Bearing and failure characteristics of conformal antenna sandwich structure under edge compression
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摘要: 共形天线由于能够实现电磁-承载-轻量化的结构功能一体化设计，因此相较于传统机载天线，共形天线更加适应现代化发展趋势，而复合材料夹层结构作为多材质叠层材料，层间承载能力较弱，天线的埋设又会引入新的界面，会对原有结构的传载特性和结构破坏模式产生重大影响，另外结构的制备技术和成型工艺发生改变也会影响力学性能。本文针对一种共形天线夹层结构，通过试验和有限元方法分析了该结构在侧压载荷下的承载特性和失效机制，并与复合材料泡沫夹层结构进行比较。结果表明，天线界面的引入使结构质量增加了38.87%，结构比强度提高1.35%，比刚度下降21.72%。对于结构的失效模式，天线阵列的引入导致结构失效模式从以分层渐进失效为主的中部折断转为沿夹具夹持端应力集中处扩展的基体压缩渐进失效；同时，共形天线夹层结构加工工艺存在溢胶问题，溢胶程度的不可控性会导致结构承载和破坏机制的变化，因此控制溢胶对提高结构力学性能至关重要。Abstract: Conformal antennas, due to their capability of integrating electromagnetic functionality, structural support, and lightweight design, exhibit greater adaptability to modern development trends compared to conventional airborne antennas. However, sandwich structures utilizing composite materials with multiple layers and materials possess inherently weak interlayer load-bearing capabilities. Embedding antennas within these structures significantly alters their load-carrying characteristics and structural failure modes due to the introduction of new interfaces. Furthermore, uncertainties arise regarding whether the structure can fulfill design requirements following changes in manufacturing technology and forming process. This paper focused on the bearing characteristics and failure mechanisms of a conformal antenna sandwich structure (CASS) under lateral pressure loads, employing both experimental and finite element analysis methodologies. We benchmarked our findings against a composite foam sandwich structure (CFSS) for comparison. Our results reveal that incorporating the antenna interface increases the structural weight by 38.87%, enhances the specific strength by 1.35%, but diminishes the specific stiffness by 21.72%. Notably, the introduction of the antenna array shifts the structural failure mode from a central fracture dominated by layered progressive failure to a progressive matrix compression failure extending along stress concentrations at the clamping ends of the fixture. Additionally, the CASS processing technology encounters glue overflow issues, and the uncontrollable degree of overflow can modify the load-bearing and failure mechanisms of the structure. Thus, mitigating glue overflow becomes pivotal for optimizing the mechanical properties of the CASS.
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图 1 单个微带贴片天线结构及共形天线夹层结构(CASS)整体结构图
Figure 1. Structure of a single microstrip patch antenna and overall structure of conformal antenna sandwich structure (CASS)
图 5 等效刚度的理论模型: (a)求整体等效模量的周期性单元; (b)周期性单元在弹性阶段承载前后的变形情况
Figure 5. Theoretical model of equivalent stiffness: (a) the periodic element for calculating the overall equivalent modulus; (b) the deformation of periodic element before and after bearing in the elastic stage
图 6 典型复合材料泡沫夹层结构(CFSS)试验件的破坏过程: (a) 破坏前照片; (b-d)破坏瞬间先后顺序三张照片
Figure 6. Typical failure process of composite foam sandwich structure (CFSS) test piece: (a) photo took before the failure; (b-d) sequence photos during the failure
图 7 CFSS的试验与有限元预测载荷位移曲线对比
Figure 7. Comparison of experimental and finite element predicted load displacement curves of CFSS samples
图 8 CFSS-04载荷-应变曲线: (a) 1,4,7号应变片数据; (b) 2,5,8号应变片数据; (c) 3,6,9号应变片数据
Figure 8. Load strain curve of CFSS-04 sample: (a) data from strain gauge 1,4,7; (b) data from strain gauge 2,5,8; (c) data from strain gauge 3,6,9
图 10 复合材料的渐进损伤失效过程
Figure 10. Progressive damage failure process of composite materials
图 12 CASS侧压试验破坏过程: (a)破坏前照片; (b-d)破坏瞬间先后顺序三张照片
Figure 12. Failure process of CASS under edge compression test: (a) photo took before the failure; (b-d) sequence photos during the failure
图 14 CASS-02载荷-应变曲线: (a) 1,4,7号应变片数据; (b) 2,5,8号应变片数据; (c) 3,6,9号应变片数据
Figure 14. Load strain curve of CASS-02 sample: (a) data from strain gauge 1,4,7; (b) data from strain gauge 2,5,8; (c) data from strain gauge 3,6,9
图 15 CASS有限元预测载荷位移曲线与试验值对比
Figure 15. Comparison between Finite Element predicted load displacement curve and experimental values of CASS samples
表 1 预浸料的力学性能参数
Table 1. Mechanical properties of prepreg
Property Value Units Description $\rho $ 1.8 ${\text{g/c}}{{\text{m}}^{\text{3}}}$ density ${E_1}$ 23500 MPa longitudinal modulus ${E_2}$ 22000 MPa transverse modulus ${E_3}$ 15000 MPa out-of-plane equivalent modulus ${\mu _{12}}$ 0.18 - poisson ratio ${\mu _{13}},{\mu _{23}}$ 0.2/0.18 - poisson ratio ${G_{12}}$ 3500 MPa shear modulus $ {G}_{13},{G}_{23} $ 4000 MPa shear modulus ${X_t}$ 600 MPa longitudinal tensile strength ${X_c}$ 450 MPa longitudinal compressive strength ${Y_t}$ 500 MPa transverse tensile strength ${Y_c}$ 420 MPa Transverse compressive strength ${Z_t}$ 59.7 MPa Out-of-plane tensile strength ${Z_c}$ 215 MPa Out-of-plane compressive strength ${S_{12}}$ 120 MPa longitudinal-transverse shear strength ${S_{13}} = {S_{23}}$ 70 MPa interlaminar shear strength 
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表 2 PMI泡沫的力学性能参数
Table 2. Mechanical properties of PMI foam
Property Value Units Description $\rho $ 71 ${\text{kg/}}{{\text{m}}^{\text{3}}}$ density $E$ 114.5 MPa young's modulus $\mu $ 0.375 - poisson ratio
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表 3 胶膜的力学性能参数
Table 3. Mechanical properties of adhersive film
Property Value Units Description $\rho $ 1.16 $ {\text{g/c}}{{\text{m}}^{\text{3}}} $ density $S$ 18.7 MPa shearing strength ${E_{nn}} = {E_{ss}} = {E_{tt}}$ 2500 MPa elastic modulus ${K_{nn}} = {K_{ss}} = {K_{tt}}$ 1000 GPa initial stiffness $t_n^0$ 6.1 MPa outside shear strength $t_s^0 = t_t^0$ 30 MPa in-plane shear strength ${G_{{\rm I}C}}$ 0.243 N/mm I-type critical fracture energy ${G_{{\rm I}{\rm I}C}},{G_{{\rm I}{\rm I}{\rm I}C}}$ 0.514 N/mm Type II and Type III critical
fracture energy release rates
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表 4 CFSS与CASS的抗压强度与抗压刚度
Table 4. Compressive strength and stiffness of CFSS and CASS
Feature CFSS CASS Mass/g 265 368 Density/(g·m−3) 1.178 1.63 compressive strength/MPa 87.38 122.98 Test value of equivalent compressive
stiffness/kN9371 10183 Theoretical prediction value of equivalent compressive stiffness/kN 11313 12134
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