StressKote brittle coatings, formerly known as Stresscoat, are typically used as a preliminary step for strain measurements with resistive strain gages. StressKote brittle coating is applied according to published instructions to the test product. The product is then subjected to static or dynamic loading. StressKote brittle coating will fracture in response to the surface strain beneath it and show the direction and magnitude of stress within the elastic limit of the base material, allowing critical stress areas to be visualized and location and orientation for strain gages to be determined.
How stresskote BRITTLE COATING is applied
Pre-Test Preparation
Note all safety concerns with StressKote brittle coating materials and maintain safety sheets for immediate access when required. Proper ventilation and personal protection methods are recommended.
A knowledge and thorough examination of the test surface to locate contaminants is very useful, particularly if synthetic oils are present. The application of the brittle coating or lacquer coating must be preceded by a thorough cleaning to free the surface of oil, dirt, loose paint, rust, etc. An undercoating of aluminized paint is advised for a uniform reflective surface to enhance crack visibility of the final coatings, and should be dried according to labeling. StressKote is then ready to be applied.
Application
StressKote brittle coating, formerly Stresscoat, is available for a wide range of test temperatures. StressKote can be easily applied to almost any test material. Test bars and the test specimen should be coated at the same time with the same batch of StressKote and dried together so that the coatings are identical. Apply the StressKote lacquer in successive, thin, wet layers, allowing a few minutes between coats for initial air drying. Using a clean, dry air supply is recommended to prevent blisters or fish-eyes. Color tone can be used to estimate the final lacquer thickness, optimally in the 0.003 inch to 0.006 inch range. Drying usually is complete within an 18-24 hour period when dry temperature is 100 degrees Fahrenheit or higher. Lower strain sensitivities will be common if the solvent volatiles are not removed with the higher drying temperatures. StressKote lacquer dries to a distinctive bronze color, offering excellent contrast for observation of crack patterns. Consideration should be given when purchasing from the selection of brittle coatings, to the size of the project and amount of coating to be used. The solvent system employed as in previous products, does evaporate quickly, with some solvent components more volatile than others. Therefore if the container is only partially used or left open the ratio of solvent components changes which may affect the performance and drying characteristics of the coating. Additional can (seals) can be supplied to properly re-seal containers to help control deterioration of the product. Addition of the coating thinner can help to reinstate a compromised solvent ratio of the coating and should be kept on hand. For smaller projects the aerosol container version available can help insure a quality product. Additional spray nozzles can be supplied to insure full use of the coatings available in that container.
Testing
After the drying period, loading can commence, as in actual operation, or loading incrementally, to derive the maximum strain distribution information. In this case, load range rings at the ends of the cracks may be appropriate to display load increments. If a single load application is used, a grease pencil or china marker can be used to mark the cracks if photocopies are used for recording data. The cracks first occur where the tensile strain levels are highest and are always oriented perpendicular to maximum principal tensile strain. If the test temperature is maintained, an approximate strain level may be determined by comparison to the test bars.
Usually, bonded resistive strain gage installations follow the StressKote brittle coating process to obtain reliable strain/stress levels and angle variations.
Compressive strains can be determined by loading the test item and maintaining a load point for a selected number of minutes or hours before releasing the load, permitting the coating to creep, thereby allowing the released load direction to look like tensile strain.
Clean Up
Clean up of surfaces with StressKote brittle coating should be done with care to avoid inhalation of the dry dust as some chemical content is retained in the dry coating. The MSDS sheets should always be referenced for properly handling and disposal of the wet and dry coating.
SK Coatings Distributors, LLC
1833 Executive Drive, Ste. 102
Oconomowoc, WI 53066
Office: 262-569-9789
Fax: 262-569-9791
24-Hour Order Contact: 262-510-9568
24-Hour US Emergency: 800-373-7542
24-Hour International Emergency: 484-951-2432
sales@stresskote.com
