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July/August 2008
UpDate

New Advanced Ceramics Standards Cover Fracture Mirror Size Analysis, Tensile Strength Data

James A. Thomas at conference

Exposed fracture surface of a ceramic rod that was broken in a laboratory strength test. The radius of the “fracture mirror,” the relatively smooth circular region marked by the arrow, can be used to estimate the fracture stress to 10% or better.

Subcommittee C28.01 on Mechanical Properties and Performance, part of ASTM International Committee C28 on Advanced Ceramics, has recently approved two new standards, C1678, Practice for Fractographic Analysis of Fracture Mirror Sizes in Ceramics and Glasses, and C1683, Practice for Size Scaling of Tensile Strengths Using Weibull Statistics for Advanced Ceramics.

C1678—Bringing Consistency to Fracture Mirror Size Analysis

Fracture mirror size analysis is a powerful quantitative tool for the interpretation of broken ceramic and glass articles. While this type of analysis can be used to determine the stress in a part at the instant of fracture, inspection and interpretation procedures have often varied, resulting in uncertainty in stress estimates. ASTM C1678, Practice for Fractographic Analysis of Fracture Mirror Sizes in Ceramics and Glasses, will bring better consistency to procedures and facilitate the collection of accurate tabulations of fracture mirror-sized parameters.

George Quinn, Ceramics Division, National Institute of Standards and Technology, and chair, Subcommittee C28.01, says that anyone dealing with broken ceramic and glass parts, whether in a testing laboratory where fractures can be created under controlled conditions or in post mortem forensic investigations of uncontrolled fractures, will find C1678 useful. “Fracture mirror size analysis will become more common as users appreciate the standard protocol,” says Quinn. “Better estimates of fracture stresses will be possible.”

Quinn says all interested parties are invited to join in C28’s standards developing work. “Committee C28 has a wide variety of new activities dealing with brittle materials,” says Quinn. “A new emphasis is being placed on applications-related standards such as for porous ceramics for diesel particulate filters or thin-walled ceramics for fuel cells. New activities in ceramic armor standards and coatings are welcome.” Quinn also notes that the committee is venturing into adopting procedures for miniature test specimens for micro-electrical machine systems and even nanoscale-sized structures.

C1683—Scaling Strength Values

ASTM C1683, Practice for Size Scaling of Tensile Strengths Using Weibull Statistics for Advanced Ceramics, provides methodology to convert fracture strength parameters estimated from data obtained with one test geometry to strength parameters representing other test geometries.

Stephen Duffy, Ph.D., chair of civil engineering, Cleveland State University, and C28 member, says that companies producing ceramics, as well as companies that design components fabricated from ceramic materials, will be able to use C1683, which is applicable to materials that exhibit size effects that are captured adequately through Weibull analysis. “It evens the playing field,” says Duffy. “With C1683, one can now scale values of strength from one specimen geometry to another.”

CONTACT

Technical Information:

(C1678) George Quinn, National Institute of Standards and Technology, Gaithersburg, Md.

Phone: 301-975-5765

(C1683) Stephen Duffy, Cleveland State University, Stow, Ohio

Phone: 330-678-7328

ASTM Staff: Joe Koury

Phone: 610-832-9804