The standard "ASTM D3170/D3170M Standard Test Method for Chipping Resistance of Coatings," developed by the American Society for Testing and Materials (ASTM), describes a test method for determining the resistance of coatings to chipping damage from stones or other flying objects. This test method is similar to the method described in the standard "SAE J-400 Chipping Resistance Test of Surface Coatings."
ASTM D3170 evaluates automotive coating systems, while SAE J-400 was originally developed for automotive OEM coating evaluation. In ASTM D3170, gravel is forced into the surface using compressed air using a gravel meter. The method is the same in SAE J-400. In ASTM D3170, the panel is placed at a fixed angle (usually 90 degrees), while in SAE J-400, the test is performed at various angles (e.g., 90 degrees, 45 degrees). ASTM D3170 uses a visual comparison based on a cracking scale (0-10 ratings), while SAE J-400 uses visual inspection and descriptive classifications or counts.
Vehicle owners consider coating fracture, particularly at the front and edges of vehicle surfaces, unacceptable. When formulating a coating or coating system to meet service requirements, resistance to fracture damage by flying objects such as gravel is a key characteristic, as it can vary significantly when other properties are adjusted. Because fracture resistance decreases at low temperatures, in part due to decreased flexibility, testing at a lower temperature can be more directly related to service conditions. This test method is designed to generate a controlled amount of impact by the media on the coated panel to improve repeatability.
The stone chip test is generally performed to evaluate the deformation caused by stone impact on coatings. At the end of the test, even if stone chips are present, the coating is considered to have a successful adhesion to the base metal as long as the paint does not separate. Such tests should always be conducted in accordance with relevant testing standards and requirements.
The fracture resistance of coatings refers to the ability of a coating material to resist damage when impacted by small, hard objects such as stones, gravel, or debris. It is a key performance indicator for protective coatings, particularly in the automotive, aerospace, and construction industries, where materials are exposed to harsh environments and physical impacts.
Fracture is the localized removal or breakage of a coating (e.g., paint, enamel, powder coating) from a substrate due to mechanical impact. This can expose the underlying base material to corrosion, abrasion, or aesthetic damage. Common standard tests for determining fracture resistance simulate real-world impact conditions. Typically, these tests spray a stream of gravel onto the coated surface under controlled conditions to assess the extent of the coating fracture. The stone chipping resistance test, described in ASTM D3170, is used primarily in automotive applications. The degree of chipping is typically rated visually or using chipping scales or optical measurement.
In short, both standards simulate stone chip damage, but the ASTM D3170 standard focuses more on a visual rating scale, while the SAE J400 standard uses quantitative chip counting or area-based damage assessment, depending on user preference.
Fragmentation resistance is considered important for the following reasons:
In short, the spall resistance of coatings is a measure of how well a surface coating can withstand mechanical impact without flaking or breaking. This is critical for ensuring long-term performance, especially in environments with flying debris or frequent mechanical contact.
The ASTM D3170 standard is primarily used to evaluate the resistance of automotive coatings to chipping by gravel or other hard objects. This test simulates real-world damage that occurs when vehicles are driven on gravel roads or in environments where debris is thrown against painted surfaces.
The purpose of this standard is to determine how well a paint or coating system resists fragmentation under standardized impact conditions. It is particularly important for the following parts: vehicle body panels, bumpers, wheel arches, and underbody components.
During testing, the coated test panel is mounted inside a chip resistance testing device, usually a gravelometer. A specific amount of standard gravel or crushed stone is forced onto the panel using compressed air. After impact, the panel is cleaned and visually inspected. The degree of cracking is graded using a chip scale, usually a template with reference images provided with the standard. The number and extent of cracks are determined on a scale from 0 (severe damage) to 10 (best, no damage) as follows:
Manufacturers may specify minimum acceptable chip resistance ratings depending on product type and use.
The ASTM D3170 standard is considered important for the following reasons:
Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the "ASTM D3170/D3170M Standard Test Method for Fracture Resistance of Coatings" standard.
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