Abstract
One of the basic problems of structural-model analysis, model photoelasticity and photoelastic coatings in the problem of mechanical and optical creep, relaxation and related phenomena. It is pointed out that, in spite of creep or relaxation, it is possible to achieve physical similarity between model and object if the model material behaves in a certain range as a linear viscoelastic material. Such a material is called a “momentarily linear material.” Several model materials behave in this way in a certain range of stress and time.
Because of creep and relaxation, the common tensile tests are, in general, not quite adequate for evaluation of physical properties of plastics used for models. Also the bending test is not always adequate. It is shown how to obtain sufficiently accurate relations between stress, strain, birefringence and time, using tapered specimens.
The problem of biaxial creep of model materials is discussed, and a simple method of evaluating the suitability of a given plastic as a model material is shown. Some conclusions concerning time-dependent factors are formulated, and some possible areas of investigation are shown.
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Abbreviations
- (E) t :
-
time-dependent value of the elasticity modulus
- m :
-
order of isochromatic
- S ε :
-
material strain-fringe value
- \(\left( {S_\sigma } \right)_t \) :
-
time-dependent material stress-fringe value
- t :
-
time
- ε:
-
strain
- \( \in _{ \in l} \) :
-
elastic strain
- \( \in _{in} \) :
-
inelastic strain
- σ:
-
stress
- d :
-
thickness of model
- R :
-
relative retardation
- λ:
-
wavelength of light
- D :
-
dispersion of birefringence
- \(\sigma _1 \) :
-
creep, stress level 1 (Fig. 1c)
- \(\sigma _2 \) :
-
creep, stress level 2 (Fig. 1c)
- (σ)0 :
-
creep recovery, after creep at stress σ (Fig. 1c)
- (σ 1)0 :
-
creep recovery, after creep at stressσ 1 (Fig. 1c)
- (σ 2)0 :
-
creep recovery, after creep at stressσ 2 (Fig. 1c)
- m 0 :
-
isochromatic order immediately (less than 0.1 sec) after loading or unloading (Fig. 5)
- m end :
-
isochromatic order before unloading (1–60 sec before), or at the end of the test (Fig. 5)
- dm/dt :
-
rate of optical creep (Fig. 5)
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Jerzy T. Pindera was Visiting Professor of Mechanics, Department of Metallurgy, Mechanics and Materials Science, Michigan State University, East Lansing, Mich. at time that paper was prepared
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Pindera, J.T. Remarks on properties of photoviscoelastic model materials. Experimental Mechanics 6, 375–380 (1966). https://doi.org/10.1007/BF02327215
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DOI: https://doi.org/10.1007/BF02327215