Housings (being tested as part of a material conversion) from an electrical appliance failed during an engineering evaluation. They had been injection molded from a commercial polycarbonate/PET blend. Parts produced from the previous material, a nylon 6/6 resin, had consistently passed the testing regimen. Grease was applied liberally within the housing assembly during production. Investigation included visual inspection, 24x SEM images, micro-FTIR in the ATR mode, and analysis using DSC. No signs of material contamination were found, but the thermograms showed a crystallization of the PET resin. The grease present within the housing assembly, analyzed using micro-FTIR, was composed of a hydrocarbon-based oil, a phthalate-based oil, lithium stearate, and an amide-based additive. The conclusion was that the appliance housings failed through environmental stress cracking caused by a phthalate-based oil that was not compatible with the PC portion of the resin blend. Thus, the resin conversion was the root cause of the failures. Additionally, during the injection molding process the molded parts had been undercrystallized, reducing their mechanical strength. More importantly, the resin had been degraded, producing a reduction in the molecular weight and reducing both the mechanical integrity and chemical-resistance properties of the parts.

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.

A housing used in conjunction with an electrical switch failed shortly after being placed into service. A relatively high failure rate had been encountered, corresponding to a recent production lot of the housings, and the failed part was representative of the problem. The housing had been injection molded from a commercially available, medium-viscosity grade of PC, formulated with an ultraviolet stabilizer. In addition to the PC housing, the design of the switch included an external protective zinc component installed with a snap-fit and two retained copper press-fit contact inserts. Investigation supported the conclusion that the switch housings failed via brittle fracture, likely through a creep mechanism. The failure was caused by severe embrittlement of the housing resin associated with massive molecular degradation produced during the molding process. A potential contributing factor was the design of the part, which produced significant interference stresses between the contact and a mating retaining tab.

Both halves of a gray cast iron transmission housing from a 50-ton dump truck were found to contain numerous cracks. The housing material was possibly G3000 grade designation for automotive gray cast iron. No service duration or material specifications were provided. Investigation (visual inspection, tensile testing, 2% nital etched 59x cross sections, and metallographic analysis) supported the conclusion that failure was due to applied stresses sufficient to fracture the castings which exhibited brittle overload cracks at highly stressed locations. No recommendations were made.

An injection-molded PVC water-filter housing fractured in service. 75x views and visual inspection supported the conclusion that failure occurred due to fatigue crack propagation, as indicated by the presence of discontinuous crack-growth bands and their evolution. However, an initial fissure was believed to have started first due to residual stresses developed during injection molding. No recommendations were made.

In a housing made of cast steel GS 20MoV12 3, weighing 42 tons, precipitates were found on the austenitic grain boundaries during metallographic inspection. According to their shape and type they were recognized as carbides that precipitated during tempering. In addition, a much coarser network of rod-shaped and plate-shaped precipitates was found, that probably corresponded to the primary grain boundaries, or to the grain boundaries or twin planes of the austenite formed during solidification of the melt. These particles could have been aluminum nitride judging by their shape and order of precipitation. Tests showed that a subsequent removal of this defect by solutioning was impractical because the annealing temperature was too high. To avoid this defect in the future the sole recommendation is to accelerate the cooling rate through the critical region between 1200 to 900 deg C to such an extent as is practicable with respect to machinability.

A sand-cast medium-carbon steel heavy-duty axle housing, which had been quenched and tempered to about 30 HRC, fractured after almost 5000 h of service. Investigation (0.4x magnification) revealed that the fracture had been initiated by a hot tear that formed during solidification of the casting. The mass of a feeder-riser system located near the tear retarded cooling in this region, creating a hot spot. This supported the conclusion that the tear causing the fracture of the axle housing was formed during solidification by hindered contraction and was enlarged in service by fatigue. Recommendations were to change the feeder location to eliminate the hot spot and thus the occurrence of hot tearing.

Several hundred leaks were reported in the type 304 stainless steel pipelines, vessels, and tanks of a chemical plant at a tropical location within a few weeks after startup. Investigation of the failure involved a site visit, metallographic examination and analysis of the material, analysis of hydrotest waters, and microbiological examination of slime that had formed in certain pipework sections. It was determined that the failure resulted from microbially induced corrosion promoted by the use of poor-quality hydrotest water and uncontrolled hydrotesting practice. Use of appropriate hydrotesting procedures was recommended to prevent similar failures.

A pressure probe assembly comprised of type 347 stainless steel housing, brazed with AMS 4772D filler metal to the pressure probe, failed due to detachment of a rectangular segment from the housing. The presence of a large brazing metal devoid region in the pressure probe-housing joint was revealed by visual examination. Fatigue marks, emanating from multiple crack origins on the inside surface of the housing at the brazed joint were revealed by further study of the fracture. A poor metallurgical bond was confirmed by the presence of large irregular voids, flux trapped braze metal and separation between braze and housing.