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Composite Materials/little clarification on testing

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QUESTION: sir,i m doing project on RICE HUSK FLOUR reinforced VINYLESTER base POLYMER COMPOSITE. i know how to fabricate but the thing is now i want to test it for tensile and flexural(3 point bending).what should be my test sample dimensions ?...is there any rule that the dimension should be this much...i choose ASTM D3039 for tensile and ASTM D790...how to calculate my test sample dimension according to this standard or is there any reference book to refer and do accordingly.

ANSWER: ASTM D3039 and D790, both tell you what speciemn dimension you must use. This is assuming that the dimensions of the geometrical features of rice husk are smaller than the specimen dimensions. What this meas is that if the material has big cells like a foam, and those cells are hugem then you need a bigger speciment. Otherwise, follow the standard.

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QUESTION: thanks for your reply,
the standards, say astm 3039 mentioned  25*250*thickness but when i did literature survey many of them took different different dimension to suit there UTM machine or to suit there requirement. how can they take it and on what calculation they have decided that this is the specimen dimension for their requirement....what i meant to say is that can there be any rule so that even if i prepare any dimension that should fall under the astm standard

Answer
If you are doing the test for someone that requires you to follow the standard, for example for aircraft certification, then you have no choice but to use exactly the dimensions in the standard unless the standard itself allows for variations (you have to read the standard carefully as they sometimes allow for variations). If you are doing the test for yourself, then you can change the dimensions but you need to know what you are doing. As a rule, you need a one dimensional state of stress in the specimen. For that, the width has to be larger than the thickness, about 5 to 10 times more or less, but not too much, otherwise you will be testing a wide plate, not a strip of material. More strict/important is that the length must be at least 10 times the width. That is how ASTM tell you to use W=25 and L=250.  

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Ever Barbero

Expertise

Structural Mechanics, Mechanics of Materials, Structural Analysis, Material Modeling (numerical, analytical), Testing (mechanical, aging, etc.) of Composites and Polymers, mainly Polymer Matrix and to lesser extent Materials Science and Processing of same. See http://mysite.verizon.net/everbarbero/

Experience

Working with Composites since 1983, two patents.

Organizations
Fellow, Society for the Advancement of Materials Process Engineering SAMPE
Fellow, American Society of Mechanical Engineers ASME
Member, American Society for Testing Materials ASTM
Member, American Institute of Aeronautics and Astronautics AIAA
Member, American Society of Engineering Education ASEE

Publications
100+ peer reviewed papers on every major journal on composites and mechanics
Introduction to Composite Materials Design, ISBN: 1-56032-701-4, http://www.mae.wvu.edu/barbero/icmd/
Finite Element Analysis of Composite Materials, ISBN: 1-4200-5433-3, http://www.mae.wvu.edu/barbero/feacm/

Education/Credentials
PhD Engineering Science, 1989, Virginia Tech.
BSME, BSEE, 1983, UNRC.

Education/Credentials
PhD Engineering Science, 1989, Virginia Tech.
BSME, BSEE, 1983, UNRC.

Awards and Honors
SAMPE Fellow (2006).
ASME Fellow (2003).
Best Overall Paper Award, Combined Composite Expo’99 and ASCE Materials Conference’99, Cincinnati, OH.
Best Paper Award, 1999 ASME J. of Composites for Construction, Vol. 4, No. 4, p. 185-191.
MAE Alumni Academy Award for Outstanding Teaching, 1999.
SAMPE Faculty Advisor Award 1998.
Researcher of the Year, College of Engineering, WVU, 1996.
Outstanding Researcher Award, College of Engineering, WVU, 1992, 1994, 1996, 1997, 1999.
Best Advanced-Composite Paper Award, Composite Institute, Society of the Plastic Industry, 1994.
Outstanding Graduate Teacher Award, College of Engineering, WVU, 1992.

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