I am currently a graduate student at UW-Milwaukee. I am working on the determination of Young's modulus for polyester/particulate composites from ultrasonic shear and longitudinal velocities. I then take my samples and determine Young's modulus by compression testing. My data suggests strongly that Young's modulus determined from NDE is about double the value obtained from compression testing. A team and myself have thoroughly checked over the calculations for error. Is this common in plastics? Is there any explanation for the data variations?

Re: NDE of Plastics : I am currently a graduate student at UW-Milwaukee. I am working : on the determination of Young's modulus for polyester/particulate : composites from ultrasonic shear and longitudinal velocities. I then take : my samples and determine Young's modulus by compression testing. : My data suggests strongly that Young's modulus determined from : NDE is about double the value obtained from compression testing. : A team and myself have thoroughly checked over the calculations for : error. Is this common in plastics? Is there any explanation for : the data variations?

Many plastics are viscoelastic ie soft at low stain rates but harder at high stain rates. Young modulus determined by a compression test is low frequency ie soft. Whereas Youngs Modulus determined ultrasonically (high frequency)will be higher as the material appears stiffer.

05:57 Jan-31-2000 Valliyappan David Natarajan Student, Research Assistant National University of Malaysia, Malaysia, Joined Jan 2000 ^{4}

Re: NDE of Plastics : I am currently a graduate student at UW-Milwaukee. I am working : on the determination of Young's modulus for polyester/particulate : composites from ultrasonic shear and longitudinal velocities. I then take : my samples and determine Young's modulus by compression testing. : My data suggests strongly that Young's modulus determined from : NDE is about double the value obtained from compression testing. : A team and myself have thoroughly checked over the calculations for : error. Is this common in plastics? Is there any explanation for : the data variations?

Mr.Niles Stenmark,

I am a graduate from the National University of Malaysia,currently pursuing my Masters's degree from the same university. My undergraduate final year project entitled "Characterization of Natural Fibre Reinforced Polymer Composites using Non-Destructive Ultrasonic Technique" involves determination of the Young Modulus and Shear Modulus of oil palm frond short fiber reinforced polyester from the ultrasonic longitudinal velocity and correlating it with the same quantities obtained from conventional tensile test (ASTM D638M). As your observation too, the results which I got strongly shows this correlation :

NDE value = 2 * TensileTest value [ or a correlation of 100% ].

Thereabout, I suggest that some mathematical modification to be made to the equations presented by the ASTM D638M standard to enhance the approximation values given by NDE method so as to validate the NDE method. Maybe the mathematical equations presented in the ASTM D638M was validated only for metals and not specific for reinforced polymers.

Please inform me if there is any efforts that you have taken in order to justify your results (ie. the difference between NDE and compression test methods and results). Thank you. email : valli_3@hotmail.com

07:20 Jan-31-2000 John A. Brunk Engineering, NDT Level III Self employed, part-time, USA, Joined Oct 1999 ^{158}

Re: NDE of Plastics The mechanical properties of many plastics and composites are strain rate sensitive. There may also be significant differences between properties measured in compression,tension, and shear. Many composites are anisotropic. 2 does seem to be a reasonable correction factor for many materials. When you want to compare the mechanical properties of samples of essentially the same material, it may be sufficient to perform the actual mechanical testing on one of the samples to determine the correlation between this data and ultrasonic velocity. Some composites exhibit different ultrasonic velocities at different frequencies as well as in different directions. It is much easier and more reliable to compare the impact of some processing variable on the properties of one material than to try to generalize about a group of materials.

07:22 Jan-31-2000 John A. Brunk Engineering, NDT Level III Self employed, part-time, USA, Joined Oct 1999 ^{158}

Re: NDE of Plastics The mechanical properties of many plastics and composites are strain rate sensitive. There may also be significant differences between properties measured in compression,tension, and shear. Many composites are anisotropic. 2 does seem to be a reasonable correction factor for many materials. When you want to compare the mechanical properties of samples of essentially the same material, it may be sufficient to perform the actual mechanical testing on one of the samples to determine the correlation between this data and ultrasonic velocity. Some composites exhibit different ultrasonic velocities at different frequencies as well as in different directions. It is much easier and more reliable to compare the impact of some processing variable on the properties of one material than to try to generalize about a group of materials.

Re: NDE of Plastics ptly for ASTM and: http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/PAGES/D638M.htm?L+mystore+ceqx4960 (Withdrawn 1998) I suppose nothing at all with standard modification, but I am very curious on the content of this standard. Could you please send me a copy.