One of the primary challenges faced by sandwich composites is facesheet-core debonding, which can be mitigated through various techniques such as z-pinning and stitching through the thickness. This study investigates the impact of stitching on the bending behavior of sandwich composites comprising E-glass composite facesheets and a polyurethane foam core, employing experimental, numerical, and analytical methods. Specimens were stitched at three stitch spacings of 0.5, 1, and 2 cm, with a stitch pitch of 0.8 cm and stitch seam angles of 0°, 90°, 0/90°, ±45°, 45°/90°, and ±60°. Analysis of facesheet bending stress, core shear stress, and bending rigidity of stitched specimens was conducted through three-point bending tests and compared with unstitched specimens. Results indicate that reducing stitch spacing, thereby increasing stitch density, improves bending strength, and the best bending behavior observed at ±45° stitch seam angles. Damage assessment revealed fractures and depression of the foam, wrinkles on the upper facesheet, and buckling failure of resin columns. Additionally, a theoretical model predicted bending rigidity, showing good agreement (4%–15%) with experimental data. Finite element analysis using the ABAQUS program validated the experimental results, suggesting numerical modeling as a viable method for predicting flexural properties of stitched foam core sandwich composites.
DawoodMTaylorERizkallaS. Two-way bending behavior of 3-D GFRP sandwich panels with through-thickness fiber insertions. Compos Struct2010; 92: 950–963.
2.
GuanZAktasAPotluriP, et al.The blast resistance of stitched sandwich panels. Int J Impact Eng2014; 65: 137–145.
3.
IcardiUSolaF. Response of sandwiches undergoing static and blast pulse loading with tailoring optimization and stitching. Aero Sci Technol2014; 32: 293–301.
4.
KarahanMGulHKarahanN, et al.Static behavior of three-dimensional ıntegrated core sandwich composites subjected to three-point bending. J Reinforc Plast Compos2013; 32(9): 664–678.
5.
KimJHLeeYSParkBJ, et al.Evaluation of durability and strength of stitched foam- cored sandwich structures. Compos Struct1999; 47: 543–550.
6.
DowMB. Development of stitched, braided and woven composite structures in the ACT program and at Langley Research Center. Washington, DC: National Aeronautics and Space Administration, Langley Research Center: 1997.
MaYHanHLuZ, et al.Theoretical prediction of the stiffness and failure strength of stitched foam-core sandwich composites. Polym Polym Compos2011; 19: 303–312.
10.
ZhangXXuFZangY, et al.Experimental and numerical investigation on damage behavior of honeycomb sandwich panel subjected to low-velocity impact. Compos Struct2020; 236: 111882.
11.
SanthanakrishnanRSamlalSStanleyAJ, et al.Impact study on sandwich panels with and without stitching. Adv Compos Mater2018; 27: 163–182.
12.
ZhangZGHaoJJSunZJ, et al.Thermal expansion process for manufacturing of stitched sandwich structures. J Reinforc Plast Compos2010; 29(9): 1418–1427.
13.
DrakeDASullivanRWLovejoyAE, et al.Influence of stitching on the out-of-plane behavior of composite materials–A mechanistic review. J Compos Mater2021; 55(23): 3307–3321.
14.
Shah KhanMZMouritzAP. Fatigue behaviour of stitched GRP laminates. Compos Sci Technol1996; 56: 695–701.
Stanley LarryEAdams DanielO. Development and evaluation of stitched sandwich panels. Washington, DC: NASA. NASA/CR-2001-211025.
17.
LascoupBAbouraZBenzeggaghM. Effect of structural parameters on mechanical behaviour of stitched sandwiches. In: Proceedings of the ECCM-11 rhodes, Rhodes, Greece, 2004.
18.
AktasAPotluriPPoratI. Multi-needle stitched composites for improved damage tolerance. In: ICCM 17 International Conference on Composite Materials, Edinburgh, UK, 27 - 31 July 2009.
19.
SinghPLa SaponaraV. Experimental investigation on performance of angle-stitchedsandwich structures. In: 45th AIAA/ASME/ASCE/AHS/ASC structures, structural dynamics & materials conference, Palm Springs, CA, 9–22 April 2004.
20.
YalkinHEIctenBMAlpyildizT. Enhanced mechanical performance of foam core sandwich composites with through the thickness reinforced core. Compos B Eng2015; 79: 383–391.
21.
TanKTYoshimuraAWatanabeN, et al.Effect of stitch density and stitch thread thickness on damage progression and failure characteristics of stitched composites under out-of-plane loading. Composites science and technolog2013; 74: 194–204.
22.
Anil KumarVBhargavAAamanchiK. Mechanical characterization of stitched foam sandwich panel by varying thread TPI. International Journal of Current Engineering and Technology2014: 62–66.
23.
SunQZhengXTLiY, et al.An experimental investigation on composites through-the-thickness stitched foam core sandwich panels. Key Eng Mater2007; 353: 1443–1446.
24.
ZhengXTZhangJFYangF, et al.Experimental and analytical study on the mechanical behavior of stitched sandwich composite panel with a foam core. Adv Mater Res2008; 33: 477–482.
25.
SanthanakrishnanRDashPStanleyAJ, et al.Flexural property evaluation of GFRP-foam sandwich composite–an experimental approach. ARPN J Eng Appl Sci2012; 7: 1300–1306.
26.
LascoupBAbouraZKhellilK, et al.On the mechanical effect of stitch addition in sandwich panel. Compos Sci Technol2006; 66(10): 1385–1398.
27.
LeeGWChoiJSLeeSS, et al.Mechanical properties and failure mechanism of the polymer composite with 3-dimensionally stitched woven fabric. Macromol Res2003; 11(2): 98–103.
28.
AiSMaoYPeiY, et al.Effect of stitch on thermodynamic properties of sandwiched thermal protection structures. Compos Struct2013; 99: 41–47.
29.
AiSChenYHeR. Effects of stitching parameters on the mechanical properties of stitched sandwich panel structures. Ceram Int2021; 47(4): 5249–5255.
30.
RajuKSTomblinJ. Energy absorption characteristics of stitched composite sandwich panels. J Compos Mater1999; 33(8): 712–728.
31.
XiaFWuX. Study on impact properties of through-thickness stitched foam sandwich composites. Compos Struct2010; 92(2): 412–421.
32.
DrakeDASullivanRWClaySB, et al.Influence of stitching on the fracture of stitched sandwich composites. Compos Appl Sci Manuf2021; 145: 1063282.
33.
DelavariKDabiryanH. Effect of Z-fiber orientation on the bending behavior of sandwich-structured composite: numerical and experimental study. Compos Struct2021; 256: 113140.
34.
YanCXuXWangT, et al.Effect of resin pins on the failure behavior of foam core sandwich beams under three-point loading. ACS Omega2022; 7(42): 37834–37845.
35.
DelucisRATonattoMLPTrindadeRS, et al.In situ L-RTM manufacturing of sandwich panels with PET foam core reinforced by polymeric pins. J Sandw Struct Mater2019; 23: 109963621983014. DOI: 10.1177/1099636219830145.
36.
LiuTDengZCLuTJ. Analytical modeling and finite element simulation of the plastic collapse of sandwich beams with pin-reinforced foam cores. Int J Solid Struct, 2008; 45(18-19): 5127–5151.
ASTM C393-00. Standard test method for flexural properties of sandwich constructions. West Conshohocken, PA: ASTM International, 2000.
39.
WangPLeiYYueZ. Experimental and numerical evaluation of the flexural properties of stitched foam core sandwich structure. Compos Struct2013; 100: 243–248.
