结构参数对CFRP蒙皮-铝蜂窝夹层板低速冲击性能的影响

针对碳纤维增强树脂复合材料（CFRP）蒙皮-铝蜂窝夹层结构,使用半球头式落锤冲击试验平台进行了低速冲击载荷下蜂窝芯单元尺寸对夹层板冲击性能影响的试验探究,并基于渐进损伤模型、内聚力模型和三维Hashin失效准则,在有限元仿真软件ABAQUS中建立了含蒙皮、蜂窝芯、胶层的CFRP蒙皮-铝蜂窝夹层板精细化低速冲击仿真模型,仿真结果与试验结果吻合较好。利用该数值模型进一步探究了蜂窝芯高度、蒙皮厚度和蜂窝芯壁厚等结构参数对于蜂窝夹层板低速冲击吸能效果的影响。结果表明:增大铝蜂窝芯的单元边长,会减小蜂窝夹层板的刚度,提升夹层板的吸能效果;芯层高度对夹层板的刚度及抗低速冲击性能影响较小;增大蜂窝夹层板的蒙皮厚度,可以提高夹层板的刚度,但会降低夹层板的吸能效果;增大蜂窝芯的壁厚,可以提高夹层板的刚度和抗低速冲击性能。      

考虑表层抗弯刚度影响的夹层板静力学等效分析

基于Hoff型夹层板理论，推导了夹层板广义的应力应变关系式，得到了等效板的弹性常数，从而建立了考虑表层抗弯刚度的夹层板静力学等效模型．通过理论分析和计算，研究了夹层板的参数对这种等效精度的影响，并给出了这种等效分析方法的适用范围．研究表明，利用等效分析方法对Hoff型夹层板进行静力分析可在一定范围内可达到满意的精度．     

Nomex蜂窝夹层结构弯曲刚度温度相关性的力学建模

胶黏剂粘接性能下降导致的面板与蜂窝芯分离是Nomex蜂窝夹层结构在高温下力学性能发生退化的主要原因。为此定义了胶黏剂的等效脱粘系数为温度升高引起蜂窝夹层结构弯曲刚度下降的损伤变量,并引入面板和蜂窝芯弹性模量的温度保持系数,建立了蜂窝夹层结构弯曲刚度温度相关性的力学模型。经外伸梁三点弯曲法试验校验,所建力学模型计算值与试验值的误差在15%内,可以较好地实现蜂窝夹层结构在高温下的弯曲刚度预报。研究成果可以用于软夹心蜂窝夹层结构在高温下弯曲刚度的估算。      

基于夹层板理论的圆形孔蜂窝结构隔声量研究

蜂窝夹层结构广泛应用于航空航天、船舶、高速列车等交通工具领域。基于三明治等效理论建立了圆形蜂窝结构层芯的等效剪切参数,从而得到简支边界条件下的圆形孔蜂窝夹层板的声振耦合振动模型及传声损失,并在仿真中数值验证了理论模型的正确性。同时基于理论计算,分析了圆形孔蜂窝结构中的层芯胞元半径、层芯壁厚和结构材料对隔声量的影响。由分析可知:层芯半径小、壁厚薄的钢材圆形蜂窝结构具有更好的隔声性能。     

整流罩声振试验蜂窝夹层板建模方法

针对整流罩主体结构由蜂窝板结构构成的特点,在使用统计能量分析法进行整流罩结构高频振动噪声环境预示研究时,重点对蜂窝夹层板建模的三明治夹芯板理论、等效板理论和蜂窝板理论三种等效方法进行比较分析。采用蜂窝夹层板的三种不同等效理论对整流罩整尺度结构进行统计能量分析建模,并将预示结果与在混响室内进行的该整流罩声振实验结果进行对比,分析表明三明治夹芯板理论更适用于研究蜂窝板的高频振动特性。     

Kagome蜂窝夹层平板的多功能优化设计

采用“等效介质模型”, 分析了复合材料夹层蜂窝平板的整体换热系数。在此基础上, 针对轻质蜂窝(相对密度小于0. 3) , 选取蜂窝面内等效剪切刚度表征夹层结构的承载能力, 综合考虑散热能力和结构承载能力, 比较了Kagome 蜂窝与传统的正三角形、正方形和正六边形蜂窝的性能。结果显示Kagome 蜂窝不但散热性能很好, 而且通过对蜂窝相对密度和尺寸的优化, 在结构质量相同的情况下, Kagome 蜂窝的综合性能比传统蜂窝具有明显优势。      

蜂窝颗粒夹层结构的等效参数及动态特性研究

为改善颗粒阻尼施加时对结构刚度的影响,探究颗粒在蜂窝夹层结构中的减振特性,对蜂窝颗粒夹层结构进行数值仿真和试验研究,通过振动功率谱测量获得颗粒等效质量和阻尼,利用非线性拟合技术建立颗粒等效单自由度模型,并采用该模型在蜂窝悬臂梁的数值仿真分析与正弦扫频实验中获得了较好的一致性,给引入颗粒的阻尼效应数值化提供了便捷方法。     

四边简支新型类方形蜂窝夹层结构振动特性研究

新型类方形蜂窝是六边形蜂窝的一种过渡形式,对其等效弹性参数和振动特性的研究具有重要意义。采用改进的Gibson公式对比分析了双壁厚与等壁厚类方形蜂窝夹芯的面内等效弹性参数的差异,并应用经典层合板理论分析了不同等效弹性参数下2种壁厚类型的四边简支类方形蜂窝夹层结构的振动特性,基于有限元仿真技术分析了不同壁厚类方形蜂窝夹层结构的振动特性,并与理论分析结果进行对比。结果表明等效弹性参数的数值模拟结果与理论值基本吻合。在蜂窝基本结构参数相同的条件下,双壁厚类方形蜂窝夹芯的面内等效剪切模量、面外刚度和等效密度均比等壁厚类方形蜂窝夹芯大;在低阶振动模态下,双壁厚类方形蜂窝夹层结构的固有频率比等壁厚类方形蜂窝夹层结构的低,在高阶振动模态下,双壁厚类方形蜂窝夹层结构的固有频率比等壁厚类方形蜂窝夹层结构的高;影响夹层结构固有频率的3个主要因素所占权重由大到小依次为蜂窝夹芯yoz面等效剪切模量、蜂窝夹芯等效密度,蜂窝夹芯壁厚。研究结果表明采用经典层结构理论计算得到类方形蜂窝夹层结构的固有频率与数值仿真结果的一致性较好,这进一步证明了采用改进Gibson公式得到的类方形蜂窝夹芯等效弹性参数的正确性,同时证明了将该振动理论运用到一般蜂窝夹层结构研究的可行性,为扩展研究其他类型蜂窝夹层结构振动特性奠定了基础。     

四边固支铝基蜂窝夹层板弯曲自由振动分析

基于经典叠层板理论, 将铝基蜂窝芯层等效为一正交异性层, 等效弹性参数由修正后的Gibson公式得出, 对四边固支薄蜂窝夹层板弯曲振动的固有频率进行了理论推导, 研究了蜂窝夹层板厚度、 芯层板厚度对蜂窝夹层板固有频率的影响。同时利用有限元软件计算了相应参数下的固有频率。计算结果表明, 经典叠层板理论可以较准确的计算四边固支蜂窝夹层板的固有频率。      

基于响应面全局优化技术的蜂窝板材料性能参数修正

蜂窝夹层板结构广泛应用于航空航天行业中,建立准确的蜂窝夹芯板有限元模型是分析和优化航天器微振动的必要前提。基于蜂窝芯的力学等效参数模型,建立了蜂窝板的动力学有限元模型。使用正交数值实验设计筛选出对蜂窝板动力学性能影响最大的蜂窝芯等效材料参数,并利用基于响应面模型自适应采样技术的全局优化方法快速地完成了蜂窝芯关键材料参数的优化修正。修正后的蜂窝板有限元模型前六阶模态频率与实验结果的平均误差小于1%。     

Stress analysis of axially and thermally loaded discontinuous tile core sandwich with and without adhesive filled core gaps

An analytical study is performed to investigate the stress states in an axially and thermally loaded sandwich structure with a discontinuous ceramic tile core. General and simplified models are developed to determine stresses in the constituents of the sandwich structure with and without adhesive in the gaps between adjacent tiles. A general model that allows local bending of the face sheet and a simplified model which assumes uniform through-thickness stress distribution in the face sheets are developed. It is shown that the normal stress in the face sheet decreases when the gap is filled by adhesive, although the tile stress increases. The analytical model shows that normal and shear stresses at the face/core interface can be reduced by filling the gaps between tiles. Filled gaps also elevate the axial stiffness of the structure. Model results are verified by comparison to a previously developed analytical model and finite element analysis.     

Interface crack in sandwich specimen

Fracture of a sandwich specimen loaded with axial forces and bending moments is analyzed in the context of linear elastic fracture mechanics. A closed form expression for the energy release rate for interface cracking of a sandwich specimen with isotropic face sheets is found from analytical evaluation of the J-integral. An approach is applied, whereby the mode mixity for any combination of the loads can be calculated analytically when a load-independent phase angle has been determined. This load-independent phase angle is determined for a broad range of sandwich configurations of practical interest. The load-independent phase angle is determined using a novel finite element based method called the crack surface displacement extrapolation method. The expression for the energy release rate is based on the J-integral and certain stress distributions along the ends of the sandwich specimen. When the stresses from the crack tip interacts with the stresses at the ends, the present analytical calculation of the J-integral becomes inaccurate. The results show that for the analytically J-integral to be accurate the crack tip must be a certain distance away from the uncracked end of the specimen. For a sandwich specimen with face sheet/core stiffness ratio of 100, this distance is in the order 10 times the face sheet thickness. For sandwich structures with face sheet/core stiffness ratio of 1,000, the distance is 30 times the face sheet thickness.     

In-plane compression of sandwich panels with debonds

The post failure behaviour of sandwich panels loaded in in-plane compression is studied by considering the structural response of such panels with symmetrically located edge debonds. A parametric finite element model is used to determine the influence of different material and geometrical properties on the failure progression, i.e. after initiation of damage. The investigated failure modes are buckling of the debonded face sheets, debond propagation and face sheet failure. The postbuckling failure mode is mainly determined by the fracture toughness of the core and the bending stiffness and strength of the face sheets. The presented approach and results can be used to determine how sandwich panels should be constituted, or not, to promote damage progression favourable for efficient energy absorption during in-plane crushing. The prolonged damage propagation is very complex as it is strongly non-linear and depends on a combination of stiffness, strength and geometry of the constituent materials.     

Sound transmission loss characteristics of unbounded orthotropic sandwich panels in bending vibration considering transverse shear deformation

A theoretical study on the sound transmission loss (STL) characteristics of unbounded orthotropic sandwich panels considering the transverse shear deformation is presented. With the transverse shear deformation taken into account, the governing equation of bending vibration for unbounded orthotropic sandwich panels is derived and implemented to the sound transmission problem. The expressions for impedance and transmission coefficient are also derived. The accuracy of the theoretical predictions is checked against available experimental data. The influence of several key parameters on the sound insulation properties of the orthotropic sandwich panel is then systematically studied, including shear rigidity of the core, face sheet thickness, and core thickness. Numerical analysis shows that shear rigidity has evident effect on coincidence critical frequency and STL property, and should not be neglected when predicting STL. Increasing face sheet thickness can move coincidence critical frequency to lower frequency region and improve STL, which is much more effective than increasing the core thickness.     

Mechanics of discontinuous ceramic tile core sandwich structure: Influence of thermal and interlaminar stresses

The stress states in a discontinuous ceramic tile core sandwich structure due to mechanical and thermal loading are investigated. The influence of coefficient of thermal expansion (CTE) mismatch between the tile and face sheet layer on the in-plane and interlaminar stresses in the sandwich structure is evaluated. The factors affecting the interlaminar stresses in the structure are of particular interest. The influence of an adhesive layer between the face sheet and core on the effective properties of the sandwich is also discussed. A study is performed to evaluate tailoring of the adhesive properties to reduce interlaminar stresses for increased durability. A parametric study is performed to study how various geometric parameters such as tile and adhesive layer thickness affect the effective properties (e.g. axial modulus and CTE). Failure of the discontinuous core sandwich structure under in-plane tension loading is analyzed. It is observed that thermal property mismatch in the structure can significantly reduce the failure loads for the tile layer. Finally, failure of the sandwich corresponding to various failure modes is discussed.     

Fatigue crack growth at the face sheet-core interface in a discontinuous ceramic-tile cored sandwich structure

The fatigue failure mechanism of a sandwich structure with discontinuous ceramic tile core is characterized. The sandwich structure in consideration comprises ceramic core tiles bonded to composite face sheet with a compliant adhesive layer. The discontinuous nature of the core results in a non-uniform stress field under in-plane loading of the sandwich. Static tensile tests performed on sandwich coupons revealed first damage as debonding at the gaps between adjacent tiles in the core. Tension–tension fatigue tests caused debonding at the gaps followed by initiation of cracks in the adhesive layer between the face sheet and core. Experimental data for crack length versus number of cycles is collected at various load levels. Crack growth rates (da/dN) are determined based on the experimental data acquired. The energy release rate available for crack propagation is computed using an analytical model and finite element analysis. Mode separation performed using the Virtual Crack Closure Technique (VCCT) revealed that crack propagation is completely dominated by shear (mode II). Fatigue crack growth behavior for the discontinuous sandwich structure is quantified by correlating the cyclic energy release rate with the rate of crack propagation. The loss of specimen stiffness with crack propagation is quantified using an analytical model.     

面板材料对泡沫铝夹芯梁抗冲击性能的影响

为考查泡沫铝夹芯梁面板材料对其抗冲击性能的影响,运用数值模拟方法计算了相同重量下面板材料分别为304#不锈钢、工业纯铝和HRB335级钢三种泡沫铝夹芯梁在不同冲量作用下的动力响应;分析了面板材料对泡沫铝夹芯梁跨中变形及芯材压缩应变的影响.结果显示,在冲量相同的情况下,面板材料对泡沫铝夹芯梁的抗冲击性能有一定的影响;爆炸...     

Face/core interface fracture characterization of mixed mode bending sandwich specimens

Debonding of the core from the face sheets is a critical failure mode in sandwich structures. This paper presents an experimental study on face/core debond fracture of foam core sandwich specimens under a wide range of mixed mode loading conditions. Sandwich beams with E‐glass fibre face sheets and PVC H45, H100 and H250 foam core materials were evaluated. A methodology to perform precracking on fracture specimens in order to achieve a sharp and representative crack front is outlined. The mixed mode loading was controlled in the mixed mode bending (MMB) test rig by changing the loading application point (lever arm distance). Finite element analysis was performed to determine the mode‐mixity at the crack tip. The results showed that the face/core interface fracture toughness increased with increased mode II loading. Post failure analysis of the fractured specimens revealed that the crack path depends on the mode‐mixity at the crack tip, face sheet properties and core density.     

Experimental investigation of compression moulding of glass/PA12-PMI foam core sandwich components

The manufacturing of sandwich components from pre-consolidated glass/polyamide 12 faces and polymethacrylimide foam core by compression moulding has been studied. A statistical experiment design was used initially to identify the dominant process parameters in terms of interfacial bond strength, evaluated using the transverse tensile test method. In a subsequent extended study, the influence of face temperature and moulding pressure on the mechanical properties of the face–core interface and the sandwich construction as a whole, were characterised in terms of mode I interfacial fracture toughness, shear strength, shear stiffness, and flexural rigidity. These properties were evaluated using a modified double cantilever beam test, shear test, and four point bend test.     

方孔蜂窝夹层板在爆炸载荷下的吸能特性

通过有限元数值模拟方法,对方孔蜂窝夹层板在爆炸冲击载荷下的变形机理和吸能特性进行了分析。在单位面积质量以及夹层板芯层薄壁间距、高度给定的情况下,通过对不同夹芯层相对密度下夹层板的吸能率以及上、下面板最大变形的比较,得出了最优的夹芯层相对密度。在此相对密度下,夹芯层吸能率最高,下面板变形最小,夹层板的抗冲击性能最优。同时还讨论了夹层板芯层薄壁间距、厚度、高度以及面板厚度对其各部分吸能率的影响,以得到最优化的夹层板结构。