Index Finger Flexion in a Pressurized EVA Glove

This Project was developed by a four-man team for a senior structural design class under Dr. Darren Hartl at Aerospace Engineering Department, Texas A & M, in Spring 2017. We modeled the flexion motion of an Index finger in an Extra Vehicular Activity (EVA) Glove’s innermost layer, the bladder. A ubiquitous problem with modern space suit systems is overly rigid EVA glove that resists astronaut finger motion and causes injuries. Finite element modelling is an important approach to study the resulting effects and improve the existing designs for efficient gloved operations. The project aimed at determining the contact pressure on the fingertip and how a pressurized glove inhibits bending of an index finger using finite element analysis (FEA). The Proximal Interphalangeal joint (PIP) was given a displacement of 0.8 radians and Distal Interphalangeal joint (DIP), 1.33 radians. The final model can take 3 hours to run and the contact force was kept within 0.188 MPa, the Pressure Discomfort Threshold (DPT). ABAQUS was used to solve a quasi-static, highly nonlinear, contact problem with hyper-elastic materials such as human skin. A realistic skeletal-model was imported from GrabCAD to obtain proximal, middle, and distal bones of an index finger. SolidWorks was used to model the final finger as 80.5 mm long with an average diameter of 19.0 mm. A pressure load of 0.03 MPa (4.3 psi) was applied on the outer surface of the skin and inner surface of the glove, as per the current Phase VI EVA Glove. Glove was designed using five design variables, Npleats, S1, R1, R2 and t, as described in the uploaded figure. A Python script based on particle swarm optimization algorithm was implemented with ABAQUS to iterate on glove design variables to converge at the best design.There are two loading steps: a general static step and an implicit dynamics step with quasi static and Nlgeom ON options. The Output variables obtained from 100 such iterations were net reaction moment (torque), contact pressure on the skin, mass of the glove and Mises stress on the glove. ABAQUS is an excellent tool for simulating complex structures with hybrid assemblies (Imported parts + ABAQUS designed geometries). Python API facilitates design implementation and iteration over varying parameters to obtain best designs. ABAQUS’ clarity in displaying modelling errors aids in capturing mistakes in the preliminary stage itself and saves user time.