静水压力对触变挤压Csf/AZ91D复合材料变形及纤维取向的影响

Effect of hydrostatic pressure on fiber orientation and deformation for Csf/AZ91D composite in thixo-extrusion

摘要:

在触变挤压过程中，通过施加静水压力（即背压）可以有效地控制纤维取向，从而改善短纤维增强复合材料的机械性能。本文试验研究了有、无背压情况下Csf/AZ91D复合材料触变挤压过程中变形场及纤维取向变化规律。基于流函数法获得了Csf/AZ91D复合材料触变挤压过程中的等效应变速率，结合图像处理技术，对挤压后纤维取向角度度进行了统计分析，探讨了背压对塑性变形区尺寸，塑性变形区内应变速率的分布以及纤维取向角度的影响。结果表明，不施加背压情况下，从坯料外壁到心部存在明显的等效应变速率梯度，在相同位置，纤维取向角度与等效应变速率几乎成正比关系，而施加背压提高了坯料充填模具外侧拐角的能力，使得坯料横截面上等效应变速率梯度变小，分布更加均匀，纤维取向角度也更加一致。研究结果对于调控Csf/AZ91D复合材料的塑性变形具有重要的指导意义。

Abstract:

In the thixo-extrusion process, the fiber orientation can be effectively controlled by applying the hydrostatic pressure (i.e., backpressure), and consequently improving mechanical properties of short fiber reinforced composites. In this paper, the variation regularities of the deformation field and fiber orientation during the thixo-extrusion process of Csf/AZ91D composites with and without backpressure were investigated experimentally. The equivalent strain rates along the flow line were obtained based on the flow function method. By employing the image processing technology, the angle of fiber orientation after extrusion was statistically analyzed. The results show that there was an obvious equivalent strain rate gradient from the outer wall to the core of the composite without applying backpressure. At the same position, the fiber orientation angle was almost proportional to the equivalent strain rate. Furthermore, the applied backpressure enhanced the ability of the composite to fill the outer corners of the mold, resulting in a smaller equivalent strain rate gradient across the cross-section. Comparing with the thixo-extrusion without backpressure, the equivalent strain rate distribution is more uniform and fiber orientation angle is more consistent by the application of backpressure. The research results have important guiding significance for regulating the plastic deformation of Csf/AZ91D composites.