Impact Damage Resistance, Response, and Mechanisms of Laminated Composites Reinforced by Through-Thickness Stitching

In this article, the study of impact damage of laminated composites reinforced by through-thickness stitching is investigated and presented in threefold. Specimens stitched with varying stitch density and stitch thread thickness are subjected to low-velocity impact via a drop-weight machine. Impact damage resistance is first studied by examining the extent of delamination area in damaged specimens using ultrasonic C-scan analysis. It is revealed that higher stitch density is more capable of impeding delamination growth by arresting cracks at closer interval and suppressing crack propagation. The use of thicker stitch thread offers slight improvement to damage resistance by marginal reduction in delamination propagation, and is more pertinent at high impact energy levels. Impact damage response is then analyzed from the impact history response curves of impacted laminates. The impact response of load–time graphs demonstrates that the onset of delamination is not influenced by stitch density and stitch thread thickness, but the maximum residual impact force is related to the delamination size of the laminates, which is sequentially related to stitch parameters. Finally, impact damage mechanisms are elucidated by employing X-ray radiography and micro-Computed Tomography to reveal subsurface damages, primarily dominated by intralaminar matrix cracks, interlaminar delamination, and stitch fiber/matrix debonding. It is revealed that stitches act as crack initiation sites, due to the presence of weak resin-rich pockets around stitch threads, thus inadvertently resulting in densely stitched composites having more stitch-induced matrix cracks upon impact loading. Contrarily, specimens with higher stitch density and thread thickness are more capable of impeding delamination growth by effectively bridging delamination cracks and arresting crack propagation. Principal mechanisms responsible for impact resistance performance of stitching namely crack arresting and crack bridging are presented and discussed.

[1]  Andrei Gregory Filippov,et al.  Mechanisms Governing the Damage Resistance of Laminated Composites Subjected to Low-Velocity Impacts , 1994 .

[2]  Stephen R Hallett,et al.  Prediction of impact damage in composite plates , 2000 .

[3]  Valentina Lopresto,et al.  Effect of stitches on the impact behaviour of graphite/epoxy composites , 2006 .

[4]  A. Mouritz,et al.  A mechanistic approach to the properties of stitched laminates , 2000 .

[5]  A. Mouritz.  Comment on the impact damage tolerance of stitched composites , 2003 .

[6]  Serge Abrate,et al.  Delamination threshold loads for low velocity impact on composite laminates , 2000 .

[7]  Arghavan Louhghalam,et al.  Prediction of Incipient Damage Sites in Composites using Classifiers , 2010 .

[8]  Phil E. Irving,et al.  Effect of resin and fibre properties on impact and compression after impact performance of CFRP , 2002 .

[9]  A. Yudhanto,et al.  A Micro—Macro Approach to Modeling Progressive Damage in Composite Structures , 2008 .

[10]  Yuyuan Tang,et al.  Impact Damage of 3D Cellular Woven Composite from Unit-cell Level Analysis , 2011 .

[11]  M. Zako,et al.  On the Damage Behavior of Fiber Reinforced Composite Materials , 2002 .

[12]  Robin Olsson,et al.  Analytical prediction of large mass impact damage in composite laminates , 2001 .

[13]  X. Zhang,et al.  IMPACT DAMAGE PREDICTION IN CARBON COMPOSITE STRUCTURES , 1995 .

[14]  Adrian P. Mouritz,et al.  A review of the effect of stitching on the in-plane mechanical properties of fibre-reinforced polymer composites , 1997 .

[15]  B. Cox,et al.  Characterizing Mode II Delamination Cracks in Stitched Composites , 1998 .

[16]  Y. Iwahori,et al.  Stitch fiber comparison for improvement of interlaminar fracture toughness in stitched composites , 2011 .

[17]  A. Mouritz,et al.  A mechanistic interpretation of the comparative in-plane mechanical properties of 3D woven, stitched and pinned composites , 2010 .

[18]  S. Jeelani,et al.  Experimental investigations on the response of stitched/unstitched woven S2-glass/SC15 epoxy composites under single and repeated low velocity impact loading , 2003 .

[19]  E. Gdoutos,et al.  Failure Modes of Composite Sandwich Beams , 2002 .

[20]  N. Watanabe,et al.  Effect of stitch density and stitch thread thickness on low-velocity impact damage of stitched composites , 2010 .

[21]  Brian N. Cox,et al.  Suppression of delaminations in curved structures by stitching , 1996 .

[22]  A. Rosakis,et al.  Impact Damage Visualization of Heterogeneous Two-layer Materials Subjected to Low-speed Impact , 2005 .

[23]  Adrian P. Mouritz,et al.  Further validation of the Jain and Mai models for interlaminar fracture of stitched composites , 1999 .

[24]  A. Mouritz,et al.  Flexural Strength and Interlaminar Shear Strength of Stitched GRP Laminates Following Repeated Impacts , 1997 .

[25]  L. Tong,et al.  A New ENF Test Specimen for the Mode II Delamination Toughness Testing of Stitched Woven CFRP Laminates , 2007 .

[26]  N. Watanabe,et al.  Material selection of z-fibre in stitched composites - Experimental and analytical comparison approach , 2009 .

[27]  Hyung Yun Choi,et al.  A New Approach toward Understanding Damage Mechanisms and Mechanics of Laminated Composites Due to Low-Velocity Impact: Part I—Experiments , 1991 .

[28]  N. Watanabe,et al.  DCB test simulation of stitched CFRP laminates using interlaminar tension test results , 2009 .

[29]  N. Watanabe,et al.  Experimental Investigation of Bridging Law for Single Stitch Fibre Using Interlaminar Tension Test , 2010 .

[30]  F. Larsson,et al.  Damage tolerance of a stitched carbon/epoxy laminate , 1997 .

[31]  M. Grassi,et al.  Improvement of low-velocity impact and compression-after-impact performance by z-fibre pinning , 2006 .

[32]  Zhengneng Li,et al.  Study on Stiffness of Stitched Laminates , 2005 .

[33]  P. Priolo,et al.  Damage response of stitched cross-ply laminates under impact loadings , 2007 .

[34]  H. Hoshi,et al.  Interlaminar Fracture Toughness of Vectran-stitched Composites - Experimental and Computational Analysis , 2010 .

[35]  B. Gu,et al.  Impact Damage of 3D Cellular Woven Composite from Unit-cell Level Analysis , 2011 .

[36]  Hyung Yun Choi,et al.  A New Approach toward Understanding Damage Mechanisms and Mechanics of Laminated Composites Due to Low-Velocity Impact: Part II—Analysis , 1991 .

[37]  Y. Mai,et al.  On the effects of stitching in CFRPs—II. Mode II delamination toughness , 1998 .

[38]  B. N. Cox,et al.  Concepts for bridged Mode ii delamination cracks , 1999 .

[39]  A. Canteli,et al.  Influence of Resin Type on the Delamination Behavior of Carbon Fiber Reinforced Composites Under Mode-II Loading , 2011 .

[40]  Serge Abrate,et al.  Impact on Laminated Composites: Recent Advances , 1994 .

[41]  M. A. Verges,et al.  X-ray computed microtomography of internal damage in fiber reinforced polymer matrix composites , 2005 .

[42]  Francesco Aymerich,et al.  Characterization of fracture modes in stitched and unstitched cross-ply laminates subjected to low-velocity impact and compression after impact loading , 2008 .

[43]  P. Theocaris,et al.  Delamination Prevention in Composites by Interleaving Techniques , 1993 .

[44]  F. Aymerich,et al.  Effect of stitching on the low-velocity impact response of [03/903]s graphite/epoxy laminates , 2007 .

[45]  S. Abrate.  Impact on Laminated Composite Materials , 1991 .

[46]  David H. Allen,et al.  Modeling of Delamination Damage Evolution in Laminated Composites Subjected to Low Velocity Impact , 1994 .

[47]  N. Takeda,et al.  Improvement on out-of-plane impact resistance of CFRP laminates due to through-the-thickness stitching , 2008 .