Failure Analysis Testing - Cause & Prevention

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Root cause failure analysis testing of metal products utilizes macroscopic and microscopic examination methods, and various investigative tools for example nondestructive testing, mechanical testing and chemical analysis. The failure analysis investigation focuses on the metallurgical aspects of the failure. They typically do not emphasize factors like stress or load distributions. The steps followed, the transaction of the steps and the failure analysis services performed during a failure investigation are vastly different 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 consists of collecting available information regarding the manufacturing, processing, fabricating method, restore history of the failed component. Processing fix records, pertinent codes, specifications and related standards, along with specifications, drawings, and design criteria should be included. Data should be provided about the materials used, mechanical properties, heat treatment, and any surface preparation for example cleaning, grinding, plating or painting. The service history ought to include the date, time, temperature, and environmental conditions with the component.

In addition to collecting the history information, photographs of the failed component as well as the failure site must be taken. These photographs will document the positioning and type of failure and will become part of the permanent record from the failure.

Nondestructive Testing
Nondestructive testing are needed in failure investigations, particularly magnetic particle inspection for ferrous metals, liquid penetrant inspection, and ultrasonic inspection. These inspection methods are used to detect surface cracks and discontinuities. Radiography can be used to examine components for internal discontinuities, such as voids and porosity.

Visual Examination
Until the investigator can check out the failed component, it should be isolated and protected from further damage. The component have to be handled carefully and should be sheltered through the corrosive environment to preserve the failure.

Your analysis should begin with a visual examination of the failure site and part. All observations should be recorded or photographed and details must be gathered prior to part is cut for destructive testing. The visual examination ought to include inspection of the fracture faces and crack paths, with an assessment of abnormal conditions or abuse that the part endured during its service life.

Macroscopic Examination
Macroscopic examination can be an extension of the visual examination and evaluates quality and homogeneity with the part. It is accustomed to determine the origin of the failure and the type of fracture such as ductile, brittle, torsion or fatigue. Macrostructural features may be used to assess internal quality, existence of hydrogen flakes, chemical segregation, hard cases, flow lines and welds.

Mechanical Testing
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 study the strength, ductility and other physical properties of materials under various conditions, for example temperature, tension, compression, impact and load.

Metallurgical Examination
Metallurgical examination is completed to determine microstructural features like inclusion content, grain size and rolling direction. Metallographic examination requires the use of high magnification microscopy. These examinations might include optical as well as scanning electron microscopy. Optical microscopic examination is used to determine grain size, microstructure and inclusion type and content. On the other hand, scanning electron microscopy is used to ascertain abnormalities, such as inclusions, segregation, and surface layers, along with fracture features and, with the aid of energy dispersive analysis, can identify inclusion type and corrodents about 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.

Chemical Analysis
In a failure investigation, chemical analysis is completed routinely to ensure that the material is what was specified. Along with obtaining the bulk composition with the material to confirm the grade used, it can be necessary to analyze surface contaminants. Chemical analysis is conducted on the base material and also corrosion products, deposits or coating layers.

Simulation Tests
It often may be helpful to determine explanation for 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 on the environment and can also confirm the heat treatment or performance from the part in a controlled environment such as salt spray. Certain types of simulation tests require accelerated testing to be able to obtain information within a reasonable time. Interpretation of accelerated tests must be done with care as the limitations of the tests have to be recognized.

Data Analysis, Conclusions and Report
Following the completion of the outlined steps, the investigator needs to be ready to interpret and summarize the data that has been collected. Many of the work performed may well not contribute in determining the root cause of the failure, yet it might be helpful in eliminating some possible causes. When combined, the steps that have been outlined will, in many instances, enable the investigator to summarize the root cause of the failure. The failure analysis report should provide the following:

� Description with the failed component
� Conditions during failure
� Background service history
� Mechanical and metallurgical data concerning the failed part
� Evaluation of the material quality
� Discussion of mechanisms that designate the cause of the failure
� Strategies for prevention of future failures or action to be taken with similar parts