Editorial

This and the next issue of the journal are dedicated to the Italian Association for Stress Analysis (AIAS). Founded in 1971, the Association gathers together researches from academia, research centres and industries devoted to the investigation on experimental mechanics and stress analysis in general. The activities of the Association and the interaction with national and international research institutions and companies are promoted by the members through a series of working groups on specific areas (Bioengineering, Civil Engineering, Composite Materials, Joining techniques, Residual stresses, Vehicle design). The issues collect some works representative of the activity of the Association in the field of experimental mechanics, selected by the AIAS Executive Committee from those presented during the XXXVII AIAS National Conference, held at University La Sapienza in Rome – September 2008. After the conference, authors were asked to prepare an extended paper which was submitted to the usual peer review process of the Journal. Subjects covered by the papers presented in the two issues are stress and strain assessment, testing procedures, material characterisation and modelling, composite materials, even for civil applications, and analysis of the in-service loading conditions. This issue contains eight papers. In the first paper by Sciammarella et al., surface plasmons, generated by free electrons in the surface of metals, have been used to characterise surface profiles and contact stress distributions. Three different applications are presented in the paper to show the robustness of the technique. The second paper, by Beghini et al., deals with the application of the influence functions, to solve the inverse problem of determining residual stresses from the measured relaxed strains. The effects of the hole eccentricity and the number of strain gauges on the accuracy of the reconstructed residual stresses are considered for typical experimental conditions. In the paper by Bonora et al., the measure of the damage through the degradation of the material Young’s modulus is critically reviewed highlighting the number of issues that may affect the measure of damage. A FE-based procedure is proposed to account for the effect of geometry variations on the stiffness loss measure and is applied to two classes of metals: a high-strength steel and a high-purity copper. The paper by Calìet al. presents an original creep prediction model, with a unified comprehensive formulation including primary, secondary and tertiary stages for variable stresses and temperature fields. The model is implemented in the ANSYS code for an improved description of the material behaviour with respect to the mono-dimensional approach and then is applied to investigate the behaviour of a turbine blade. Somàet al. investigated the mechanical behaviour of microswitches at pull-in. The paper illustrates the results of out-of-plane bending tests on microswitches and the application of FEM approaches already proposed by the authors to include both the geometrical and electromechanical non-linearities and to evaluate the residual stress in microswitches. A reverse analysis is implemented, and some preliminary criteria to correlate the residual stress occurring and the microfabrication process are drawn. The paper by Filippini et al. deals with the combined cycle fatigue (CCF) and low cycle fatigue (LCF) testing, with and without dwell, on an investment cast polycrystalline nickel superalloy, at temperatures up to 870° C, on specimens with pre-cracked coating. Comparison of the CCF and the LCF tests with dwell with conventional LCF tests are presented. The paper by Olmi et al. investigates the influence of surface finishing on the fatigue behaviour of high-strength steel shot-peened gears. Sensitivity of residual stress distribution and fatigue limit to shot diameter and Almen intensity is discussed. Two theories for fatigue prediction are reviewed and validated by comparison between experimental and numerical results. In the last paper, an experimental test methodology to investigate the strain rate influence on the mechanical behaviour of thin sheet metals at large strains is presented by Broggiato et al. Dynamic tensile tests at medium strain rate are carried out on an electromechanical material testing machine and a specifically developed clamping device. A numerical model of the testing system is created to optimise the shape of the strain rate pulse and digital image correlation technique is used for strain measurement on specimen surface. After this brief analysis of the content of the Issue, I would like to thank all the authors for their valuable contributions and the reviewers who carefully verified the quality of the papers and their suitability for the journal and provided the authors with helpful comments and suggestions. Eventually, even on behalf of the Italian Association for Stress Analysis, I would also like to express my personal gratitude to my Editor-in-Chief, Professor Emmanuel Gdoutos, for giving the Association the opportunity to publish these special issues, for his help during the entire review process and for his continuous encouragement and support during the whole project.