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为解决各向异性材料双向加载性能测试理论模型存在的测试物理量过多且实测困难的问题,提出了一种采用管状试样胀形直接测试双向加载力学性能的新方法:一点法。利用圆几何轮廓线为显性函数表达式的特征,推导了胀形过程中最高点轴向曲率半径和壁厚理论模型。仅需在胀形过程中测量最高点胀形高度,即可获得材料双向加载下的力学性能,为建立一个简单可靠且能在线实时测量的材料力学性能测试方法奠定了基础。并利用所建立的测试方法进行了AA6061铝合金挤压管坯的胀形实验。结果表明:管坯自由胀形时,其最高点实时壁厚和曲率半径均可表示为最高点胀形高度的显示函数。轮廓形状理论模型的预测精度随膨胀率的增大先提高后降低,膨胀率约为13%时预测精度最高,当膨胀率超过20%后,预测精度开始下降,但最大误差不超过±0.9%。最高点实时壁厚理论模型的预测精度基本不受试件几何尺寸的影响,长径比和径厚比改变时,差异很小,预测误差均不超过0.8%,这对保证双向加载条件下的力学性能测试精度是非常有益的。一点法可同时测得环向和轴向的应力应变分量,这为进一步分析各向异性对复杂应力状态下材料的流动及后继屈服奠定了基础。
In order to solve the problem of too much test physical quantity and difficult measurement in the theoretical model of bi-directional loading performance test of anisotropic materials, a new method of directly testing the bi-directional loading mechanical properties by using tubular specimen bulging is proposed. Using the circular geometric contour as the characteristic of the explicit function expression, the theoretical model of axial radius of curvature and wall thickness of the highest point during bulging is derived. Simply measuring the maximum bulging height during bulging can obtain the mechanical properties of the material under bi-directional loading, which lays the foundation for the establishment of a simple and reliable method for testing the mechanical properties of materials in real-time on-line measurement. The bulging experiment of AA6061 aluminum alloy extruded tube was carried out by using the established test method. The results show that the real-time wall thickness and the radius of curvature of the highest point of free-form tube can be expressed as the display function of the highest point of bulging height. The prediction accuracy of the contour shape theory model first increases and then decreases with the increase of the expansion rate, and the prediction accuracy is the highest when the expansion rate is about 13%. When the expansion rate exceeds 20%, the prediction accuracy begins to decline but the maximum error does not exceed ± 0.9% . The prediction accuracy of the theoretical model of real-time wall thickness at the highest point is basically unaffected by the geometrical dimension of the specimen. When the aspect ratio and diameter-thickness ratio are changed, the difference is small and the prediction error is not more than 0.8% Mechanical test accuracy is very useful. The one-point method can measure both the circumferential and axial stress-strain components at the same time, which lays the foundation for the further analysis of the anisotropy to material flow and subsequent yielding under complex stress conditions.