Fracture simulation of CFRP laminates in mixed mode bending

Abstract

This paper analyses the progressive mixed mode delamination failure in unidirectional and multidirectional composite laminates using fracture experiments, finite element (FE) simulations and an analytical solution. The numerical model of the laminate is described as an assembly of damageable layers and bilinear interface elements subjected to mixed mode bending. The analytical approach is used to estimate the total mixed mode and decomposed fracture energies for laminates with different stacking sequences, which is also validated through experiments. It is concluded that the interlaminar fracture toughness of multidirectional laminates is considerably higher than that of the unidirectional ones. The effect of initial interfacial stiffness and element size is studied and it is also shown that their value must not exceed a definite limit for the numerical simulations to converge. The model can also be further extended to simulate the mixed mode fracture in hybrid fiber metal laminates.

Mixed-Mode Delamination Failures of Quasi-Isotropic Quasi- Homogeneous Carbon/Epoxy Laminated Composite

“…Nevertheless, the shear cusps in the MMF specimen were less significant and more random compared to the ENF specimen, which was similar to the observation by Naghipour et al [6]. In addition, the roughness of the MMF specimen was less than the ENF specimen [7].…”

“…However, significant shear cusps were observed on the 0 l a y e ri nt h e4 5 direction, which was attributed to the shear mode loading. It has also been reported that the high shear mode would draw large shear cusps [6,7]. A certain amount of matrix cracking was observed on the 45 layer, which was believed to be due to the interaction between 0 and 45 layers during shearing.…”

“…In addition, in the use of laminated composites, multidirectional laminates have been generally known to have higher interlaminar fracture toughness compared to the unidirectional laminates [6,7]. This could be attributed to relatively blunt crack tip or intralaminar crack [7].…”

Effect of layer variations on CFRP strengthened steel circular hollow members under bending: numerical studies

“…Adhesive layers between the fibre layers were modelled using the eight-node threedimensional cohesive elements COHD8. Cohesive elements are generally capable of simulating damage and delamination in composites (Naghipour et al 2009;Shi et al 2012;Al-Zubaidy et al 2013). A triangular traction-separation cohesive law with linear softening is used to characterize the material behaviour of the adhesive.The CFRP patches are meshed with an 8-node quadrilateral in-plane general-purpose continuum shell, reduced integration with hourglass control, finite membrane strains (SC8R).…”

Finite-element modelling of bending of CFRP laminates: Multiple delaminations

“…Since cohesive elements represent zeroor infinitesimal-thickness interfaces, high stiffness is required to model the connections. Therefore, the interface stiffness should be large enough to avoid relative displacements between the connected ply elements but also not too large to cause numerical problems such as spurious oscillations in interfacial traction of the cohesive element [11,12,27]. This stiffness is usually calibrated by numerical 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 12 simulations as it cannot be measured directly through the experiments.…”