Development of Hail Material Model for High Speed Impacts on Aircraft Engine

Hail impacts represent a threat for aircrafts and their engines. As experimental tests on aircraft engines are expensive and they can not be done in early stages of the development, numerical simulations to predict hailstone impacts on engine blades have to be developed. The purpose of this work is to present a new material model for simulating hailstone impacts on engine blades. Aeronautical industry has already developed numerical models for similar problems of bird impacts using LS- DYNA®. They simulate the bird using SPH particles to predict projectile failure and Lagrangian solid elements for the blade.. In order to simulate hail impact, numerical model for bird strike is used and projectile material is replaced by a new material model. Experimental results show hail has a brittle behavior which is similar to concrete’s, so mechanical behavior may be simulated by an elastic damage model based on Mazars’ law used for concrete. Damage Mazars’ model is improved by adding traction and compression damage and a delay effect is added in order to reduce mesh dependence. This hail law is developed in LS-DYNA code through a user defined material (UMAT), tested on simple cases of plate impact and used for impacts on the aircraft engine blade. This paper presents the existing LS-DYNA models simulating hail impact and their limits and describes hail tests used to study the material law and to develop the numerical model. Validation tests are presented to show out the behavior of hail, effects of model parameters, and the role of delay effect. Hailstone impact tests on an aluminum plate carried out by British Royal Aircraft Establishment (RAE) and Office national d'études et de recherches aérospatiales (ONERA) are used in order to identify the model. An impact on a blade is then simulated with the identified model and is compared with Snecma’s test.