An improved version of EXOS software allows for the modeling of fabrics, mixtures, and porous materials, and also provides the ability to accept hex mesh geometries. The code employs a novel numerical method, a hybrid particle finite element approach, as well as particles and elements in tandem, each modeling distinct aspects of the physics. Ellipsoidal particles are used to model contact-impact and volumetric thermomechanical response (Euler parameters provide a singularity-free description of particle rotations). Elements are used to model “strength” effects; namely, tensile inter-particle forces and elastic-plastic deviatoric deformation.

This method has significant advantages. The slideline, rezoning, mass, and energy discard issues of finite element methods are avoided. Strength and fragmentation modeling issues of Eulerian methods are avoided. Tensile instability, numerical fracture, and strength modeling issues of particle methods are avoided.

In the case of orbital debris impact simulation, a particular advantage arises in the modeling of fragments. The particle kinematics included in the code are well suited to model fragment transport and contact-impact of all intact and failed material. The finite element kinematics included in the code are well suited to model the history-dependent material failure process. As a result, unlike alternative Eulerian codes, EXOS provides an explicit description of fragment mass, shape, velocity, temperature, etc. Hence, a “fragment model” based on internal state variables is not required.

This work was done by Eric P. Fahrenthold of the University of Texas for Johnson Space Center. MSC-24803-1

NASA Tech Briefs Magazine

This article first appeared in the February, 2016 issue of NASA Tech Briefs Magazine.

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