A numerical method based on pore‐pressure cohesive zone modeling for simulation of debulking in resin‐saturated composite prepregs

Abstract

Aircraft composite parts are commonly manufactured from resin‐saturated thermoset pre‐impregnated plies laid‐up over a rigid tool and consolidated and cured in an autoclave. In many applications, autoclave consolidation alone is not sufficient to remove the air, or bulk, that has been entrapped within the laminate during layup. Entrapped bulk can lead to the formation of defects, including wrinkles and voids, which can significantly affect structural performance. Vacuum consolidation, or “debulking,” has been a standard practice extensively used by aircraft manufacturers to reduce the amount of bulk and mitigate defect formation. Yet, the underlying physical principles governing formation of defects during these early stages are not well understood. This work presents the development of a new finite element‐based method for simulation of debulking with the objective to contribute to a better understanding of the key physics involved. The model includes pore‐pressure cohesive elements inserted at ply interfaces for discrete representation of entrapped air pockets and modeling air flow during debulking; and cohesive contact between the plies for simulating the typical tacky behavior of uncured thermoset tape prepregs. The debulking of a two‐ply laminate with an initial seeded wrinkle is considered for illustration of the approach and comparison with experimental results.

Spatial and temporal constraints of the cohesive modeling: A unified criterion for fluid‐driven fracture

“…This technique provides an approximate approach to characterize a wide range of damage phenomena in the narrow region ahead of the crack tip, such as crazing in polymers, micro-cracking in brittle materials, and void growth in ductile materials. 3,4 Notably, as a criterion for fracture initiation and propagation, the CZM can be integrated into most traditional numerical methods, such as the finite element method (FEM), 5 the extended finite element method (XFEM), [6][7][8] and the phase-field method (PFM). 9,10 In this context, the CZM empowers these numerical methods to model cohesive fracture and simulate its propagation by introducing the zero-thickness interface.…”

Effect of Resin Bleed Out on Compaction Behavior of the Fiber Tow Gap Region during Automated Fiber Placement Manufacturing

“…The present study considers the effect of resin bleed out on the formation of non-uniform morphology around the region of the fiber tow gap. To model prepreg behavior around the internal void, like in the case of debulking, a negative internal pressure gradient can be considered inside of the void using porous-cohesive elements [ 26 ]. Another approach is to consider the flow front filling the gap via a one-dimensional numerical model [ 27 ].…”

Numerical Analysis of Thermoplastically Welded CFRP Structures

“…Furthermore, by using hanging nodes on the discontinuities and interfaces, the calculation costs could be reduced. Seon et al [25] introduced a new finite element-based method to simulate the debulking by using pore-pressure cohesive elements (PPCE) at ply interfaces. The PPCE therefor are used to consider entrapped air pockets as well as to model the air flow during debulking in prepreg materials.…”