Manufacturing & Prototyping

Attaching Thermocouples by Peening or Crimping

These techniques are simple, effective, and minimally invasive. Two simple, effective techniques for attaching thermocouples to metal substrates have been devised for high- temperature applications in which attachment by such conventional means as welding, screws, epoxy, or tape would not be effective. The techniques have been used successfully to attach 0.005-in. (0.127-mm)-diameter type-S thermocouples to substrates of niobium alloy C-103 and stainless steel 416 for measuring temperatures up to 2,600 °F (1,427 °C). The techniques are equally applicable to other thermocouple and substrate materials.

Posted in: Manufacturing & Prototyping, Briefs

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Submarine Design Certified on FEA and Sensor Testing

The American Bureau of Shipping certified a submarine solely on the basis of finite element analysis (FEA) and strain sensor testing. Submarine design typically follows American Bureau of Shipping (ABS) code, which establishes properties such as hull thickness, frame stiffness, and porthole and hatch design. During certification, ABS evaluates whether a design follows the relevant codes and then certifies it or not on that basis. The design of a deep-diving submarine was so unique that some ABS rules could not be adhered to.

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Simplified Fabrication of Helical Copper Antennas

From concept to working prototype takes just a few hours. A simplified technique has been devised for fabricating helical antennas for use in experiments on radio-frequency generation and acceleration of plasmas. These antennas are typically made of copper (for electrical conductivity) and must have a specific helical shape and precise diameter.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Repairing Chipped Silicide Coatings on Refractory Metal Substrates

Two methods have been demonstrated to be feasible. The space shuttle orbiter’s reaction control system (RCS) is a series of small thrusters that use hypergolic fuels to orient the orbiter in space. The RCS thrusters are constructed from a special niobium-based alloy — the C-103. This alloy retains excellent mechanical properties from cryogenic temperature all the way up to 2,500 °F (1,370 °C). Despite its excellent, high-temperature properties, C-103 is susceptible to rapid oxidation at elevated temperatures. Were the naked C-103 alloy exposed to the operational thruster environment, it would rapidly oxidize, at least losing all of its structural integrity, or, at worst, rapidly “burning.” Either failure would be catastrophic. To prevent this rapid oxidation during thruster firing, the RCS thrusters are coated with a silicide-based protective coating — the R512a. Over time, this protective coating becomes weathered and begins to develop chips. Launch Commit Criteria limit the diameter and depth of an acceptable pit; otherwise, the thruster must be removed from the orbiter — a very costly, time-consuming procedure. The authors have developed two methods to repair damaged R512a coatings on C-103.

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Strain Gauges Indicate Differential-CTE-Induced Failures

Failures are indicated by changes in slopes of strain versus temperature. A method of detecting mechanical failure induced by variation in temperature at an adhesive bond between two materials that have different coefficients of thermal expansion (CTEs) involves monitoring of strain-gauge readings. This method can be regarded as an exploitation of the prior observation that the readings of strain gauges commonly used in tensile and compressive testing of material specimens include features indicative of incremental failures in the specimens. In this method, one or more strain gauges are bonded to either or both of the two materials near the bond between the materials. (The adhesive used to bond the strain gauges would not ordinarily be the same as the one used to bond the two materials). Then strain-gauge readings are recorded as the temperature of the materials is varied through a range of interest. Any significant discontinuity in the slope of the resulting strain-versus- temperature curve(s) is taken to be a qualitative indication of a failure of the bond between the two materials and/or a failure within one of the materials in the vicinity of the bond.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Counterrotating-Shoulder Mechanism for Friction Stir Welding

The weights and costs of fixtures for holding workpieces could be reduced. A counterrotating- shoulder mechanism has been proposed as an alternative to the mechanism and fixtures used in conventional friction stir welding. The mechanism would internally react most or all of the forces and torques exerted on the workpiece, making it unnecessary to react the forces and torques through massive external fixtures.

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Core-Cutoff Tool

Damage and waste are reduced. A tool makes a cut perpendicular to the cylindrical axis of a core hole at a predetermined depth to free the core at that depth. The tool does not damage the surrounding material from which the core was cut, and it operates within the core-hole kerf.

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