缝纫复合材料层合板面内力学性能研究
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摘要
缝纫复合材料作为一种新型复合材料以其优良的层间力学性能和较低的制造成本，在航天和航空领域具有很好的应用前景。但是在缝纫过程中也造成面内的局部损伤，这些损伤都会有意无意地对面内力学性能产生不同程度的影响。为了从理论上研究缝纫对复合材料层合板面内力学性能的影响，建立了纤维弯曲模型（FDM），并且分析了缝纫参数和几何参数对层合板等效模量和拉伸强度的影响。
从缝纫孔附近纤维变形的细观结构出发，建立的纤维弯曲模型，以面内纤维的弯曲变形作为缝纫影响层合板面内力学性能的主要原因，同时考虑了纤维变形区、厚度增强区以及树脂富集区的影响，得到单向板内任意一点处的纤维偏转角和纤维体积百分含量。由细观力学的知识得到单层板的刚度，不同铺层的刚度经过坐标旋转后进行叠加得到层合板的刚度。纤维弯曲模型（FDM）只有两个几何参数（最大纤维偏转角和变形区宽度）需要由实验确定。
采用纤维弯曲模型分析了缝纫复合材料单层在缝纫孔附近的最大纤维偏转角、缝纫影响区以及缝纫复合材料单层及层合板工程常数的变化，发现工程常数具有很明显的区域性，能够看出各层中树脂富集区的痕迹。研究了不同的最大纤维偏转角和变形区宽度对层合板弹性常数的影响，发现随着和的增加纵向弹性模量和面内剪切模量逐渐降低，横向弹性模量和主泊松比变化不明显。
建立了二维的有限元分析模型，研究了缝纫参数（缝纫针距、缝纫行距以及缝纫线直径）和几何参数（最大纤维偏转角和缝纫变形区宽度）对缝纫复合材料层合板面内等效模量和拉伸强度的影响。研究结果表明：随着缝纫密度、缝纫线直径、最大纤维偏转角和缝纫变形区宽度的增加，缝纫复合材料层合板面内等效模量逐渐降低，最大降幅一般在5%左右；缝纫复合材料层合板的拉伸强度随缝纫针距的增加而增大，随缝纫行距的增加而降低，因此缝纫密度对拉伸强度的影响程度要看具体的缝纫针距和行距。缝纫复合材料层合板拉伸强度随缝纫线直径、最大纤维偏转角和缝纫变形区宽度的增加而降低，最大降幅在10-20%之间。
As a new type of composite, stitched composite has an encouraging prospect of applications in aeronautic and aerospace industries because of the excellent through-thickness properties and lower cost of manufacture. During the process of stitching, however, there are some in-plane local damages, which have effects on the in-plane mechanical performances unintentionally. In this thesis the Fiber Distortion Model (FDM) is presented to analyze the effect of stitching and geometry parameters on the equivalent modulus and tensile strength of the stitched composite laminates.
The fiber distortion model is set up based on the microstructure of fibers near the stitch holes. The distortion of in-plane fibers is considered to be the main reason for the effect of stitching on the in-plane mechanical properties, and the fiber distortion region, the resin-rich pocket and the through-thickness reinforcement section are taken into account. The fiber misalignment angle and the inhomogeneous fiber volume fraction caused by stitching have been determined within the lamina. The elastic constants of a lamina are calculated using a micromechanical model, then the constitutive equations of the stitched composite laminates can be composed. It is clearly that only two geometrical parameters i.e. maximal misalignment angle () and distortion width (S) need to be determined experimentally.
The engineering constants around the stitch hole in the composite laminate are analyzed using the FDM. It is found that the elastic constants have distinct region character and the traces of the resin-rich pocket in different lamina are clear. The longitudinal Young's modulus and the in-plane shear modulus decrease with the increase of the maximum misalignment and the distortion width, but the transverse Young's modulus and main Poisson's ratio have no obvious change.
The in-plane equivalent elastic modulus and tensile strength of stitched composite laminates are studied, and it's found that the in-plane equivalent elastic modulus decreases with the increase of stitch density, stitch thread diameter, maximal misalignment angle and the distortion width, and the range is about 5%. The tensile strength of stitched composite laminate increases with the increase of stitch step and decreases with the stitch space. The
increase of the stitch thread diameter, maximal misalignment and the distortion width will reduce the tensile strength of stitched composite laminates in the range of 10-20%.
从缝纫孔附近纤维变形的细观结构出发，建立的纤维弯曲模型，以面内纤维的弯曲变形作为缝纫影响层合板面内力学性能的主要原因，同时考虑了纤维变形区、厚度增强区以及树脂富集区的影响，得到单向板内任意一点处的纤维偏转角和纤维体积百分含量。由细观力学的知识得到单层板的刚度，不同铺层的刚度经过坐标旋转后进行叠加得到层合板的刚度。纤维弯曲模型（FDM）只有两个几何参数（最大纤维偏转角和变形区宽度）需要由实验确定。
采用纤维弯曲模型分析了缝纫复合材料单层在缝纫孔附近的最大纤维偏转角、缝纫影响区以及缝纫复合材料单层及层合板工程常数的变化，发现工程常数具有很明显的区域性，能够看出各层中树脂富集区的痕迹。研究了不同的最大纤维偏转角和变形区宽度对层合板弹性常数的影响，发现随着和的增加纵向弹性模量和面内剪切模量逐渐降低，横向弹性模量和主泊松比变化不明显。
建立了二维的有限元分析模型，研究了缝纫参数（缝纫针距、缝纫行距以及缝纫线直径）和几何参数（最大纤维偏转角和缝纫变形区宽度）对缝纫复合材料层合板面内等效模量和拉伸强度的影响。研究结果表明：随着缝纫密度、缝纫线直径、最大纤维偏转角和缝纫变形区宽度的增加，缝纫复合材料层合板面内等效模量逐渐降低，最大降幅一般在5%左右；缝纫复合材料层合板的拉伸强度随缝纫针距的增加而增大，随缝纫行距的增加而降低，因此缝纫密度对拉伸强度的影响程度要看具体的缝纫针距和行距。缝纫复合材料层合板拉伸强度随缝纫线直径、最大纤维偏转角和缝纫变形区宽度的增加而降低，最大降幅在10-20%之间。
As a new type of composite, stitched composite has an encouraging prospect of applications in aeronautic and aerospace industries because of the excellent through-thickness properties and lower cost of manufacture. During the process of stitching, however, there are some in-plane local damages, which have effects on the in-plane mechanical performances unintentionally. In this thesis the Fiber Distortion Model (FDM) is presented to analyze the effect of stitching and geometry parameters on the equivalent modulus and tensile strength of the stitched composite laminates.
The fiber distortion model is set up based on the microstructure of fibers near the stitch holes. The distortion of in-plane fibers is considered to be the main reason for the effect of stitching on the in-plane mechanical properties, and the fiber distortion region, the resin-rich pocket and the through-thickness reinforcement section are taken into account. The fiber misalignment angle and the inhomogeneous fiber volume fraction caused by stitching have been determined within the lamina. The elastic constants of a lamina are calculated using a micromechanical model, then the constitutive equations of the stitched composite laminates can be composed. It is clearly that only two geometrical parameters i.e. maximal misalignment angle () and distortion width (S) need to be determined experimentally.
The engineering constants around the stitch hole in the composite laminate are analyzed using the FDM. It is found that the elastic constants have distinct region character and the traces of the resin-rich pocket in different lamina are clear. The longitudinal Young's modulus and the in-plane shear modulus decrease with the increase of the maximum misalignment and the distortion width, but the transverse Young's modulus and main Poisson's ratio have no obvious change.
The in-plane equivalent elastic modulus and tensile strength of stitched composite laminates are studied, and it's found that the in-plane equivalent elastic modulus decreases with the increase of stitch density, stitch thread diameter, maximal misalignment angle and the distortion width, and the range is about 5%. The tensile strength of stitched composite laminate increases with the increase of stitch step and decreases with the stitch space. The
increase of the stitch thread diameter, maximal misalignment and the distortion width will reduce the tensile strength of stitched composite laminates in the range of 10-20%.
引文
[1] Jain, L.K. Improvement of the interlaminar properties in advanced fibre composites with through-thickness reinforcement. Cooperative Research Centre for Aerospace Structures Ltd. CRC-AS TM94012,1994.
[2] Jain, L.K. and Mai, Y-W. Determination of Mode Ⅱ delamination toughness of stitched laminated composites. Comp. Sci. and Tech. 1995;55:241-253.
[3] Mouritz AP, Leong KH, Herszberg I. A review of the effect of the stitching on the in-plane mechanical properties of fiber reinforced polymer composites.J. Composites A 1997;28:979-991.
[4] Kang, T.J. and Lee, S.H., Effect of stitching on the mechanical and impact properties of woven laminate composites. J. Comp. Mat.,1994;28:1574-87.
[5] Mouritz, A.P., The damage to stitched GRP laminates by underwater explosion shock loading. J. Comp. Sci. and Tech., 1995;55:365-374.
[6] Pang, F., Wang, C.H. and Bathgate, R.G., Creep response of woven fibre composites and the effect of the stitching. J. Comp. Sci. and Tech., 1997;57:91-98.
[7] Reed JR. Stitching vs a toughened matrix: compression strength effects. Comp Mater 1995;29:2464-87.
[8] Mouritz AP, Gallagher J, Goodwin AA. Flexural and inerlaminar shear properties of stitched GRP laminates following repeated impacts. Com. Sci. Tech, 1996;57:509-22.
[9] Shah Khan MZ, Mouritz A.P., Fatigue behaviour of stitched GRP laminates. Com. Sci. Tech, 1996;56:695-701.
[10] Mouritz AP, Cox BN. A mechanistic approach to the properties of stitched laminates. Composites A ,2000;31:1-27.
[11] 汪海，刘书田，程狄东．缝合复合材料板的破坏机理．固体力学学报，2002;23: 108-113.
[12] Dransfield KA, Baillie C, Mai Y-W. Improving the delamination resistance of CFRP by stitching—a review. Comp Sci Tech, 1994, 50(3): 305-17.
[13] Dransfield KA, Jain LK, Mai Y-W. On the effects of stitching in CFRPs-(. Mode ( delamination toughness[J]. Comp Sci Tech, 1998, 58(7): 815-27.
Warrior N.A, Rudd C.D, Gardner S.P. Experimental studies of embroidery for the local reinforcement of composites structures 1. Stress concentrations[J]. Comp Sci
[14] Tech, 1999,59:2125-2137.
[15] Herszberg I, Bannister MK. Compression and compression-after-impact properties of thin stitched carbon/epoxy composites[C]. Presented at 5th Aust Aero Conf, 20-23 March 1993.
[16] Enboa Wu, Jyue Wang. Behavior of stitched laminates under in-plane tensile and transverse impact loading. Comp Mater 1995;29:2254-79.
[17] Farley GL. A mechanism responsible for reducing compression strength of through-the-thickness reinforced composite material[J].Comp Mater 1992, 26: 1784-1795.
[18] Aymerich F, Priolo,P Sanna R, Sun CT. Fatigue behavior of stitched composite laminates. Prensented at 13th Comp Mater Conf, BeiJing 25-29 June 2001.
[19] Whiney JM, Daniel IM, Byron R. Experimental mechanics of the fiber reinforced composite materials. Society for experiment stress analysis, New Jersey (1982).
[20] Whitney JM, Nuismer RJ. Stress fracture criteria for laminated composites containing concentrations. J Comp Mater 1974;8:253-65.
[21] Tan SC. A progressive failure model for composite laminates containing openings. J Comp Mater 1991;25:556-77.
[22] Erikssion I, Aronsson CG. Strength of tensile loaded graphite/epoxy laminates containing cracks, open and filled holes. J Comp Mater 1990;24:456-82.
[23] Afaghi-Khatibi A, Ye L, Mai Y-W. An effective crack growth model for residual strength evaluation of composite laminates with circular holes. J Comp Mater 1996;30:142-63.
[24] Jin Z-H, Mai Y-W. Residual strength of an ARALL laminate containing a crack. J Comp Mater 1997;31:746-61.
[25] Chang FK, Lessard LB. Damage tolerance of laminated composites containing an open hole and subjected to compressive loading. J Comp Mater 1991;25:2-43.
[26] Kortschot MT, Beaumont PWR. Damage mechanics of composite Materials: IV-the effect of lay-up on damage growth and notched strength. Comp Sci Tech 1991;40:167-79.
[27] Curtin WA, Takeda N. Tensile strength of fiber-reinforced composites: I. Model and effects of local fiber geometry J Comp Mater 1998;32:2042-59.
[28] Govindan PK, Nageswara B, Srivastava VK. Tensile fracture strength of boron/aluminum laminates with holes and slits J Materials Science Engineering 2001;302:244-252.
[29] Morais AB. Open-hole tensile strength of Quasi-isotropic Laminates. J Comp Sci Tech 2000;60:1997-2004.
[30] Chen PH, Shen Z, Wang JY. Prediction of the strength of notched fiber-dominated composite laminates. J Comp Sci Tech 2001;61:1311-1321.
[31] 沈真，陈普会，唐啸东等．含损伤复合材料剩余强度估算方法研究新进展．第十一届全国复合材料学术会议论文集．中国科学技术大学出版社，2000．
[32] 沈真．复合材料结构损伤容限特性．航空学报，1998;9（2）:B1-10．
[33] Larsson F, Damage tolerance of a stitched carb/epoxy laminate. Composites Part A, 1997;28:923-934.
[34] 桂良进, 范子杰，寇长河等．缝纫层合板的本构关系研究（II）缝纫层合板刚度分析与实验．复合材料学报，2002;19:101-106.
[35] 桂良进, 范子杰，寇长河等．缝纫层合板的本构关系研究（I）缝纫单层板有效弹性常数分析．复合材料学报，2002;19:95-100.
[2] Jain, L.K. and Mai, Y-W. Determination of Mode Ⅱ delamination toughness of stitched laminated composites. Comp. Sci. and Tech. 1995;55:241-253.
[3] Mouritz AP, Leong KH, Herszberg I. A review of the effect of the stitching on the in-plane mechanical properties of fiber reinforced polymer composites.J. Composites A 1997;28:979-991.
[4] Kang, T.J. and Lee, S.H., Effect of stitching on the mechanical and impact properties of woven laminate composites. J. Comp. Mat.,1994;28:1574-87.
[5] Mouritz, A.P., The damage to stitched GRP laminates by underwater explosion shock loading. J. Comp. Sci. and Tech., 1995;55:365-374.
[6] Pang, F., Wang, C.H. and Bathgate, R.G., Creep response of woven fibre composites and the effect of the stitching. J. Comp. Sci. and Tech., 1997;57:91-98.
[7] Reed JR. Stitching vs a toughened matrix: compression strength effects. Comp Mater 1995;29:2464-87.
[8] Mouritz AP, Gallagher J, Goodwin AA. Flexural and inerlaminar shear properties of stitched GRP laminates following repeated impacts. Com. Sci. Tech, 1996;57:509-22.
[9] Shah Khan MZ, Mouritz A.P., Fatigue behaviour of stitched GRP laminates. Com. Sci. Tech, 1996;56:695-701.
[10] Mouritz AP, Cox BN. A mechanistic approach to the properties of stitched laminates. Composites A ,2000;31:1-27.
[11] 汪海，刘书田，程狄东．缝合复合材料板的破坏机理．固体力学学报，2002;23: 108-113.
[12] Dransfield KA, Baillie C, Mai Y-W. Improving the delamination resistance of CFRP by stitching—a review. Comp Sci Tech, 1994, 50(3): 305-17.
[13] Dransfield KA, Jain LK, Mai Y-W. On the effects of stitching in CFRPs-(. Mode ( delamination toughness[J]. Comp Sci Tech, 1998, 58(7): 815-27.
Warrior N.A, Rudd C.D, Gardner S.P. Experimental studies of embroidery for the local reinforcement of composites structures 1. Stress concentrations[J]. Comp Sci
[14] Tech, 1999,59:2125-2137.
[15] Herszberg I, Bannister MK. Compression and compression-after-impact properties of thin stitched carbon/epoxy composites[C]. Presented at 5th Aust Aero Conf, 20-23 March 1993.
[16] Enboa Wu, Jyue Wang. Behavior of stitched laminates under in-plane tensile and transverse impact loading. Comp Mater 1995;29:2254-79.
[17] Farley GL. A mechanism responsible for reducing compression strength of through-the-thickness reinforced composite material[J].Comp Mater 1992, 26: 1784-1795.
[18] Aymerich F, Priolo,P Sanna R, Sun CT. Fatigue behavior of stitched composite laminates. Prensented at 13th Comp Mater Conf, BeiJing 25-29 June 2001.
[19] Whiney JM, Daniel IM, Byron R. Experimental mechanics of the fiber reinforced composite materials. Society for experiment stress analysis, New Jersey (1982).
[20] Whitney JM, Nuismer RJ. Stress fracture criteria for laminated composites containing concentrations. J Comp Mater 1974;8:253-65.
[21] Tan SC. A progressive failure model for composite laminates containing openings. J Comp Mater 1991;25:556-77.
[22] Erikssion I, Aronsson CG. Strength of tensile loaded graphite/epoxy laminates containing cracks, open and filled holes. J Comp Mater 1990;24:456-82.
[23] Afaghi-Khatibi A, Ye L, Mai Y-W. An effective crack growth model for residual strength evaluation of composite laminates with circular holes. J Comp Mater 1996;30:142-63.
[24] Jin Z-H, Mai Y-W. Residual strength of an ARALL laminate containing a crack. J Comp Mater 1997;31:746-61.
[25] Chang FK, Lessard LB. Damage tolerance of laminated composites containing an open hole and subjected to compressive loading. J Comp Mater 1991;25:2-43.
[26] Kortschot MT, Beaumont PWR. Damage mechanics of composite Materials: IV-the effect of lay-up on damage growth and notched strength. Comp Sci Tech 1991;40:167-79.
[27] Curtin WA, Takeda N. Tensile strength of fiber-reinforced composites: I. Model and effects of local fiber geometry J Comp Mater 1998;32:2042-59.
[28] Govindan PK, Nageswara B, Srivastava VK. Tensile fracture strength of boron/aluminum laminates with holes and slits J Materials Science Engineering 2001;302:244-252.
[29] Morais AB. Open-hole tensile strength of Quasi-isotropic Laminates. J Comp Sci Tech 2000;60:1997-2004.
[30] Chen PH, Shen Z, Wang JY. Prediction of the strength of notched fiber-dominated composite laminates. J Comp Sci Tech 2001;61:1311-1321.
[31] 沈真，陈普会，唐啸东等．含损伤复合材料剩余强度估算方法研究新进展．第十一届全国复合材料学术会议论文集．中国科学技术大学出版社，2000．
[32] 沈真．复合材料结构损伤容限特性．航空学报，1998;9（2）:B1-10．
[33] Larsson F, Damage tolerance of a stitched carb/epoxy laminate. Composites Part A, 1997;28:923-934.
[34] 桂良进, 范子杰，寇长河等．缝纫层合板的本构关系研究（II）缝纫层合板刚度分析与实验．复合材料学报，2002;19:101-106.
[35] 桂良进, 范子杰，寇长河等．缝纫层合板的本构关系研究（I）缝纫单层板有效弹性常数分析．复合材料学报，2002;19:95-100.