A Re-Examination of Failure Analysis and Root Cause Determination

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26CHEMICAL ANALYSISA chemical analysis was performed on chips machined from the weld crown. Theresults are given in the table below. The weld metal conforms to the chemicalcomposition requirements for grade E7018 welding electrode as specified in AWS A 5.1Table 7. The weld metal also conforms to the chemical composition requirements forseveral other grade E70xx welding electrodes.NS = Not SpecifiedChemical Analysis (wt%)ELEMENT WELD METAL AWS A 5.1 E 7018Carbon 0.164 NSManganese 1.01 1.60 MAXPhosphorus 0.015 NSSulfur 0.013 NSSilicon 0.48 0.75 MAXChromium 0.06 0.20 MAXNickel 0.04 0.30 MAXMolybdenum
27(2.5) (0.0625 inches) = 0.156 inches (ie 5/32 inch)The actual chamfer was measured to be 0.157 inches deep. This should also be theweld depth for static loading conditions.CONCLUSIONThe failure of the hydraulic cylinder occurred as a tensile shear fracture solely within thecircumferential weld at the end cap. The weld did not have enough strength to supportthe applied loads. The failure occurred as a single event with fracture occurring at alllocations around the circumference of the cap simultaneously. The failure is attributedto insufficient depth of weld penetration. The reduced cross-sectional area at the weldwas unable to support the applied load. This conclusion is corroborated by thecontinued presence of the machined chamfer at the weld root. The chamfer should havebeen covered by the weld. It is recommended that during manufacturing of the part thatthe weld be completed in two passes to ensure that sufficient penetration is achieved atthe weld root.IMPORTANT FAILURE ANALYSIS PRINCIPLES REPRESENTED IN THIS CASEHISTORYThe root-cause of this failure was identified as an incorrectly applied process, so achange in the process was recommended. The process specified for welding the top ofa hydraulic cylinder was inadequate to create a good weld. Changing the process wouldchange the outcome and eliminate the failure. This is a sound root-cause determination.Case History #4. Aircraft Component Failure AnalysisIntroductionBoth halves of a broken steel pin were submitted for examination. The sample wasidentified as Left Hand Main Landing Gear, AC 809. At a later date an unbroken pinidentified as Right Hand Main Landing Gear, AC 809 was also submitted. We wereasked to determine the mode, not the cause, of failure.
Page 1 and 2: A Re-Examination of Failure Analysi
Page 3 and 4: 3I. IntroductionThe purpose of fail
Page 5 and 6: 5These ideas provide the philosophi
Page 7 and 8: 7V. How to conduct a failure analys
Page 9 and 10: 94. Visually examine the sample. Ex
Page 11 and 12: 11high magnification. Take careful
Page 13 and 14: 13the stress conditions are known f
Page 15 and 16: 15• Tensile stress.Cylindrical sp
Page 17 and 18: 17Contact Fatigue - Elements that r
Page 19 and 20: 19characteristic of ASTM A572 grade
Page 21 and 22: 21Tensile Property TestingA tensile
Page 23 and 24: 23tensile properties for the materi
Page 25: 25Figure 4. Elongated dimples Figur
Page 29 and 30: 29Metallographic ExaminationA trans
Page 31 and 32: 31ResultsThe simulation found that
Page 33: 33In addition to an undetectable fa

A Re-Examination of Failure Analysis and Root Cause Determination

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