利用管狀試樣測試各向異性材料雙向應(yīng)力狀態(tài)力學(xué)性能的新方法

利用管狀試樣測試各向異性材料雙向應(yīng)力狀態(tài)力學(xué)性能的新方法Analytical model and testing method for hardening behavior of anisotropic materials under bi-axial loading

為解決目前各向異性材料雙向加載性能測試?yán)碚撃Ｐ痛嬖诘臏y試物理量過多且實測困難的問題，提出了一種采用管狀試樣脹形直接測試雙向加載力學(xué)性能的新方法-一點法。利用圓幾何輪廓線為顯性函數(shù)表達(dá)式的特征，推導(dǎo)了脹形過程中最高點軸向曲率半徑和壁厚理論模型。僅需在脹形過程中測量最高點徑向位移，即可獲得材料雙向加載下的力學(xué)性能，為建立一個簡單可靠且能在線實時測量的材料力學(xué)性能測試方法奠定了基礎(chǔ)。并利用所建立的測試方法進(jìn)行了AA6061鋁合金擠壓管坯的脹形實驗。結(jié)果表明：管坯自由脹形時，其最高點實時壁厚和曲率半徑均可表示為最高點脹形高度的顯示函數(shù)。輪廓形狀理論模型的預(yù)測精度隨脹形率的增大先提高后降低，膨脹率約為13%時預(yù)測精度最高，當(dāng)脹形率超過20%后，預(yù)測精度開始下降，但最大誤差不超過±0.9%。最高點實時壁厚理論模型的預(yù)測精度基本不受試件幾何尺寸的影響，長徑比和徑厚比改變時，差異很小，預(yù)測誤差均不超過2%，這對保證雙向加載條件下的力學(xué)性能測試精度是非常有益的。一點法可同時測得環(huán)向和軸向的應(yīng)力應(yīng)變分量，這為進(jìn)一步分析各向異性對復(fù)雜應(yīng)力狀態(tài)下材料的流動及后繼屈服奠定了基礎(chǔ)。

In order to solve the problems that there are excessive physical quantities in the theoretical model of tube bulging test for testing the mechanical properties of tubes under biaxial stress state, and they are difficult to obtain during the experiment. A method for directly testing the mechanical properties of tubes under biaxial stress state was proposed in this paper, which will be referred to as "one point method". Because of circular model is characterized by a dominant function expression, theoretical models of both the pole axial curvature radius and the pole thickness during bulging test are derived under supposing the geometrical models for bulging zone as circular. Thus, the mechanical properties of tubes under biaxial stress state can be obtained only through measuring the bulging height at the pole point during the bulging test, which laid the foundation for the establishment of a simple and reliable method for testing the mechanical properties of the tube online. Based on the above proposed method, the extruded aluminum alloy tubes AA6061 were tested. The results showed that: both the pole axial curvature radius and the pole thickness during bulging test can be expressed as display functions pertaining to the bulging height at the pole point. For the theoretical model of the pole axial curvature radius, as the bulging rate increases, the prediction accuracy increases at beginning, and decreases at the end when using circular as the theoretical geometrical models for bulging zone. The prediction accuracy is the highest as the bulging rate is about 13%, the prediction accuracy decreases after the bulging rate is more than 20%. Fortunately, the overall prediction error is small. The maximum error does not exceed ± 0.9%. The prediction accuracy of the pole thickness using the theoretical model is almost unaffected by the specimen geometry. When the ratios of length to diameter and diameter to thickness change, the difference is very small, the prediction error is not more than 2%. This is very helpful to ensure the accuracy of mechanical testing under biaxial loading conditions. Using the "one point method", the stress and strain components along the circumferential and axial directions can be simultaneously measured, this laid the foundation for further analysis of the anisotropic property impacting on the flow and subsequent yield under complex stress state.

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