Link: Engineering Analysis

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Contents

Engineering Analysis

Introduction

Prior to proceeding onwards to the content detailing the Engineering Analysis, it is suitable to consider where in particular it would be applied in the course of the industry-standard design process. First and foremost, it is necessary to observe that the nature of the Engineering Analysis qualifies it at a stage beyond the conceptual phase, throughout which the engineering eliminates redundancies in the conceptual model performs both quantitative qualitative analyses, thereby streamlining the conceptualized design.

Considering the Engineering Analysis treats concerns pertaining to the product's conceivable failure, and locating the component(s) responsible for such systemically catastrophic event, it is immediately manifest that it belongs to the stage of the design process during the conceptual model undergoes rigorous testing. This "testing phase" yields data that, in turn, provides additional fodder for expanding the analysis of the model, which are namely of the descriptive, functional variety requiring computer-driven numerical methods.

In general, the Engineering Anlaysis expanded below would prove duly situated in the "testing stage" in which are examined both functionality and performance in the given design. In the case of the Piston and Rod Assembly, functionality- or performance-measuring analyses would lead to recommendations for adjusting material strength, and therefore necessitating a different grade of aluminum or another comparably cost-effective alloy altogether, or for using different manufacturing schemes, so as to reduce friction generated along the lubricant-deprived interface between interacting contact surfaces of the Piston and the internal extrusion of the combustion chamber.

With the due transition adequately formed, the Engineering Analysis now follows.


Problem Statement

In the event that a user of the product were to neglect the necessary maintenance of it and continue with the presence of oil entirely depleted, what level of frictional forces would develop between the piston and the engine block? Would these frictional forces alone prove sufficient to cause the engine to seize, and therefore cause the entire machine to fail?


Assumptions

  • Outer Diameter of End of Rod = 15/16 inch
  • Inner Diameter of End of Rod = 9/16 inch
  • Height of Middle of Rod = 6/16 inch
  • Thickness of Rod = 7/32 inch
  • Ultimate stress (U_s) of Aluminum 6061 = 42,000 pounds per square inch (psi)
  • Dry Coefficient of friction between two aluminum surfaces (μ_Kd ) = 1.4
  • Greased Coefficient of friction between two aluminum surfaces (μ_Kd ) = .3


  • Piston, Rod and Engine block are comprised of Aluminum 6061.
  • When deprived of oil, the two surfaces lack grease between one another, thereby causing direct contact between the aluminum parts.
  • Force due to gravity is negligible, owing the force applied through the rod is appreciably greater.
  • The smallest possible angle of the rod to the piston is 45 degrees.
  • The situation under analysis transpires during a single instant, and therefore can be treated as a static problem rather than a dynamic one.
  • No previous galling has occurred.
  • There are no manufacturing defects in the product.
  • Impact of heat due to friction is inconsequential in this calculation as we are only concerned with friction.


Schematics, Governing Equations, and Solution

In an effort to preserve the special formatting of symbolic text involved in the conjectural diagram of the system, the notation of the prevailing equations and the resulting calculations, details of the foregoing are documented in a file whose link is posted below for access to its contents.

The following links to the diagrams used to show this analysis.

http://farm3.static.flickr.com/2502/4147396171_fb0dd50e3e_b.jpg

The following links to the Governing Equations used in this analysis.

http://farm3.static.flickr.com/2564/4148155680_e9c3761b6d_b.jpg

The following links to the Solution calculations used for this analysis.

http://farm3.static.flickr.com/2632/4148155772_ae10408d9a_b.jpg


Solution Check

It is very reasonable that, with a coefficient of friction greater than one, the magnitude of the frictional force would exceed that of the vertical force. Also, the greased piston calculation is valid because the coefficient of friction of .3 would yield a frictional force less than that of the vertical force. Further, apart from maintaining dimensional homogeneity, the quantities of force appear sensible, owing primarily to their being determined using the ultimate (yield) strength of aluminum.


Discussion

This situation is very possible to occur, provided the dereliction of responsible maintenance of the product on the part of the typical homeowner. If the oil between the piston and the cylinder within the engine block wears away and the user does not replenish it, high levels of friction would generate, and this certainly to mechanical detriment. This, according to performed calculations, could potentially be the culprit for engine failure.


Calculations demonstrate that, if not properly maintained, the engine on a line trimmer could fail, thus causing the machinery in its entirety to fail due to friction alone. When not properly oiled, the piston could directly contact the engine block and seize by virtue of the friction developed by way of the action of aluminum on aluminum.


If the aluminum-on-aluminum contact does not cause the piston to seize, then the wear on both surfaces could cause galling. Galling occurs when two chemically similar metal surfaces rub against each other. In this situation, both edges will wear at a similar rate but unevenly so, thus leading to a surface roughness which can increase the chance of the piston’s seizing.


Moreover, the amount of heat that generates owing to friction could also lead to failure if the metal piston expanded, thereby producing additional friction, or melted to the engine block, and thereby creating a need for expensive part replacement, if not entire product replacement.


References to Supplementary Material

[1] The following serves as an embedded link to information provided by the Alcoa organization on alloy 6061, which is considered in the "Engineering Analysis" subsection of the Coordination Review. Click the link located below to access the document obtained via the Wiki page: <http://en.wikipedia.org/wiki/6061_aluminium_alloy>

The referenced link: http://farm3.static.flickr.com/2798/4148156406_5636f15536_b.jpg


[2] An additional source containing insights into the practical value of various alloys, in particular aluminum 6061. The link to the web page hosting the source follows: <http://www.aircraftspruce.com/catalog/mepages/aluminfo.php>


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