Strain controlled biaxial stretch: An experimental characterization of natural rubber

In this paper we provide new experimental data showing the response of 40A natural rubber in uniaxial, pure shear and biaxial tension. Real-time biaxial strain control allows for independent and automatic variation of the velocity of extension and retraction of each actuator to maintain the pre-selected deformation rate within the gage area of the specimen. The remaining part of the paper focuses on the Valanis-Landel hypothesis that is used to verify and validate the consistency of the data. We use a three term Ogden model to derive stress-stretch relations to validate the experimental data. The material model parameters are determined using the primary loading path in uniaxial and equibiaxial tension. Excellent agreement is found when the model is used to predict the response in biaxial tension for different maximum in-plane stretches. The application of the Valanis-Landel hypothesis also results in excellent agreement with the theoretical prediction

Forward Elastic Scattering of Light on Light, \gamma+\gamma\to\gamma+\gamma

The forward elastic scattering of light on light, {\em i.e.,} the reaction $\gamma+\gamma \to \gamma+\gamma$ in the forward direction, is analyzed utilizing real analytic amplitudes. We calculate $\rho_{\gamma \gamma}$, the ratio of the real to the imaginary portion of the forward scattering amplitude, by fitting the total $\gamma \gamma$ cross section data in the high energy region $5 GeV \le \sqrt s \le 130$ GeV, assuming a cross section that rises asymptotically as $\ln^2 s$. We then compare $\rho_{\gamma\gamma}$ to $\rho_{nn}$, the ratio of the even portions of the $pp$ and \pbar p forward scattering amplitudes, as well as to $\rho_{\gamma p}$, the $\rho$ value for Compton scattering. Within errors, we find that the three $\rho$-values in the c.m.s. energy region $5 GeV \le \sqrt s \le 130$ GeV are the same, as predicted by a factorization theorem of Block and Kadailov.Comment: 5 pages, Latex2e, 2 postscript figures, uses epsfig.st