Analysis of impact on soft soil and its application to aircraft crashworthiness

Abstract

The current crashworthiness design criteria only address crash impacts on rigid surfaces. However, accident statistics indicate that up to 80 percent of civil and military aircraft crashes occur on soft soil and water. There is very little data on crash impacts on soft soil. The development of the soil model is an important issue in soil impact simulation and vehicle/aircraft crashworthiness. In this paper, a finite element model of soil is developed. The soil model is validated using the available test data. The Sphere and cone drop tests on soft soil were modelled using MSC.Patran software. The aluminium impactors are modelled using the Belytschko-Lin-Tsay four node shell elements, and close agreements were obtained between experimental and analytical results of the drop tests. A finite element model of an airplane is generated and is used for the simulation of airplane impact on soft soil. An actual airplane drop test at NASA Impact Dynamics Research Facility is simulated using a model having identical mass of the actual airplane impacting the developed soil model at predetermined test velocity and angles. The development of soil model and also the simulation of crash impacts are conducted using non-linear finite element analysis code LS-DYNA. The soil was modelled using solid elements and the aircraft model had shell elements. A Master-slave contact algorithm was used for the impact. Appropriate data were used to simulate the soil eroding effect. The entire fuselage was badly damaged and the tail also got crushed similar to the crush of the test plane. Acceleration data obtained at centre of mass of the airplane model reasonably duplicate the ones obtained during the test at different locations of the plane.