Composite Joint Connector

The Multi-Link Spherical Joint developed at NASA Johnson Space Center provides a substantial improvement over typical joints in which only two linearly actuated links move independently from one another. It was determined that the rotation point of a trussed link needed to be collocated at a shared point in space for maximum articulation. If not allowed separate rotation, the line of action through a universal joint and hinge acts effectively as another linkage. This leads to a much more complex and uncontrollable structure, especially when considering multiple dimensions. Comprising the Multi-Link Spherical Joint, a spherical shell encases the cupped ends of each six possible attachments and allows each of those attachments to be independently controlled and rotated without inhibiting the motion of the others. To do this, each link is precisely limited to 15 degrees of rotation off the link centerline, thus allowing a total of 30 degrees of rotation for each link. The shell-and-cup structure can handle the loads of linear actuators that may be used to control and vary the geometry of a truss system utilizing the new joint technology. The calculated operating load that the truss system must handle can be used to scale the size of the joint, further allowing customization of any potential truss system. Additionally, the incorporated linear actuators can be controlled and powered by wiring routed through the joint without putting undo stress on the wires during operation. Accordingly, this innovative joint technology enables more efficient deployment and precise operation of articulating structures. The Multi-Link Spherical Joint is at technology readiness level (TRL) 4 (component and/or breadboard validation in laboratory environment) and is available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.

The square form joint has several novel features to improve reliability, performance and robustness. Most simply, the square tubes are stronger than round for a specified maximum cross-section dimension. Structural benefits include nearly complete perimeter contact geometry for improved structural efficiency, improved cantilever beam response via linear bending response about y and z axis, and linear torsional response about x axis. Additionally, there is betterlinear axial response along x axis due to simple geometry and large contact surfaces, higher torsional/torque capability (about x axis), higher bending capability about all axes, higher axial capability, and is more cost effective to manufacture. It also offers a bonding strap and treated contact surfaces that provide electrical conductivity through the joint. Switching to square cross section joints provides packaging efficiency, along with numerous improvements for robotic assembly applications such as providing rotational registration, robotically compatible tool designs, both mechanical and visual indicators to verify locking operation, preload and capture spring forces with a unique stop plate in the drive train that can be designed to default to the assembled condition without a preload, yet spring back if forced toward unlocked. After assembly, preload can be adjusted for security. Designed for robust assembly, the robotic tools are built to actuate the joint.

Designers are constantly seeking to improve the power-to-weight ratio of components in rotorcraft and other flight vehicles. One approach has involved using lightweight carbon fiber composite materials to replace gear web portions and other components that are typically made from steel. The problem with using fiber composite materials comes when more complex shapes are required. To create thickness variation and other accommodations for complex shapes, manufacturers can stack cut continuous fiber plies and/or form short, fiber-reinforced composite material to the desired shape. Unfortunately, these methods leave cut fiber ends within the structure, which often become initial sites for high cycle fatigue damage in high speed, high power density applications. Glenn's new method tackles this problem with one of three approaches. The first approach is applicable to gears that are planar in shape and have a single hub and a single rim. The hub and web sections of the gear are made as an integrated structure with decreased thickness from the hub inner diameter to the web outer diameter. The thickness variation is accomplished using multiple layers of continuous fiber composite material formed to specific shapes and separated by filler materials. The second approach is applicable to gears that have an extended gear body in the axial direction rather than a simple planar structure. In this approach, the gear body is made using multiple layers of continuous fiber composite material in the shape of a solid of revolution. The third approach is a power transfer assembly made by combining approaches one and two. With any of these three approaches, the material can be tailored to the structure by the properties of fibers used, the number of fiber layers used, and the location of the fibers relative to the neutral axis of the structure. Glenn's innovation opens the door for carbon fiber composite materials to be used for many applications for which they were previously unsuited.

NASA used three strategies to develop a family of modified epoxy resins for use in an improved composite layup configuration. By tailoring molecular structures, incorporating secondary additives, and adjusting composite architecture, NASA has produced fiber-reinforced polymer composites that suppress viscoelastic creep and relaxation. Specifically the three strategies were: (1) Controlling the cross-linking density using reactive functional groups and selecting appropriate monomers with stoichiometry adjustments. A higher stoichiometric ratio is responsible for reduced relaxation compared to a lower ratio (resulting in 26% relaxation after 1 year vs. 49%). (2) Increase the steric hindrance by reducing free volume and enhancing intermolecular interaction. This involved the preparation of two different reactive low molecular weight oligomers The best epoxy resin created was from the VCD/HAA additives with 15-17% relaxation; DEGBA/HAA had 22-25% relaxation. (3) Optimizing different carbon fiber layup configurations for woven structures made into a highly stiff boom, highly flexible boom, a small size boom, and a large size boom application. The best configuration was that of a highly stiff boom with 4-5% relaxation. Other carbon fiber layup configurations had 16-30% relaxation. As shown in the figure below, NASA tested the relaxed composite using an accelerated test with variable temperatures.

The C-Gauge is made of a 3D-printed aluminum body with strain gauges attached to the inner and outer walls of the connecting beam. The legs of the gauge attach firmly to the cord. When the cord is stretched, the tension in the cord goes through the legs and into the beam, causing it to bend. This bending creates a tension and compression stress in the bottom and top surface of the beam, respectively. The strain gauges capture the tension and compression, which are then used to determine the tension in the cord. The use of multiple strain gauges mitigates any torsion loading of the gauge and provides a direct measurement of the axial tension load of the cord. The C-Gauge is a low-profile, non-invasive system that can be installed onto an existing cord in a system (e.g., the suspension, reefing, or riser lines in a parachute) without the need to remove or re-install the cord. It is small and lightweight and does not add stiffness or weight to the cord and thus does not affect the dynamics of the parachute or the structural response of the system. The C-Gauge can be scaled to larger and smaller sizes to measure larger and smaller load capabilities, dependent on the cord. The C-Gauge is at a TRL 4 (component and/or breadboard validation in a laboratory environment) and it is now available for your company to license and develop into a commercial product. Please note that NASA does not manufacture products itself for commercial sale.