, in
- t 0 :
-
original coating thickness, in
- x i :
-
distance from a pointi on the reference radial trace to the shear plane ψ, in
- y n :
-
distance from symmetrical center of cylinder to point under investigation, in
- x,y,z :
-
Cartesian coordinate system (z thickness of coating)
- δ:
-
equal increment on the radial trace=(y 1 −y n )/(n−1)
- ∈ 11 :
-
principal strain in the 11 privileged direction
- ∈ 22 :
-
principal strain in the 22 privileged direction
- ∈ 33 :
-
longitudinal strain of the thick-walled cylinder
- θ:
-
reference angle, deg
- μ:
-
Poisson's ratio
- σ 11 :
-
principal stress in the 11 privileged direction
- σ 22 :
-
principal stress in the 22 privileged direction
- σ ψ :
-
shear stress, psi
- ψ:
-
angle at which shear acts, deg
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This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under ARPA Contract Letter Order No. 107-60 and NAS 7-100 sponsored by the National Aeronautics and Space Administration.
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San Miguel, A., Silver, R.H. A normal-incidence reflective polariscope for viscoelasticity measurements. Experimental Mechanics 5, 345–352 (1965). https://doi.org/10.1007/BF02327538
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DOI: https://doi.org/10.1007/BF02327538