Analytical and numerical approaches to modelling severe plastic deformation

Mechanical properties and corrosion behavior of Al/SiC composites

This paper deals with the vibration characteristics of shear deformable functionally graded material (FGM) plates. The theoretical models are based on Taylor's series expansion of in-plane and transverse displacements in thickness coordinate defining the plate deformations. Poisson's ratio of the FGM plates are assumed to be constant, whereas the effective mechanical properties i.e. Young's moduli and material densities vary continuously in thickness coordinate according to the volume fraction of constituents. A C0 continuous isoparametric finite element formulation has been employed to accomplish the results, and the accuracy of the formulation is demonstrated by comparing with the available literature. Parametric study has been performed for volume fraction indices, thickness ratios, aspect ratio and various boundary constraints. Natural frequencies of the FGM plates with various unconventional boundary constraints have also been presented.

Vibration characteristics of functionally graded material plate with various boundary constraints using higher order shear deformation theory

https://biblio.ugent.be/publication/7076955/file/7076969.pdf

Effect of pitch difference between the bolt–nut connections upon the anti-loosening performance and fatigue life

https://www.tandfonline.com/doi/pdf/10.1080/14693062.2020.1831430

Decarbonising the critical sectors of aviation, shipping, road freight and industry to limit warming to 1.5–2°C

The work described in this paper concerns a novel method for directly forming curved profiles/sections from billets in one extrusion operation using two opposing punches. Its mechanics are based on internal differential material flow, and it has been given the acronym, differential velocity sideways extrusion (DVSE). A tool set enabling sideways extrusion to be performed using opposing punches moving with different velocities was used for a series of experiments in which punch velocity ratio and extrusion ratio were process parameters. Plasticine was used as a model work-piece material and a series of compression tests were undertaken, to determine its constitutive properties and gain an estimate of work-piece die friction for use in process simulation. Curvature of extrudate can be controlled and varied using a difference between the velocities of the two punches, defined by velocity ratio. Greater curvature is achieved with lower velocity ratio. Curvature is also dependent on extrusion ratio, an increase in which increases curvature, although curvature is less sensitive to it than to velocity ratio. The extent of work-piece flow velocity gradient across the die exit orifice, which causes curvature, has been identified. Severe plastic deformation of the extrudate occurs in a way similar to channel angular extrusion (CAE), thus a greatly promoted effective strain level is achieved, though it is not always uniform across a section. The inner bending region of an extrudate experiences maximum localised effective strain, which decreases with decrease in curvature. To the authors' knowledge this is the first publication in which extrudate curvature is deliberately induced using opposing punches with differential velocities. Although only fixed velocity ratio values have been used in the work described in this paper the ability to change during operation exists and the process has the potential for the production of a profile with different curvature along its length.

/pdf/feasibility-studies-of-a-novel-extrusion-process-for-curved-45dkrpewmk.pdf

Feasibility studies of a novel extrusion process for curved profiles: Experimentation and modelling

For structural and aerodynamic reasons, curved profiles are widely used in the transport industry for manufacturing lightweight structures. In the present work, a curved AA1050 bar with fine grains and high strength was manufactured by a novel forming technique, differential velocity sideways extrusion (DVSE). The evolution of grain structure and micro-texture during DVSE and the mechanical properties of the formed bar were studied, and the grain refinement mechanism was revealed. Due to the severe strains arising in the process, (greater than that for conventional one pass equal channel angular extrusion), significant grain refinement in the curved bar (grain size ∼3 μm) was achieved from the original billet (grain size ∼357 μm) in one extrusion operation. Coarse band-like structures containing subgrains with low angle boundaries in the shearing zone gradually transformed into fine shear band-like structures containing equiaxed (sub)grains with a mixture of low and high angle boundaries. The fine shear band-like structures inclined approximately along the shear intersection planes. Severe plastic deformation induced a high dislocation density that initiated subgrain walls with low angle boundaries, which gradually transformed into grain boundaries with high misorientation, indicating that refinement of AA1050 grains in the DVSE process is due mainly to continuous dynamic recrystallization (cDRX). Due to the appearance of greater effective strain on the inner bend of the extruded bar, the grain refinement degree and high angle boundary fraction of the material on the inner bend are slightly greater than those of the material on the outside. DVSE resulted in a weak C-type shear-texture component which can be determined by a proper rotation of the negative simple shear texture. Compared with the billet, significant increase of the hardness, yield strength and ultimate tensile strength by 134.8%, 354.0% and 116.8% respectively was achieved in the formed curved bar, although the elongation to fracture was decreased by 60.0%.

/pdf/manufacturing-a-curved-profile-with-fine-grains-and-high-2n6em416d4.pdf

Manufacturing a curved profile with fine grains and high strength by differential velocity sideways extrusion

Load distribution in threads of porous metal–ceramic functionally graded composite joints subjected to thermomechanical loading

Effects of external mechanical loading on stress generation during lithiation in Li-ion battery electrodes

Ceramic–metal functionally graded materials (FGMs) have been extensively used in aerospace engineering where high strength and excellent heat insulation materials are desired. In this paper, the thermodynamic behavior of the Thermal Protection System (TPS) used bolted joints made up of porous ZrO 2 /(ZrO 2  + Ni) FGMs is investigated by finite-element (FE) modeling. The bolted joint is subjected to reentry heating corresponding to the Access to Space Vehicle. Thermodynamic simulations are carried out to yield the transient response of the porous ZrO 2 /(ZrO 2  + Ni) functionally graded bolted joint (FGBJ). The effects of the preload on the thermomechanical behavior and service reliability of the bolted joint are numerically analyzed in detail by ABAQUS codes. It is found that the preload relaxation of the bolted joint occurs at elevated temperature, and the preload has significant influence on service reliability of the bolted joint under transient thermomechanical circumstances. With the increase of the preload, stress concentration which occurs at the root of the first thread of the bolt increases rapidly and predominates in service reliability. Proper preload is thus defined to balance the service reliability and tightness of the bolted joint. Further studies show that the shape of the nut has a great effect on the stress concentration of the thread, the optimized nut is designed to reduce the stress concentration of the thread, and thus the reliability of the bolted joint is also improved.

Wenbin Zhou

Papers

Feasibility studies of a novel extrusion process for curved profiles: Experimentation and modelling

Manufacturing a curved profile with fine grains and high strength by differential velocity sideways extrusion

Load distribution in threads of porous metal–ceramic functionally graded composite joints subjected to thermomechanical loading

Effects of external mechanical loading on stress generation during lithiation in Li-ion battery electrodes

Preparation and thermodynamic analysis of the porous ZrO2/(ZrO2+Ni) functionally graded bolted joint