Automated evaluation of stone chip resistance in automotive coatings

A newly developed method enables the automated identification of the main delamination level in stone chip resistance tests in accordance with DIN EN ISO 21227-2. The approach is based on confocal chromatic measurement and combines statistical with visual analysis.

Automated analysis is becoming increasingly important in adhesion testing of coatings in the automotive industry. A recent research project introduces a novel method to automatically assess the damage progression in multilayer coatings subjected to stone chip impact. The method utilises confocal chromatic sensors to generate detailed topographic data of the tested surface. These depth measurements are interpreted as statistical distributions, visualised in histograms that form the basis for determining the main delamination level.

The core of the method is a two-step approach to defining the interval used for peak area calculation. Initially, the width of the peak at a defined relative height is determined. These points serve as input for identifying the outer boundaries based on slope, allowing for the differentiation between core and peripheral damage. This enables a more detailed characterisation of the coating failure.

Bridging normative and visual evaluation

An additional assessment criterion was introduced to include visual perception. The analysis delivers both a mathematically defined and a visually derived main delamination level. This ensures compliance with DIN EN ISO 21227-2 while replicating conventional visual assessments. The method thus offers objective, reproducible results and improved comparability with legacy data obtained manually.

The developed method provides reliable automated identification of the delamination zone and could be transferred to other adhesion test types. In the future, it may also be expanded to describe damage development within the coating layers. Moreover, this approach could simplify digital documentation processes and support targeted development of stone chip-resistant coatings.

Source: Wefels, Franziska (2025): Method development for automated analysis of damage progression in multilayer coatings subjected to stone chip resistance testing in the automotive industry.