Search Results for connectors

Pitostatic system connectors were being found cracked on several aircraft. Two of the cracked connectors made of 2024-T351 aluminum alloy were submitted for failure analysis. The connectors had cut pipelike threads that were sealed with Teflon-type tape when installed. Longitudinal cracks were located near the opening of the female ends of each connector. A cross section showed intergranular cracking with multiple branching in one connector. Scanning electron microscopy (SEM) showed intergranular cracking and separation of elongated grains. A cross section of connector threads showed an incomplete thread form resulting from improper tapping. It was concluded that the pitostatic system connectors failed by SCC. The stress was caused by forcing the improperly threaded female nut over its fully threaded male counterpart to effect a seal. The one connector tested for chemical composition was not made of 2024 aluminum alloy as reported but of 2017 aluminum. It was recommended that the pitostatic system connector manufacturing process be revised to produce full-depth threads rather than pseudo pipe threads. Wall thickness should be increased to increase the hoop stress bearing area if pipe threads were to be used. A determination of proper torque values for tightening the connectors was suggested also.

A stainless steel flexible connector failed after a short period of service. Visual examination of the failed part revealed that a fracture had occurred in the thin-walled stainless steel bellows brazed into the flanges at each end. Surface examination by SEM fractography showed that failure of the bellows occurred via fatigue. The crack in the bellows had widened considerably after the fracture, and the bellows had been severely compressed on the fracture side prior to failure. Based on these observations, it was concluded that bellows had been damaged prior to installation. The damage resulted in high mean tensile stresses upon which were superimposed cyclic stresses, with fatigue failure the final result.

An 1100 aluminum alloy connector of a high-tension aluminum conductor steel-reinforced (ACSR) transmission cable failed after more than 20 years in service, in a region of consider able industrial pollution. The steel core was spliced with a galvanized 1020 carbon steel sheath. Visual examination showed that the connector had undergone considerable plastic deformation and necking before fracture. The steel sheath was severely corroded, and the steel splice was pressed off-center in the axial direction inside the connector. Examination of the fracture surface and micro-structural analysis indicated that the failure was caused by mechanical overload, which occurred because of weakening of the steel support cable by corrosion inside the fitting. The corrosion was ascribed to defective assembly of the connector which allowed moisture penetration.

Coaxial cable connectors made of brass were failing at a high rate after less than one year of service in an outdoor industrial environonment. The observed failures, which consisted of cracks in the body and end cap, were analyzed and found to be brittle fractures due to stress-corrosion cracking. Two common stress-corrosion cracking tests for copper materials were conducted on new connectors from the same manufacturing lot, confirming the initial determination of the fracture mode. Additional testing as was done in the investigation is often helpful when analyzing corrosion failures.

Four cadmium-plated ASTM A193 grade B studs from a steam line connector associated with a power turbine failed unexpectedly in a nil-ductility manner. Fracture surfaces were covered with a light-colored, lustrous deposit. Optical microscope, SEM, and EDS analyses were conducted on sections from one of the studs and revealed that the coating on the fracture surface was cadmium. The fracture had multiple origins, and secondary cracks also contained cadmium. The fracture topography was intergranular. The failures were attributed to liquid metal embrittlement caused by the presence of a cadmium plating and operating temperatures at approximately the melting point of cadmium. It was recommended that components exposed to the cadmium be replaced.

A sand-cast steel eye connector used to link together two 54,430 kg capacity floating-bridge pontoons failed prematurely in service. The pontoons were coupled by upper and lower eye and clevis connectors that were pinned together. The eye connector was found to be cast from low-alloy steel conforming to ASTM A 148, grade 150-125. The crack was found to have originated along the lower surface initially penetrating a region of shrinkage porosity. It was observed that cracking then propagated in tension through sound metal and terminated in a shear lip at the top of the eye. The fracture of the eye connector was concluded to have occurred by tensile overload because of shrinkage porosity. Sound metal was ensured by radiographic examination of subsequent castings.