... | @@ -119,17 +119,22 @@ The whole problem has reflection symmetry so the final result would not be funda |
... | @@ -119,17 +119,22 @@ The whole problem has reflection symmetry so the final result would not be funda |
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There are two ways to implement the reflective photoelasticimetry. One is by using particles with reflective bases. The other is by putting particles on mirror.
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There are two ways to implement the reflective photoelasticimetry. One is by using particles with reflective bases. The other is by putting particles on mirror.
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### 3.1. Particles with reflective base
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### 3.1. Particles with reflective base
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This method requires to make one side of the particles reflective. This is usually achieved by coating a layer of reflective material. Note the reflective layer can not be harder than the material so that the elastic property of the particle would not change after coating. Current technique involves painting the particles using the mirror effect powders (link to be added, citation to be added).
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This method requires to make one side of the particles reflective. This is usually achieved by coating a layer of reflective material. Note the reflective layer can not be harder than the material so that the elastic property of the particle would not change after coating. Current technique involves painting the particles using the mirror effect powders (link to be added, citation to be added).
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Advantages:
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Advantages:
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1. The particles can be used on a air table where a mirror table can not be used.
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1. The particles can be used on a air table where a mirror table can not be used.
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2. This method does not have all the problems associated with a mirror table described below.
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Disadvantages:
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Disadvantages:
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1. The reflective light intensity is sensitive to the tilting angle of the particle if the light source is not very uniform. (Fig) This problem introduces non-negligible errors in the stress estimations (both for qualitative $`G^2`$ method and the quantitative inverse problem solver). This problem can be overcomed by rescaling the light intensity using a non polarized image.
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1. The reflective light intensity is sensitive to the tilting angle of the particle if the light source is not very uniform. (Fig) This problem introduces non-negligible errors in the stress estimations (both for qualitative $`G^2`$ method and the quantitative inverse problem solver). This problem can be overcomed by rescaling the light intensity using a non polarized image.
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2. The reflection ratio for the powders is usually not as good as a commercial mirror, creating larger noise to signal ratio in the detection of photoelastic patterns. (Calibration?)
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2. The reflection ratio for the powders is usually not as good as a commercial mirror, creating larger noise to signal ratio in the detection of photoelastic patterns. (Calibration?)
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### 3.2. Mirror base
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### 3.2. Mirror base
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In this method, the particles are transparent but they are put on a big mirror.
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In this method, the particles are transparent but they are put on a big mirror.
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Advantage:
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Advantage:
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1. No need for coating the particles so the particles used for this experiment can also used in other experiments with non-reflective polariscopes.
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1. No need for coating the particles so the particles used for this experiment can also used in other experiments with non-reflective polariscopes.
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2. Particle tilting will not cause light inhomogeneity.
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2. Particle tilting will not cause light inhomogeneity.
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3. The reflection ratio is better so the signal-to-noise ratio is better.
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3. The reflection ratio is better so the signal-to-noise ratio is better.
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Disadvantage:
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Disadvantage:
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1. For particles that is not directly beneath camera, the mirror image of their boundaries will be recorded, which reduces the accuracy of the boundary detection and thus the center detection. (Fig)
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1. For particles that is not directly beneath camera, the mirror image of their boundaries will be recorded, which reduces the accuracy of the boundary detection and thus the center detection. (Fig)
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2. For base-driven experiments to apply internal shear (cite), the split between bottom slats or bottom rings will cause discontinuous photo elastic fringes, increasing errors in the stress estimations.
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2. For base-driven experiments to apply internal shear (cite), the split between bottom slats or bottom rings will cause discontinuous photo elastic fringes, increasing errors in the stress estimations.
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