Opportunity at Air Force Research Laboratory (AFRL)
Analysis of Low-Velocity Impact on Laminated Composites
Aerospace Systems Directorate, RQ/Aerospace Structures, Aerodynamics, and Flight Controls
||Wright-Patterson AFB, OH 454337542
Finite element method (FEM) and finite difference method (FDM) are two of the widely used numerical methods that require the discretization of problem domain with a mesh or a gird. Fracture and fragmentation will present challenges to both of these methods in handling newly created surfaces and forcing the numerical scheme to regenerate the mesh frequently. Formation of discontinuities in an undamaged material is a sudden event and the knowledge of the location and the external conditions for such an event is not available in advance. The mathematical framework used in the classical theory of continuum mechanics requires the use of partial derivatives to calculate the displacement field and these derivatives are undefined along the discontinuities. In order to overcome this difficulty, geometry of the continuum has to be redefined so that the discontinuity becomes a new boundary for the continuum body. The redefinition of boundary requires the location of the discontinuity in advance, limiting the possibility of predicting the formation of spontaneous discontinuities, such as dynamic cracks. Therefore, new techniques are necessary to reformulate the equations of the continuum mechanics to utilize the same set of equations for the calculations at discontinuities and elsewhere.
Basic research opportunities exist to develop advanced analysis methods (e.g., Peridynamics, Smooth Particle Hydrodynamics) to predict the behavior of composites under low-velocity impact. Current state-of-the-art analysis methods fall short in the area of capturing damage during an impact event. Sub-surface delamination is the predominant cause of failure observed in experiments, but matrix cracking, fiber breakage and ply-splitting also take place during an impact. Development of advanced numerical tools to capture these failure mechanisms and predict the remaining strength after impact is expected. Facilities at AFRL can accommodate state-of-art testing and characterization, including high fidelity NDI techniques, high-speed imaging capabilities, instrumented impact testing, and large-scale structural testing.
Ranatunga V, Stephen Clay SB: "Cohesive Modeling of Damage Growth in Z-Pinned Laminates under Mode-Loading". Journal of Composite Materials 47(26): 2013
Mesh-free methods; Peridynamics; Smooth particle hydrodynamics; Impact damage; Delamination; Composite structures; Finite element Modeling;
Open to U.S. citizens
Open to Postdoctoral and Senior applicants