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Article evaluation

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This section is to record observations and what I've learned.

I chose to read the wikipedia Fracture page to consider possible updates. The article content is relavent, but seems short considering the body of work on the topic. The text also seems highly technical and perhaps difficult for a general reader. The Talk page rates the article as a C-class with mid importance. The most recent comment on the talk page is from 2013.

Some possible areas for improvement:

  • One claim in the Brittle Fracture section gives an example of the Titanic that is "widely reported". A better and more definite example could be given.
  • Further information and citations from Barsom and Rolfe would be useful.
  • Reference #3 does not have a title and a better source may be available.
  • A sub-topic of sudden brittle fracture would be a good addition.
  • Crack separation models section has no citations!
  • Other possible additions/links: Fracture control, Charpy V-notch, AASHTO/ASTM requirements, relationship to fatigue, etc.

Ideas for article assignment

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Three ideas for article topics are below. These are generally in order of preference. The first two topics are equally appealing, except the Rosenthal topic is new and may be more challenging to start from scratch. Finding sufficient content could be a challenge since I'm somewhat limited to online searches as a distance student.

  1. Improve Fracture article - one or several parts. This would include citations where missing, linking to other sections, and possibly writing a section on sudden brittle fracture due to triaxially-constrained welds with examples, such as link to Hoan Bridge and/or factors that make welded structures prone to fracture, i.e. fracture toughness of metal, crack characteristics, and tensile stress.
  2. Rosenthal Point Source Model - it appears there is nothing about Daniel Rosenthal or his models on Wikipedia. This would be a new article. Possible sources: article given in class, "The Theory of Moving Sources of Heat and Its Application to Metal Treatments" and [1] or other general heat flow textbooks or papers, Computational Welding Mechanics[2], Joining of Advanced Materials[3], and [4]. Content can include applicability, assumptions, and advantages and disadvantages of the model. Another possible subtopic is refinements to model.
  3. Welding defects - updating one or more parts of the existing article, such as a more thorough explanation of the mechanics of distortion. This article has a high importance rating and C rating on Wikipedia quality scale. The last comment on the talk page is from 2009 and lists several suggested additions. Possible sources are Chapter 7 of the Practical Welding Engineer[5] and Chapter 9 of Welding Inspection Handbook[6]. These sources can be used to update citations and fill gaps of any missing information.

These are general reference sources.[7][8]

Instructor Comments

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Improving the fracture article is a good choice. You may want to focus on one or two of the proposed areas of improvement to make the project more manageable in the time available.

Article draft and updates

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Updates to Fracture.

As an existing article, only changed text is below with notes in [brackets] about which paragraphs are affected. Also, the first and last "External links" didn't work and were deleted.

A fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface of displacement, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially to the surface of displacement, it is called a shear crack, slip band, or dislocation.[1]

Brittle fractures occur with no apparent deformation before fracture; ductile fractures occur when visible deformation does occur before separation. Fracture strength or breaking strength is the stress when a specimen fails or fractures. A detailed understanding of how fracture occurs in materials may be assisted by the study of fracture mechanics.

Brittle fracture

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In brittle fracture, no apparent plastic deformation takes place before fracture. Brittle fracture typically involves little energy absorption and occurs at high speeds (up to 7000 ft/sec in steel).[9] In most cases brittle fracture will continue even when loading is discontinued.[10]

In brittle crystalline materials, fracture can occur by cleavage as the result of tensile stress acting normal to crystallographic planes with low bonding (cleavage planes). In amorphous solids, by contrast, the lack of a crystalline structure results in a conchoidal fracture, with cracks proceeding normal to the applied tension. [Removed Titanic reference as it's in new section now.]

[keep existing text except replace the last paragraph with the one below]

The basic sequence in a typical brittle fracture is: introduction of a flaw either before or after the material is put in service, slow and stable crack propagation under recurring loading, and sudden rapid failure when the crack reaches critical crack length based on the conditions defined by fracture mechanics.[10] Brittle fracture may be avoided by controlling three primary factors: material fracture toughness (Kc), nominal stress level (σ), and introduced flaw size (a).[9] Residual stresses, temperature, loading rate, and stress concentrations also contribute to brittle fracture by influencing the three primary factors.[9]

Under certain conditions, ductile materials can exhibit brittle behavior. Rapid loading, low temperature, and triaxial stress constraint conditions may cause ductile materials to fail without prior deformation.[9]

Ductile fracture

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[new since student reviews: just updating missing citation in the 1st paragraphs where "[citation needed]" was shown and deleted last sentence defining ductility as toughness since they're not exactly the same as written.] In ductile fracture, extensive plastic deformation (necking) takes place before fracture. The terms rupture or ductile rupture describe the ultimate failure of ductile materials loaded in tension. Rather than cracking, the material "pulls apart," generally leaving a rough surface. In this case there is slow propagation and an absorption of a large amount energy before fracture.[11]

Fracture modes and characteristics

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Main article: Fracture mechanics

There are three standard conventions for defining relative displacements in elastic materials in order to analyze crack propagation[9] as proposed by Irwin.[12] In addition fracture can involve uniform strain or a combination of these modes.[10]

  • Mode I crack – Opening mode (a tensile stress normal to the plane of the crack)
  • Mode II crack – Sliding mode (a shear stress acting parallel to the plane of the crack and perpendicular to the crack front)
  • Mode III crack – Tearing mode (a shear stress acting parallel to the plane of the crack and parallel to the crack front)

The manner by which the crack propagates through the material gives insight into the mode of fracture. With ductile fracture the crack moves slowly and is accompanied by a large amount of plastic deformation around the crack tip. The ductile crack will usually not propagate unless an increased stress is applied and generally cease propagating when loading is removed.[10] In a ductile material, the crack may progress to a section of the material where stresses are slightly lower and stop due to the blunting effect of plastic deformations at the crack tip. On the other hand, with brittle fracture, cracks spread very rapidly with little or no plastic deformation. The cracks that propagate in a brittle material will continue to grow once initiated.

Crack propagation is also categorized by the crack characteristics at the microscopic level. A crack that passes through the grains within a material is undergoing transgranular fracture. A crack that propagates along the grain boundaries is termed an intergranular fracture. Typically, the bonds between material grains are stronger at room temperature than the material itself, so transgranular fracture is more likely to occur. When temperatures increase enough to weaken the grain bonds, intergranular fracture is the more common fracture mode.[10]

Notable fracture failures

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Failures caused by brittle fracture have not been limited to any particular category of engineered structure.[9] Though brittle fracture is less common than other types of failure, the impacts to life and property can be more severe.[9] The following notable historic failures were attributed to brittle fracture:

Notes

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  1. ^ Drake, E. R. G. Eckert; Robert M. (1987). Analysis of heat and mass transfer (Repr. ed.). Washington: Hemisphere Publishing Corp. ISBN 3540177086.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ^ Akhlaghi, John A. Goldak, Mehdi (2005). Computational welding mechanics ([Online-Ausg.] ed.). New York: Springer. ISBN 0387232885.{{cite book}}: CS1 maint: multiple names: authors list (link)
  3. ^ Messler, Robert W. Joining of Advanced Materials. Butterworth-Heinemann. ISBN 0750690089.
  4. ^ Eagar, T.W. (Dec 1983). "Temperature Fields Produced by Traveling Distributed Heat Sources". Welding Research Supplement.
  5. ^ Lochhead, J. Crawford; Rodgers, Ken (2000). The practical welding engineer. Miami, FL: American Welding Society. ISBN 0871716208.
  6. ^ Committee, prepared by AWS Committee on Methods of Inspection under the direction of AWS Technical Activities (2000). Welding inspection handbook (3rd ed. ed.). Miami, Fla.: American Welding Society. ISBN 0871715600. {{cite book}}: |edition= has extra text (help)
  7. ^ Rolfe, John M. Barsom, Stanley T. (1999). Fracture and fatigue control in structures : applications of fracture mechanics (3. ed ed.). West Conshohocken, Pa.: ASTM. ISBN 0803120826. {{cite book}}: |edition= has extra text (help)CS1 maint: multiple names: authors list (link)
  8. ^ Manual for Repair and Retrofit of Fatigue Cracks in Steel Bridges (PDF). US Department of Transportation, Federal Highway Administration. 2013. {{cite book}}: Cite has empty unknown parameter: |FHWA Publication No. FHWA-IF-13-020= (help)
  9. ^ a b c d e f g h i j Rolfe, John M. Barsom, Stanley T. (1999). Fracture and fatigue control in structures : applications of fracture mechanics (3. ed ed.). West Conshohocken, Pa.: ASTM. ISBN 0803120826. {{cite book}}: |edition= has extra text (help)CS1 maint: multiple names: authors list (link)
  10. ^ a b c d e f g h Campbell, edited by F.C. (2012). Fatigue and fracture : understanding the basics. Materials Park, Ohio: ASM International. ISBN 1615039767. {{cite book}}: |first1= has generic name (help)
  11. ^ Perez, Nestor (2016). Fracture Mechanics (2nd ed.). Switzerland : Springer. ISBN 3319249975.
  12. ^ Jin, C.T. Sun, Z.-H. (2012). Fracture mechanics. Waltham, MA: Academic Press. ISBN 9780123850010.{{cite book}}: CS1 maint: multiple names: authors list (link)
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