Cure shrinkage defects in epoxy resins

The cure of a thermoset matrix in the formation of composites is always accompanied by chemical shrinkage that generates internal stresses. In composites with high fiber content, the matrix is cured under three-dimensionally constrained conditions. The results of the preuiou~ experimental and theoretical modeling of formation of shrinkage damage under these conditions in epoxy-amine system~ are briefly discu~ed. The effect of the model geometry (tube and plate models), scale factor, cure schedule, and chemical structure of composites is analyzed. A theoretical model for predicting the possibility of formation of shrinkage damage in fiber composites is proposed. A regular square structure wa~ considered. Analysis showed that the ma:dmum level of shrinkage stress in the matrix at the ultimate fiber fraction ~+ was close to the stress level ~ in an experimental long tube model, where the formation of shrinkage damage took place. The experimental results for the short tube model showed that the shrinkage damage in epoxy-amine systems occurred up to approximately a*/3. The damage development took place within the whole range of fiber content from ~+ to ~* (where the shrinkage stress level u~ about o+/3). In the long tube model, cohesive defects always nucleated inside the matrix. The damage grew, reached the inner surface of the tube, and then extended as adhesive debondings. A similar situation is expected in composites with a high fiber content. The damage considered is local, and the total monolithic character of a composite product is conserved.Polymer composite materials (PCM) contain two components with different physical-mechanical properties that during formation of the material inevitably lead to the appearance of internal (technological) stresses. The reasons for their origin on the micro-and macrolevel, the role of various factors in their formation, as well as their control methods are considered, for example, in [1][2][3].On the microlevel, the temperature stresses caused by the noniaothermal process of forming a polymer composite, as a rule, make the basic contribution to internal residual stresses. The influence of the stresses generated by chemical shrinkage of the polymeric matrix during synthesis is usually neglected, since at this stage the elastic characteristics of the matrix are very low. However, under certain conditions considered further on, the role of the chemical shrinkage stresses can considerably increase, and these stresses can evidently lead to the appearance of shrinkage damage in the composite on the microlevel.

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“…The above features were observed in all the systems [13]. The above features were observed in all the systems [13].…”

Section: Results Of Modeling the Formation Of Shrinkage Damagesupporting

confidence: 51%

Experimental and theoretical modeling of shrinkage damage formation in fiber composites

Коротков¹,

Розенберг²

1998

Mech Compos Mater

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“…3 That is, the presence of fibers in a laminate and the curing cycle alter the behavior of the matrix during the curing process. Defect formation due to constrained curing of epoxy has also been demonstrated by Plepys and Ferris 4 and Chekanov et al 5 Basically, the system undergoes shrinkage due to chemical processes, and thus, builds internal stresses. Depending on the constituent chemistry and thermal cycle that is used during cure, a fiber reinforced composite can and may undergo damage and cracking during the curing process, most likely due to gradients in stress and strain fields generated during cure, resulting in significant residual stresses.…”

Section: Introductionmentioning

confidence: 90%

Influence of Fiber Packing on the Deformation and Damage Development in Fiber Reinforced Laminates during Curing

Prabhakar

Waas

2014

55th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference

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The influence of fiber packing on the deformation and damage evolution, during the process of manufacturing and subsequently, in fiber reinforced composites is investigated by considering a cluster of fibers within a matrix that is undergoing curing and subsequently subjected to mechanical loads. The residual stress development due to cure shrinkage and polymerization of the matrix, during the curing process, is modeled using the finite element (FE) framework. The model is based on the notion of polymer networks that are continuously formed in a body of changing shape due to changes in temperature, chemistry and external loads. Nonlinear material behavior due to post-damage response that can lead to cracking in the matrix is incorporated through a crack band model that preserves mesh objectivity in the FE calculations. The combined thermo-chemo-mechanical response of the composite due to curing and subsequent mechanical loading is investigated in detail in this paper.

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“…Depending on the constituent chemistry of the matrix, the thermal cycle prescribed, and the fracture and strength properties of a curing matrix, a fiber-reinforced composite can and may undergo damage and cracking in the matrix during the cure cycle. Chekanov et al [4] have reported various types of defects that may form in a constrained epoxy resin system undergoing curing. Rabearison et al [5] studied the curing of a thick epoxy tube using a finite element model and concluded that high stress gradients developed during differential curing can cause cracking.…”

Section: Introductionmentioning

confidence: 99%

Effect of the curing process on the transverse tensile strength of fiber-reinforced polymer matrix lamina using micromechanics computations

D’Mello

Maiarù

Waas

2015

Integr Mater Manuf Innov

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The effect of the curing process on the mechanical response of fiber-reinforced polymer matrix composites is studied using a computational model. Computations are performed using the finite element (FE) method at the microscale where representative volume elements (RVEs) are analyzed with periodic boundary conditions (PBCs). The commercially available finite element (FE) package ABAQUS is used as the solver, supplemented by user-written subroutines. The transition from a continuum to damage/failure is effected by using the Bažant-Oh crack band model, which preserves mesh objectivity. Results are presented for a hexagonally packed RVE whose matrix portion is first subjected to curing and subsequently to mechanical loading. The effect of the fiber packing randomness on the microstructure is analyzed by considering multi-fiber RVEs where fiber volume fraction is held constant but with random packing of fibers. The possibility of failure is accommodated throughout the analysis-failure can take place during the curing process prior to the application of in-service mechanical loads. The analysis shows the differences in both the cured RVE strength and stiffness, when cure-induced damage has and has not been taken into account.

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Cure shrinkage defects in epoxy resins

Cited by 39 publications

References 9 publications

Experimental and theoretical modeling of shrinkage damage formation in fiber composites

Experimental and theoretical modeling of shrinkage damage formation in fiber composites

Influence of Fiber Packing on the Deformation and Damage Development in Fiber Reinforced Laminates during Curing

Effect of the curing process on the transverse tensile strength of fiber-reinforced polymer matrix lamina using micromechanics computations

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