词条 | Specific modulus | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
释义 |
Specific modulus is a materials property consisting of the elastic modulus per mass density of a material. It is also known as the stiffness to weight ratio or specific stiffness. High specific modulus materials find wide application in aerospace applications where minimum structural weight is required. The dimensional analysis yields units of distance squared per time squared. The utility of specific modulus is to find materials which will produce structures with minimum weight, when the primary design limitation is deflection or physical deformation, rather than load at breaking—this is also known as a "stiffness-driven" structure. Many common structures are stiffness-driven over much of their use, such as airplane wings, bridges, masts, and bicycle frames. To emphasize the point, consider the issue of choosing a material for building an airplane. Aluminum seems obvious because it is "lighter" than steel, but steel is stronger than aluminum, so one could imagine using thinner steel components to save weight without sacrificing (tensile) strength. The problem with this idea is that there would be a significant sacrifice of stiffness, allowing, e.g., wings to flex unacceptably. Because it is stiffness, not tensile strength, that drives this kind of decision for airplanes, we say that they are stiffness-driven. The connection details of such structures may be more sensitive to strength (rather than stiffness) issues due to effects of stress risers. Specific modulus is not to be confused with specific strength, a term that compares strength to density. ApplicationsSpecific stiffness in tensionThe use of specific stiffness in tension applications is straightforward. Both stiffness in tension and total mass for a given length are directly proportional to cross-sectional area. Thus performance of a beam in tension will depend on Young's modulus divided by density. Specific stiffness in buckling and bendingSpecific stiffness can be used in the design of beams subject to bending or Euler buckling, since bending and buckling are stiffness-driven. However, the role that density plays changes depending on the problem's constraints. Beam with fixed dimensions; goal is weight reductionExamining the formulas for buckling and deflection, we see that the force required to achieve a given deflection or to achieve buckling depends directly on Young's modulus. Examining the density formula, we see that the mass of a beam depends directly on the density. Thus if a beam's cross-sectional dimensions are constrained and weight reduction is the primary goal, performance of the beam will depend on Young's modulus divided by density. Beam with fixed weight; goal is increased stiffnessBy contrast, if a beam's weight is fixed, its cross-sectional dimensions are unconstrained, and increased stiffness is the primary goal, the performance of the beam will depend on Young's modulus divided by either density squared or cubed. This is because a beam's overall stiffness, and thus its resistance to Euler buckling when subjected to an axial load and to deflection when subjected to a bending moment, is directly proportional to both the Young's modulus of the beam's material and the second moment of area (area moment of inertia) of the beam. Comparing the list of area moments of inertia with formulas for area gives the appropriate relationship for beams of various configurations. Beam's cross-sectional area increases in two dimensionsConsider a beam whose cross-sectional area increases in two dimensions, e.g. a solid round beam or a solid square beam. By combining the area and density formulas, we can see that the radius of this beam will vary with approximately the inverse of the square of the density for a given mass. By examining the formulas for area moment of inertia, we can see that the stiffness of this beam will vary approximately as the fourth power of the radius. Thus the second moment of area will vary approximately as the inverse of the density squared, and performance of the beam will depend on Young's modulus divided by density squared. Beam's cross-sectional area increases in one dimensionConsider a beam whose cross-sectional area increases in one dimension, e.g. a thin-walled round beam or a rectangular beam whose height but not width is varied. By combining the area and density formulas, we can see that the radius or height of this beam will vary with approximately the inverse of the density for a given mass. By examining the formulas for area moment of inertia, we can see that the stiffness of this beam will vary approximately as the third power of the radius or height. Thus the second moment of area will vary approximately as the inverse of the cube of the density, and performance of the beam will depend on Young's modulus divided by density cubed. However, caution must be exercised in using this metric. Thin-walled beams are ultimately limited by local buckling and lateral-torsional buckling. These buckling modes depend on material properties other than stiffness and density, so the stiffness-over-density-cubed metric is at best a starting point for analysis. For example, most wood species score better than most metals on this metric, but many metals can be formed into useful beams with much thinner walls than could be achieved with wood, given wood's greater vulnerability to local buckling. The performance of thin-walled beams can also be greatly modified by relatively minor variations in geometry such as flanges and stiffeners.[1][2][3] Stiffness versus strength in bendingNote that the ultimate strength of a beam in bending depends on the ultimate strength of its material and its section modulus, not its stiffness and second moment of area. Its deflection, however, and thus its resistance to Euler buckling, will depend on these two latter values. Approximate specific stiffness for various materials
See also
References1. ^{{Cite web |url=http://nptel.iitm.ac.in/courses/IIT-MADRAS/Design_Steel_Structures_II/5_cold_form_steel/3_local_buckling.pdf |title=Archived copy |access-date=2010-11-22 |archive-url=https://web.archive.org/web/20110627003741/http://nptel.iitm.ac.in/courses/IIT-MADRAS/Design_Steel_Structures_II/5_cold_form_steel/3_local_buckling.pdf |archive-date=2011-06-27 |dead-url=yes |df= }} {{DEFAULTSORT:Specific Modulus}}2. ^{{Cite web |url=http://www.bgstructuralengineering.com/BGSCM/BGSCM008/Flexure/BGSCM0080205.htm |title=Archived copy |access-date=2010-11-22 |archive-url=https://web.archive.org/web/20100527070319/http://www.bgstructuralengineering.com/BGSCM/BGSCM008/Flexure/BGSCM0080205.htm |archive-date=2010-05-27 |dead-url=yes |df= }} 3. ^{{cite web|url=http://catalogue.nla.gov.au/Record/4024828|title=Local buckling and crippling of composite stiffener sections|first1=David L.|last1=Bonanni|first2=Eric R.|last2=Johnson|first3=James H.|last3=Starnes|date=31 July 1988|publisher=College of Engineering, Virginia Polytechnic Institute and State University|via=National Library of Australia (new catalog)}} 4. ^{{cite web|url=http://www.engineeringtoolbox.com/density-solids-d_1265.html|title=Densities of Solids|website=www.engineeringtoolbox.com}} 5. ^[https://web.archive.org/web/20031118100625/http://dynalabcorp.com/technical_info_hd_polyethylene.asp] 6. ^1 {{cite web|url=http://www.goodfellow.com/E/Polypropylene.html|title=Polypropylene - online catalogue source - supplier of research materials in small quantities - Goodfellow|last=www.goodfellow.com|website=www.goodfellow.com}} 7. ^{{Cite web |url=http://www.makeitfrom.com/data/?material=MDF |title=Material Properties Data: Medium Density Fiberboard (MDF) |access-date=2010-11-11 |archive-url=https://web.archive.org/web/20110519140920/http://www.makeitfrom.com/data/?material=MDF |archive-date=2011-05-19 |dead-url=yes |df= }} 8. ^1 {{cite web|url=http://www.simetric.co.uk/si_wood.htm|title=Mass, Weight, Density or Specific Gravity of Wood|website=www.simetric.co.uk}} 9. ^1 {{cite web|url=http://www.indoorfreeflight.com/balsa.htm|title=Balsa Stiffness Calculator|first=Don|last=Slusarczyk|website=www.indoorfreeflight.com}} 10. ^{{Cite web |url=http://www.f1d.biz/F1DBizAboutBalsa.htm |title=Archived copy |access-date=2011-01-02 |archive-url=https://web.archive.org/web/20110706144859/http://www.f1d.biz/F1DBizAboutBalsa.htm |archive-date=2011-07-06 |dead-url=yes |df= }} 11. ^{{Cite web |url=http://www.a2zcorp.us/TruWeightBalsa/BalsaInventoryView.asp?Cguid=56F196FB-36EC-4CB1-AEE4-B4596BFD8DF4 |title=Archived copy |access-date=2011-01-02 |archive-url=https://web.archive.org/web/20110903021227/http://www.a2zcorp.us/TruWeightBalsa/BalsaInventoryView.asp?Cguid=56F196FB-36EC-4CB1-AEE4-B4596BFD8DF4 |archive-date=2011-09-03 |dead-url=yes |df= }} 12. ^{{cite web|url=http://www.substech.com/dokuwiki/doku.php?id=polyester_matrix_composite_reinforced_by_glass_fibers_fiberglass|title=Polyester Matrix Composite reinforced by glass fibers (Fiberglass) [SubsTech]|website=www.substech.com}} 13. ^{{cite web|url=http://www.matweb.com/search/datasheet.aspx?matguid=3f2253a553404b13893830617250b5d8&ckck=1|title=MatWeb - The Online Materials Information Resource|website=www.matweb.com}} 14. ^{{cite web|url=http://www.fiberglassrebar.com/mat_properties.htm|title=V-Rod fiberglass rebar - Retaining walls|last=VROD}} 15. ^1 {{cite web|url=http://www.sitkaspruce.nl/product_1.html|title=Touchwood BV - Sitka Spruce|website=www.sitkaspruce.nl}} 16. ^1 {{dead link|date=August 2018}} 17. ^1 {{Cite web |url=https://fp.auburn.edu/sfws/sfnmc/class/ss.html |title=Archived copy |access-date=2010-11-11 |archive-url=https://web.archive.org/web/20110716073337/https://fp.auburn.edu/sfws/sfnmc/class/ss.html |archive-date=2011-07-16 |dead-url=yes |df= }} 18. ^{{Cite web |url=http://www.corning.com/assets/0/965/3557/3577/3615/71759a443535431395eb34ebead091cb.pdf |title=Archived copy |access-date=2015-04-13 |archive-url=https://web.archive.org/web/20150413161426/http://www.corning.com/assets/0/965/3557/3577/3615/71759a443535431395eb34ebead091cb.pdf |archive-date=2015-04-13 |dead-url=yes |df= }} 19. ^{{cite journal|url=https://academic.oup.com/bmb/article/31/2/115/345945|title=COMPOSITION OF DENTAL ENAMEL|first=J. A.|last=Weatherell|date=1 May 1975|journal=British Medical Bulletin|volume=31|issue=2|pages=115–119|via=bmb.oxfordjournals.org|doi=10.1093/oxfordjournals.bmb.a071263}} 20. ^1 {{Cite web |url=http://www.rapra.net/composites/material-selection/reinforcement-types.asp |title=Archived copy |access-date=2010-11-11 |archive-url=https://web.archive.org/web/20101220143522/http://www.rapra.net/composites/material-selection/reinforcement-types.asp |archive-date=2010-12-20 |dead-url=yes |df= }} 21. ^{{cite web|url=https://www.azom.com/article.aspx?ArticleID=764|title=E-Glass Fibre|date=30 August 2001|website=AZoM.com}} 22. ^1 {{cite web|url=https://www.azom.com/article.aspx?ArticleID=769|title=S-Glass Fibre|date=30 August 2001|website=AZoM.com}} 23. ^{{cite web|url=http://hypertextbook.com/facts/2004/ShayeStorm.shtml|title=Density of Glass - The Physics Factbook|first=Glenn|last=Elert|website=hypertextbook.com}} 24. ^{{Cite web |url=http://www.isowave.com/pdf/materials/Yttrium_Iron_Garnet.pdf |title=YIG properties |access-date=2010-11-11 |archive-url=https://web.archive.org/web/20090225155636/http://www.isowave.com/pdf/materials/Yttrium_Iron_Garnet.pdf |archive-date=2009-02-25 |dead-url=yes |df= }} 25. ^{{cite web|url=http://resources.metapress.com/pdf-preview.axd?code=t068n73845p4185r&size=largest|title=Metapress - A Fast Growing Resource for Young Entrepreneurs|date=14 December 2017}} 26. ^ {{dead link|date=August 2018}} 27. ^{{cite web|url=http://www.compositesinnovation.ca/biofibre_workshop/Natural_Fibre_Composites_Development_and_Testing_-_Chad_Ulven.pdf |title=Microsoft PowerPoint - Ulven Natural Fiber Presentation.ppt |date= |accessdate=2018-08-01}} 28. ^{{Cite web |url=http://www.agrofibrecomposites.com/thesisBos.pdf |title=Archived copy |access-date=2010-11-11 |archive-url=https://web.archive.org/web/20110707093937/http://www.agrofibrecomposites.com/thesisBos.pdf |archive-date=2011-07-07 |dead-url=yes |df= }} 29. ^[https://web.archive.org/web/20120317122939/http://www.sailing.man.ac.uk/temp/jute.pdf] 30. ^1 {{cite web|url=http://www2.dupont.com/Kevlar/en_US/assets/downloads/KEVLAR_Technical_Guide.pdf|title=Kevlar® Properties - Kevlar® Technical Guide - DuPont USA|last=admin|website=www2.dupont.com}} 31. ^1 {{cite journal | url = http://www.springerlink.com/content/tm70817q6v27mv70/ | doi=10.1007/BF00550757 | bibcode=1980JMatS..15.2523P | volume=15 | issue=10 | title=Compression strength of carbon, glass and Kevlar-49 fibre reinforced polyester resins | year=1980 | journal=Journal of Materials Science | pages=2523–2538 | last1 = Piggott | first1 = M. R. | last2 = Harris | first2 = B.}} 32. ^1 {{cite web|url=http://www.dyneema.com/en_US/public/dyneema/downloads/Comprehensive_factsheet_UHMWPE.pdf|title=Home - Dyneema®|website=www.dyneema.com}} 33. ^{{cite web|url=http://www.ioffe.ru/SVA/NSM/Semicond/Si|title=Physical properties of Silicon (Si)|website=www.ioffe.ru}} 34. ^[https://archive.is/20120721025408/http://www.azom.com/Details.asp?ArticleID=5464 ] 35. ^{{cite web|url=http://www.saffil.com/newwebsite.nsf/0/4FD62D9CDA2A6BFC8025733F004A91CE?OpenDocument&Expand=071E32C6DBA462B38025731000444FA2|title=saffil|website=www.saffil.com}} 36. ^{{cite web|url=http://www.substech.com/dokuwiki/doku.php?id=epoxy_matrix_composite_reinforced_by_70_carbon_fibers|title=Epoxy Matrix Composite reinforced by 70% carbon fibers [SubsTech]|website=www.substech.com}} 37. ^{{cite web|url=http://www51.honeywell.com/sm/afc/common/documents/PP_AFC_Honeywell_spectra_fiber_2000_Product_information_sheet.pdf |title=Product info |date=2000 |website=www51.honeywell.com }} 38. ^{{cite web|url=http://www.specmaterials.com/boronfiberproperties.htm|title=Boron Fiber Properties|website=www.specmaterials.com}} 39. ^{{cite journal | url = http://www.springerlink.com/content/vj8k40l122405223/ | doi=10.1007/BF01184586 | volume=30 | issue=9 | title=Mechanical and physical properties of post-creep, pitch-based carbon filaments | year=1995 | journal=Journal of Materials Science | pages=2352–2357 | last1 = Lavin | first1 = J. Gerard | last2 = Kogure | first2 = Kei | last3 = Sines | first3 = G.| bibcode=1995JMatS..30.2352L }} 40. ^{{Cite web |url=http://www.csudh.edu/oliver/chemdata/woods.htm |title=Archived copy |access-date=2010-11-22 |archive-url=https://web.archive.org/web/20100609005909/http://www.csudh.edu/oliver/chemdata/woods.htm |archive-date=2010-06-09 |dead-url=yes |df= }} 1 : Materials science |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识,基本涵盖了大多数领域的百科知识,是一部内容自由、开放的电子版国际百科全书。