Chobert Rivets

Chobert rivets are made with either snap or countersunk heads.  The action of closing a Chobert rivet is illustrated.  When the mandrel is pulled through the tapered hole the rivet head is formed.  As the mandrel continues pulling through the rivet, the shank expands and fills the hole.

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Sealing pins can be fitted in the rivet bore.  This increases the shear strength of the rivets and prevents moisture entering.

The manufacturer’s rivet part number is in the form of a code giving rivet material and diameter and grip length in ¹/₃₂ in.

Chobert rivets with oversize shanks are available for repair work on aircraft.

The chobert rivet is closed with a steel mandrel which forms part of the riveting tool.  A different sized mandrel is used with each diameter of rivet.  Before use it should be checked for diameter using an approved gauge.  The mandrel must also be inspected for scratches or other damage and must be clean and lightly lubricated.  Mandrels must be replaced when the head diameter has been reduced by 0.002 inch.

Impact Testing of Metals

The impact test is designed to determine the toughness of a material and the two most commonly used methods are those using the ‘Charpy’ and ‘Izod’ impact-testing machines.

The Izod test  uses a notched specimen supported on one side only. The pendulum strikes the specimen that is not held by the machine. The Charpy test also uses a notched sample, but this is supported on both sides with the pendulum hammer striking the middle of the specimen.

Both tests use specimens of standard dimensions, which record the energy absorbed by the test piece on impact to give a measure of toughness. A brittle material will break easily and will absorb little energy, so the swing of the pendulum (which is recorded against a calibrated scale) will not be reduced significantly. A tough material will absorb considerably more energy, and greatly reduce the recorded pendulum swing.



Most materials show a drop in toughness with a reduction in temperature, though some materials show a rapid drop as the temperature is progressively reduced. This temperature range is called the Transition Zone, and components, which are designed for use at low temperature, should be operated above the material’s Transition Temperature.