力约束管材自由胀形试验研究与材料性能测试

相较于单向拉伸试验,通过管材胀形试验(TBT,Tube Bulging Test)获得的材料性能参数能够更准确地反映材料在高压流体作用下的塑性成形性能,不同的管端边界将会严重影响管材胀形试验的测试结果.针对国际上现有试验方法和设备存在的不足,研制出了一套约束边界清晰、加载精确的管材自由胀形试验系统.在管材测试过程中,基于位移随动力主动加载的控制策略和比例伺服油缸,实现实时的轴向力、轴向位移和内压力的精确加载.端部约束的测试管材通过特殊设计的工装保证了其轴向自由滑动.实时内压力和胀形管材顶点处材料的壁厚和胀形高度信息通过超高压压力传感器、超声测厚仪和磁致伸缩位移传感器采集,进而基于Swift材料本构模型和采集到的数据拟合出材料应力应变曲线和材料性能参数.试验结果表明,管材两端侧推力与内压力对管材内腔端面的作用力和管材轴向自由对称收缩的平衡条件始终处于动态稳定中,试验设备能够准确获得实时胀形高度、顶点厚度、轴向收缩长度和内压力的信息,能够为材料性能测试和工艺设计提供可信的材料参数.

Tube free bulging experiment with force-end and material properties testing

Compared with uniaxial tension, the material property parameters obtained by tube bulging test (TBT) can accurately reflect the plastic forming properties of materials under high-pressure fluid condition. Different end-conditions will seriously affect the experiment results of TBT. According to the defects of existed experimental method and equipment internationally, a special TBT system, with accurate boundary conditions and loading units, was successfully designed and developed. The axial force, axial displacement, and the internal pressure are the key points of the system which could be accurately controlled in real-time bycontrol strategy of displacement under dynamic active loading state and proportional servo valves. The free sliding of fixed tube ends was implemented by a special designed fixture. During the experimental process, the real-time thickness and bulging height in the pole, and the real-time internal pressure were monitored by the ultrasonic thickness gauge, the magnetostrictive displacement sensor and the ultra-high pressure sensor. The stress-strain curve and material properties were derived by the Swift material constitutive model and the monitor data. The experimental data demonstrate that the two load balance conditions, which are the balance of two axial forces with internal pressure and the balance of two axial contractive displacements, are always satisfied during all the test process. The test data processing results show that the monitor data have good repeatability and can be used to get the material properties.