氧等离子体改性超高分子量聚乙烯纤维复合材料层间损伤声发射特征分析

Analysis of interlayer damage acoustic emission characteristics of oxygen plasma modified ultra-high molecular weight polyethylene fiber composite materials

为研究氧等离子体改性超高分子量聚乙烯(UHMWPE)/乙烯基酯复合材料层间断裂韧性的损伤模式对其界面性能的影响,首先对不同密度UHMWPE织物进行氧等离子体改性,使用真空辅助树脂灌注成型工艺制备UHMWPE/乙烯基酯复合材料,结合声发射(AE)检测技术对复合材料的Ⅰ型层间断裂韧性(G_(ⅠC))和Ⅱ型层间断裂韧性(G_(ⅡC))进行测试,并对其损伤动态演变过程进行表征和定位。结果表明:界面性能是复合材料层间断裂韧性的主导因素,在G_(ⅠC)和G_(ⅡC)测试过程中,通过在UHMWPE/乙烯基酯复合材料层间预裂纹处产生应力集中,损伤机制表现为张开型和滑移型;低经密UHMWPE织物结构松散,具有良好的改性均匀度,经氧等离子体改性后其制备的复合材料的G_(ⅠC)和G_(ⅡC)分别提高约36.8%~80%、75%~1120%,达到层间增韧效果,同时由于界面结合性能提高,不同损伤模式减少或消除;通过对声发射信号进行聚类分析可有效识别出复合材料基体开裂、纤维/基体脱黏和纤维断裂3种损伤模式及其特征频率范围。

Objective As a lightweight fiber-reinforced composite material with high strength and modulus,ultra-high molecular weight polyethylene(UHMWPE)plays an important role in modern aviation,aerospace,marine defense equipment,and other fields.Because its smooth surface is chemically inert and does not contain polar groups,the poor binding with the resin matrix would affect its interface performance.The chemical composition reconstruction on the surface of UHMWPE fiber was carried out by oxygen plasma modification,which effectively provided more polar sites for the interface layer to improve the interface binding performance between UHMWPE fiber and resin matrix.Method In order to investigate the influence of damage mode on interlayer fracture toughness of oxygen plasma modified UHMWPE/vinyl ester composites.UHMWPE plain fabrics with a weft density of 200 picks/(10 cm)and warp density of 160,200 and 240 picks/(10 cm)were woven and modified by oxygen plasma.UHMWPE/vinyl ester composites were prepared by vacuum-assisted resin infusion molding(VARI).Mode I(G_(ⅠC))and modeⅡ(G_(ⅡC))interlayer fracture toughness tests were carried out.The damage patterns were analyzed by the acoustic emission(AE)technique.Results After oxygen plasma modification of UHMWPE fabrics,the water contact angle of the fiber surface was found to be reduced(Fig.2),improving surface energy.For G_(ⅠC),the maximum loads of G_(ⅠC)of samples U03 and P03 were 19.49 and 27.05 N,respectively.It was found that the plasma modified G_(ⅠC)of sample P03 by 36.8%,and the modeⅠinterlayer fracture angles of samples P01 and P03 were 26°and 10°,respectively(Fig.3).P01 displayed the greatest change in interlayer fracture angle.The G_(ⅠC)of UHMWPE/vinyl ester composites was mainly related to the interfacial bonding properties,the woven fabrics structure,the state of the pre-crack tip,and the brittleness of the matrix.During the G_(ⅠC)test,AE cumulative energy of UHMWPE/vinyl ester composites increased as the warp density of UHMWPE fabric increased(Fig.4).Because of the influence of the compact structure of UHMWPE fabric on the uniformity of modification,the interface bonding appeared to be poor.The three damage modes in the process of the G_(ⅠC)test responded to acoustic emission of three types of signals,respectively,i.e.Class-1 signal indicating matrix cracking,Class-2 signal fiber/matrix debonding,and Class-3 signal fiber fracture(Fig.5).After oxygen plasma modification,the intensity of the Class-2 signal was reduced,suggesting improvement in the fiber/matrix bonding.For G_(ⅡC),the maximum loads of G_(ⅡC)of samples U03 and P01 were 106.99 and 244.58 N.The plasma modification improved G_(ⅡC)of sample U01 by 1120%,and the minimum crack propagation length of sample P03 became 0.8 mm.The maximum bending fracture angle was 145°(Fig.7).Sample P01 showed good G_(ⅡC)after oxygen plasma modification,and sample P03 demonstrated the smallest crack propagation length and flexural fracture angle.The G_(ⅡC)of UHMWPE/vinyl ester composites was mainly related to the interfacial bonding properties,stiffness,the state of the initial crack tip,and the brittleness of the matrix.During the G_(ⅡC)test,UHMWPE/vinyl ester composites modified by oxygen plasma delayed the start time of AE as cumulative energy,and different damage modes were reduced or eliminated(Fig.8).The three AE signals generated by the damage modes during the G_(ⅡC)test were the same as those in the G_(ⅠC)test(Fig.9).After oxygen plasma modification,the signal intensity of Class-3 in the sample was reduced,and the fiber fracture was reduced.Conclusion UHMWPE/vinyl ester composites are prepared by oxygen plasma modification of UHMWPE fabrics with different warp densities,and G_(ⅠC)and G_(ⅡC)were evaluated.The oxygen plasma modified UHMWPE/vinyl ester composites can effectively strengthen the G_(ⅠC)and G_(ⅡC),improve the interface bonding strength and prevent crack propagation.For the loose structure of UHMWPE fabric with low warp density,the uniformity of oxygen plasma modification is the best,which has the effect of interlayer toughening.Three damage modes of UHMWPE/vinyl ester composites in G_(ⅠC)and G_(ⅡC)tests are detected by acoustic emission testing,which are matrix cracking,fiber/matrix debonding,and fiber fracture.The overlapped signals of the three damage modes in the amplitude distribution interval indicate that the damage does not appear alone,and the appearance of new damage is usually accompanied by the expansion of the previous damage,leading to the simultaneous appearance of different damage modes.Oxygen plasma modification can effectively weaken or eliminate interlayer damage and inhibit interlayer crack propagation.