Tracing hail stone impact on external thermal insulation composite systems (ETICS) – An evaluation of standard admission impact tests by means of high-speed-camera recordings

Abstract

Hail impact damage on External Thermal Insulation Systems (ETICS) is increasingly recognized by insurance companies owing to increased storm occurrence frequency and storm intensity. To develop hail resistant ETICS for houses and better understand existing admission tests, high-speed-camera recordings of ice ball impacts at an angle of 45° and steel ball impacts at angles of 90° and 45° were used to characterize the impact process and to derivate the damaging mechanisms of impacts on facades.Recorded surface deformation is characterized by high indentation depth of the impactor and high flexural bending causing high surface parallel strain. Analyses of the impact process allowed the identification of the mechanisms and timing of fracture formation in different regions.Additionally, differences in the impact process of the European steel ball impact test (90°, ETAG 004) and the Swiss ice ball impact test (45°, VKF P. No 8) are discussed in detail. Caused by the difference in impact angle, the 45° ice ball impacts lead to lower indentation depth and consequently to lower tensile strain and damage. However, surface parallel movement of the impactor caused the formation of an elongated damage pattern in the 45° impacts. To avoid the observed brittle failure behavior, the development of flexible materials with the ability to elastically accommodate impact strains is favorable to reduce hail stone impact damage.