Center for Composite Materials - University of Delaware

Research Summary

Materials, Manufacturing and Testing for the Ankle-Foot Orthosis

Authors: S. Sharma, Dr. S. Yarlagadda, Prof. J. W. Gillespie Jr.

OVERVIEW

Definition
• Orthotics is concerned with the design, manufacture and application of orhtoses. An Orthosis is “an externally applied device used to modify the structural and functional characteristics of the neuromuscular and skeletal system”.

Function
• Control, guide, limit or immobilize a joint or body segment
• Facilitate movement and provide load bearing capacity
• Aid in rehabilitation from injuries
• Correct the shape and or function of the body

Ankle-Foot Orthosis
• Specially designed to assist with ankle related injuries
• Could include limited or complete debilitation of the angle joint
• Provides support and load bearing capacity to the ankle joint

SYSTEM PROTOTYPE

MANUFACTURING AND TESTING

• Carbon/Epoxy Pre-preg
-Number of plies and layup based on stiffness requirements
• Vacuum Pressure
• Cure Temperature < 250F
• Thermocouple Control – Cure Cycle
• De-Bulking Steps
-De-bulk after every 5 layers
• Silicone Caul Plate

QUALITY ASSESSMENT MEASURES

FATIGUE TESTS

• Load Control Test
• Strain Limit: 2/3 Failure Strain [Material]
• Load Range: Load at 2/3 Failure Strain
• Target: 3 Million Cycles
• Stiffness Check: 0 Cycles, 1.5 Million, 3 Million Cycles

DEVICE MANUFACTURING

• Toray Carbon/Epoxy Unidirectional Pre-Preg Used for Manufacturing
• Steel mold used for Layup, rubber layer used to apply an even pressure distribution on the part
• De-bulk steps for good consolidation
• Total Cure time: 2 Hours
• Thickness measurements, visual inspection and microscopy conduced to determine the quality of the manufactured parts

CURRENT AND FUTURE WORK

• Continue exploring new materials and building the material database
• Fatigue tests on laminates to finish the S/N curve for different layups to meet the entire stiffness requirements
• L-Bracket (Device) manufacturing for different stiffness requirements [ 1- 99 Percentile ]
• Fatigue testing on Device
• Integration of the L-Bracket (Device) with a 3D Printed form factor to facilitate fitting on patient foot

ACKNOWLEDGEMENTS

Gerhard Wischmann, Emily Readdy, Mike Furr

This funding for this project is supported by DARPA

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