Failure Analysis Flashcards
What three trends can be tracked by using a fluid testing schedule?
Wear rates of internal components Rate of fluid and additive detioration External contamination (Ingressed)
What is the main concern during the break in period?
During the break in period, extremely small particles will be broken away and suspended within the oil, but not trapped within the filter. Smaller than 15 microns.
At what point does predictive maintenance become failure maintenance?
Once the inspections begin to show more wear particles and you are in the high risk period.
What three items are investigated during oil analysis?
Deteroiration of the oil and additives
Amount of particles in the oil
Presence of foreign particles
How many ounces is a typical oil sample?
4 oz
What 3 main sections are on an oil sample lab report?
Metals
Physical properties
Other properties
What is Viscosity of a fluid?
How is a change in viscosity caused?
Viscosity is a measure of a fluids resistance to flow
Contamination by other products
High temps
Extended service intervals
How does water get into a system, and what does it cause?
Water is ingested as contamination, or created as condensation.
Components can rust, oils can become acidic, and can act as a catalyst causing creation of metallic substances.
What do solids in the oil indicate, and how is it caused?
Solids indicate varnish, sludge and soot created by the combustion process.
These are caused by high operating temperatures, or outside contamination.
If your oil analysis indicates increased tin content, what could this be coming from?
Tin wear is caused by wearing of sacrificial overlays during break in periods.
If Aluminum is highlighted on the oil sample report, what could be the cause?
Pistons, superchargers, turbochargers, bearings, engine blocks and gearbox housings.
Your lab report comes back with large amounts of Silicon in the oil, what caused this?
Dirt ingested in the sample is most likely
If lab results indicate excessive Chromium in your oil, what could be the cause?
Hard surfacing is being removed
Piston Rings wearing
Gearbox bearings and shaftsd
If there is Nickel found in your oil sample report, what does this indicate?
Frictionless roller bearings, shafts or gears are wearing.
What are three sources of coolant contamination?
Wearing components
Corrosion
Environmental Sources ingressed
When performing an exhaust gas analysis, what are three items being measured? How are they formed?
Hydrocarbons from low combustion temperatures
Carbon Monoxide from restricted supply air
Nitrogen from high combustion temperatures
What is Failure Analysis by definition
A Systematic process to reduce costs and limit risks/liability
What is the term for the grainy texture of a broken metal part?
Lattice Structure
What determines a parts Overall Strength and Ductility?
The amount of carbon in the steel, and heat treating processes.
What is the carbon content of low carbon steel?
0.02-0.25%
What is the carbon content of medium carbon steel?
0.25-0.50%
What is the carbon content of high carbon steel?
0.5-2%
What are the three types of metal fractures?
Fatigue Fracture,
Brittle Fracture
Ductile Fracture
How do you determine a failure to be a fatigue fracture?
There will be a clear initiation site, with beach marks indicating prolonged fracturing of the material. Ending with a clear snapping point called the shear lip.
How do you determine a failure to be a brittle fracture?
There will be a clear and rough break, typically due to a one time shock load.
How do you determine a failure to be a ductile fracture?
The ductile fracture will have plastic deformation, where the part was clearly stretched or stressed past its original shape, ending with a clear snapped off area.
What are three ways that wear can be classified?
Type of stress
Movement of the part
Damage to the wear surface
What is adhesive wear?
Without proper lubrication, two metal parts will begin to contact, causing a bonding and breaking action. This creates ridges causing further surface wear and heat.
What is abrasive wear?
Abrasive wear is the scraping stress caused by particles caught between two surfaces in motion.
What does surface fatigue wear look like?
On rolling surfaces such as cam lobes or bearing races, where the load is applied and released it causes surface wear in its normal use.
An apprentice is installing a new wheel bearing, it in an interference fit on the spindle and they strike it with a hammer unevenly, what has happened?
True Brinelling: shows up as indentations on the bearing race all the way around, due to improper installation.
This can also be seen with improper preload causing the rollers to impact the race in normal operation.
While inspecting the Steering Shaft U joints for reassembly, you notice that the ends have impact marks on only 50% of the surface, what caused this?
False brinelling: the wear or removal of material on a bearing surface in one spot, due to improper lubrication. Typically the wear site will have a reddish tinge due to oxidation of the lubricant.
How might you determine that parts have corrosive wear?
Chemical or electrochemical reaction between surfaces, shown by rusting, scaling and pitting.
If you see a cylinder liner with pitting around the water jacket, what is this a sign of?
Erosive wear caused by cavitation.
What are the two main reasons for component failure?
improper installation
poor maintenance procedures
At what temperature are Nitrogen oxides formed in the exhaust gas?
2500 fahrenheit
