Failure Analysis and Prevention: Fatigue and Fracture
Sponsored by: MS&T Organization
Program Organizers: Andrew Spowage, The University of Nottingham, Malaysia Campus; Tom Ackerson, IMR Metallurgical Services; Larry Hanke, Materials Evaluation and Engineering, Inc
Thursday 2:00 PM
October 20, 2011
Room: D235
Location: Greater Columbus Convention Center
Session Chair: Nick Cherolis, Rolls-Royce Corporation; Daniel Benac, Baker Engineering and Risk Consultants, Inc.; Erhan Ulvan, Acuren Group Inc.
2:00 PM
Fatigue in the Aerospace Industry - Is it HCF or LCF?: Nicholas Cherolis1; 1Rolls-Royce Corporation
One of the most important tasks in examining a fatigue fracture is determining whether a fatigue fracture is high cycle fatigue or low cycle fatigue (HCF or LCF). There is a continuum from low cycle fatigue with its one high stress cycle per flight and slow growing crack to high cycle fatigue with its vibration induced high frequency low alternating stress cycles. Most cracks in jet engine hardware fall into one category or the other. Our purposes involve understanding the underlying driving force of the crack, slowly applied high alternating stresses or vibration. There are several aspects of a crack that help distinguish mode that will be discussed.
2:20 PM
Avoiding Fatigue Failures: Learning from Past Fatigue Investigations: Daniel Benac1; 1BakerRisk Engineering
Many failures of equipment, components, structures and rotating equipment are due to fatigue and cyclic loading conditions. Therefore, it is crucial that equipment and structures are designed and maintained to not failure by fatigue. This session will focus on lessons learned from historic and recent fatigue failures to mitigate fatigue by good design and maintenance practices. Many examples from aerospace, nuclear, and the oil and petrochemical industry will be discussed on why fatigue failures occurred and how they can be avoided.
2:40 PM
Reverse Engineered Forging Fatigue Failure: Edward Vojcak1; 1A. Finkl & Sons
Large quenched and tempered 4330 forging steel was machined to replace an original equipment manufacturer’s (OEM) part into a vibrating working beam on a concrete rubblizer application. The OEM part’s lead time was un-acceptably long so a sub-contactor reverse engineered the beam. Reportedly, after two hours of operation at 44 Hz the resonant beam fractured. The presentation will show how an inadvertent weld utilized for temporary fixturing at a foreign machine shop damaged an expensive machined forging with a long delivery.
3:00 PM
Architectural Failure of an Historical False Ceiling in a High School Building: Giovanni Barla1; Pier Giorgio Debernardi1; Donato Firrao1; Paolo Matteis1; 1Politecnico di Torino
A false ceiling collapsed in a building constructed in Italy in the 1930s, renovated in the 1960s, and then used as a school. The false ceiling was made of clay blocks assembled with mortar reinforced by horizontal steel bars and was suspended to vertical steel wires. Several concurring causes lead to a chain failure of the 4 mm diameter, low-carbon steel wires, which underwent brittle cleavage fracture without macroscopic deformation. The fracture surfaces exhibit oxidized prior cracks, probably caused by wire twisting operations during the construction. High load rate tensile tests of recovered wire segments with prior cracks showed similar brittle fractures and low strength, whereas quasi-static tests of wire segments without cracks showed satisfactory strength and elongation. The overload which ultimately caused the collapse was originated by a sudden air pressure variation, due to an abrupt interruption of the air flow through the room, during a moderately windy day.
3:20 PM Break
3:40 PM
Summary of Failure Analyses Activities at Brookhaven National Laboratory: Carl Czajkowski1; 1Brookhaven National Laboratory
Brookhaven National Laboratory has for many years conducted related to the failure of nuclear materials and components. These investigations (1985-2000) have included both field and laboratory studies for various U.S. government agencies in the areas of metallurgy, welding, materials evaluation, failure analysis, corrosion and life extension. Failure and root cause analyses have included radioactive and non-radioactive components from nuclear reactors and commercial fossil fuel plants for major materials systems currently in use. Components evaluated have included pumps, valves, piping, welds, supports, bolts and fasteners, flanges, fittings, tanks and vessels. Failure modes investigated have encompassed: fatigue, corrosion fatigue, stress corrosion cracking, hydrogen embrittlement, wear, thermal shock, temper brittleness, overheating, de-alloying, and erosion-corrosion, etc. The results of these examinations which have previously appeared in various formats (formal and informal reports, journal articles, etc.) have been collected and summarized in this paper and will be discussed.
4:00 PM
Trailer Hitch Receiver Failure on a Class A Motorhome: William Carden1; Eric Van Iderstine1; 1McSwain Engineering, Inc.
An engineering investigation was performed on a failed receiver hitch from a Class A motorhome. Failure of the crossmember resulted in the separation of the vehicle-in-tow from the motorhome while traveling on an interstate highway. The analysis found that the receiver had failed due to metal fatigue. The investigation included optical microscope examination, scanning election microscopy, finite element analysis, and comparison to exemplar receiver hitches. Finite element analysis of the hitch assembly revealed that the areas of highest stress were in the lower corners at the intersection of the receiver tube to crossmember. The fatigue initiated at this location that also coincided with a defective weld termination. Research into the standards governing receiver hitches determined that the structural integrity of the receiver hitch was based upon the weight of the vehicle in tow without regard to the towing vehicle and the mounting configuration.
4:20 PM
An Analysis of a Premature Fatigue Failure of an Acid Bath Mixer's Shaft under the Combined Effects of Stresses, Stress Concentrators and Corrosion Fatigue : Root Causes and Solutions: Pierre Dupont1; 1Schaeffler Belgium Sprl/Bvba
In most of the metal postprocessing industries dedicated to the strip, wire or sheet coating or painting, one uses to exploit degreasing and rincing baths in order to insure an higher grip quality of the further deposition of the coating or painting. Such kind of devices usually works at average temperatures of 150 [°C] with machines components partially "embedded" within the corrosive media and strongly exposed to acid vapors and condensates. This presentation aims to develop here the practical case of an prematured fatigue failure of a processing shaft under the combined effect of corrosion fatigue, high bending stresses and local stress concentrators. After a complete overview of the working conditions, chemical properties of the media, material characteristics and stress distribution within this shaft, it will be make emphasis on the solutions put in place to avoid fatigue failure, stress corrosion cracking and increase the shaft lifetime under operation.
4:40 PM
Holistic Fracture Analysis: Debbie Aliya1; 1Aliya Analytical Inc.
At a basic level, we all know that something breaks when the stress exceeds the strength. At a more useful level, we have to come to grips with whether it was nominally the static strength or some sort of dynamic strength that was exceeded, or whether there was another type of environmental factor at work. Before we get to work on any specific project, we have to clarify whether it is a single event which we wish to understand, or whether an entire design process has been called into question. If we are consultants, whether in house or outside, we have to be able to negotiate an investigation protocol that simultaneously balances business, human, and technical factors . This will be somewhat of a right brain presentation, founded on left brained data.
5:00 PM
Fatigue Analysis of Titanium Fitting: Ashley Vayer-Jenkins1; 1Spirit AeroSystems
A titanium 6Al-4V fitting cracked during fatigue testing. The fitting was cycled in constant amplitude fatigue with loads applied at a 35 degree angle, R=0.1. Calculations showed only 14,000 flight cycles before failure when the expected design service value was 75,000 flight cycles. The fitting was investigated for causes leading to crack initiation. Examination using a scanning electron microscope determined crack length and number of load cycles. The crack received a total of 26,176 cycles. It was concluded from data that the crack initiated at 426,070 load cycles under a 50 kip load. Gouges found in the bushing of the fitting closely aligned with the initiation location; possibly causing an area of localized stress. Whether the bushing material caused the crack initiation could not be verified. Other factors, such as chemistry and microstructure, did not contribute to failure. Design criteria were re-evaluated to prevent defects from acting as stress concentrators.
5:20 PM
Failure Analysis of a Furling Mast of a 42-Foot Catalina Boat: Erhan Ulvan1; 1Acuren Group Inc.
A boat mast section with cracks in the vicinity of a bulge was received. Visual examination revealed no evidence of mechanical damage. SEM examination of the fracture surface showed intergranular cracking with a network of dimples covering the exposed grain boundary faces. Hydrostatic pressure testing of the mast revealed that it burst at a pressure of 2350psi. The mast, an Al-Zn-Mg alloy, showed evidence of grain boundary precipitation in the as-received condition. It was observed that solutionizing and aging improved the tensile properties of the material; with a doubling of ductility. When this heat treated material was tested to failure, the resultant crack propagation mode was largely transgranular ductile failure. The findings of the failure analysis indicated that the cracks at the bulge likely formed from expansion of frozen water. The investigation shows that solutionized and aged mast material would perform better and be more resilient to cracking.
5:40 PM Cancelled
Failure Analysis of Ruptured CNG Cylinder: RAM PRASAD1; 1IIT BOMBAY
The refillable seamless type I compressed natural gas cylinder made of Cr-Mo steel in quenched and tempered condition failed prematurely in less than five years. The investigation revealed that hardness in the inner surface was higher compared to the outer surface. The ratio of yield to tensile strength was close to 0.9. The inside of the CNG cylinder was exposed to methane, CO2, H2S and water. The macro and micro fractographs show that the inside surface of the CNG cylinder when contacted by water, CO2 and H2S, creates colonies of parallel cracks in the rolling direction. The coalescence of the crack eroded the steel, thus reducing the thickness of the cylinder. This reduced the pressure carrying capacity; finally leading to the burst of the cylinder. The analysis reveals that stress oriented hydrogen induced cracking is possible in the cylinder for the analyzed microstructure, heat treatment and mechanical properties.
6:00 PM Cancelled
Fatigue Failure in Tungsten Carbide: Theodore Wilken1; 1Exova, Inc
One commonly associates fatigue failure with metals that are ductile by nature but suffer brittle fracture. Less ductile metal alloys, however, can also suffer fatigue failure. Cemented carbides can be produced by carburizing tungsten metal to produce tungsten carbide, which can be combined with a binder such as cobalt. By applying powder metallurgy technology, one can make a billet of tunsten carbide, but not with full density. One can measure the density and compare that to the theoretical density to identify the percent porosity. Mercury porosimetry can be applied to determine the percent interconnected porosity. This paper describes the results from examining a tungsten carbide tool that failed while making parts. During our examination, we observed two sets of beach marks on the fracture surface around a bolt hole. We located the fracture origins and found that one of these displayed the features of porosity within the material.