K-cor夹层结构湿热环境力学性能及其影响研究

发布时间：2019-03-07 14:04

【摘要】：K-cor结构是应用Z-pin技术增强的一种新型高性能夹层结构,更好的满足了航空航天轻质高强的需求。目前国内外对K-cor结构在工程应用过程中湿热环境影响研究报道较少。本文针对K-cor结构在湿热、低速冲击以及湿热下低速冲击的力学性能变化,研究Z-pin的增强机制、结构的损伤机理以及失效模式,以便设计综合性能优异的K-cor夹层结构。研究了Z-pin植入与面板铺层角度对K-cor结构吸湿性的影响,结果表明:Z-pin的植入并不会影响K-cor结构的吸湿性,反而会提高结构的界面结合强度,增加尺寸稳定性;在水汽浓度较大的情况下,面板铺层角度变化越小,结构的吸湿增重率越低。采用三点弯曲和压缩性能试验来研究湿热后K-cor结构芯材力学性能的变化,结果表明:Z-pin植入密度的增加能明显提高湿热前后试样三点弯曲强度和压缩强度,且具有较高的强度保持率,Z-pin密度为12mm×12mm的K-cor夹层结构湿热处理试样的三点弯曲强度比未湿热处理空白试样的要高11.1%,8mm×8mm K-cor湿热处理试样的芯部压缩强度比未湿热处理空白夹层结构试样要高17.5%,体现出K-cor夹层结构优异的抗湿热性能;Z-pin植入角度的减小能明显提高试样湿热处理前后的压缩强度,0°植入的K-cor试样湿热处理后芯部的压缩强度基本上与40°植入的K-cor试样未湿热处理基本相同,但植入角度对三点弯曲强度影响较小。利用落锤冲击开展K-cor夹层结构的低速冲击试验,并结合红外无损检测和剩余压缩强度(CAI)试验,研究K-cor结构的抗冲击性能。结果表明:K-cor夹层结构的芯材越厚,则其冲击损伤面积越大,但剩余强度保持率越高;Z-pin折弯长度在不超过植入间距的前提下增长,能显著的降低K-cor结构冲击后的损伤面积,提高剩余压缩强度;在相同芯材密度的情况下,提高Z-pin的折弯长度比增大植入密度更有利于减少K-cor试样冲击后的损伤面积,提高试样的剩余压缩强度和其强度保持率。另外冲头参数为10mm/1.28Kg的落锤比冲头参数为12.5mm/2Kg的落锤对K-cor结构造成的冲击损伤更为严重。综合考虑湿热环境以及低速冲击对K-cor结构性能的影响,设计湿热处理后K-cor结构的落锤冲击,并进行测量损伤面积、损伤深度以及CAI的试验,研究结果表明:Z-pin植入密度的增加有效降低了湿热环境对K-cor夹层结构的冲击损伤面积和损伤深度的负面影响,缓解了试样在侧压模式下失效机制的改变所引起的剩余强度大幅度下降,使K-cor结构抗冲击性能更稳定。
[Abstract]:K-cor structure is a new type of high performance sandwich structure strengthened by Z-pin technology, which better satisfies the requirements of aerospace lightweight and high strength. At present, there are few reports at home and abroad on the influence of wet-heat environment of K-cor structure in engineering application. In this paper, the mechanical properties of K-cor structure under wet-heat, low-speed impact and low-speed impact are studied, and the strengthening mechanism, damage mechanism and failure mode of Z-pin structure are studied. In order to design K-cor sandwich structure with excellent comprehensive performance. The effect of Z-pin implantation and overlay angle on the hygroscopicity of K-cor structure was studied. The results showed that Z-pin implantation did not affect the hygroscopicity of K-cor structure, but increased the interfacial bonding strength and dimensional stability of the structure. In the case of large water vapor concentration, the smaller the change of the laminate angle is, the lower the moisture absorption and weight gain rate of the structure is. Three-point bending and compression tests were used to study the changes of mechanical properties of K-cor core after hot and humid conditions. The results showed that the increase of Z-pin implant density could significantly increase the three-point bending strength and compressive strength of samples before and after wet-heat treatment. The three-point bending strength of the K-cor sandwich structure with Z-pin density of 12mm 脳 12mm is 11.1% higher than that of the blank sample without wet heat treatment. The compressive strength of 8mm 脳 8mm K-cor wet-heat treated specimen is 17.5% higher than that of non-wet-heat treated blank sandwich structure, which shows the excellent hygrothermal resistance of K-cor sandwich structure. The reduction of Z-pin implantation angle can obviously improve the compressive strength of the samples before and after wet-heat treatment. The compressive strength of the core of the K-cor samples implanted in 0 掳after wet-heat treatment is basically the same as that of the K-cor samples implanted in 40 掳without wet-heat treatment. However, the implantation angle has little effect on the three-point bending strength. The low-speed impact test of K-cor sandwich structure was carried out by means of drop hammer impact, and the impact resistance of K-cor structure was studied by means of infrared nondestructive test and residual compressive strength (CAI) test. The results show that the thicker the core of K-cor sandwich structure is, the larger the impact damage area is, but the higher the retention rate of residual strength is. With the increase of bending length of Z-pin, the damage area of K-cor structure after impact can be significantly reduced and the residual compressive strength can be improved by increasing the bending length without exceeding the distance between implants. Under the condition of the same core density, increasing the bending length of Z-pin is more beneficial to reduce the damage area of K-cor specimen after impact than to increase the implant density, and improve the residual compressive strength and the strength retention rate of the sample. In addition, the impact damage of the K-cor structure caused by the drop hammer with the punch parameter of 10mm/1.28Kg is more serious than that of the drop hammer with the punch parameter of 12.5mm/2Kg. Considering the influence of wet-heat environment and low-speed impact on the performance of K-cor structure, the falling hammer impact of K-cor structure after wet-heat treatment is designed, and the damage area, damage depth and CAI are measured. The results show that the increase of Z-pin implant density effectively reduces the negative effect of wet-heat environment on the impact damage area and damage depth of K-cor sandwich structures. The residual strength caused by the change of failure mechanism under lateral pressure mode is alleviated and the impact resistance of K-cor structure is more stable.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB383.4

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