Phenomenological analysis of constrained in-plane compression of paperboard using micro-computed tomography Imaging

Large deformations under in-plane compression of paperboard appear in forming processes like hydroforming, pressforming and deep drawing, but the mechanisms of deformation have not been studied on a micromechanical level. A constrained in-plane compression test is presented. This test allows for in-plane compression, buckling, wrinkling and compaction. The constrained compression test is realized using a DEBEN CT-500 in-situ tester for laboratory microtomography and synchrotron microtomography. Experiments with five different materials spanning from laboratory handsheets to commercially available multi-layered paperboards are performed. Image processing is used to observe the local out-of-plane fiber orientation and compaction. A phenomenological investigation of the deformation behavior of these materials is presented. Delamination is found to be the primary mechanisms of failure in the multi-layered boards. Furthermore, a porous network structure, created by using long and minimally refined softwood fibers, is found to facilitate the formation of uniform wrinkles and compaction.

Effect of components on the properties of composite materials

Methods for the creation and characteristics of composite materials reinforced with carbon, aramid and UHMWPE-fibers based on polymer matrices are considered. The properties of more than 50 composite materials are given. Technologies for their production from wound nonwoven and woven fiber reinforcements are proposed, with regulation of activation, composition and arrangement of components in the material. Experimental methods for studying polymer com- posites, such as wet-pull-out (W-P-O), full-pull-out (F-P-O) and impact break (IB) have been deve­loped. It allows one to study the interfacial interaction of components during the creation of CM, regulate the activation of fibers by non-equilibrium low-temperature plasma and fluo­ rination, and analyze mechanisms of deformation and destruction of CM, in statics and upon impact with the help of uniform universal samples. Monograph – reference book is intended for scientific and engineering staff, teachers, stu- dents, graduate students, and inventors involved in the development, production and use of poly­ mer composite materials.

Determining the mechanisms of deformation in flexible crystals using micro-focus X-ray diffraction

While the first report of molcular crystals that could bend without breaking was well over a decade ago, the development of suitable characterisation tools remains a priority. Due to the...

Review of Non-Classical Features of Deformation Twinning in hcp Metals and Their Description by Disconnection Mechanisms

The study of deformation twinning has long history. However new, sometimes surprising, findings have shown that the phenomenon of deformation twinning still is not completely understood. During recent years, some debates are taking place in the scientific literature concerning deformation twinning mechanisms in metals with hcp structure. These debates deal with the importance of special twin boundary dislocations named disconnections, growth and nucleation of twins, non-Schmid behavior of twinning, difference of deformation produced by twins from simple shear. They invoked new propositions for atomistic mechanisms of deformation twinning. The purpose of this review is to compare the classical theories of interfacial defects with the new findings and prove that many of these findings can be understood in terms of these well-established theories. The main attention is paid to summarizing the explanations of different phenomena in terms of disconnection mechanisms in order to show that there is no contradiction between these mechanisms and the new findings.

Проявление низкоэнергетических ориентационных возбуждений в механически нагруженных аморфных полимерах по данным низкочастотной ИК- и раман-спектроскопии

Author: Ryzhov V.A. Ioffe Institute, St. Petersburg, 194021 Russia e-mail: [email protected] Abstract Experimental data on the effect of mechanical loading (tension and compression) of glassy polymethylmethacrylate and polyvinyl chloride on low-frequency IR and Raman spectra are obtained. Their analysis made it possible to detect absorption and scattering due to low-energy orientational excitations in a disordered polymer exposed to external influences. It was shown that these spectral data carry information on the molecular mechanisms of deformation and the relaxation dynamics of macromolecules. A possible scenario of the development of the initial stage of the deformation process is considered.

Mechanical behaviour and microstructural evolution in fine grain Ti-6Al-4V alloy under superplastic conditions

Ti-6Al-4V is able to support high level of deformations like superplastic deformation for aeronautical structural applications. However, the applied temperature during forming induces changes in phase fraction, which may have an impact on the mechanisms of deformation involved and the final part. Mechanisms described in the literature, like dislocation glide, diffusional creep, Grain Boundary Sliding (GBS) accommodated by dislocation or diffusion, are still controversial as there are mainly based on post mortem analysis or on stress-strain data. The purpose of this work was to combine interrupted tensile tests and heat treatments to improve the understanding of the mechanisms of deformation on each stage of deformation. The chosen test temperatures were 750°C and 920°C which correspond to different β phase fractions. The microstructural features like grain size and phase fraction were studied by Scanning Electron Microscope (SEM) combined with image analysis. Moreover, EBSD was used to follow the change of crystalline orientation of α grains to distinguish the involved mechanisms as a function of the deformation. Indeed, it would appears that several mechanisms could be activated depending on the deformation stage and on the temperature.