Search Results for standard reference materials

This article considers two mechanisms of cavitation failure: those for ductile materials and those for brittle materials. It examines the different stages of cavitation erosion. The article explains various cavitation failures including cavitation in bearings, centrifugal pumps, and gearboxes. It provides information on the cavitation resistance of materials and other prevention parameters. The article describes two American Society for Testing and Materials (ASTM) standards for the evaluation of erosion and cavitation, namely, ASTM Standard G 32 and ASTM Standard G 73. It concludes with a discussion on correlations between laboratory results and service.

This glossary contains the definitions of terms related to the characterization and failure analysis of plastics.

Cerclage wire, which was used with two screws and washers for a tension band in a corrective internal fixation, was found broken at several points and corroded after nine months in service. The material was examined using energy-dispersive x-ray analysis and determined not to be in compliance with standards (type 304 stainless steel without molybdenum). The screws and washers were found to be made of remelted implant-quality type 316L stainless steel and were intact. Signs of sensitization, characterized by chromium carbide precipitates at the grain boundaries, were revealed by the microstructure. Intercrystalline corrosion with pitted grains was indicated by SEM fractography. Improper heat treatment of the steel was interpreted to have led to intercrystalline corrosion and implant separation.

This article presents a general overview of outdoor weather aging factors, their effects on the performance of polymeric materials, and the accelerated test methods that can be used to investigate those effects. These test methods are used to characterize material performance when subjected to specific, often controlled, and well-defined factors. The article also presents an overview of weathering instrument types that simulate outdoor stress factors.

Cracks occurred in a new ship hull after only three months in service. It was noted that the 5xxx series of aluminum alloys are often selected for weldability and are generally very resistant to corrosion. However, if the material has prolonged exposure at slightly elevated temperatures of 66 to 180 deg C (150 to 350 deg F), an alloy such as 5083 can become susceptible to intergranular corrosion. Investigation (visual inspection, corrosion testing, SEM images) supported the conclusion that the cracks occurred because during exposures to chloride solutions like seawater, galvanic couples formed between precipitates and the alloy matrix, leading to severe intergranular attack. No recommendations were made.

Linear indications on the outer surface of a cross in a piping system were revealed by dye-penetrant examination. The cross was specified to be SA403 type WP 304 stainless steel. The cross had been subjected to induction-heating stress improvement. The linear indications on the cross were located in wide bands running circumferentially below the cross-to-cap weld and above the cap-to-discharge-pipe weld. The material was found to conform to the requirements both in terms of hardness and strength. Intergranular cracks filled with oxide were observed on metallographic analysis of a sectioned and oxalic acid etched sample. The grain size was found to exceed the ASTM standard. No indications of sensitization were observed during testing with practice A of ASTM A 262. Definitive evidence of contaminants to support SCC as the failure mechanism was not disclosed during analysis. It was concluded that overheating or burning of the forging, which classically results in large grain size, intergranular fractures, and fine oxide particles dispersed throughout the grains was the possible reason for the failure.

A stainless steel screw securing an orthopedic implant fractured and was analyzed to determine the cause. Investigators used optical and scanning electron microscopy to examine the fracture surfaces and the microstructure of the austenitic stainless steel from which the screw was made. The results of the study indicated that the screw failed due to fatigue fracture stemming from surface cracks generated by stress concentration likely caused by grooves left by improper machining.

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.

This article presents a failure analysis of an aluminum cylinder head on an automotive engine. During an endurance test, a crack initiated from the interior wall of a hole in the center of the cylinder head, then propagated through the entire thickness of the component. Metallurgical examination of the crack origin revealed that casting pores played a role in initiating the crack. Stress components, identified by finite element analysis, also played a role, particularly the stresses imposed by the bolt assembly leading to plastic strain. It was concluded that the failure can be prevented by eliminating the bolt hole, using a different type of bolt, or adjusting the fastening torque.

This investigation characterizes five surgical stainless steel piercings and one niobium piercing that caused adverse reactions during use, culminating with the removal of the jewelry. Chemical composition shows that none of the materials are in accordance with ISO standards for surgical implant materials. Additionally, none of the stainless steel piercings passed the pitting-resistance criterion of ISO 5832-1, which implies that [%Cr + 3.3(%Mo)] > 26. Under microscopic examination, most of the jewelry revealed the intense presence of linear irregularities on the surface. The lack of resistance to pitting corrosion associated with the poor surface finishing of the stainless steel jewelry may induce localized corrosion, promoting the release of cytotoxic metallic ions (such as Cr, Ni, and Mo) in the local tissue, which can promote several types of adverse effects in the human body, including allergic reactions. The adverse reaction to the niobium jewelry could not be directly associated with the liberation of niobium ions or the residual presence of cytotoxic elements such as Co, Ni, Mo, and Cr. The poor surface finish of the niobium jewelry seems to be the only variable of the material that may promote adverse reactions.

Optical testing of plastics includes the characterization of materials and the analysis of optical components. If a material is tested for transmission, haze, yellowness, and refractive index, the knowledge of its optical properties is nearly complete. For optical components, surface irregularity, birefringence, and internal contamination must also be considered. These characteristics are a function of the material and the fabrication method. Gloss and color also are affected by the base material and measured as optical properties.

A material is flammable if it is subject to easy ignition and rapidly flaming combustion. The plastics that are most widely used are the least expensive and tend to be the most flammable. This article describes the two basic approaches to improving the fire resistance of a polymeric material: modifying or substituting the basic polymer so that exposure to heat and oxygen will not produce rapid combustion, and using flame-retardant additives. It also provides an overview of the burning process and presents two flammability test methods.

A fan support casting failed unexpectedly while running at 1800 rpm in pulp at 65 deg C (150 deg F). The leading edge of the blade exhibited deep spongy holes leading to reduced section and finally to fracture of the part when the remaining section size was insufficient to support the load. Analysis showed the support casting to be a standard 8620 type composition with a hardness of 311 HRB. The design of the casting was not streamlined. There were several square corners present where great pressure differences could be generated. This was a case of erosion-corrosion with the classic spongy appearance of cavitation. Two changes were proposed: streamlining the part to avoid abrupt changes in fluid flow; and a change in alloy to a more corrosion-resistant material (304 or preferably 316) to increase the tenacity of protective films.

Mechanical testing is an evaluative tool used by the failure analyst to collect data regarding the macro- and micromechanical properties of the materials being examined. This article provides information on a few important considerations regarding mechanical testing that the failure analyst must keep in mind. These considerations include the test location and orientation, the use of raw material certifications, the certifications potentially not representing the hardware, and the determination of valid test results. The article introduces the concepts of various mechanical testing techniques and discusses the advantages and limitations of each technique when used in failure analysis. The focus is on various types of static load testing, hardness testing, and impact testing. The testing types covered include uniaxial tension testing, uniaxial compression testing, bend testing, hardness testing, macroindentation hardness, microindentation hardness, and the impact toughness test.

Alloy steel forgings used as structural members of a ski chair lift grip mechanism were identified to have contained forging laps (i.e., sharp-notched discontinuities) during an annual magnetic particle inspection of all chair lift grip structural members at a mountain resort. The material was confirmed to be 34Cr-Ni-Mo6. A heavy oxide on the dark area of one of the broken-open laps was revealed by scanning electron microscopy in conjunction with EDS. A bright area that contained ductile dimple rupture was observed adjacent to the dark area. The oxidized portion of the fracture was established to be the preexisting forging lap while the bright area was created during the breaking-open process. As a corrective action all forgings showing laps were recommended to be removed from service. Critical review and revision of the forging process and revisions to the nondestructive evaluation procedures at the forging supplier was recommended.

Sucker-rod pumps are operating in very aggressive environments in oil well production. The combined effect of a corrosive environment and significant mechanical loads contribute to frequent cases of failure of the rod string during operation. Standards and recommendations have been developed to control and avoid those failures. This study presents various failure cases of sucker rods in different applications. The heat treatment of the steel material and the resulting microstructure are an important factor in the behavior of the sucker rod. A spheroidized microstructure presents a weaker resistance to corrosion affecting the rod life. Non-metallic inclusions are a pitting preferential site leading to fatigue crack initiation. Heterogeneous microstructure as banded martensite and ferrite/pearlite decreases the ductility of the material affecting the fatigue propagation resistance.

This article provides the framework for the investigation of bridge failures. It explains the types of bridge loading and presents the regulatory provisions for bridges. Some bridge failures in the U.S. that resulted in significant changes in bridge manufacturing, design, regulation, and/or maintenance are also discussed. In addition, the article provides information on traffic damage and fatigue cracking that result in bridge failures. The need for steels with better fracture toughness in bridge design is also discussed.

A die-cast zinc adapter used in a snowthrower failed catastrophically in a brittle overload manner. The component had a chemical composition similar to standard zinc alloy ZA-27 (UNS Z35840), although the iron content was much higher and the copper slightly lower. The mechanical properties and alloy designation were not specified. Investigation (visual inspection, 187x SEM images, unetched 30x images, hardness testing, and chemical analysis) of both the failed adapter and an exemplar casting from known-good lot supported the conclusion that the casting failed as a result of brittle overload fracture due to excessive iron-zinc phase and gross porosity. These conditions acted synergistically to reduce the strength of the material. The composition was nonstandard, and the inherent brittleness suggested that it was unlikely that this material was an intentional proprietary alloy. No recommendations were made.

A special eyebolt was used to lift prefabricated concrete panels weighing approximately 16 cwt. Two eyebolts were used with a spreader bar to give a vertical lift on each eyebolt. Following failure of one eyebolt, which resulted in dropping of the load and subsequent failure of the other one, a complete eyebolt was submitted for assessment. Microscopic examination indicated a medium carbon-manganese steel had been used for the lower screwed portion of the eyebolt. Failure may have been due to brittle fracture or to fatigue, both of which could have been initiated at cracks in the hardened material in the region of the weld securing the screwed portion to the intermediate collar and which may have formed at the time of manufacture. Out-of-squareness of the thread with the collar, as was seen in the example submitted, gave rise to bending stresses when the bolt was tightened down, and this could have been a further factor which promoted failure. It was suggested that the design and construction could be improved by either making the component in one piece or, if it was desired, to adapt a standard eyebolt.

Stainless steel is frequently used for bone fracture fixation in spite of its sensitivity to pitting and cracking in chloride containing environments (such as organic fluids) and its susceptibility to fatigue and corrosion fatigue. A 316L stainless steel plate implant used for fixation of a femoral fracture failed after only 16 days of service and before bone callus formation had occurred. The steel used for the implant met the requirements of ASTM Standard F138 but did contain a silica-alumina inclusion that served as the initiation point for a fatigue/corrosion fatigue fracture. The fracture originated as a consequence of stress intensification at the edge of a screw hole located just above the bone fracture; several fatigue cracks were also observed on the opposite side of the screw hole edge. The crack propagated in a brittle-like fashion after a limited number of cycles under unilateral bending. The bending loads were presumably a consequence of leg oscillation during assisted perambulation.