【作者】 王鑫；

【导师】 尹维龙；

【作者基本信息】 哈尔滨工业大学 ， 工程力学， 2020， 硕士

【摘要】 在现代战争中雷达隐身已经成为航空飞行器的重要指标。而在飞行器中蜂窝夹芯结构是作为减轻飞机重量的重要结构材料,同时蜂窝夹芯结构具有非常强的可设计性。为了使作为蒙皮材料的蜂窝夹芯结构具有电磁波吸收功能,需要对蜂窝夹芯结构进行结构隐身一体化设计,兼顾力学和吸波双重设计指标。上面板应具有电磁波透射/承载功能,下面板具有电磁波反射/承载功能,蜂窝芯子通过挂壁或填充功能材料使其具有电磁波吸收功能。由于这种电磁吸波功能的引入,造成了蜂窝夹芯板几何结构的非对称和材料体系的非对称,进而影响到蜂窝夹芯结构的力学性能。本论文重点研究非对称蜂窝夹芯板的抗冲击性能。由于复合材料在动态加载时,材料强度会随应变率的变化而变化。首先用Cowper Symonds模型拟合了复合材料的强度随应变率变化的规律。然后利用LS-DYNA建立了非对称蜂窝夹芯结构的有限元模型,将拟合的结果引入到有限元模型中。利用建立的有限元模型研究了非对称蜂窝夹芯板在不同低速冲击能量下的失效模式。仿真结果表明,在低能量范围内,主要为上面板基体拉伸失效,蜂窝芯子屈曲,芯子和面板脱粘,芯子变形范围只集中在冲击区域内。功能填充材料的引入会抑制面板的损伤,分层损伤减小了4.1%。同时功能材料密度较低,质量并没有明显的增加,保留了蜂窝夹芯结构轻质、高强的特点。研究了芯子高度、几何结构不对称和材料体系不对称对非对称蜂窝夹芯板抗冲击性能的影响。发现芯子高度在5-15mm范围内对接触力的响应影响较小,相比之下芯子为10mm时的非对称蜂窝夹芯板损伤面积较小。与冲头直接接触的上面板对接触力的响应影响较大,在相同质量下,上下面板厚度比从0.5到2变化时,基体的损伤面积减小。下面板厚度改变会影响结构的整体刚度,从而对接触力响应产生影响,但相比上面板影响效果较小。上面板的材料体系是影响冲击响应的重要因素,当面板厚度不变时,改变材料体系对抗冲击性能的影响较大。上面板为玻纤/环氧的抗冲击性能较好。开展了蜂窝夹芯板的低速落锤试验和冲击后剩余强度试验研究。利用落锤试验验证了有限元仿真模型的准确性。在相同质量下,非对称蜂窝夹芯板的压缩强度低于对称蜂窝夹芯板的压缩强度,约为对称蜂窝夹芯板强度的三分之二。在3.5J的能量冲击下,非对称蜂窝夹芯板的剩余强度降低了17.6%,而对称蜂窝夹芯板的剩余强度降低了39.5%。由此可见,非对称蜂窝夹芯板的抗冲击性能要优于对称蜂窝夹芯板。探究了非对称蜂窝夹芯板在高速侵彻情况下的响应。结果表明:非对称蜂窝夹芯板的弹道极限比对称蜂窝夹芯板降低了10.5%,非对称蜂窝夹芯板10%的能量由蜂窝芯子吸收,50%能量被碳纤/环氧吸收,40%能量被玻纤/环氧吸收。在相同质量下,非对称蜂窝夹芯板的抗侵彻能力相比于对称蜂窝夹芯板略有下降。研究了非对称蜂窝夹芯板的鸟撞问题。在115m/s的速度下,非对称蜂窝夹芯板会被击穿。上面板的损伤小,维持原有形貌的能力高于下面板,上面板抗冲击性能好;下面板的能量吸收多,对内部结构的保护能力大于上面板。更多还原

【Abstract】 In modern military applications,radar stealth has become an important demand for next generation aircrafts.The honeycomb sandwich structure is an effective strategy to meet the light-weight requirement of aircraft.In order to endow the honeycomb sandwich structure with both high mechanical strength and electromagnetic wave absorption(EMA)function,it is necessary to carry out the integrated design of mechanics and radar stealth properties.Thus,the top facesheet of honeycomb sandwich structure requires both electromagnetic wave transmission and mechanical bearing capability,the bottom facesheet needs to be reflective for electromagnetic wave and mechanically loadable.While featuring the honeycomb core with strong EMA ability through coating or filling with additional EMA materials.These additional electromagnetic wave absorption design results in asymmetry in both geometry and material system,which notably affects the mechanical properties of the honeycomb sandwich structure.This paper focuses on the impact resistance design of asymmetric honeycomb sandwich structure.Under dynamic loading,the failure strength of composite material varies with the strain rate.Firstly,the failure strength and strain rate of the composite were fitted by Cowper Symonds model.Then the finite element model of asymmetric honeycomb sandwich structure was established by LS-DYNA.The failure mechanism of asymmetric honeycomb sandwich structure under different impact energy is studied.The simulation results show that in the energy range of 1.5-3.5J,the main factors are the epoxy matrix tensile failure of top facesheet,honeycomb buckling as well as the debonding of them.The deformation of honeycomb core only occurs at the impact area.The introduction of functional filling material can inhibit panel failure.Delamination damage is reduced by 4.1 %.What’s more,considering the low density of EMA functional materials,the light-weight and high-strength feature of the honeycomb sandwich structure is well maintained.The effects of honeycomb core height,geometric and material asymmetry on the impact resistance of asymmetric honeycomb sandwich structure were studied.It is found that the core height within the range of 5-15 mm has little influence on theresponse to contact force and the asymmetric honeycomb sandwich structure with a core of 10 mm shows small damage area and good impact resistance.The top facesheet plays the dominate role in influencing the response of contact force.Without changing the integral density,increasing top to bottom facesheet thickness ratio leads to smaller damage area of the matrix.When the same thickness is given to top and bottom facesheet,an optimized smallest total damage is obtained.Moreover,under the condition of constant top facesheet thickness,changing the thickness of bottom facesheet has little influence on the response of contact force.Impact response was mainly determined by the material system of top facesheet.With fixed thickness,different top facesheet material result in dramatically different impact resistance performance.The glass fiber/epoxy top facesheet shows better impact resistance.The low-speed drop hammer test and compression-after-impact test were carried out.The accuracy of the finite element simulation model was verified by the drop weight test.With the same nominal density,the compression strength of asymmetric honeycomb sandwich structure is obviously lower than that of symmetric honeycomb sandwich structure,which is about two-thirds of the strength of the symmetric ones.After a 3.5J impact,the residual strength of asymmetric honeycomb sandwich structure decreased by 17.6%,while that of symmetric honeycomb sandwich structure decreased by 39.5%,indicating that the impact resistance performance of asymmetric honeycomb sandwich structure is better than that of symmetric honeycomb sandwich structures.The response of asymmetric honeycomb sandwich structure under high-speed penetration was studied.The results show that the ballistic limit of asymmetric honeycomb sandwich structure is 10.5% lower than that of symmetric honeycomb sandwich structure.10% of the energy of the asymmetric honeycomb sandwich structure is absorbed by the honeycomb core,50% of the energy is absorbed by carbon fiber/epoxy,and 40% of the energy is absorbed by glass fiber/epoxy.Under the same density,the penetration resistance of asymmetric honeycomb sandwich structure is slightly lower than that of symmetric honeycomb sandwich structure.The bird strike problem of asymmetric honeycomb sandwich structure is studied.At a speed of 115m/s the asymmetric honeycomb sandwich structure will be broken through.The damage of the top facesheet is small,the ability to maintain the original shape is higher than that of the bottom facesheet.And the top facesheet has good impact resistance.The bottomfacesheet has more energy absorption,and the protection ability of the internal structure is greater than that of the top facesheet.更多还原