本文選題：應力三軸度 + 壓剪試驗��； 參考：《上海交通大學》2015年碩士論文

【摘要】：在板料成形領域,精沖成形工藝已成為一種重要的成形手段。精沖成形過程中,材料處于三向壓應力狀態(tài),塑性變形能力得到了極大改善。但是,精沖成形過程中也常常伴隨著復雜的損傷斷裂等問題,其適用的韌性斷裂準則需借助剪切試驗進行試驗驗證和參數標定。因此,有必要對金屬板料在低應力三軸度狀態(tài)下的韌性斷裂行為進行研究。本文通過構建一種新型的壓剪試驗裝置作為切入點,運用數值模擬和物理實驗相結合的方法對處于低/負應力三軸度的壓剪試驗進行研究。結合數值模擬結果和壓剪試驗結果分析了不同材料的壓剪試驗試樣在不同應力狀態(tài)下的塑性變形行為和斷裂失效特征。通過宏微觀斷口的定性和定量分析,研究了壓剪試驗的斷裂機制和試樣斷口表征響應。主要研究成果如下:1)圍繞現有板料剪切試驗方法的特點和不足,構建了一種新的板料壓剪試驗。通過預加載,實現了特定應變路徑下的剪切成形,通過調整試樣幾何結構實現了低/負應力三軸度范圍的剪切成形。2)壓剪試樣較拉剪試樣的塑性變形能力有所改善,相同條件下壓剪試樣較晚發(fā)生斷裂失效。材料的抗拉強度越高,壓剪試驗所需的成形載荷越大,最終斷裂位移量越小。壓剪試樣的裂紋起源于靠近變形區(qū)切槽邊緣的內側位置,裂紋擴展角和主加載方向的夾角值隨著β角增大而呈現逐漸減小的趨勢。3)試樣宏觀斷口大致可分為光滑平整、剪切平面密集的I區(qū)和韌窩密集存在的II區(qū)。β角增大,I區(qū)所占比例增加。斷面兩側I區(qū)是明顯的剪切斷裂特征,剪切平面臺階狀分布,孔洞極少且?guī)缀鯖]有擴展。斷面中心II區(qū)為典型的拋物線型韌窩斷裂,韌窩密集且沿著剪切方向拉長,韌窩底部存在形核粒子。β角增大,II區(qū)的韌窩取向性更加明顯,其等效平均韌窩直徑d略有增加。4)相同條件下,同種材料(不同β角)獲得的平均韌窩直徑d和長短軸徑比相差不大。β角增大,平均韌窩直徑d略微增大,約在0.4~0.5μm左右,而韌窩密度ρ則呈現明顯減小的趨勢。材料抗拉強度增加,平均韌窩直徑d減小,而韌窩密度ρ則出現拋物線形狀。
[Abstract]:In the field of sheet metal forming, precision stamping has become an important forming method. In the process of precision stamping, the material is in the state of three dimensional compressive stress, and the plastic deformation ability is greatly improved. However, in the process of precision stamping, there are some complicated problems such as damage and fracture. The applicable ductile fracture criterion needs to be verified by shear test and calibrated by parameters. Therefore, it is necessary to study the ductile fracture behavior of sheet metal under low stress triaxiality. In this paper, a new type of compression shear test device is constructed as a starting point, and the compression shear test with low / negative stress triaxiality is studied by means of numerical simulation and physical experiment. The plastic deformation behavior and fracture failure characteristics of different materials under different stress states are analyzed by combining the numerical simulation results and the compression shear test results. The fracture mechanism of compression shear test and the response of specimen fracture were studied by qualitative and quantitative analysis of macro and micro fracture. The main research results are as follows: (1) A new compression shear test of sheet metal is constructed around the characteristics and shortcomings of the existing shearing test methods. By preloading, shear forming under specific strain path is realized. By adjusting the geometric structure of the specimen, the plastic deformation ability of the compression shear specimen is improved compared with that of the tensile shear specimen, and the shear forming of low / negative stress triaxiality range is realized. Under the same conditions, the fracture failure of the compressive shear specimen occurred later. The higher the tensile strength of the material is, the greater the forming load is and the smaller the final fracture displacement is. The crack of compression shear specimen originates from the inner position near the edge of the notch in the deformation zone, and the angle between the crack propagation angle and the main loading direction decreases gradually with the increase of 尾 angle. 3) the macroscopic fracture surface of the specimen can be roughly divided into smooth and smooth. The ratio of 尾 -angle increasing in I region and II region in dimple densification increased with the increase of shear plane density and dimple density. The I region on both sides of the section is an obvious shear fracture feature. The shear plane is a step like distribution with very few holes and almost no expansion. Section II is a typical parabolic dimple fracture, the dimple is dense and elongated along the shear direction, and nucleation particles exist at the bottom of the dimple. Under the same condition, the average dimple diameter d and the long axis diameter ratio obtained by the same material (different 尾 angle) were not different. The 尾 angle increased, the average dimple diameter d increased slightly, and the average dimple diameter was about 0.4 ~ 0.5 渭 m. However, the dimple density 蟻 decreased obviously. With the increase of tensile strength, the average dimple diameter d decreases, while the dimple density 蟻 appears parabola shape.
【學位授予單位】：上海交通大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TG115

【參考文獻】

相關期刊論文 前1條

1 湯安民,師俊平;鋁合金材料剪切斷裂實驗分析[J];力學季刊;2002年01期

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本文編號：1882059