摩擦材料在无围压和加围压条件下的形变比较

研究铜基粉末冶金摩擦材料在无围压和加围压条件下的动态力学特性及其形变特征。试验在Hopkinson压杆上完成,通过试验发现,材料在无围压、应变率低于1000-1s时,有应变率强化效应;在更高应变率下,材料有损伤软化效应。微观分析可以看到试件上大量的平行滑移裂纹导致了材料破坏,形变是滑移伴随少量的孪晶;裂缝中有大量的碳纤维组织,这些纤维状组织对裂纹的扩展起抑制作用。而材料在加围压下的性能得到了很大的改善,同一应变率下最大应力、屈服极限和动态杨氏模量均有提高。在高应变率时,无论是加围压还是无围压,破碎的硬质颗粒都是长条状的。由此得出推论,球状、细化的硬质颗粒,可提高基体的强度。

Deformation comparison between confined pressure and non-confined pressure for friction material

The dynamic behavior and deformation properties of Cu-matrix powder metallurgy friction material under impact loading with confined pressure and non-confined pressure is investigated. Quasi-static tests were performed before the dynamic tests in order to make a comparison. The elastic modulus and elastic and plastic Poisson's ratios were measured. Impact tests were conducted on Hopkinson pressure bar, strain rate hardening effect was observed at strain rates under 1000 s~(-1), whereas weakening effect was seen at higher strain rates, It was shown from microscopic analysis that there were a large number of paralleling sliding cracks on the surface that induced material failure. A large amount of carbon fiber tissue was found in cracks, which could resist the development of cracks. The plastic deformation was dominated by sliding accompanying a small amount of twinning. The confined pressure improved the material properties, value of the maximum stress, yield stress and dynamic young's modulus all were increased at the same strain rate, Whatever confined pressure or non-confined pressure, only stripe like hard particles were broken. The experimental result indicates that the fine spheroid shape hard particles embedded in the matrix are responsible for the improved strenth of the material.