2014 IR&D Annual Report

Investigation of Computational Methods for Modeling Bird Strike Impacts on Aircraft Structures, 18-R8477

Principal Investigators
James Mathis
Sidney Chocron
Joseph Bradley
Andrew Barnes
Matthew Grimm

Inclusive Dates: 07/01/14 – Current

Background — Collisions with bird and aircraft have been a problem since the beginning of aviation. A bird strike during flight can be a major threat to the aircraft depending on the size of the bird, speed of the aircraft, and location of the strike. All aircraft components that are at risk for bird strike are required by regulating authorities to undergo a certification process aimed at demonstrating that a safe landing is possible after a bird strike event. Designers and manufacturers of these components rely heavily on experiments; however, costs to conduct research and development tests are substantial due to the destructive nature of the test and limited production prototypes. In recent years there has been a shift toward the use of computational tools to simulate the behavior of components during an impact event. Unfortunately, the simulations are not always accurate due to the complex composite materials that are often used on forward-facing surfaces in an effort to save weight. Clearly trends are shifting toward the use of numerical simulations for early design efforts and in some limited cases, full certification by analysis. With these challenges in mind, SwRI is conducting a research project aimed at developing and demonstrating SwRI’s capabilities to accurately model bird strike impact into aircraft structures using finite element analysis techniques. The intent is to demonstrate this capability through a coupled experimental and computational approach using our existing experimental expertise and computational tools.

Approach — Based on our history in supporting many clients with quality bird strike testing services, combined with our general expertise in computational modeling of ballistic impact and material response, we believe that we are well poised not only to support this emerging market opportunity but also to push the state of the art by generating reliable bird and aircraft structure material models that can accurately predict deformation and failure. We begin with a brief review of current methods used to simulate bird impacts. Sources of existing experimental data will be identified that can be used to aid in validating our simulations. Experiments will be designed and conducted to collect data related to the loading produced by bird strike impacts. Computations will be conducted simultaneously to validate a methodology for reproducing the impact loads measured experimentally. Experiments will also be conducted to determine material constants needed to accurately represent the bird. Actual aircraft material coupon samples will be tested to collect data relevant to understanding the behavior of the materials/structure under the dynamic loading due to bird strike. Computations will then be conducted to demonstrate our ability to accurately model the material and structural response of composites and certain transparencies due to a variety of impact conditions.

Accomplishments — Initial simulations using modeling methodologies including Smooth Particle Hydrodynamics (SPH) and Arbitrary Lagrangian Eulerian (ALE) to represent the bird have been carried out. Simulations were performed to replicate a set of experiments conducted previously on rigid targets instrumented with pressure sensors to measure the loading magnitude and profile due to bird impacts at various angles of incidence (Figure 1).

Figure 1.  Typical SPH simulation results of a 45-degree bird impact against a rigid surface.
Figure 1. Typical SPH simulation results of a 45-degree bird impact against a rigid surface.

The simulation results using ALE and SPH methods along with bird material models available in literature were compared with the available experimental data. Overall good results have been achieved (Figure 2); however, we look forward to incorporating our bird material characterization experimental data as it becomes available later in this project.

Figure 2.  SPH steady flow pressure distribution for a normal impact
Figure 2. SPH steady flow pressure distribution for a normal impact.

Initial simulations of bird impacts against deformable targets have also been carried out. Experiments were previously conducted by impacting birds against aluminum panels and measuring reaction forces and strains during those impacts. Equally favorable results have been achieved.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 10 technical divisions.