Effect of degree of cure on irreversible (viscoplastic) shear strain development in layers of glass fibre/ epoxy resin (LY5052 epoxy resin) [+45 °/−45 °]s laminate is studied performing a sequence of constant stress creep and viscoelastic strain recovery tests. For fixed values of degree of cure in range from 79.7% to 100%, the viscoplastic strains were measured as dependent on time and stress and Zapa's integral representation was used to characterize the observed behaviour. It is shown that at all degrees of cure the viscoplastic behaviour can be described by Zapa's model with parameters dependent on degree of cure. It is shown that for degree of cure lower than 80% the viscoplastic strains grow much faster and are much more sensitive to the increase of the applied shear stress. These irreversible strains developing in the final phase of the curing can significantly alter the residual stress state in the composite structure.
LeeWILoosACSpringerGS. Heat of reaction, degree of cure, and viscosity of Hercules 3501-6 resin. J Compos Mater1982; 16: 510–520.
2.
O'BrienDJMatherPTWhiteSR. Viscoelastic properties of an epoxy resin during cure. J Compos Mater2001; 35: 883–904.
3.
SaseendranSWysockiMVarnaJ. Evolution of viscoelastic behavior of a curing LY5052 epoxy resin in the glassy state. Adv Manuf: Polym Compos Sci2016; 2: 74–82.
4.
SaseendranSWysockiMVarnaJ. Evolution of viscoelastic behaviour of a curing LY5052 epoxy resin in the rubbery state. Adv Compos Mater2017; 26: 553–567.
5.
SaseendranSWysockiMVarnaJ. Cure-state dependent viscoelastic Poisson's ratio of LY5052 epoxy resin. Adv Manuf: Polymer Compos Sci2017; 3: 92–100.
6.
KarkanasPIPartridgeIKAttwoodD. Modelling the cure of a commercial epoxy resin for applications in resin transfer moulding. Polym Int1996; 41: 183–191.
ThiruppukuzhiSVSunCT. Models for the strain-rate-dependent behavior of polymer composites. Compos Sci Technol2001; 61: 1–12.
9.
GiannadakisKMannbergPJoffeRVarnaJ. The sources of inelastic behavior of glass fibre/vinylester non-crimp fabric [ ± 45] s laminates. J Reinforc Plast Compos2011; 30: 1015–1028. .
10.
GiannadakisKVarnaJ. Analysis of nonlinear shear stress–strain response of unidirectional GF/EP composite. Compos Appl Sci Manuf2014; 62: 67–76.
11.
FrankGJBrockmanRA. A viscoelastic–viscoplastic constitutive model for glassy polymers. Int J Solid Struct2001; 38: 5149–5164.
12.
GhorbelE. A viscoplastic constitutive model for polymeric materials. Int J Plast2008; 24: 2032–2058.
13.
Kiasat MS. Curing shrinkage and residual stresses in viscoelastic thermosetting resins and composites. PhD Thesis, TU Delft, Netherlands, 2000.
14.
HossainMPossartGSteinmannP. A small-strain model to simulate the curing of thermosets. Comput Mech2009; 43: 769–779.
15.
HossainMSteinmannP. Degree of cure-dependent modelling for polymer curing processes at small-strain. Part I: consistent reformulation. Comput Mech2014; 53: 777–787.
16.
Brockman RA, Lee CW, et al. OMC processing simulation using an elastic-viscoplastic material model. In: International SAMPE technical conference, Baltimore, MD, USA, 18–21 May 2015.
17.
LieblCJohlitzMet al.Simulation of curing-induced viscoplastic deformation: a new approach considering chemo-thermomechanical coupling. Arch Appl Mech2012; 82: 1133–1144.
18.
LieblCJohlitzMet al.Three-dimensional chemo-thermomechanically coupled simulation of curing adhesives including viscoplasticity and chemical shrinkage. Comput Mech2012; 49: 603–615.
19.
MahnkenRSchlimmerM. Simulation of strength difference in elastoplasticity for adhesive materials. Int J Numer Meth Eng2005; 63: 1461–1477.
20.
ZapasLJCrissmanJM. Creep and recovery behaviour of ultra-high molecular weight polyethylene in the region of small uniaxial deformations. Polymer1984; 25: 57–62.
21.
NordinLOVarnaJ. Nonlinear viscoplastic and nonlinear viscoelastic material model for paper fiber composites in compression. Compos Appl Sci Manuf2006; 37: 344–355.
22.
MarklundEVarnaJWallströmL. Nonlinear viscoelasticity and viscoplasticity of flax/polypropylene composites. J Eng Mater Technol2006; 128: 527–536.
23.
PupureLVarnaJet al.An analysis of the nonlinear behavior of lignin-based flax composites. Mech Compos Mater2013; 49: 139–154.
24.
PupureLVarnaJJoffeR. On viscoplasticity characterization of natural fibres with high variability. Adv Compos Lett2015; 24: 125–129.
25.
DasappaPLee-SullivanPXiaoX. Development of viscoplastic strains during creep in continuous fibre GMT composites. Compos B Eng2010; 41: 48–57.
26.
ZaoutsosSPPapanicolaouGC. On the influence of preloading in the nonlinear viscoelastic–viscoplastic response of carbon–epoxy composites. Compos Sci Technol2010; 70: 922–929.
27.
Svanberg JM. Predictions of manufacturing induced shape distortions. PhD Thesis, Luleå University of Technology, Sweden, 2002.
28.
KamalMRSourourS. Kinetics and thermal characterization of thermoset cure. Polym Eng Sci1973; 13: 59–64.
