ISBN: 378-26-138420-01
INTERNATIONAL CONFERENCE ON CURRENT TRENDS IN ENGINEERING RESEARCH, ICCTER - 2014
Analytical Study of General Failure in Prominent Components 1
Balaji V.R1, Amitesh Jain1,A.Kirthivasan1 ,D.Ananthapadmanaban2 Under graduate students, SSN College of Engineering,Kalavakkan-603110,Tamilnadu,India 2 Associate Professor, Department of Mechanical Engineering, SSN College of Engineering,Kalavakkam-603110, Tamilnadu, India Email: ananthapadmanaband@ssn.edu.in Email: balaji12303@mech.ssn.edu.in
I.
Abstract
The importance and value of failure analysis for safety, reliability, performance, and economy are well documented in this paper. To prevent failure of machine components failure analysis are made on the component before and after manufacturing. Even though the various test are conducted, failures happen at some stage. In this paper, a brief overview of causes of failure has been discusses. Some case studies have been given and the possible causes of failure have been analyzed. Key words: Failure Analysis, Case histories, recent trends.
II.
analysis of the physical evidence alone may not be adequate to reach this goal. The scope of a failure analysis can, but does not necessarily, lead to a correctable root cause of failure. Many times, a failure analysis incorrectly ends at the identification of the failure mechanism. A material or component shows gradual deformation or creep when subjected to sustained loading especially at elevated temperatures. It occurs even if the applied stresses are below the proportional limit. It occurs in both metals and non-metals. Similarly when a component is subjected repeated continuous load, it tends to gradually deteriorate resulting in fatigue failure. Fatigue occurs in three stages namely crack initiation, crack propagation and unstable rapid growth.
Introduction
The defects in quality, design, process or part application are the underlying cause of a failure. The human errors are considered, when failure depends on the user of the product or process. The failure analysis includes the area of creep, fatigue, structural resonance, crack initiation, crack propagation, spalling and pitting, fretting and wear, component failure. The components are subjected to failure analysis before and after manufacturing. Even though the various tests are conducted, failure happens at one stage.
Fatigue failure may also occur due propagation of the cracks originating from the surface of the component. They are of two types namely spalling and pitting. It occurs due to sub surface tensile and shear stresses that exceed materials fatigue limits. Gears and bearings are usually subjected to such stresses. When surfaces of two components mate each other they are subjected to normal pressure and tangential oscillatory motion fretting failure occurs. The surface undergoes failure due to fatigue, high normal forces or wear and failure can be accelerated in the presence of chemical attack.
The mechanism of failure can be attributed to multiple factors which simultaneously plays an influential role. These include corrosion, abnormal electric current welding of contacts, returns spring fatigue failure, unintended failure, dust accumulation and blockage of mechanism, etc.
III.
Failure analysis-History and Inception
The importance and value of failure analysis to safety, reliability, performance, and economy are well documented.
The strategy for safety is to make various test before the product comes into the usage. The investigation of failure is vividly illustrated in the pioneering efforts of the consideration of physical evidence and the use of engineering and scientific principles and analytical tools. Often, the reason why one performs a failure analysis is to characterize the causes of failure with the overall objective to avoid repetition of similar failures. However,
For example, the importance of investigating failures is vividly illustrated in the pioneering efforts of the Wright Brothers in developing self-propelled flight. In fact, while Wilbur was traveling in France in 1908, Orville was conducting flight tests for the U.S. Army Signal Corps and was injured when his Wright Flyer crashed (Fig. 1). His
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INTERNATIONAL CONFERENCE ON CURRENT TRENDS IN ENGINEERING RESEARCH, ICCTER - 2014 passenger sustained fatal injuries [1]. Upon receiving word of the mishap, Wilbur immediately ordered the delivery of the failed flyer to France so that he could conduct a thorough investigation. This was decades before the formal discipline called “failure analysis” was introduced. Unfortunately, there are many dramatic examples of catastrophic failures that result in injury, loss of life, and damage to property. For example, a molasses tank failed in Boston in 1919, and another molasses tank failed in Bellview, NJ, in 1973 [2]. Were the causes identified in 1919? Were lessons learned as a result of the accident? Were corrective actions developed and implemented to prevent recurrence?
A micrograph of sample taken few millimetres behind fracture surface reveals that it was subjected to much higher temperatures than area directly beneath the tile. From these images it is clear that second phase particles present in the microstructure composed of copper, manganese and iron melted and subsequently wetted the grain boundaries upon exposure to high temperature causing significant weakening of grain boundaries, ultimately resulting in intergranular failure.
Fig.2 Light optical microscopy micrograph of panel skin
section at fracture surface. Notice that liquation is observed across entire micrograph. A crack along a grain boundary is also present. [4]
Fig.1 Crash of the Wright Flyer, 1908. Courtesy of the National Air and Space Museum,Smithsonian Institution Photo A-42555-A[1]
Conversely, failures can also lead to improvements in engineering practices. The spectacular failures of the Liberty ships during World War II were studied extensively in subsequent decades, and the outcome of these efforts was a significantly more thorough understanding of the phenomenon of fracture, culminating in part with the development of the engineering discipline of fracture mechanics [3]. Through these and other efforts, insights into the cause and prevention of failures continue to evolve. Space shuttle, Columbia orbitter failed upon its re-entry into the earth’s atmosphere. Earlier it was believed that failure was caused by foam piece which got dislodged from external tank during takeoff and struck the leading edge of the left wing. This damaged the latter made of carboncarbon composites thereby providing a breach in the shuttle leading to catastrophic failure [4]. The foam tiles on analysis show signs of erosion due to high temperatures exceeding 2000K during re-entry which is sufficient enough to melt aluminium. Hence it is quite apparent that Aluminium Sandwich Panel Skins below the tiles were protected during re-entry. Hence an analysis was carried out on the Aluminium Sandwich Panel Skin recovered from the debris field. They were 0.6mm thick sheets made up of 2000-series Aluminium alloy.
The Sandwich Panel was locally heated to cause liquation only near the fracture surface whereas aluminium microstructure directly beneath an insulating tile shows no sign of liquation. This lead to formation of local hotspots where there was no thermal protection due to loss of insulation resulting from the accident. These localised hotspots lead to the failure of the aluminium sandwich panel and hence failure of the space shuttle.
IV.
Recent trends and advancements
Modern automobiles increasingly utilize high-strength lowweight alloys for better fuel efficiency. Aluminium alloys seem to serve the purpose owing to its high strength to weight ratio. Several major automobile components such as engine blocks, pistons, intake manifold, carburettors and brake parts make use of aluminium castings. Since aluminium alloys such as Al-356 is extensively used, a study to realize the reason for their mechanical failure is necessary. S. Nasrazadani and L. Reyes investigated a clutch pedal lever made of permanent mould cast Al 356-T6 aluminium by way of metallography, SEM, hardness testing and visual inspection [5]. They concluded that the parts in clutch assembly must be designed with thicker sections to resist the applied stress. Fatigue and brittle failure occurs due to presence of dendrite phases and micro-porosity and it can be avoided by production of heat treated Al 356-T6.
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Fig. 3 Image of the fractured part showing two visible cracks[5]
Fig.4 Oxidation product visible at the grain boundary (arrows)
[6]
Y. Huang and Y. Zhu metallurgically examined the section of a fractured spindle from an axle housing of a truck. It was found that after about 8,000 miles of service the axle fractured at the friction weld interface. Metallographic and SEM examinations at the fractured site revealed the existence of micro-porosity and formation of ferrite layer. This had reduced the impact strength of the weld resulting in overload fracture. Due to air exposure at the molten layer interface, a band of oxides was formed and the solidification of liquid film leads to microshrinkage.
with other oxidized grain boundaries (encircled) [7]
The results showed that both were made of the same steel grade X2NiCoMo18-8-5. The samples were cut from both defected and non-defected regions and were analysed using optical microscopy. From the analysis it was observed that welding bead had serious problems due to the oxidation of the plate. The surface of metal plate was deposited by oxidation products due to under machining of the plate, before welding. Hence during welding, the oxidation products get entrapped within weld bead or may appear on the surface of the weld. This weakens the weld thereby causing failure.
V.
Fig. 5 The assembly fractured along the weld interface (a ferrite band with oxides), etched, 2% natal[6]
A lap welded steel joint had failed when it was operated under very high speeds[7]. This joint was fabricated by a laser beam welding using high energy coherent optical source of heat at low pressure. The steel sheets used for this purpose was 0.5 mm thick. The components of the debris was put into failure analysis for metallurgical investigation. The sheet and plate used to form this joint were analysed for their chemical composition.
Failure analysis is considered to be the examination of the characteristics and causes of equipment or component failure[8]. In most cases this involves the consideration of physical evidence and the use of engineering and scientific principles and analytical tools. Often, the reason why one performs a failure analysis is to characterize the causes of failure with the overall objective to avoid repeat of similar failures. However, analysis of the physical evidence alone may not be adequate to reach this goal. The scope of a failure analysis can, but does not necessarily, lead to a correctable root cause of failure. Many times, a failure analysis incorrectly ends at the identification of the failure mechanism and perhaps causal influences. The principles of root-cause analysis (RCA) may be applied to ensure that the root cause is understood and appropriate corrective actions may be identified. An RCA exercise may simply be a momentary mental exercise or an extensive logistical charting analysis. Many volumes have been written on the process and methods of RCA. The concept of RCA does not apply to failures alone, but is applied in response to an undesirable event or condition (Fig. 4). Root-cause analysis is intended to identify the fundamental cause(s) that if corrected will prevent recurrence.
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Root-Cause Analysis
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Conclusions
Various procedures followed during failure analysis have been documented in this paper. Root cause analysis has been discussed. Starting from the history of failure analysis some case studies have been presented. It can be concluded that failure analysis is a very vast field of research and any analysis can give the possible cause of failure only.Sometimes there may be a a combination of factors for a material or component to fail.
VIII.
References
[1]. P.L. Jakab, Visions of a Flying Machine: The Wright Brothers and the Process of Invention, Smithsonian Institution, 1990, p 226 [2]. R.W. Hertzberg, Deformation and Fracture Mechanics of Engineering Materials, John Wiley & Sons, 1976, p 229–230 Fig. 6 Root-cause analogy [8]
VI.
[3]. D.J. Wulpi, Understanding How Components Fail, 2nd ed., ASM International, 1999
Recent Case History
Building in Chennai under construction crashed recently (2014) when there was rain for about 1 or 2 hours. Most probably the soil itself must have been loose around that area, Chennai being home to clayey soil[9]. Another reason could be-lack of proper curing of foundation. In earlier days, foundations used to be cured for close to 3 weeks. These days, it is not certain whether proper procedures are followed. Most often, there is a combination of factors involved each of which contributes to the ultimate failure. So, it is suggested that at each stage, mandatory checks be followed so that even if a structure fails, one can exactly pinpoint what went wrong and at which stage it went wrong.
[4].Metals Handbook,American Society of Metals,Volume 5,Failure Analysis and prevention. [5] S. Nasrazadani• L. Reyes ,Failure Analysis of Al 356T6 Clutch Lever, Failure Analysis of Al 356-T6 Clutch Lever [6]. Y. Huang and Y. Zhu, Failure Analysis of Friction Weld (FRW) in Truck Axle Application, Submitted: 17 September 2007 / in revised form: 16 November 2007 / Published online: 20 December 2007_ ASM International 2007 [7]. A. Nusair Khan • W. Mohammad • I. Salam..: Failure Analysis of Laser Weld Joint of X2NiCoMo18-8-5 Steel. [8]. http://en.wikipedia.org/wiki/Root_cause_analysis [9]. http://www.thehindu.com/news/cities/chennai/ap-cmannounces-exgratia-for-telugu-victims-in-chennaibuilding-collapse/article6159984.ece
Fig.7 The Hindu 11 floor building collapse at Bai kadai junction
Moulivakkam,near Porur on Sunday.in Chennai-TN.India[9]
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