Materials Science students participate in Spring Term Design Day. For Spring 2017, the ten teams conducted the following failure analysis investigations:
The Block Heads: A Die Block Failure: Classical or Unique
An H-13 steel forging die block that had catastrophically failed was selected for further study. The fracture is thought to have occurred during a routine high stress load. Charpy and fatigue bars were created using material from the failure to examine the die block’s fracture toughness and fatigue life. Other samples were prepared and mounted in order to observe the microscopic aspects of the failure. The failure as a whole was thoroughly macroscopically studied in order to find any anomalies. Through all of these experiments, the team will draw a sound conclusion on the cause of failure and design preventative measures in order to ensure a failure such as this will not again occur.
Los Tres Amigos: Converse Eyeglasses Hinge Failure
This project investigates a broken hinge on a pair of eyeglasses. The glasses had a thin stainless steel insert into an acetate frame that failed after several years of everyday use. The exact type of stainless steel is unknown. Fracture occurred in a low-stress situation that the glasses experienced semi-frequently. Although the hinge experienced some stress during its lifespan, as with
any frequently used object, this would not be enough to cause failure normally. There are no known significant events preceding failure that could have drastically weakened the part. Considering this information, tests will be run predominantly to determine corrosion and fatigue levels.
D-Fence: Investigation of the Cause of Failure and Associated Mechanisms in Fencing Blades
Catastrophic failures in fencing blades are a well-documented occurrence in the sport, potentially causing serious injuries, if not fatalities. The current project is interested in uncovering any specific factors that may lead to these fractures. Specifically, the potential fracture modes will be investigated by examining the fracture surfaces of several sabre and epee blades, in particular focusing on two sabre fractures. Blades were shown to fracture either in the hilt or near the tip of the blade, thus both will be examined. First, the steel grade of the blades will be identified. Then, investigations will examine the following potential features: the surface condition of the blades, the effect of fatigue versus sudden impact, and the potential for bending in the blades.
Cranky Engineers: Ford Crankshaft
The crankshaft in question failed while the engine was under load. The failure likely caused catastrophic damage to the lower engine block webbing, requiring a full engine swap. Additionally, a failure of this magnitude could have caused injuries or worse to the person(s) in the vehicle, depending on the driving situation. A full failure analysis of this part is imperative, in order to draw valid conclusions about how failure occurred. A series of experimental tests and their respective interpretations will be conducted by the team to that end. These tests include stereo microscopy, ultrasonic crack detection, dye penetrant inspection, scanning electron microscope (SEM) observation, energy dispersive spectroscopy (EDS) and other metallographic inspection techniques. Over the course of ten weeks, the Cranky Engineers Team will perform these tests to better understand how this potentially catastrophic failure occurred.
Escape from Kroger: Ford Escape Rim Fracture Analysis
During a cold night in a Kroger parking lot, the driver of a 2003 Ford Escape was turning left and unexpectedly hit a patch of black ice. This caused the car to slide and hit a curb resulting in a fracture on
the front right rim of the car. A group was then formed to plan and execute an array of destructive and non-destructive testing methods to explain the causes of failure and speculate upon its implications and potential material/design improvements. Additionally, this project aims to provide MSE 466 students with a valuable learning experience regarding failure analysis techniques that can be applied throughout their careers.
Brace for Impact!: Failure Analysis of an Upper Puck Pan from a Cirrus SR22 Aircraft
An upper puck pan is considered a critical component in the front landing gear of a Cirrus 22 aircraft. Due to the importance of the part, it is checked routinely and, if it has failed, a new upper puck pan is installed. In this case, an upper puck pan failed in two different welded areas. Welds on the top face of the puck cracked at the weld toe while welds on the outer edge of the puck cracked through the weld metal. In this analysis, both welded areas were evaluated to determine the root cause of the failure through metallography and fractography.
Breaking Waves: Failure Analysis of an SEI Propeller Shaft
All devices will fail at some point. The goal is to make that failure predictable, occurring after the design life of the product. When failures occur before the design life, or in an unpredictable manner, they must be analyzed in order to seek out the root cause of the failure. In August of 2015, a Sterndrive Engineering Inc. propeller shaft failed well before its design life by fracturing at the rear oil seal of the sterndrive. To find the origins of this failure, various tests and calculations were performed. Once the failure circumstances were better understood, design changes were specified to ensure that this failure does not occur again.
The Spaghetti Monsters: Ceramic Dinner Plate Failure Analysis
A common dinner plate with a ‘microwave-safe’ sticker on the bottom cracked while a serving of spaghetti was being heated in the microwave, depleting a young college student’s hard-earned savings. The plate remained intact, though five obvious cracks diverged in the center of the plate. One of the cracks breached the outer circumference. Needless to say, the plate was decommissioned. The specimen did not appear to be in imminent danger of shattering, which allowed ample time to examine it. Utilizing their years of experience in the lab, the Spaghetti Monsters established a meticulous series of state-of-the-art tests under the watchful eye of seasoned material scientists in order to determine the cause of failure.
Shearing Hubs: Metallographic Failure Analysis of a Shear Hub
For our Failure Analysis and Design (MSE 466) project, we are evaluating the failure of an industrial parts-autoloader’s shear hub that fractured a large portion of the shear hub, instead of the shear pin as intended. To analyze the cause of fracture, we will be doing many different tests such as Ultra-Sonic Testing, Hardness Testing (of the shear hub, shear pin, and shear sleeve), Electron Microscopy, and Chemistry Analysis. After preliminary inspections, we predict that it will be, at least in part, due to fatigue and will be looking for evidence that either supports or debunks this hypothesis.
Don’t Die (Casting): Die-cast Aluminum Idler Wheel Mount Failure
Idler wheel blocks used on snowmobiles are subject to vibrational and dynamic forces due to the distributed load from the track. Early failure analysis of the idler wheel block found that the part failed along the thinnest section at 45o to the spacing along the snowmobile rail. Upon stereomicroscopy and macrophotography, it was discovered that the sample had a large amount of porosity. These pores can lead to micro-cracks that grow during cyclic loading and ultimately result in failure. The cold environment likely contributed to the failure because of an increase in brittleness and a mismatch in coefficient of thermal expansion between dissimilar materials. Destructive testing was done on exemplars of the idler wheel blocks including Charpy, tensile, and Microhardness testing. The data collected during destructive testing was used to analyze how temperature affected the amount of fracture, how hardness of interior of the specimen defers from the surface, and the three-dimensional stress state of the part.