复合材料单向板偏轴拉伸试验方法的研究

Investigation of the Off-axis Tension Specimen of Fibre Reinforced Composites

通过复合材料单向板的偏轴拉伸试验可以获得材料在拉伸和剪切应力作用下的力学响应,对于研究复合材料的损伤和失效行为有重要意义。研究了聚醚醚酮(PEEK)/碳纤维(CF)单向板偏轴拉伸试件以及加强片的形式。结合理论分析,提出了一种带斜角的加强片形式,并确定了不同偏轴角度下理想的加强片倾斜角度。结合有限元建模分析,对比了不同加强片形式对偏轴拉伸试件的应力场和变形场分布的影响。结果显示,使用方形加强片的试件在偏轴拉伸过程中由于偏轴应力影响,出现应力集中并导致弯曲变形。使用斜形加强片可有效消除试件中的弯矩和应力集中现象。为避免斜形加强片尖端在加载过程中发生脱黏,进一步提出了对斜形加强片尖端进行倒圆角的优化方法,并通过有限元建模分析了优化后加强片附近的应力场分布,与使用未倒角加强片的试件对比发现,对于偏轴角度小于30°的试件,所获得的各方向最大应力相差不大,可采用斜形加强片并倒圆角,以获得更准确的试验数据。该设计有效改善了加强片尖端处的应力集中问题。

The off-axis tension test was critical in understanding the tension/shear coupled damage and failure mechanical behaviour of fibre reinforced composite materials.The off-axis tension specimen and end-tab designs of polyetheretherketone(PEEK)/carbon fiber(CF)unidirectional composite were investigated.A new oblique end-tab for off-axis tension test was developed based on theoretical analysis.The corresponding end-tab oblique angles of PEEK/CF thermoplastic composite off-axis tension specimens with different off-axis angles were calculated.The designs of the off-axis tension specimen and end-tab were investigated using finite element method.The influences of different end-tab geometries on the stress and deformation fields of specimens were evaluated.Results show that bending stresses are generated by the off-axis loading and lead to stress concentrations within the specimens.The oblique end-tab can eliminate the bending movement and even the stress distribution within off-axis specimen.To avoid debonding at the tip of the oblique end-tab during test,an optimization of the oblique end-tab was carried out by chamfering the tip area.The effect of the optimization on the stress distribution was simulated by using finite element analysis.Results show that compared to unchamfered end-tabs,the maximum stresses in different directions are similar for tension specimen with off-axis angles smaller than 30°.It is suggested to use chamfered oblique end-tabs in off-axis tension tests to obtain accurate experimental results.The optimization design eliminates the stress concentration at the tip area of the oblique end-tab.