The evaluation of failed parts and assemblies requires the use of a number of different analytic tools. The tools used to evaluate failures are generally located in a laboratory with a controlled environment. These tools include but are not limited to:
1. The key to the evaluation is a qualified failure analyst that ideally has an education in Materials Science and Engineering (or some related field) and experience in evaluating failures. This person must be able to collect all of the data and information necessary to come to a conclusion regarding the failure mode and ideally offer some assistance in avoiding the failure in the future via redesign, material change, heat treatment, etc.
2. A location set aside for taking high quality photographs of the part or assembly being analyzed. A variety of lighting, backdrops and scales that can be placed in the photos is important. A digital camera with close-up capabilities is also of great importance.
3. The stereo microscope with a magnification of up to approximately 50X is a requirement for performing the initial examination of the fracture surface and any other features that are of importance such as witness marks, damage, etc. Again, photographic documentation is important.
4. The ability to clean parts and fracture surfaces using an ultrasonic cleaner is a standard failure analysis tool.
5. A variety of sectioning tools and equipment is a necessity in moving forward in most failure analysis investigations as most samples need to be reduced in size for subsequent analyses such as metallographic examination and SEM/EDS analysis. Sectioning tools include the simple hacksaw (with a variety of blades), a Dremel-like tool with a variety of cut-off wheels, die grinders, band saws (again, with an assortment of blades), metallurgical cut-off saws that provide a coolant spray during sectioning. On occasion EDM and/or water jet capabilities are of great help – these sectioning requirements often need to be “out-sourced” as most laboratories don’t have these capabilities.
6. Hardness testers for measuring the hardness of the parts and materials being analyzed. Depending on the material, geometry and area of interest, a variety of hardness measurement techniques may be needed. These include Rockwell hardness (including superficial), microhardness, Brinell hardness and sometimes a simple file hardness is of assistance.
7. The ability to prepare, polish and etch metallographic mounts is also of great importance. Mounting presses and molds, a variety of mounting media, and a complete set of polishing wheels with various grinding and polishing discs are a requirement. A variety of etchants should be available.
8. A quality metallograph (again, with the ability to take photographs) is a requirement for examining and documenting the metallographically prepared sample sections. Typically magnifications between 50X and 500X are useful, however, the ability to examine samples at 1000X magnification can also be helpful. The metallograph is essential in documenting the sample microstructure both generally and at fracture origin and/or suspect defect locations.
9. The Scanning Electron Microscope (SEM) has become more and more important in the evaluation of fracture surfaces. It is so commonly used in today’s failure analysis investigations that it could probably be regarded as a required piece of equipment. Additionally, a SEM with an integrated Energy Dispersive Spectroscopy (EDS) chemical analysis system can be of great service when a suspect material, defect, coating, etc. needs to be chemically identified at high magnification during the SEM evaluation. SEM photographs and the EDS spectra are included in the final failure analysis test report.
10. The ability to perform a chemical analysis of a material with a high degree of accuracy such as with an Optical Emission Spectroscopy (OES) system may be necessary especially if questions arise regarding the composition of the material in question. Infrequently, a fractured part being analyzed is found to have been manufactured from the wrong material for the application or even worse a material other than that specified by the part print.
To summarize, all of the tools identified above can be critical in performing a detailed failure analysis investigation. On a case-by-case basis some tools are going to be more important than others in identifying the key information required to develop a conclusion regarding the failure mode. An open mind should be kept regarding the use of other tools such as X-ray, which although not routinely a part of a failure analysis, it may become useful in special situations. The ability to write a detailed test report that aids the parties of interest in understanding the findings is of critical importance when the evaluation is completed. rockwell hardness tester for sale