brittle coating and test
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2Definition
Brittle coat testing is a Stress coat brittle coating, is one of the most straightforward and effective methods of experimental stress analysis used to improve product design. It locates critically stressed areas and visually presents principal strain directions, as well as information on the strain gradients – all of which are needed for the proper selection, location and orientation of strain gages for accurate measurement of peak stresses.
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3Types of Coating
• Resin based coating (Stress Coat)• Ceramic based coating (All temp)• Tens Lac Brittle Lacquer.
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4Resin based coatingStress coat
1/3rd zinc resinate + 2/3rd. Carbon Disulphlide small amount of plasticizer + di-butylphthalate.
Thickness 0.1-0.15mm ; Strain sensitivity 0.003-0.003m ; Coating can be used up temp 600c. This can applies by spray
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5Resin Based coating
Floor epoxy coating Epoxy Resin
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6Ceramic based coatingAll temp
• Finely ground ceramic particles suspended in a solvent + drying + heated up to 5400c (until ceramic particles melt and coalesce).• Thickness 0.1-0.15mm ; • Stress sensitivity 0.002-0.002m ; • Coating can be used up to temp 3700c.
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7Ceramic based coating
High Heat Titanium Ceramic Coating
Spark plug
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8Tens. Lac Brittle Lacquer
• High sensitivity, non-flammable, odorless, and of low toxicity brittle lacquer.• Thickness 0.075mm • sensitivity 500u cm/cm • temp 1000c.
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9Classification
Property Stress coat All temp 1 Minor change in temp Very sensitive Insensitive 2 Limiting temperature 37.7’ c -45’c to 370’c 3 Effect of oil and water Influenced Not influenced 4 Firing of coating Not required Very high temperature
of 537.75 Visual observation Possible Not possible 6 Strain Sensitivity 300 to
3000micro cm/cm
200 to 2000 micro m/m
7 Suitable for All material Except those having melting point less than 537.7’c
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10Steps followed for brittle coating:
• Select the type of coating material.• Clean the surface of the specimen under
consideration.• Provide an undercoat to provide better reflective
characters.• Application of base coat and allowed to dry for 24
hours.• Testing of specimen.• Detection and Analysis of crack patterns.
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11Test Procedure
• The specimen with brittle coating is loaded then load is maintained for 15 seconds on the specimen then load is released.
• After unloading entire coating examined • Load on specimen increased and entire process repeated. • Crack pattern located after each loading are encircled and
marked with Number corresponding to load which produces the strain.
• Isentric line is loci of point of approximately constant principle stress.
• If the test is performed on cylindrical pressure 1st family of cracks perpendicular to (hoop stress and 2nd family of cracks are perpendicular to axial stress)
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12Cracks formed
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13References:
• Experimental Stress Analysis: Jindal
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Thank you