本文選題：高壓扭轉(zhuǎn) + 有限元分析��； 參考：《山東農(nóng)業(yè)大學(xué)》2017年碩士論文

【摘要】：高壓扭轉(zhuǎn)(High pressure torsion,HPT)是眾多大塑性變形(Severe plastic deformation,SPD)工藝中行之有效的工藝之一,能夠有效制備出亞微米或納米塊體超細(xì)晶(Ultrafine grained, UFG)材料。塊體超細(xì)晶材料由于其表面結(jié)構(gòu)和晶粒結(jié)構(gòu)發(fā)生特殊變形,使其具備優(yōu)異的力學(xué)性能和加工性能,備受世界各國(guó)研究學(xué)者關(guān)注,成為目前金屬納米材料研究領(lǐng)域的熱點(diǎn)。雖然通過試驗(yàn)研究工藝參數(shù)對(duì)材料高壓扭轉(zhuǎn)過程塑性變形的影響非常直觀有效,但在高壓扭轉(zhuǎn)過程中,試樣應(yīng)力應(yīng)變場(chǎng)的測(cè)試較為困難,并且試樣的不均勻塑性變形一直沒有得到足夠的重視,這成為塊體超細(xì)晶材料高壓扭轉(zhuǎn)制備原理分析及工藝優(yōu)化的難題之一�；诖�,本文采用ANSYS和DEFORM-3D有限元數(shù)值模擬與物理實(shí)驗(yàn)相結(jié)合的方式對(duì)不同材料高壓扭轉(zhuǎn)過程中的不均勻塑性變形特征及影響因素進(jìn)行了研究。本文的主要研究結(jié)果如下所示: ~(1)在壓力對(duì)壓縮階段試樣不均勻塑性變形的影響、扭轉(zhuǎn)圈數(shù)對(duì)高壓扭轉(zhuǎn)試樣塑性變形的影響的研究中發(fā)現(xiàn),隨著壓力和扭轉(zhuǎn)圈數(shù)的增加,試樣等效應(yīng)變、硬度及顯微組織結(jié)構(gòu)的不均勻分程度加大,且三者不均勻分布規(guī)律相一致,自心部到邊緣位置應(yīng)變、硬度增加,晶粒細(xì)化:心部等效應(yīng)變低、晶粒粗大、晶界明顯、硬度低;中間區(qū)域應(yīng)變、硬度較高,分布較為均勻;邊緣位置等效應(yīng)變、硬度高,呈等軸細(xì)晶組織。并且,發(fā)現(xiàn)心部的硬度峰、凹槽處的變形死區(qū)以及徑向中心線邊緣處的軟區(qū)三個(gè)與整體變形規(guī)律不相符的特征區(qū)域。此外,高壓扭轉(zhuǎn)扭轉(zhuǎn)階段,相對(duì)壓縮階段產(chǎn)生劇烈變形,晶格畸變嚴(yán)重,晶粒細(xì)化更明顯。(2)在模具參數(shù)(凹槽深度d、凹槽傾角Φ)對(duì)試樣塑性變形影響的研究中發(fā)現(xiàn),隨著凹槽深度的增加,純銅試樣壓縮階段的不均勻塑性變形程度增加,自心部到邊緣,試樣整體上變形越來越劇烈。并且,變形死區(qū)的范圍越來越大,軟區(qū)徑向?qū)挾仍絹碓酱?并且試樣徑向塑性流動(dòng)距離增加。隨著凹槽傾角的增加,試樣整體塑性變形減小,其不均勻分布程度降低,變形逐漸趨于平穩(wěn),而硬度峰區(qū)域的應(yīng)變峰值、軟區(qū)徑向范圍以及變形死區(qū)范圍均隨之降低。(3)摩擦對(duì)高壓扭轉(zhuǎn)兩個(gè)階段塑性變形的影響以及高壓扭轉(zhuǎn)后試樣上下表層變形滯后的研究結(jié)果表明:在摩擦對(duì)高壓扭轉(zhuǎn)兩個(gè)階段塑性變形影響的研究中發(fā)現(xiàn),無論是在壓縮階段還是扭轉(zhuǎn)階段,隨著摩擦系數(shù)的增加,試樣整體塑性變形增加,其不均勻分布程度加深,并且,與整體變形規(guī)律不符的特征區(qū)域(硬度峰、軟區(qū)、變形死區(qū))將隨著摩擦系數(shù)的變化,產(chǎn)生相應(yīng)的改變。在高壓扭轉(zhuǎn)后試樣的組織觀察中發(fā)現(xiàn),由于上下模之間不同的運(yùn)動(dòng)形式及模具與試樣間摩擦的存在,導(dǎo)致試樣上下表面的塑性變形程度出現(xiàn)差異,上表面的變形滯后于下表面,并且,隨著扭轉(zhuǎn)圈數(shù)的增加,變形滯后性范圍將向邊緣位置靠近。
[Abstract]:High pressure torsion pressure is one of the most effective processes for large plastic deformation plastic deformation.Submicron or nanocrystalline ultrafine grained (UFG) materials can be prepared effectively. Due to the special deformation of the surface structure and grain structure of bulk ultrafine crystalline materials, they have excellent mechanical properties and processing properties, which have attracted the attention of researchers all over the world, and have become a hot spot in the field of metal nanomaterials. Although the effect of process parameters on the plastic deformation during high pressure torsion is very direct and effective, it is difficult to measure the stress and strain field in the process of high pressure torsion. And the inhomogeneous plastic deformation of the sample has not been paid enough attention to, which has become one of the difficult problems in the preparation principle analysis and process optimization of bulk ultrafine grain material under high pressure torsion. Based on this, the inhomogeneous plastic deformation characteristics and influencing factors of different materials during high pressure torsion are studied by means of ANSYS and DEFORM-3D finite element numerical simulation and physical experiments. The main results of this paper are as follows: (1) in the study of the effect of pressure on the uneven plastic deformation of specimens in compression stage, and the effect of torsion circle number on plastic deformation of high-pressure torsional specimens, it is found that, with the increase of pressure and torsional cycles, The equivalent strain, hardness and the inhomogeneity of the microstructure of the sample are increased, and the distribution of the three inhomogeneity is consistent. The hardness increases from the center to the edge, and the grain size is fine: the equivalent strain in the core is low, the grain is coarse, The grain boundary is obvious, the hardness is low, the strain in the middle region is higher, the hardness is higher, the distribution is more uniform, the edge position is equivalent strain, the hardness is high, and the structure is equiaxed fine crystal. In addition, the hardness peak of the center, the deformational dead zone at the groove and the soft zone at the edge of the radial center line are found to be three characteristic regions which do not accord with the law of global deformation. In addition, in the high pressure torsion stage, the relative compression stage produces severe deformation, the lattice distortion is serious, and the grain refinement is more obvious. It is found in the study of the influence of die parameters (groove depth d, groove dip angle 桅) on the plastic deformation of the specimen. With the increase of groove depth, the degree of inhomogeneous plastic deformation of pure copper specimen increases during compression, and the deformation of the sample is more and more intense from the center to the edge. Moreover, the range of dead zone of deformation is increasing, the radial width of soft zone is increasing, and the radial plastic flow distance of specimen is increasing. With the increase of groove inclination angle, the whole plastic deformation of the specimen decreases, the degree of uneven distribution decreases, the deformation gradually tends to be stable, and the strain peak in the hardness peak region, The influence of friction on the plastic deformation in the two stages of high pressure torsion and the study on the lag of the upper and lower surface deformation of the specimen after high pressure torsion show that the friction has a negative effect on the high pressure torsion. In the study of the effect of plastic deformation in two stages, it is found that, Whether in compression or torsion stage, with the increase of friction coefficient, the plastic deformation of the whole specimen increases, and the uneven distribution of the specimen increases, and the characteristic region (hardness peak, soft zone) that does not conform to the law of integral deformation, The deformed dead zone) will change with the change of friction coefficient. In the observation of the microstructure of the specimen after high pressure torsion, it is found that due to the different motion forms between the upper and lower die and the existence of friction between the mould and the specimen, the plastic deformation degree of the upper and lower surface of the specimen is different, and the deformation of the upper surface lags behind that of the lower surface. Moreover, with the increase of the number of torsion cycles, the lag range of deformation will be near to the edge.
【學(xué)位授予單位】：山東農(nóng)業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TB30

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