Abstract
Last decades, increased attention is paid to the deep understanding of the process induced residual stresses (locked-in) and their effect on shape distortion and fracture. Residual stresses evaluation is particularly important in multilayered composites with anisotropic thermo-mechanical properties, where the ply orientations and stacking sequences highly influence the appearing of manufacturing stresses. In the present study, the effect of free edge on residual stresses inherited during manufacturing of thermoset multilayered composites was investigated. In order to understand the stress-strain state in samples after free edge cut a simplified 2D plane strain finite element analysis was performed. Many phenomena, such as sensitivity of the results to the size of the numerical grid, stress redistribution and size of the area affected by free edge was analyzed. In the current research, the behavior of AS4/8552-1 carbon-epoxy composite during manufacturing cycle was studied by means of finite element modeling in ABAQUS. To describe the behavior of the composite material during the manufacturing process − including processes of formation, polymerization, development of residual strains and stresses was done by developed user subroutine-UMAT, describing the visco-elastic material behavior of the material. The program was implemented in ABAQUS and validated on the basis of literature data. The results of the study can be applied for prediction of residual stresses in composite structure by means of virtual simulation and further understanding the nature of fracture of composites.
Highlights
A well-known stress concentration problem − the socalled free-edge effect was investigated by a large number of scientists (Mittelstedt & Becker, 2007; Rasuo & Dinulovic, 2011; Hu, Karpur, Matikas, Shaw, & Pagano, 1995; Solis, Sánchez-Sáez, & Barbero, 2018; Amrutharaj, Lam, & Cotterell, 1996; Islam & Prabhakar, 2017; Hajikazemi & Van Paepegem, 2018)
Explained by the mismatch of the elastic material properties between two adjacent dissimilar laminate layers, the free-edge effect is characterized by the concentrated occurrence of three dimensional and singular stress fields at the free edges in the interfaces between two layers of composite laminates
As the FE analysis is mesh dependent it is required to provide a mesh refinement study. Such analysis was provided by tabulating the result a specific location versus the characteristic element size for solutions from different meshes – 1, 2, 4, 8, 16, 32 elements per composite layer in the free edge zone
Summary
A well-known stress concentration problem − the socalled free-edge effect was investigated by a large number of scientists (Mittelstedt & Becker, 2007; Rasuo & Dinulovic, 2011; Hu, Karpur, Matikas, Shaw, & Pagano, 1995; Solis, Sánchez-Sáez, & Barbero, 2018; Amrutharaj, Lam, & Cotterell, 1996; Islam & Prabhakar, 2017; Hajikazemi & Van Paepegem, 2018). In Shoufeng Hu et al (1995) carried out a detailed study of the free edge effect on redistribution of residual stresses, radial residual stress reversal and interfacial debonding through theoretical modeling, numerical analysis and experimental. Process modeling of carbon-epoxy composites: residual stress development during. The developed technique will allow evaluating free edge effects for composites with arbitrary lay-up, geometry and shape of the notch
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