The Aerospace industries of the 21st century demand the use of cutting edge materials and manufacturing technology. New manufacturing methods such as hydroforming are relatively new and are being used to produce commercial vehicles. This process allows for part consolidation and reducing the number of parts in an assembly compared to conventional methods such as stamping, press forming and welding of multiple components. Hydroforming in particular, provides an endless opportunity to achieve multiple crosssectional shapes in a single tube. A single tube can be pre-bent and subsequently hydroformed to create an entire component assembly instead of welding many smaller sheet metal sections together. The knowledge of tube hydroforming for aerospace materials is not well developed yet, thus new methods are required to predict and study the formability, and the critical forming limits for aerospace materials.ududIn order to have a better understanding of the formability and the mechanical properties of aerospace materials, a novel online measurement approach based on free expansion test is developed using a 3D automated deformation measurement system (Aramis®) to extract the coordinates of the bulge profile during the test. These coordinates are used to calculate the circumferential and longitudinal curvatures, which are utilized to determine the effective stresses and effective strains at different stages of the tube hydroforming process.ududIn the second step, two different methods, a weighted average method and a new hardening function are utilized to define accurately the true stress-strain curve for post-necking regime of different aerospace alloys, such as inconel 718 (IN 718), stainless steel 321 (SS 321) and titanium (Ti6Al4V). The flow curves are employed in the simulation of the dome height test, which is utilized for generating the forming limit diagrams (FLDs).ududThen, the effect of stress triaxiality, the stress concentration factor and the effective plastic strain on the nucleation, growth and coalescence of voids are investigated through a new user material for burst prediction during tube hydroforming. A numerical procedure for both plasticity and fracture is developed and implemented into 3D explicit commercial finite element software (LS-DYNA) through a new user material subroutine. The FLDs and predicted bursting pressure results are compared to the experimental data to validate the models.ududFinally, the new user material model is used to predict the bursting point of some real tube hydroforming parts such as round to square and round to V parts. Then, the predicted bursting pressure results are compared to the experimental data to validate the models in real and multistep tube hydroforming processes.
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机译：21世纪的航空航天业要求使用最先进的材料和制造技术。诸如液压成形的新制造方法是相对较新的，并且被用于生产商用车辆。与传统方法（例如冲压，冲压成型和焊接多个组件）相比，此过程可实现零件固结并减少装配中零件的数量。特别地，液压成形为在单个管中获得多个横截面形状提供了无限的机会。可以预弯单个管，然后液压成形以形成整个组件，而不是将许多较小的钣金件焊接在一起。航空材料的管液压成形的知识尚未得到很好的发展，因此需要新的方法来预测和研究可成形性以及航空材料的关键成形极限。航空航天材料的机械性能，使用3D自动变形测量系统（Aramis®）开发了基于自由膨胀测试的新颖在线测量方法，以提取测试过程中凸起轮廓的坐标。这些坐标用于计算周向曲率和纵向曲率，这些曲率用于确定管液压成形过程不同阶段的有效应力和有效应变。 ud ud第二步，两种不同的方法，加权平均法和利用新的硬化功能，可以准确定义不同航空航天合金（如因科镍合金718（IN 718），不锈钢321（SS 321）和钛（Ti6Al4V））的缩颈后状态的真实应力-应变曲线。流动曲线用于圆顶高度测试的模拟中，用于生成成形极限图（FLD）。 ud ud然后，应力三轴性，应力集中系数和有效塑性应变对形核的影响，通过新的用户材料研究了空洞的生长和合并，以预测管材液压成形期间的爆裂。通过新的用户材料子例程，开发了可塑性和断裂的数值程序，并将其实施到3D显式商业有限元软件（LS-DYNA）中。将FLD和预测的爆破压力结果与实验数据进行比较，以验证模型。 ud ud最后，使用新的用户材料模型来预测某些实际管液压成型零件的爆破点，例如，圆角到方形和圆角到V部分。然后，将预测的爆破压力结果与实验数据进行比较，以验证实际和多步管液压成型过程中的模型。
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