Failure Analysis Testing - Cause & Prevention
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Cause failure analysis testing of metal products employs macroscopic and microscopic examination methods, as well as other investigative tools like nondestructive testing, mechanical testing and chemical analysis. The failure analysis investigation concentrates on the metallurgical aspects of the failure. They generally do not emphasize factors like stress or load distributions. The steps followed, the order of the steps along with the failure analysis services performed during a failure investigation can vary greatly depending on the type of failure being investigated.
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Collecting and Assembling History
The root cause failure analysis investigation must start by obtaining background information on the failure. This includes collecting available specifics of the manufacturing, processing, fabricating method, and repair history of the failed component. Processing and repair records, pertinent codes, specifications and related standards, along with specifications, drawings, and style criteria should be included. Data needs to be provided about the material used, mechanical properties, heat treatment, and then any surface preparation including cleaning, grinding, plating or painting. The service history should include the date, time, temperature, and environmental conditions of the component.
In addition to collecting the setting information, photographs from the failed component as well as the failure site should be taken. These photographs will document the place and type of failure and definately will become part of the permanent record of the failure.
Nondestructive testing can be handy in failure investigations, particularly magnetic particle inspection for ferrous metals, liquid penetrant inspection, and ultrasonic inspection. These inspection methods are employed to detect surface cracks and discontinuities. Radiography is utilized to examine components for internal discontinuities, including voids and porosity.
Before investigator can check out the failed component, it ought to be isolated and protected from further damage. The component should be handled carefully and has to be sheltered on the corrosive environment to preserve the failure.
The investigation should begin with a visual study of the failure site and part. All observations should be recorded or photographed and information must be gathered prior to part is cut for destructive testing. The visual examination should include inspection of the fracture faces and crack paths, with an assessment of abnormal conditions or abuse how the part endured during its service life.
Macroscopic examination is surely an extension of the visual examination and evaluates quality and homogeneity from the part. It is accustomed to determine the origin of the failure and the form of fracture such as ductile, brittle, torsion or fatigue. Macrostructural features can be used to assess internal quality, presence of hydrogen flakes, chemical segregation, hard cases, flow lines and welds.
The mechanical properties of an metal can be used to determine all the various usefulness and the service which can be expected from the material. Mechanical testing services look at the strength, ductility and other physical properties of materials under various conditions, for example temperature, tension, compression, impact and cargo.
Metallurgical examination is carried out to determine microstructural features such as inclusion content, grain size and rolling direction. Metallographic examination demands the use of high magnification microscopy. These examinations can sometimes include optical as well as scanning electron microscopy. Optical microscopic examination can be used to determine grain size, microstructure and inclusion type and content. However, scanning electron microscopy is used to determine abnormalities, such as inclusions, segregation, and surface layers, and also fracture features and, if you use energy dispersive analysis, can identify inclusion type and corrodents on the fracture face. Microhardness testing is performed to measure case depths, evaluate cold work, determine weld quality and find out mechanical properties of small parts.
Inside a failure investigation, chemical analysis is conducted routinely to ensure that the material is what was specified. In addition to obtaining the bulk composition in the material to confirm the grade used, it could be necessary to analyze surface contaminants. Chemical analysis is conducted on the base material and also corrosion products, deposits or coating layers.
Often it may be helpful to determine the main cause of the failure by way of testing that simulates the physical conditions under which the failure occurred. The simulation may provide information regarding the suitability of the material to the environment and can also read the heat treatment or performance of the part in a controlled environment including salt spray. Some kinds of simulation tests require accelerated testing as a way to obtain information within a reasonable time. Interpretation of accelerated tests has to be done with care for the reason that limitations of the tests have to be recognized.
Data Analysis, Conclusions and Report
Following the completion of the outlined steps, the investigator ought to be ready to interpret and summarize the information that has been collected. A few of the work performed may well not contribute in determining the basis cause of the failure, yet it could be helpful in eliminating some possible causes. In combination, the steps that have been outlined will, in most cases, enable the investigator in summary the root cause of the failure. The failure analysis report ought to provide the following:
� Description in the failed component
� Conditions during the time of failure
� Background service history
� Mechanical and metallurgical data regarding the failed part
� Evaluation in the material quality
� Discussion of mechanisms that designate the cause of the failure
� Recommendations for prevention of future failures and action to be taken concentrating on the same parts