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Strain Hardening of Glassy Polymers Mark O. Robbins (Johns Hopkins University) DMR 0454947

(a). Strain Hardening of Glassy Polymers Mark O. Robbins (Johns Hopkins University) DMR 0454947.

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Strain Hardening of Glassy Polymers Mark O. Robbins (Johns Hopkins University) DMR 0454947

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  1. (a) Strain Hardening of Glassy PolymersMark O. Robbins (Johns Hopkins University) DMR 0454947 • The stress needed to shear glassy polymers increases with the amount of deformation or stretch l. Simulations of this “strain hardening” reproduced experimental results and revealed fundamental inconsistencies with traditional models that assume polymers act like rubber. • The results explain why: • stresses are 100 times larger than in rubbers and decrease with temperature • polymers remember their shape • They also reveal a direct connection between hardening, plastic deformation, and the orientational order of polymers. • Strain hardening can prevent or delay fracture and improved understanding is needed to predict and improve the mechanical behavior of polymers. (b) (a) Yield and hardening stress drop as T rises(b) Results for chains of length 10 to 350 depend only on orientation measured by leff

  2. Strain Hardening of Glassy PolymersMark O. Robbins (Johns Hopkins University) DMR 0454947 Outreach efforts included talks and demos for over 200 eighth grade students and their parents at “Nanoday” (2/23/08) sponsored by the JHU MRSEC and Center for Talented Youth. Java applets illustrating the atomic origins of friction were developed. These applets and other demos were presented to the hundreds of participants at the annual JHU Physics Fair (4/26/08). Strain hardening of polymers is important in preventing fracture in mechanical components. Improved understanding of mechanisms may lead to improved materials. Please insert an image or group of images here to illustrate your broader impacts activities. If you need more space, you may reduce the adjacent textbox. Please use lettering that is clearly visible (i.e. not too small). Please include a brief figure caption. Demos illustrating friction are available at www.pha.jhu.edu/~javalab/friction. Windows show atomic dynamics, mean motion and forces. Key physical parameters can be varied and the site includes suggested exercises, explanations and references.

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