A Novel Modeling Method in Metal Strip Leveling Based on a Roll-Strip Unit

In the metal strip-multiroll leveling process, the action behavior of each roll is different. However, modeling each roll individually will result in redundancy which is not conducive to the modeling of the entire leveling process. To overcome this problem, a roll-strip unit (RSU) model is proposed to uniformly describe the behavior of each roll during the leveling process. The RSU and its equivalent model are defined on the basis of analyzing the force relationship between the roll and the strip. According to the linear distribution of the bending moment in the longitudinal direction of the strip, the position of the zero bending moment, that is, the virtual fulcrum, is obtained to determine the interval of the RSU. A plastic deformation function is established to describe the influence of plastic extension on the tension and velocity of the strip. The fitting of the deformation curve of the strip is optimized by the tension influence factor and the zero curvature moment. The static friction condition between the roll and the strip which ensures the normal operation of the RSU is given. The AMESim model of the RSU is established to lay the foundation for the dynamic modeling of the multiroll leveler.

Friction and Wear Morphology between Hydrogenated Titanium Alloy and Cemented Carbide

Ti-6Al-4V alloy was hydrogenated at 800°C by thermohydrogen treatment technology. Sliding friction and wear tests were carried out in a special tribometer assembled on CA6140 turning lathe to investigate the friction and wear morphology between hydrogenated titanium alloys and WC-Co cemented carbides. The morphological analyses of the worn surface were made by scanning electron microscope. It was found that the friction coefficient and the friction area temperature of the pair both firstly decreased and then increased with the increase of hydrogen content, and the friction coefficient decreased and the friction area temperature increased with increasing sliding speed. The main wear morphologies of the unhydrogenated alloys were serious plastic deformation, ploughing, adhesion tearing pit and fatigue microcrack, but the main wear morphologies of the hydrogenated alloys were boundary of plastic extension, slight scratch and slight adhesion tearing. Besides, the main wear morphology of the tool corresponding to unhydrogenated alloys was massive spalling, but the main wear morphology of the tool corresponding to the titanium alloy with 0.29% hydrogen content was punctate spalling.

Analysis of the Plastic Extension of Parking Cracks on Casing after Testing

To avoid the fatigue fracture of casing inside slips, the plastic extension of casing cracks near slips under inner pressure after taking RTTS packer out should be analyzed. The plastic zone size of instability extension of two/three-dimensional cracks on casing was derived based on the theory of fracture mechanics. Analysis results show that hoop stress caused by inner pressure of casing is a key factor to lead to the instability extension of casing radial cracks after testing. The plastic extension zone size of cracks on casing near slips increases with the inner pressure or hoop stress. And, the plastic extension of cracks on casing near slips reduces the burst strength of casing significantly. The materials of casing materials and the inner pressure should be appropriately controlled to control the propagation of cracks.

Measurement of Micro Residual Stresses Near the Grain Boundary in Copper Bicrystal

Residual stresses near the grain boundary of a bicrystal were measured by synchrotron radiation of SPring-8 at Japan Synchrotron Radiation Research Institute. A copper bicrystal specimen with a 90-degree tilt boundary was deformed 30% in tension. After the plastic extension, kink bands developed in a deformed matrix along the grain boundary. In this study, we focused on the residual stresses in the deformed matrix and the kink band. Residual stresses were evaluated by the X-ray single crystal measurement method. Stereographic projections were used to determine crystal orientations of deformed regions. Our observation showed that crystal orientations were different between the deformed matrix and the kink band. Residual stresses in the direction along the grain boundary in the deformed matrix and kink band were compressive. Residual stresses in the direction vertical to the grain boundary were seen opposite between the deformed matrix and the kink band.

Indentation size effects in polymers and related rotation gradients

Similar to metals, the hardness of many polymers increases with decreasing indentation depths at depth ranges from several microns down to several nanometers. While for metals such phenomena are commonly attributed to geometrically necessary dislocation densities, such an explanation cannot be applied to polymers. To provide a micromechanically motivated model for the indentation size effect in polymers, here we propose an elasto-plastic extension of the higher order elasticity model recently developed by the authors. In this model, size effects in polymers (as well as in nematic liquid crystals) are related to Frank elasticity arising from bending distortions of the polymer chains and their interactions. On the basis of this theory, we derive a simple model for indentation size effects in polymers. Unlike other models, our model includes only elastic size effects due to rotational gradients. It is shown that the proposed model can explain the experimentally observed size effects in polymers. Together with the existing experimental data mentioned here, new experimental data for silicon rubber are also presented and discussed.