Papers by Keyword: Stretching

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Authors: Li Yong Ni, Suo Qing Yu, L. Li, S.Y. Zhu, Hua Gui Huang
Abstract: High transversal properties requirements of heavy axial forgings, traditionally, often are met through the selection of high-performance materials, the improvement of metallurgical quality and repeated forging. But the production costs and power consumption are both high. A new slant forging method is adopted, by controlling the metal flow direction in forgings, to achieve the increase of transversal mechanical properties. Finite element method was applied to study the influence of forging process parameters on flow lines in axial forgings, providing theoretical guidance for the eventual realization of the forging method.
Authors: Hai Gong, Yun Xin Wu, Zhao Peng Yang, Kai Liao
Abstract: 7050 aluminum alloy thick plates are usually heat treated and then aged to improve mechanical properties; however, residual stresses in the plates are developed during quenching. In this study, the influences of non-uniform factors on residual stresses in aluminum alloy thick plates during the quenching and stretching processes are studied. The results show strong inhomogeneity of the residual stress distribution in the plates, and the length of influenced area of the stretched plate is discussed.
Authors: Anatoliy Veselov, Yury Pukharenko
Abstract: Actuality of study of the problem of longitudinal crack formation along reinforcement taking into account concrete nonlinear strain is pointed out in this article. It is known that at collaboration of steel and concrete plastic strains occur in concrete surrounding bar. Previously, in the work [6], solution on determination of splitting cracks at elastic work of concrete in the area of active bond to steel was proposed. In this article, theoretical solution on determination of longitudinal cracks both in supporting area and in the area of collaboration of steel and concrete between cracks along element is suggested. For establishing equations taking into account inelastic work of concrete, the theory of plastic properties suggested by G.A. Geniev was used. Component stress-strain relation is recorded by analogy with studies performed by G.A. Geniev and N.N. Malinin. At that, design dependencies are linked with normative factors of concrete, such as concrete ultimate tensile strength, Poisson ratio and concrete elastic strain ratio at stretching. All this allowed to significantly simplify the use of expressions offered.
Authors: Shi Cheng Xiao, L.P. Zhang, Li Yong Ni, Wen Hua Yang, H.L. Liu
Abstract: Research was conducted for stretching with horizontal V-shaped anvils (HVA) and common flat anvils (FA). The forgoing research gave the simulation results of single blowing during stretching, and did not pay attention to the influence of the deformation, resulting from the previous blowing, upon the next blowing. ANSYS software is adopted to simulate the through-continuous blowing of HVA and FA forging methods. The transversal stress distribution along the horizontal central axis on the crosssection of the stretched forging is analyzed. The simulation results show that during the stretching with flat anvils, when the ratio of the flat anvil width to the billet height is 1.0 and the ratio of the billet width to the billet height is 0.5, the transversal stress is tensile all the time, and increases as the stretching goes. On the contrary, during the HVA stretching, the stress is compressive and its absolute value increases gradually. The results show that the HVA stretching method is prior to the FA stretching method in the controlling of transversal stress. Conducted physical experiment verified the results.
Authors: M. Tashiro, Yoshihide Honda, T. Yamaguchi, P.K. Pujari, N. Kimura, T. Kozawa, Seiichi Tagawa
Authors: Shohei Kajikawa, Takashi Iizuka, Takashi Kuboki
Abstract: This paper presents a new stretch forming method that applies compressive force for forming a deep cup with a flange. In this method, a punch and a die having a hole are used, and the main parameters are the depth of the die hole, ddh, and the clearance between the punch and the die, c. The effect of ddh and c was investigated by using an aluminum blank of thickness 2 mm in an experiment and a finite element analysis (FEA). When ddh was too small, the material flow could not be controlled appropriately, and when ddh was too large, a local thinning occurred during initial stretching into the die hole. When c was set at large, the side wall thickness of the formed cup was uneven, but a deep cup could be obtained by setting c below a half of the blank thickness. As a result, a deep cup of height 8.3 mm and with a flange was formed successfully under the condition that ddh was 1.5 mm and c was 0.5 mm.
Authors: Hitoshi Takagi, Antonio Norio Nakagaito, Yuya Sakaguchi
Abstract: The presence of nanoscale cellulosic fiber; namely cellulose nanofiber, increases year by year because the mechanical and physical properties are believed to be comparable to those of common glass fibers. On the other hand, most of the reported strength data for the cellulose nanofiber-reinforced polymeric composite materials was not as high as expected. In order to obtain high-strength cellulose nanofiber-reinforced polymer composites, we tried to optimize the fiber orientation of cellulose nanofibers in poly (vinyl alcohol)-based polymer matrix by using a repeated mechanical stretching treatment. The fiber orientation of cellulose nanofibers in the poly (vinyl alcohol) matrix can be modified by changing the total amount of stretching strain applied during the multiple stretching treatments. The degree of fiber alignment was directly evaluated by observing the cellulose nanofibers on the sample surface with a digital microscope. The efficacy of proposed nanofiber alignment control has been explored experimentally and theoretically. The tensile strength and modulus of the cellulosic nanocomposites after applying the multiple stretching treatments increased by approximately 80% and 40% respectively, as compared with those of the untreated nanocomposites.
Authors: Yong Hua Li, Jing Zhang, Wei Yi Liu
Abstract: Stretching is a commonly used process to manufacture forgings with good quality. In this paper, the stretching process of cylinder forging with materials properties in materials engineering was investigated by finite element method. The metal flow law of cylinder stretching process was studied, based on the simulation and analysis of the effect of tool geometry like flat and V-shaped anvils on strain and stress distribution state in the forging. The reasonable tool geometry for stretching was V-shaped anvil.
Authors: Tao Chen, Hong Ling Liu, Wei Dong Yu
Abstract: In order to understand the influence of stretching on the nanotribological properties of human hair, the European hair with stretching ratios at 20, 40, 60 and 80% were studied using atomic force microscopy (AFM). The results show that appropriate stretching ratios (40-60%) make the European hair surface smoother and the friction measurements also verify the result. When the stretching ratio is 80%, the European hair has the highest coefficient of friction. The reason is that cuticle damages lead to the local ratchet and collision between AFM tip and the sample obviously increased. With the increase of stretching ratios, the adhesive force of European hair is nonlinear change, which is attributed to the influence of contact area, water molecules absorbed and the amount of polar molecules.
Authors: Sang Woo Kim
Abstract: Periodic cellular metals (PCMs) based on lattice truss structure have been developed for a wide range of potential applications with their lightweight and multi-functionality. Although divers methods to fabricate truss PCMs, such as investment casting, perforation-bending, and extrusion-EDM, have been reported, the processes have been limited to fabricate flat plates. The paper proposes a new method, multiple pin stretch forming, to fabricate the truss PCM with various cross-sectional shapes. The process has some advantages to fabricate the truss architecture with locally different height and reduce the waste of material during perforation process compared with conventional processes. However, since a 3-D truss structure is built up by tensile deformation of truss members in the process, it is important to design the geometry of precursor sheet to avoid unexpected fracture and make full use of elongation of a given material. The paper focused on the design of precursor sheet through the investigation on failure limit in multiple pin stretch forming. The forming failure were predicted by FE simulations combined with a ductile fracture criterion for various geometrical conditions, and a forming failure diagram was constructed and verified with experiments. And finally, pyramidal truss PCMs with flat and stepped cross section were fabricated successfully without any defects.
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