Abstract
The mechanism of brittle fracture of high-polymer solids is experimentally investigated under one-or two-dimensional stress states by a new photoelastoplastic method suggested by the author. The application of the photoelasto-plastic method on the brittle-fracture problem is based on the principle that breaking stress can be computed in brittle fracture by the measurement of the fringe orderN B of isochromatic lines at fracture point.
Bending under three-point and four-point loads, and the plane problems, some having stress concentration and others being under contacting load, are examined by using rigid polyester cast resin containing styrol as a model specimen; and, in conclusion, the brittle fracture of high-polymer solids under one- or two-dimensional stress states is decided by the constant tensile stress, whose magnitude depends only upon the material used as a model specimen, and is larger than its ultimate tensile strength.
Many kinds of factors in fracture are defined, and stress-concentration factors in fracture are compared with stress-concentration factors in elasticity. A new photoelasto-plastic simple method for the determination of stress-concentration factors in elasticity is suggested by utilization of the experimental results on this brittle fracture of high-polymer solids and is examined on the perforated plane problem having finite width under tension in comparison with theoretical analysis and the experimental results by other measuring methods.
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Abbreviations
- σ t :
-
tensile stress, Kg/mm2
- ε t :
-
tensile strain, %
- N :
-
fringe order of isochromatic line, F.O.
- λ:
-
wave length of monochromatic, circularly polarized light, Å
- α:
-
photoelastic sensitivity, F.O./Kg/mm
- N B :
-
fracture fringe order at fracture point in test specimen, F.O.
- t :
-
thickness of plate test specimen, mm
- (σ1 - σ2):
-
difference of principal stresses, Kg/mm2
- \({\bar \sigma }\) :
-
effective stress, Kg/mm2
- \(\bar \varepsilon\) :
-
effective strain, %
- M B :
-
breaking bending moment, Kg/mm
- b σBN :
-
extreme fiber stress at fracture measured by photoelasto-plastic method, Kg/mm2
- b σB cal :
-
extreme fiber stress at fracture computed from breaking bending moment, Kg/mm2
- σT :
-
ultimate tensile strength of test specimen, Kg/mm2
- σC :
-
ultimate compressive strength of test specimen, Kg/mm2
- c :
-
distance between two supports for a beam in three-point bending, mm
- σA, σE :
-
stress at pointsA andE, respectively, of perforated-plate specimen, Kg/mm2
- l :
-
initial length of specimen, mm
- w :
-
initial width of specimen, mm
- d :
-
initial diameter of circular hole in perforated-plate specimen, mm
- σ c ′, ε c ′:
-
apparent compressive stress and strain for perforated-plate specimen, computed on the basis of the cross-sectional area without a hole, Kg/mm2, %
- P :
-
applied load, Kg
- c σm :
-
mean compressive stress in plate specimen in the cross section without a hole, Kg/mm2
- c σBM :
-
mean compressive stress in plate specimen in the cross section without a hole at fracture, Kg/mm2
- c σBN :
-
fracture stress at fracture point of plate specimen under compressive load, measured by photoelasto-plastic method, Kg/mm2
- k A ,k E :
-
analytical value of stress-concentration factor in elasticity at pointsA andE, respectively, for perforated specimen under uniform tension, computed on the basis of mean stress in the cross section with a hole
- k A′ ,k E′ :
-
analytical value of stress-concentration factor in elasticity at pointsA andE, respectively, for perforated specimen under uniform tension, computed on the basis of mean stress in the cross section without a hole
- N max :
-
maximum fringe order of isochromatic lines, F.O.
- d P :
-
diameter of circular, load-carrying pin, mm
- t σBN :
-
fracture stress at fracture point of plate specimen under tensile load, measured by photoelasto-plastic method, Kg/mm2
- t σBM :
-
mean tensile stress in plate specimen in the cross section without a hole, at fracture, Kg/mm2
- P B :
-
breaking load, Kg
- t P B :
-
breaking tensile load, Kg
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Ito, K. Photoelasto-plastic studies on brittle fracture of high-polymer solids. Experimental Mechanics 1, 159–168 (1961). https://doi.org/10.1007/BF02327587
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DOI: https://doi.org/10.1007/BF02327587