SAE J400 Chip Resistance Testing of Surface Coatings

An SAE aviation standard, “SAE J400 Chip resistance testing of surface coatings,” describes a laboratory procedure for testing and evaluating the resistance of a surface coating to fracture by gravel impact.

This test method is designed to reproduce the impact of gravel or other media hitting the exposed paint or coated surfaces of an automobile and is correlated with actual field results. The purpose of this method is to evaluate organic surface coatings or systems on flat test panels. However, if the results are interpreted in terms of the limitations and objectives implied by the original test procedures and rating system, it may be possible to extend such tests to finished parts or other types of materials such as anodized aluminum or coated plastics.

This standard may contain hazardous materials, processes and equipment. This standard is not intended to address all safety issues associated with its use. It is the responsibility of the person using this standard to consult and establish safety and health practices and to determine the applicability of regulatory limitations prior to use.

All dimensions are nominal unless otherwise stated.

According to this standard, three replicates are made for each test sample. The sample size is usually flat 10 cm x 30 cm.

This test consists of projecting road gravel onto a suitable test panel using controlled air blast. Prior to testing, the sample should reach ambient temperature for at least 15 minutes.

The gravel for this test should be water-worn road gravel. There should be no crushed limestone or rock. In addition, when the gravel is graded, it should pass through a 15,86 mm mesh sieve. The gravel should also be washed prior to testing.

During gravel exposure, no more than 10 pt of gravel is allowed to collect on the sizing sieve. After 10 pt is collected, smaller rocks are removed by scraping through the sieve.

After the gravel hit, tape is applied to remove loose paint particles from the panel.

There are two methods to determine the degree of cracking:

• Method I: Tabulates the exact number of chips in each size range.
• Method II: Visually compares the tested panel to the SAE chip rating standard.

Once the test is complete, the report will include the rating and all applicable test conditions used. The report will also include the test results, material type, thickness and any pre-surface treatment of the test panel.

The equipment used in the tests is used to test and evaluate the impact resistance of test pieces or surface coatings against gravel impact. The gravel impact resistance testing machine is a testing device that meets the gravel impact resistance test of different automotive materials and surface coatings standards. In these devices, the test program can be set as control variables for gravel impact test, pressure, time and other variables. These devices have a large volume storage compressed air tank, and the adjustable highest range is generally 8 bar, and the accuracy is 1 percent of the last fixed value.

In tests, the resistance of coatings to stone chips is tested by projecting many small sharp-edged impact tools. The bombardment material is defined as a cooled iron particle that is struck by compressed air onto the coating at a certain angle. The working pressure, the mass of the bombardment material, the crusting time and the construction of the test apparatus affect the extent of damage.

Briefly, this standard includes a procedure for assessing the resistance of automobile coatings and other coatings to cooled particles projected onto the tested surface to simulate the impact of small stones. The resistance of the tested coating to stone chips is checked by projecting a large number of small sharp-edged bodies onto it in a short time. The extent of the damage produced depends not only on the angle, but also on the pressure level, the mass of the projectiles, the duration of the bombardment and the design of the test apparatus.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services in accordance with the "SAE J400 Surface coatings chip resistance test" standard are also provided to businesses.