Brittle Coat Test

Davalsab.M.L M.Tech (Machine Design)

Reva University, Bangalore

Daval.techno@gmail.com

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.

3Types of Coating

• Resin based coating (Stress Coat)• Ceramic based coating (All temp)• Tens Lac Brittle Lacquer.

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

5Resin Based coating

Floor epoxy coating Epoxy Resin

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.

7Ceramic based coating

High Heat Titanium Ceramic Coating

Spark plug

8Tens. Lac Brittle Lacquer

• High sensitivity, non-flammable, odorless, and of low toxicity brittle lacquer.• Thickness 0.075mm • sensitivity 500u cm/cm • temp 1000c.

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

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.

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)

12Cracks formed

13References:

• Experimental Stress Analysis: Jindal

Thank you