ASTM E1300 Uniform Load Strength Reduction Factor Not ... · ASTM E1300 is Based on The Strength of...

A. William Lingnell, P.E.Lingnell Consulting Services

W. Lynn Beason, Ph.D., P.E.Beason Brackin & Associates, LLC

Michael S. Brackin, Ph.D., P.E.Beason Brackin & Associates, LLC

ASTM E1300 Uniform Load Strength Reduction Factor Not Required for Ceramic Enameled Glass

Lingnell Consulting Services

ASTM E1300

• Provides a conservative glass thickness procedure

▪ Flat Glass Plates

▪ Uniform Pressure Loads

• All publicized problems with HS ceramic enameled glass

▪ Thermal Stress

• No publicized problems with HS ceramic enameled glass▪ Uniform Pressure Loads


Therefore, changes to ASTM E1300 will not directly address the only known issue with HS ceramic enameled glass

THIS IS A THERMAL STRESS ISSUE,

NOT A UNIFORM LOAD ISSUE!


Proposed Load Factor Reductions for HS Ceramic Enameled Glass

• Based on the comparison of uncoated glass strength to ceramic enameled glass

▪ Mean Strengths

▪ Freshly Manufactured

• These suggest that the strength of freshly manufactured ceramic enameled glass is less than the strength of freshly manufactured uncoated clear glass

▪ Assuming the same type and geometry

• However, ASTM E1300 glass thickness recommendations are based on the strength of in-service glass and not the strength of freshly manufactured glass


ASTM E1300 is Based on The Strength of In-Service Glass

• Results of research conducted by Beason in the 1970’s and others proved that in-service glass has significantly less strength than freshly manufactured glass

• This understanding was the main driver for the original development of ASTM E1300.

▪ In-service glass is weaker than freshly manufactured

• ASTM E1300 states:

“use of the practice assumes that the surface condition of the glass is typical of glass that has been in service for several years, and is weaker than freshly manufactured glass due to minor abrasions on exposed surfaces”


Therefore, comparisons of the strengths of freshly manufactured ceramic enameled glass with the analogous strengths of freshly manufactured clear glass are irrelevant with respect to determining whether ASTM E1300 strength factors need to be adjusted.

ASTM E1300 IS BASED ON IN-SERVICEGLASS STRENGTH!


ASTM E1300 Design Procedure for HS Glass Plates

• First, determine the design load of an AN glass plate

▪ Desired geometry

▪ Glass thickness chart presented in ASTM E1300

• Next, the AN glass design load is increased by multiplying it by a strength factor

▪ 2.0 for HS glass

• Finally, this factored load is taken to be the design load for the HS glass


Origin of the 2.0 HS Strength Factor

• It’s not “mysterious”, but a hold over from historic US glass design procedures.

• Assumptions

▪ Linear load/deflection response

▪ Minimum residual surface compression of 3,500 psi

• More realistic estimates of the strength of HS glass conducted by Beason have shown that the historic 2.0 HS strength factor is actually a good lower limit and in many cases a much larger strength factor can be justified

▪ It is conservative


Origin of the 2.0 HS Strength Factor

• ASTM incorporated a strength factor of 2.0 for HS glass based on

▪ Research performed by Beason

▪ A strong desire to continue a link with historic glass design procedures


ASTM E1300 is Based on the Glass Failure Prediction Model (GFPM) Originally Presented by Beason in the 1980’s

• The GFPM is based on a relatively obscure statistical failure theory for brittle materials that was originally presented by Weibull

• It is NOT based on a Weibull Distribution

• The GFPM incorporates two parameters, m and k

▪ Represent the severity and distribution of flaws across the surface of the glass


• RATHER, they represent the characteristics of the surface flaws that control the strength of glass.

• It is believed by the writers that these characteristics are a result of in-servicemechanical exposures.

• This is WHY m and k are called “surface flaw parameters” and NOT “glass strength parameters”

“m” & “k” ARE NOT BASIC MATERIAL PROPERTIES –


m - Surface Flaw Parameter

• m is most closely related to the coefficient of variation (COV) of a glass strength sample.

• Widely accepted in historic US glass design procedures that the COV for AN glass should be on-the-order-of 20%

▪ Conservative design

• Original ASTM E1300 Task Group selected a value of 7 for m

▪ Based on discussions and information presented by Beason

▪ Most closely corresponds to historic design COV on-the-order-of 20%


k - Surface Flaw Parameter

• K is most closely related to the central tendency of a glass strength sample

▪ Mean strength

• Original ASTM E1300 Task Group selected a value for k

▪ Based on wide-range of in-service glass strength data, NOT one set of strength data

▪ Settled on a value believed to conservatively represent in-service glass.


The Surface Flaw Parameters Values (m and k) are Intended to Represent the Surface Condition Associated with In-Service Glass and are Independent of Geometry

RATHER, they reflect historic understandings of the COV and the collective judgement of the original task group based upon in-service glass strength data available at the time.

THEY ARE NOT THE RESULT OF A DIRECT “BEST-FIT” ANALYSIS!


Extension of ASTM E1300 Surface Flaw Parameters to HS Glass

• REMEMBER that the GFPM Surface Flaw Parameters represent the physical condition of the surface of the glass

• At this point in time, there is no reason to believe that the surface of HS glass is less resistant to in-service mechanical damage than AN glass

• Therefore, if the GFPM is properly extended to include HS glass, there is no reason to believe that m and k should be modified for HS glass


Multiple Levels of Intended Conservatism Originally Built into ASTM E1300

• The use of the 2.0 strength factor is conservative and in many cases very conservative

▪ Based on information presented by Beason

• In-service Surface Flaw Parameters selected to inject significant conservatism when compared to freshly manufactured glass.

• It is difficult to imagine that it is possible to purchase HS glass from a standard production run that would have a residual surface compression that is even close to the minimum required of 3,500 psi


The Reduction in Strength of HS Ceramic Enameled Glass Would Have to be

to arrive at a point where it is Necessary to Reduce the ASTM E1300 HS Strength Factor Below 2.0!

VERY SEVERE


The Most Direct Way to Evaluate the Applicability of ASTM E1300 to HS Ceramic Enameled Glass is to Compare Measured Loads on Full-Scale HS Ceramic Enameled Plates to Design Loads Predicted by ASTM E1300.

• Results of one set of full-scale ceramic enameled HS glass strength tests developed by the writers is examined.

• Results of four sets of full-scale ceramic enameled HS glass strength tests developed by Berger, et al. are examined.


Full-Scale HS Glass Tests Conducted by the Writers

• Specimen size was 40 x 60 x ¼ in.

• One set of 10 freshly manufactured, uncoated HS glass plates tested to failure

• One set of 10 freshly manufactured, ceramic enameled HS glass plates with 100% coverage tested to failure.

• Breakage loads were converted to 3-sec durations and data processed by the writers.

• Testing performed at the Beason Brackin & Associates Test Lab in Bryan Texas


Beason Brackin & Associates Test Lab in Bryan Texas

B|B Test LabCOPYRIGHT 2017


ASTM E1300 Design Load for 40 x 60 x ¼ in. HS Glass

• Design load for 40 x 60 x ¼ in. AN glass

▪ 55 psf

• Design load for 40 x 60 x ¼ in. HS glass

▪ HS strength factor of 2.0

▪ 110 psf


Results of Full-Scale HS Glass Tests Conducted by the Writers

Mean 3-sec Breakage Load

COV of 3-sec Breakage Load

Probability of Breakage Design Load

Design Load Greater Than Required by ASTM E1300

Uncoated Glass 501 psf 8.1% 403 psf 3.66 X

Ceramic Enamel Glass 288 psf 2.9% 268 psf 2.44 X


Full-Scale HS Glass Tests Conducted by Berger et al.

• Specimen size was 38 x 76 x ¼ in.

• One set of 26 freshly manufactured, uncoated clear HS glass plates tested to failure

• Four sets of 26-27 freshly manufactured, ceramic enameled HS glass plates tested to failure.

• The four sets of ceramic enameled HS glass had ceramic coverage ranging from 40 to 100%

• Breakage loads were converted to 3-sec durations and data were processed by Berger et al.


ASTM E1300 Design Load for 38 x 76 x ¼ in. HS Glass

• Design load for 38 x 76 x ¼ in. AN glass

▪ 41.8 psf

• Design load for 38 x 76 x ¼ in. HS glass

▪ HS strength factor of 2.0

▪ 83.6 psf


Results of Full-Scale HS Glass Tests Conducted by the Writers

Mean 3-sec Breakage Load

COV of 3-sec Breakage Load

Probability of Breakage Design Load

Design Load Greater Than Required by ASTM E1300

Uncoated Glass 424 psf 14.1% 272 psf 3.25 X

Ceramic Enamel Glass 219- 292 psf 5.9- 8.1% 169- 228 psf 2.02- 2.73 X

NOTE: Ranges shown for 4 ceramic enameled HS glass data sets


Major Conclusions

• Freshly manufactured ceramic enameled HS glass has a significantly lower mean strength compared to an analogous uncoated HS glass

• HOWEVER, in the worst case presented, the design strength of ceramic enameled HS glass was more than twice that required to meet ASTM E1300.

• In all cases, ceramic enameled HS glass has a significantly lower COV compared to that of uncoated HS glass

• The effects of long term in-service exposure on the strength of ceramic enameled HS glass have not been fully developed

▪ Intuitively this does not seem to be an issue, but more work should be done to examine this issue.


There is NO SCIENTIFIC REASON to question the applicability of ASTM E1300 as applied to ceramic enameled glass subjected to UNIFORM LATERAL LOADS Based on the results of the full-scale tests presented herein

THIS IS A THERMAL STRESS ISSUE AND SHOULDBE ADDRESSED IN THE APPROPRIATE FORUM!


Questions?

W. Lynn Beason, Ph.D., [email protected]

Michael S. Brackin, Ph.D., [email protected]

A. William Lingnell, [email protected]

Beason Brackin & Associates, LLC3000 Hummingbird Cir | Bryan, TX USA(979) 985-2090 | www.beasonbrackin.com

Beason Brackin & Associates, LLC3000 Hummingbird Cir | Bryan, TX USA(979) 985-2090 | www.beasonbrackin.com

Lingnell Consulting Services1270 Shores Court | Rockwall, TX USA(972) 771-1600

mailto:[email protected]



http://www.beasonbrackin.com/

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