复合材料层压板修理后动力学特性和稳定性影响研究
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摘要
复合材料层压板已广泛应用于飞机结构,其在服役的各种环境出现损伤不可避免,出于结构安全性和经济性考虑,对于修理容限内的损伤必须实施修理。挖补修理因具有适用范围广、修理效率高、修理效果好以及对结构气动外形影响小等优点成为复合材料层压板损伤修理的基本方法之一。当前层压板挖补修理的力学研究很多,大多集中于静强度方面,对修理后结构的稳定性和动力学特性关注较少。但挖补修理对结构稳定性和动力学特性的影响也必须得到足够重视,例如,飞机结构存在大量承受压、剪载荷的复合材料薄壁结构,其挖补修理应避免修理后结构过早发生屈曲失稳,对于在工作力学环境下需关心其动力学特性的层压板结构,须避免修理后与周边结构发生耦合振动等问题。因此,我国目前实施的大型民机科技重大专项有关飞机结构损伤修理的研究也提出了开展复合材料层压板修理后稳定性和动力学特性研究的迫切需求。基于以上工程背景,本文利用有限元方法研究了挖补修理参数对层压板结构的动力学特性和稳定性的影响。
首先,从工程实际出发,提出了一种复合材料层压板挖补修理方案的数字化设计方法,对复合材料蒙皮典型分层损伤的修理应用实例表明该方法可实现挖补修理快捷、有效的数字化设计。
其次,基于ABAQUS有限元分析软件建立不同修理构型的三维分析模型,研究了挖补角度?、挖除孔径D、表面覆盖层对四种典型载荷下修理结构稳定性的影响。研究表明,受单轴压缩载荷时,结构稳定性对D的改变不敏感,对?则较敏感;双轴压缩载荷下,减小D和增大?均能增强修理结构抗双轴压缩失稳能力,且增大对提高结构稳定性更有效;四边受剪时,一定、增大D可提高结构稳定性,而当D一定时,存在一个值使结构抗剪失稳能力最弱(本文为5°),对于主要承剪的板壳结构在进行挖补修理时应避免选择此角度。表面覆盖层对修理结构的屈曲极限载荷和屈曲模态均有重要影响,可显著强化结构抗剪失稳能力;压-剪复合载荷下,D一定时,也存在一个小的使修理结构稳定性最弱。而一定时,增加挖除孔径在特定工况下可能减弱结构稳定性;表面覆盖层在四种载荷下均能显著提高修理结构稳定性,与具体工况无关。
进一步研究了这三个修理参数和胶层材料性能对修理结构固有频率和稳态简谐响应特性的影响。研究结果显示,挖补修理对结构基频和谐响应特性有显著改变,修理后结构基频显著提高,谐响应共振频率均在一阶固有频率附近,共振幅值均明显降低,且降低幅度随的增大而增大;一定时,增大D和表面覆盖铺层的出现将降低结构固频,而在10°范围内,增加将显著提高系统固频;表面覆盖层和胶层材料参数对固频影响均可忽略,但前者对谐响应共振幅值的影响取决于其对结构刚度和质量影响两种因素谁占主导。对于一定的修理构型, D较小时(50.8mm)质量因素占主导,表面覆盖层的出现使共振幅值增大,其它情况下刚度因素占主导,均在一定程度上降低了稳态简谐响应共振幅值。
Composite laminates have been widely applied in the aircraft structures. Since damages of laminates occurred during the whole service life is inevitable, repairs must be executed in time when the damage meet the limit of repair tolerance for the sake of structural safety and economical efficiency. The scarf repair has turned to be one of the fundamental repairing methods of laminates with the characteristics of wide-field of application, efficiency, good repairing effect and small impact on aerodynamic shape.
The majority of present relevant researches focus on the static strength of scarf-repaired laminates, while less attention is paid to its stability and dynamics characteristics. However, the influences of scarf repair on stability and dynamics of composite laminates must be paid highly attentions as well. Take the large number of application of thin-walled composite structures in airplanes for example, the scarf repair should be designed not to cause premature buckling of the repaired structures. For those laminates whose dynamics should be concerned in working circumstances, coupling resonance with surrounding structures caused by repairs must be avoided. For the same consideration, the major national S&T program on large civil aircraft being implemented at present also demands urgent researches on the impacts of scarf repair on stability and dynamics of composite laminates. Based on engineering background above, the effects of different scarf-repairing parameters on the stability and dynamics of laminates are analyzed by means of finite element method in this paper.
Firstly, a digital design method for scarf-repairing plan of laminates is proposed based on engineering reality. The application of this method to the repair of typical delamination of skin demonstrates that the method can fulfill digital design of scarf repair quickly and effectively.
Then, three-dimensional finite element analysis models with different repair parameters are built up via ABAQUS to investigate the effects of scarf angle , the aperture D and over-laminating plies on the stability of repaired laminates subjected to four kinds of typical loading. Studies show that the stability of repaired laminates is insensitive to the change of D but is more sensitive to the change of under uniaxial compression. Decreasing D or increasing can both strengthen the stability of repaired structure under biaxial compression while the change of brings more notable effect.
When the repaired laminates is subjected to in-plane shear loading, the increase of D results in higher stability with a constant value of . It is also found that there is a particular value of which brings in the weakest repaired pattern when D is constant. This value is5degrees in this paper and should be avoided for those panels who are mainly exposed to shear loading. The over-laminating plies have an important influence on the critical buckling loads and modes and can strengthen stability of repaired laminates dramatically when loaded with shear stress.
As far as the compression-shear-combined load is concerned, there is also a small value of which results in the lowest critical buckling load when D is constant. Increasing D may weaken the stability under some particular load cases when is fixed. The stability of all repaired panels under four kinds of loading above can gain a outstanding reinforcement with the presence of over-laminating plies regardless of load cases.
More research is made to examine the influences of D, , over-laminating plies and material property of adhesive layer on natural frequencies and steady-state harmonic response of repaired structures. The results indicate that the structural fundamental frequency is raised significantly by repair and the structural resonance frequency of harmonic response is near the first natural frequency. Scarf repair also lower the amplitude of resonance dramatically and the reduced magnitude of amplitude increases with the increase of ? . Structures with larger D and over-laminating plies have lower natural frequencies when scarf angle is fixed. When scarf angle is smaller than 10 degrees, small increase of ? could elevate natural frequencies significantly. Both of the over-laminating plies and material property of adhesive layer have little effect on structural natural frequencies. What’s more, the impact of over-laminating plies on the amplitude of resonance depends on the stiffness effect and quality effect caused by the presence of over-laminating plies. When ? is constant, the quality is the dominant factor for repairing patterns with smaller D and larger resonance amplitude could be gained. Otherwise, the stiffness is the dominant factor and the presence of over-laminating plies lowers the amplitude.
首先,从工程实际出发,提出了一种复合材料层压板挖补修理方案的数字化设计方法,对复合材料蒙皮典型分层损伤的修理应用实例表明该方法可实现挖补修理快捷、有效的数字化设计。
其次,基于ABAQUS有限元分析软件建立不同修理构型的三维分析模型,研究了挖补角度?、挖除孔径D、表面覆盖层对四种典型载荷下修理结构稳定性的影响。研究表明,受单轴压缩载荷时,结构稳定性对D的改变不敏感,对?则较敏感;双轴压缩载荷下,减小D和增大?均能增强修理结构抗双轴压缩失稳能力,且增大对提高结构稳定性更有效;四边受剪时,一定、增大D可提高结构稳定性,而当D一定时,存在一个值使结构抗剪失稳能力最弱(本文为5°),对于主要承剪的板壳结构在进行挖补修理时应避免选择此角度。表面覆盖层对修理结构的屈曲极限载荷和屈曲模态均有重要影响,可显著强化结构抗剪失稳能力;压-剪复合载荷下,D一定时,也存在一个小的使修理结构稳定性最弱。而一定时,增加挖除孔径在特定工况下可能减弱结构稳定性;表面覆盖层在四种载荷下均能显著提高修理结构稳定性,与具体工况无关。
进一步研究了这三个修理参数和胶层材料性能对修理结构固有频率和稳态简谐响应特性的影响。研究结果显示,挖补修理对结构基频和谐响应特性有显著改变,修理后结构基频显著提高,谐响应共振频率均在一阶固有频率附近,共振幅值均明显降低,且降低幅度随的增大而增大;一定时,增大D和表面覆盖铺层的出现将降低结构固频,而在10°范围内,增加将显著提高系统固频;表面覆盖层和胶层材料参数对固频影响均可忽略,但前者对谐响应共振幅值的影响取决于其对结构刚度和质量影响两种因素谁占主导。对于一定的修理构型, D较小时(50.8mm)质量因素占主导,表面覆盖层的出现使共振幅值增大,其它情况下刚度因素占主导,均在一定程度上降低了稳态简谐响应共振幅值。
Composite laminates have been widely applied in the aircraft structures. Since damages of laminates occurred during the whole service life is inevitable, repairs must be executed in time when the damage meet the limit of repair tolerance for the sake of structural safety and economical efficiency. The scarf repair has turned to be one of the fundamental repairing methods of laminates with the characteristics of wide-field of application, efficiency, good repairing effect and small impact on aerodynamic shape.
The majority of present relevant researches focus on the static strength of scarf-repaired laminates, while less attention is paid to its stability and dynamics characteristics. However, the influences of scarf repair on stability and dynamics of composite laminates must be paid highly attentions as well. Take the large number of application of thin-walled composite structures in airplanes for example, the scarf repair should be designed not to cause premature buckling of the repaired structures. For those laminates whose dynamics should be concerned in working circumstances, coupling resonance with surrounding structures caused by repairs must be avoided. For the same consideration, the major national S&T program on large civil aircraft being implemented at present also demands urgent researches on the impacts of scarf repair on stability and dynamics of composite laminates. Based on engineering background above, the effects of different scarf-repairing parameters on the stability and dynamics of laminates are analyzed by means of finite element method in this paper.
Firstly, a digital design method for scarf-repairing plan of laminates is proposed based on engineering reality. The application of this method to the repair of typical delamination of skin demonstrates that the method can fulfill digital design of scarf repair quickly and effectively.
Then, three-dimensional finite element analysis models with different repair parameters are built up via ABAQUS to investigate the effects of scarf angle , the aperture D and over-laminating plies on the stability of repaired laminates subjected to four kinds of typical loading. Studies show that the stability of repaired laminates is insensitive to the change of D but is more sensitive to the change of under uniaxial compression. Decreasing D or increasing can both strengthen the stability of repaired structure under biaxial compression while the change of brings more notable effect.
When the repaired laminates is subjected to in-plane shear loading, the increase of D results in higher stability with a constant value of . It is also found that there is a particular value of which brings in the weakest repaired pattern when D is constant. This value is5degrees in this paper and should be avoided for those panels who are mainly exposed to shear loading. The over-laminating plies have an important influence on the critical buckling loads and modes and can strengthen stability of repaired laminates dramatically when loaded with shear stress.
As far as the compression-shear-combined load is concerned, there is also a small value of which results in the lowest critical buckling load when D is constant. Increasing D may weaken the stability under some particular load cases when is fixed. The stability of all repaired panels under four kinds of loading above can gain a outstanding reinforcement with the presence of over-laminating plies regardless of load cases.
More research is made to examine the influences of D, , over-laminating plies and material property of adhesive layer on natural frequencies and steady-state harmonic response of repaired structures. The results indicate that the structural fundamental frequency is raised significantly by repair and the structural resonance frequency of harmonic response is near the first natural frequency. Scarf repair also lower the amplitude of resonance dramatically and the reduced magnitude of amplitude increases with the increase of ? . Structures with larger D and over-laminating plies have lower natural frequencies when scarf angle is fixed. When scarf angle is smaller than 10 degrees, small increase of ? could elevate natural frequencies significantly. Both of the over-laminating plies and material property of adhesive layer have little effect on structural natural frequencies. What’s more, the impact of over-laminating plies on the amplitude of resonance depends on the stiffness effect and quality effect caused by the presence of over-laminating plies. When ? is constant, the quality is the dominant factor for repairing patterns with smaller D and larger resonance amplitude could be gained. Otherwise, the stiffness is the dominant factor and the presence of over-laminating plies lowers the amplitude.
引文
[1]陈绍杰.复合材料结构修理指南[M].北京:航空工业出版社,2001.
[2] Campilho R.D.S.G., Demoura M. F. S. F., Domingues J. J. M. S. Stress and failure analyses of scarf repaired CFRP laminates using a cohesive damage model[J]. Adhesion Sci. Technol, 2007, 21(9):855–870.
[3]王萍萍,等.碳纤维蜂窝夹层结构动特性分析[J].复合材料学报,2002,19(6):134-136.
[4]比尔·伯切尔,陈亚莉.波音787复合材料结构的修理问题[J].国际航空,2006,(11):63-64.
[5] Srivatsa K. S., Krishna Murty A.V. Stability of laminated composite plates with cut-outs[J]. Computers and Structures, 1992, 43(2):273-279.
[6] Bailey R., Wood J. Post-buckling behavior of square compression loaded graphite epoxy panels with square and elliptical cut-outs[J]. Thin-Walled Structures,1997,28:373-397.
[7] Lee H.H., Hyer M.W. Post-buckling failure of composite plates with central holes [Dissertation]. Virginia: Virginia Polytechnic Institute and State University.1992.
[8] Giulio Romeo. Analytical and experimental behavior of laminated panels with rectangular opening under biaxial Tension, compression and shear loads[J]. Journal of Composite Materials, 2001,35(8):639-663.
[9]许良梁.复合材料层合板剪切屈曲及后屈曲行为研究[硕士学位论文].西安:西北工业大学.2006.
[10]白瑞祥,王蔓,陈浩然.具有分层损伤的不同加筋形式复合材料层合板的后屈曲形态研究[J].计算力学学报,2006,23(2):186-190.
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[12] Soutis C., Hu F. Z. Failure analysis of scarf-patch-repaired carbon fiber/epoxy laminates under compression[J]. AIAA Journal,2000,38(4):737-740.
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[14] Kwon Y. W., Marrón A., Scarf joints of composite materials: testing and analysis[J]. Appl Compos Mater ,2009, 16:365–378.
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[2] Campilho R.D.S.G., Demoura M. F. S. F., Domingues J. J. M. S. Stress and failure analyses of scarf repaired CFRP laminates using a cohesive damage model[J]. Adhesion Sci. Technol, 2007, 21(9):855–870.
[3]王萍萍,等.碳纤维蜂窝夹层结构动特性分析[J].复合材料学报,2002,19(6):134-136.
[4]比尔·伯切尔,陈亚莉.波音787复合材料结构的修理问题[J].国际航空,2006,(11):63-64.
[5] Srivatsa K. S., Krishna Murty A.V. Stability of laminated composite plates with cut-outs[J]. Computers and Structures, 1992, 43(2):273-279.
[6] Bailey R., Wood J. Post-buckling behavior of square compression loaded graphite epoxy panels with square and elliptical cut-outs[J]. Thin-Walled Structures,1997,28:373-397.
[7] Lee H.H., Hyer M.W. Post-buckling failure of composite plates with central holes [Dissertation]. Virginia: Virginia Polytechnic Institute and State University.1992.
[8] Giulio Romeo. Analytical and experimental behavior of laminated panels with rectangular opening under biaxial Tension, compression and shear loads[J]. Journal of Composite Materials, 2001,35(8):639-663.
[9]许良梁.复合材料层合板剪切屈曲及后屈曲行为研究[硕士学位论文].西安:西北工业大学.2006.
[10]白瑞祥,王蔓,陈浩然.具有分层损伤的不同加筋形式复合材料层合板的后屈曲形态研究[J].计算力学学报,2006,23(2):186-190.
[11] Campilho R.D.S.G. , M.F.S.F. de Moura , Pinto A.M.G. Modelling the tensile fracture behaviour of CFRP scarf repairs[J]. Composites: Part B ,2009, 40 : 149–157.
[12] Soutis C., Hu F. Z. Failure analysis of scarf-patch-repaired carbon fiber/epoxy laminates under compression[J]. AIAA Journal,2000,38(4):737-740.
[13] Kumara S.B., Sridhar I., Sivashanker S., et al. Tensile failure of adhesively bonded CFRP composite scarf joints[J]. Materials Science and Engineering B, 2006, 132:113–120.
[14] Kwon Y. W., Marrón A., Scarf joints of composite materials: testing and analysis[J]. Appl Compos Mater ,2009, 16:365–378.
[15]孟凡颢,陈绍杰,童小燕.层压板修理设计中的参数选择问题[J].复合材料学报,2001,18(4):123-127.
[16]李兆远.复合材料层合板挖补修理强度分析[D].南京:南京航空航天大学,2008.25-49.
[17]汪海,陈秀华,郭杏林,等.复合材料蜂窝夹芯结构修理后强度研究[J].航空学报,2001,22(3):270-273.
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