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This paper reports measurements of thermal expansion in polyethylene naphthalate films and relates them to the crystal texture. X-ray diffraction shows that the naphthalate ring planes are distributed with a strong maximum in the plane of the film. The crystal c axes are aligned in the machine direction for uniaxially drawn films but have a bimodal distribution for biaxially oriented samples. Parameters extracted from the distributions were combined with experimental and estimated values of the thermal expansion and stiffness constants for the isotropic amorphous and anisotropic crystalline phases to obtain predictions of thermal expansion coefficient using Ward's aggregate model. The Voigt average (crystals and amorphous regions in parallel) is very close to the uniaxial experimental expansion coefficients. In the biaxial samples, the model predicts the widthwise variation of principal directions of the expansivity tensor well. A linear combination of the Voigt and Reuss (series arrangement) averages reproduces the measured values.

This paper outlines the standardisation process for the XRPD method that is currently being considered by a Working Group (WG10) of Technical Committee 138 "Non-destructive Testing" of the European Committee for Standardisation CEN. Several Standard Documents are on the verge of being released. These documents concern the general principles of (X-ray) diffraction, its terminology, and the basic procedures applied. Another document concerns the instruments used and it offers procedures to characterise and control the performance of an X-ray diffractometer properly. It is intended to issue Standard Documents on specific methods, e.g. determination of residual stresses. In fact work is in progress on this subject. The Standard Documents can be used by industry, government organisations, and research centres with activities related to safety, health and the environment, as well as for educational purposes.