Abstract
In this work, an approach based on the Virtual Crack Closure Technique, included in the commercial finite element code ABAQUS, is adopted to study the propagation of delamination in composite structures under quasi-static and fatigue loads. The methodology, originally capable of simulating only delamination under quasi-static loads, has recently been extended introducing the possibility to analyze damage progression under fatigue load condition. The approach is assessed on simple specimens, Double Cantilever Beam and Mixed Mode Bending test, comparing the results with literature data. Afterwards, the behavior of a single-stringer specimen with an initial delamination is numerically investigated considering compressive loading conditions. At first, the single-stringer specimen is analyzed under quasi-static compressive load showing a clear correlation between local buckling phenomena and delamination growth. Then, a cyclic compressive load is applied such that the specimen switches between pre- and post-buckling conditions in a single load cycle. The outcomes of the numerical analyses are compared with the experimental data obtained from an experimental test campaign previously performed, showing the advantages of the adopted numerical technique but also the limitations that need to be addressed to properly analyze this phenomenon.
Highlights
Modern thin-walled aeronautical structures, such as fuselage and wing structures, make extensive use of composite stiffened panels where the stringers are typically joined to the skin through adhesive bonding or co-curing
A number of issues with the original Virtual Crack Closure Technique (VCCT) formulation, such as the problem of orthogonality between the crack front and the structural mesh or the bi-material interface simulation, have been identified and addressed by a variety of researchers across a large number of publications [17,18,19]. This methodology has still some limitations when dealing with fatigue delamination problems [20] and requires an initial damage, it currently represents an effective solution for the simulation of fatigue crack growth in structural components
The numerical investigation of delamination growth under quasi-static and fatigue load using an approach based on Virtual Crack Closure Technique and available in the finite element code ABAQUS has been conducted
Summary
Modern thin-walled aeronautical structures, such as fuselage and wing structures, make extensive use of composite stiffened panels where the stringers are typically joined to the skin through adhesive bonding or co-curing. Numerical approaches derived from the fracture mechanics are based on the direct application of the Paris law in conjunction with a methodology for the calculation of the energy release rate, such as the Virtual Crack Closure Technique (VCCT) [13,14,15] This approach, developed for simulating delamination propagation under quasi-static load conditions [16], is implemented into several commercial Finite Element (FE) codes. The intent is to improve the ease and affordability with which the response of stiffened panels can be experimentally determined, enabling the study of their failure behavior and damage tolerance in the post-buckling regime This specimen provides the opportunity to verify and validate quasi-static and fatigue damage models due to its relatively complex geometry compared to coupon specimens, and its small size, which makes it computationally tractable.
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