NASA engineers have developed new peening techniques for attaching thermocouples to metal parts. The technique was developed specifically for parts used in high-temperature applications, where other assembly methods, such as welding, fastening or adhesive bonding, would be ineffective.

The peening techniques were invented by engineers at John F. Kennedy Space Center in Florida and ASRC Aerospace Corp. (Greenbelt, MD). The techniques have already been used successfully to attach Type S thermocouples, 0.005 inch in diameter, to parts made of C-103 niobium alloy and 416 stainless steel.

In the first technique, a hole slightly larger than twice the diameter of one thermocouple is drilled in the part. The thermocouple is placed in the hole, and the edge of the hole is then peened in several spots using a punch. The deformed material at the edge secures the thermocouple.

In the second technique, a hole is drilled in the part as in the first technique. Then, an annular relief area is machined around the hole, resulting in a structure reminiscent of a volcano in a crater. The thermocouple is placed in the hole, and the sides of the "volcano" are either peened or crimped. This method is preferable for securing thermocouples less than 0.005 inch in diameter, because the first technique could break the wire.

Compared with other assembly methods, the new peening technique is fast, simple and does not affect the thermal properties of the materials. In addition, it can be used to attach thermocouples at locations where access is restricted by surrounding objects.

For more information on peening methods for attaching thermocouples, visit, or eInquiry 22.