Polymer matrix composites are attractive structural materials in automotive, defense, and aerospace industries due to their high strength to low weight ratios. However, due to their low shear strength, compression dominated failure mechanisms such as plastic microbuckling lead to the development of kink bands, which are a key strength-limiting factor in modern polymer matrix composites. This phenomenon has been studied extensively, particularly for uniaxial compression; however, experimental measurements of the strain fields leading to and developing inside these bands under bending are not well explored. In this study, digital image correlation is used to measure strains inside kink bands developing during three-point bending of cross-plied [0/90] laminated composite Dyneema™ HB80. Measurements indicated large normal and shear strains developed inside the band in a way that suggested systematic increases in ply rotation angle as the band evolved with increased bending deflection. Results also suggested intermittent buckling events involving fiber bundles that correlate with oscillations observed in the load–displacement curve. Optical microscopy of failed samples showed failure resulted from a combination of plastic microbuckling and axial splitting.
PimentaSGutkinRPinhoST, et al.
A micromechanical model for kinkband formation: part I experimental study and numerical modeling. Compos Sci Technol2009;
69: 948–955.
13.
Greszczuk LB. On failure modes of unidirectional composites under compressive loading. In: Shih GC and Tamuze UP (eds) Symposium on fracture of composite materials. Boston, MA: Martimus Nijhoff Publishers, 1982, pp.231–244.
14.
VoglerTJKyriakidesS.
On the initiation and growth of kink bands in fiber composites. Part I: experiments. Int J Solids Struct2001;
38: 2639–2651.
15.
DavidsonPWaasA.
The effects of defects on the compressive response of thick carbon composites: an experimental and computational study. Compos Struct2017;
176: 582–596.
16.
WilhelmssonDTalrejaRGutkinR, et al.
Compressive strength assessment of fibre composites based on a defect severity model. Compos Sci Technol2019;
181: 107685.
17.
LeeSHWaasAM.
Compressive response and failure of fiber reinforced unidirectional composites. Int J Fract1999;
100: 275–306.
18.
PrabhakarPWaasA.
Interaction between kinking and splitting in the compressive failure of unidirectional fiber reinforced laminated composites. Compos Struct2013;
98: 85–92.
19.
LeongMOvergaardLCTThomsenO, et al.
Investigation of failure mechanisms in GFRP sandwich structures with face sheet wrinkle defects used for wind turbine blades. Compos Struct2012;
94: 768–778.
20.
SunWVassilopoulosAKellerT.
Finite element analysis of initial imperfection effects on kinking failure of unidirectional glass fiber-reinforced polymer composites. Compos Struct2018;
203: 50–59.
21.
NizolekTJBegleyMRMcCabeRJ, et al.
Strain fields induced by kink band propagation in Cu-Nb nanolaminate composites. Acta Mater2017;
133: 303–315.
22.
BloomLDWangJPotterKD.
Damage progression and defect sensitivity: an experimental study of representative wrinkles in tension. Compos Part B Eng2013;
45: 449–458.
23.
ElhajjarRShamsS.
A new method for limit point determination in composite materials containing defects using image correlation. Compos Sci Technol2016;
122: 140–148.
24.
WisnomMR.
The effect of fibre waviness on the relationship between compressive and flexural strengths of unidirectional composites. J Compos Mater1994;
28: 66–76.
25.
WisnomMRAtkinsonJW.
Constrained buckling tests show increasing compressive strain to failure with increasing strain gradient. J Compos1997;
28A: 959–964.
26.
WisnomMR.
Size effects in the testing of fiber-composite materials. Compos Sci Technol1999;
59: 1937–1957.
27.
SunCTJunAW.
Compressive strength of unidirectional fiber composites with matrix non-linearity. Compos Sci Technol1994;
52: 577–587.
28.
Liu G, Thouless MD, Deshpande VS, et al. Collapse of a composite beam made from ultra-high molecular-weight polyethylene fibres. Master’s Thesis, Cambridge University, 2013.
29.
Patel J and Peralta P. Mechanisms for kink band evolution in polymer matrix composites: a digital image correlation and finite element study. In: ASME International Mechanical Engineering Congress and Exposition, Volume 9: Mechanics of Solids, Structures and Fluids; NDE, Diagnosis, and Prognosis, Phoenix, Arizona, USA, 11–17 November 2016, paper no. IMECE2016-67482, V009T12A055.
30.
ASTM D7264/D7264M - 07. Standard test methods for flexural properties of polymer matrix composite materials. West Conshohocken, PA: ASTM International, 2015.
GreszczukLB. Prediction of transverse strength and scatter in test data for unidirectional composites.
West Conshohocken, PA:
American Society for Testing and Materials, 1974, pp.311–316.
33.
Di LandroLPegoraroM.
Carbon fibre thermoplastic matrix adhesion. J Mater Sci1987;
22: 1980–1986.
34.
GreszczukLB.
Interfiber stresses in filamentary composites. AIAA J1971;
9: 1274–1280.
35.
KurashigeM.
Compressive strength of a laminated fiber-reinforced material. Bull Jpn Soc Mech Eng1984;
27: 2694–2697.
36.
PaganoNJ.
Interlaminar response of composite materials. Compos Mater Ser1989;
5: 1–259.
