基于红外热成像法5A06铝合金疲劳行为各向异性研究
发布时间：2018-07-16 12:08
【摘要】：铝合金由于其自身的优点在车辆、化工、机械工程等众多领域具有广泛的应用，这些领域的结构往往承受疲劳载荷作用，其在应用过程中不可避免地存在疲劳问题，由于传统试验方法存在耗时长等缺点，红外热像法以其实时、快速、非接触、无损等一系列的优势，被应用到材料的疲劳研究中；此外金属材料在不同方向力学性能所表现出来的各向异性会限制其应用，性能相对较差的加工成型方向往往作为工程设计的依据。因此基于红外热成像法研究5A06铝合金高周疲劳性能的各向异性具有重要的现实意义。 本文采用红外成像仪记录了平行轧制方向和垂直轧制方向的5A06铝合金在室温下拉伸和高周疲劳断裂过程及疲劳裂纹扩展过程中的温度演化，研究了5A06铝合金的疲劳性能及产热机制；对比分析两个方向的拉伸和疲劳断裂过程中的温度场信息，并用红外热像法对两个方向的疲劳强度进行预测，与传统的疲劳试验方法所得的结果进行对比；采用电子背散射衍射(EBSD)的方法测量5A06铝合金母材的织构，研究其对平行轧制方向和垂直轧制方向5A06铝合金疲劳性能及疲劳裂纹扩展性能各向异性的影响。 结果表明：5A06铝合金平行轧向和垂直轧向表现出明显的塑性各向异性。传统试验方法测得的平行轧向和垂直轧向5A06铝合金的疲劳强度分别为113MPa和61MPa。采用红外热像法测得的平行轧向和垂直轧向的5A06铝合金的疲劳强度分别为114.6MPa和64MPa，与传统试验方法的相对误差分别为1.4%和4.9%。红外热像法对于疲劳强度的预测与传统试验方法测得的疲劳强度具有很好的一致性。 5A06铝合金施加高于疲劳强度的载荷时，平行轧向和垂直轧向具有相同的温度演化趋势，即试件表面的温度变化均分为四阶段：初始温升阶段，温度缓慢下降阶段，温度快速升高阶段，温度最终下降阶段。在拉伸试验和同应力下的疲劳测试过程中，垂直轧向的断裂温升值要高于平行轧向。由此发现，垂直轧向的试件断裂时，其释放的能量更多。同时，，也可以发现，在相同的应力下，平行轧向的疲劳寿命明显高于垂直轧向的疲劳寿命，这是由于平行轧向试件的阻止疲劳裂纹萌生的能力更强。 对平行轧向和垂直轧向的标准拉伸紧凑(CT)试件施加相同的载荷时，裂纹沿平行轧制方向的扩展速率明显大于垂直轧制方向的速率。疲劳裂纹扩展过程中，采用红外热像仪观察平行轧向和垂直轧向CT试件表面的温度演化，发现铝合金在疲劳裂纹扩展过程中分为三个阶段：初始的缓慢温升阶段、试件断裂时的急剧温升阶段和试件断裂后的自然降温阶段。在相同应力下，垂直轧向的试件断裂温升值要高于平行轧向。 采用电子背散射衍射(EBSD)方法，得到沿轧制方向和垂直轧制方向的极图与反极图，平行和垂直轧向取向密度最高值分别达到7.79和8.14。说明5A06铝合金母材晶粒中存在择优取向，即有强织构存在。垂直轧向的取向极密度值较大，表明垂直轧向的晶粒更容易转动，其塑性变形能力相对于平行轧向更强。强度和塑性有相反的对应关系，这与之前做的拉伸和疲劳试验结果具有很好的一致性。 施密特(Schmid)因子的峰值指数和平均值指数，平行轧制方向均低于垂直轧制方向，即垂直轧向的塑性性能要要优于平行轧向，相应的力学性能，平行轧制方向要优于垂直轧制方向，这与拉伸试验结果与疲劳试验结果具有很好的一致性。
[Abstract]:Because of its own advantages, aluminum alloys are widely used in many fields, such as vehicle, chemical engineering, mechanical engineering and so on. The structure of these fields is often subjected to fatigue load, and the fatigue problem inevitably exists in the application process. Because of the disadvantages of the traditional test method, the infrared thermal image method is in fact, fast and non contact. A series of advantages, such as lossless and so on, are applied to the fatigue study of materials. In addition, the anisotropy of the mechanical properties of metal materials in different directions will limit its application. The processing direction of relatively poor performance is often used as the basis for engineering design. Therefore, the high cycle fatigue of 5A06 aluminum alloy is studied based on the infrared thermal imaging method. The anisotropy of energy has important practical significance.
In this paper, the temperature evolution of 5A06 aluminum alloy in parallel rolling direction and vertical rolling direction at room temperature and high cycle fatigue fracture and fatigue crack propagation are recorded by infrared imager. The fatigue property and heat production mechanism of 5A06 aluminum alloy are studied, and the tensile and fatigue fracture processes of the two directions are compared and analyzed. The fatigue strength of two directions was predicted by infrared thermal image method and compared with the results obtained from the traditional fatigue test method. The texture of 5A06 aluminum alloy was measured by electronic backscatter diffraction (EBSD), and the fatigue properties and fatigue properties of 5A06 aluminum alloy in parallel rolling and vertical rolling were studied. The effect of anisotropy on crack propagation properties of fatigue.
The results show that the parallel rolling and vertical rolling of 5A06 aluminum alloy show obvious plastic anisotropy. The fatigue strength of the parallel rolling and vertical rolling 5A06 aluminum alloy measured by the traditional test method is 113MPa and 61MPa., respectively, and the fatigue strength of the parallel rolled and vertical rolled 5A06 aluminum alloy measured by the infrared thermal image method is 114., respectively. 6MPa and 64MPa, the relative error of the traditional test method is 1.4% and the 4.9%. infrared thermal image method is in good agreement with the fatigue strength predicted by the traditional test method.
When the load of 5A06 aluminum alloy is higher than the fatigue strength, the parallel rolling and vertical rolling have the same temperature evolution trend. That is, the temperature change on the surface of the specimen is divided into four stages: the initial temperature rise stage, the slow decline stage of the temperature, the stage of rapid temperature rise, the final stage of temperature decline. During the test, the fracture temperature of vertical rolling is higher than that of parallel rolling. It is found that when the vertical rolling specimen is broken, it releases more energy. At the same time, it can be found that the fatigue life of parallel rolling is obviously higher than that of the vertical rolling fatigue life under the same stress, which is due to the prevention of fatigue crack in the parallel rolled specimen. The ability to grow is stronger.
When the same load is applied to the standard tensile compact (CT) specimen with parallel rolling and vertical rolling, the propagation rate of crack along the parallel rolling direction is obviously greater than that in the vertical rolling direction. In the process of fatigue crack propagation, the temperature evolution of the surface of parallel rolling and vertical rolling to the surface of CT is observed by infrared thermograph, and the aluminum alloy is found in the process of fatigue crack propagation. The fatigue crack propagation process is divided into three stages: the initial slow temperature rise stage, the rapid temperature rise stage of the specimen fracture and the natural cooling stage after the specimen fracture. Under the same stress, the fracture temperature appreciation of the vertical rolled specimen is higher than that of the parallel rolling.
The electron back scattering diffraction (EBSD) method is used to get the polar and reverse pole maps along the direction of rolling and vertical rolling. The highest orientation density of the parallel and vertical rolling direction is 7.79 and 8.14., respectively, indicating that the preferred orientation exists in the grain of 5A06 aluminum alloy, that is, the strong texture exists. The rolled grain is easier to rotate, and its plastic deformation ability is stronger than that of parallel rolling. There is a opposite relationship between the strength and the plasticity, which is in good agreement with the previous tensile and fatigue test results.
The peak index and average value index of Schmidt (Schmid) factor are lower in parallel rolling direction than in vertical rolling direction. That is, the plastic properties of vertical rolling are better than parallel rolling, and the corresponding mechanical properties are better than the vertical rolling direction. This is in good agreement with the results of tensile test and fatigue test.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.21
[Abstract]:Because of its own advantages, aluminum alloys are widely used in many fields, such as vehicle, chemical engineering, mechanical engineering and so on. The structure of these fields is often subjected to fatigue load, and the fatigue problem inevitably exists in the application process. Because of the disadvantages of the traditional test method, the infrared thermal image method is in fact, fast and non contact. A series of advantages, such as lossless and so on, are applied to the fatigue study of materials. In addition, the anisotropy of the mechanical properties of metal materials in different directions will limit its application. The processing direction of relatively poor performance is often used as the basis for engineering design. Therefore, the high cycle fatigue of 5A06 aluminum alloy is studied based on the infrared thermal imaging method. The anisotropy of energy has important practical significance.
In this paper, the temperature evolution of 5A06 aluminum alloy in parallel rolling direction and vertical rolling direction at room temperature and high cycle fatigue fracture and fatigue crack propagation are recorded by infrared imager. The fatigue property and heat production mechanism of 5A06 aluminum alloy are studied, and the tensile and fatigue fracture processes of the two directions are compared and analyzed. The fatigue strength of two directions was predicted by infrared thermal image method and compared with the results obtained from the traditional fatigue test method. The texture of 5A06 aluminum alloy was measured by electronic backscatter diffraction (EBSD), and the fatigue properties and fatigue properties of 5A06 aluminum alloy in parallel rolling and vertical rolling were studied. The effect of anisotropy on crack propagation properties of fatigue.
The results show that the parallel rolling and vertical rolling of 5A06 aluminum alloy show obvious plastic anisotropy. The fatigue strength of the parallel rolling and vertical rolling 5A06 aluminum alloy measured by the traditional test method is 113MPa and 61MPa., respectively, and the fatigue strength of the parallel rolled and vertical rolled 5A06 aluminum alloy measured by the infrared thermal image method is 114., respectively. 6MPa and 64MPa, the relative error of the traditional test method is 1.4% and the 4.9%. infrared thermal image method is in good agreement with the fatigue strength predicted by the traditional test method.
When the load of 5A06 aluminum alloy is higher than the fatigue strength, the parallel rolling and vertical rolling have the same temperature evolution trend. That is, the temperature change on the surface of the specimen is divided into four stages: the initial temperature rise stage, the slow decline stage of the temperature, the stage of rapid temperature rise, the final stage of temperature decline. During the test, the fracture temperature of vertical rolling is higher than that of parallel rolling. It is found that when the vertical rolling specimen is broken, it releases more energy. At the same time, it can be found that the fatigue life of parallel rolling is obviously higher than that of the vertical rolling fatigue life under the same stress, which is due to the prevention of fatigue crack in the parallel rolled specimen. The ability to grow is stronger.
When the same load is applied to the standard tensile compact (CT) specimen with parallel rolling and vertical rolling, the propagation rate of crack along the parallel rolling direction is obviously greater than that in the vertical rolling direction. In the process of fatigue crack propagation, the temperature evolution of the surface of parallel rolling and vertical rolling to the surface of CT is observed by infrared thermograph, and the aluminum alloy is found in the process of fatigue crack propagation. The fatigue crack propagation process is divided into three stages: the initial slow temperature rise stage, the rapid temperature rise stage of the specimen fracture and the natural cooling stage after the specimen fracture. Under the same stress, the fracture temperature appreciation of the vertical rolled specimen is higher than that of the parallel rolling.
The electron back scattering diffraction (EBSD) method is used to get the polar and reverse pole maps along the direction of rolling and vertical rolling. The highest orientation density of the parallel and vertical rolling direction is 7.79 and 8.14., respectively, indicating that the preferred orientation exists in the grain of 5A06 aluminum alloy, that is, the strong texture exists. The rolled grain is easier to rotate, and its plastic deformation ability is stronger than that of parallel rolling. There is a opposite relationship between the strength and the plasticity, which is in good agreement with the previous tensile and fatigue test results.
The peak index and average value index of Schmidt (Schmid) factor are lower in parallel rolling direction than in vertical rolling direction. That is, the plastic properties of vertical rolling are better than parallel rolling, and the corresponding mechanical properties are better than the vertical rolling direction. This is in good agreement with the results of tensile test and fatigue test.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.21
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