Influence of interface ply orientation on delamination growth in composite laminates

Abstract

The standard experimental procedures for determining the interlaminar fracture toughness are designed for delamination propagation in unidirectional specimens. However, in aerospace structural components, delamination usually occurs between plies at different orientations resulting in different damage mechanisms which can increase the value of the fracture toughness as the delamination propagates. Generally, numerical analyses employ the value measured at the delamination onset, leading to conservative results since the increase resistance of the delamination is neglected. In this paper, the fracture toughness and the R-curves of carbon/epoxy IM7/8552 are experimentally evaluated in coupons with delamination positioned at 0°/0° and 45°/−45° interfaces using Double Cantilever Beam (DCB) and Mixed-Mode Bending (MMB) tests. A simplified numerical approach based on the Virtual Crack Closure Technique (VCCT) is developed to simulate variable fracture toughness with the delamination length within a Finite Element code using a predefined field variable. The results of the numerical analyses compared with the experimental data in terms of load-displacement curves demonstrate the effectiveness of the proposed technique in simulating the increase resistance in delamination positioned between plies at 45°/−45° interface.

A Numerical Assessment of the Influence of Local Stress Ratio in the Fatigue Analysis of Post-Buckled Composite Single-Stringer Specimen

“…One of the main reasons for this discrepancy are the interface properties adopted in the numerical analysis which are obtained from the standard DCB and MMB specimens with a delamination positioned between 0° plies, while in the SSC the skin-stringer separation is positioned between −45° and 45° plies. Previous work [34] has shown that delamination The evolution of the out-of-plane displacements predicted by the numerical model is in agreement with the DIC images from a qualitative point of view. Initially, the global buckling of the specimen starts in the skin with two half-waves on the side of the delamination and three on the opposite (Figure 10a,e).…”

“…One of the main reasons for this discrepancy are the interface properties adopted in the numerical analysis which are obtained from the standard DCB and MMB specimens with a delamination positioned between 0 • plies, while in the SSC the skin-stringer separation is positioned between −45 • and 45 • plies. Previous work [34] has shown that delamination between differently oriented plies results in a large increase of the fracture toughness as the delamination propagates due to the presence of fiber-bridging and delamination migration to adjacent plies, phenomena which were both observed during the performed experimental tests.…”

“…The FE model and boundary conditions are shown in Figure 7. The elastic material properties were determined through a previous experimental campaign of material characterization [34], while the interface material properties and fatigue properties were taken from the literature [27]. The values adopted for the numerical analyses are reported in Table 1.…”

Resistance of Polymeric Laminates Reinforced with Fabrics against the Growth of Delaminations

“…In [ 8 ], resistance against delamination under Mixed-Mode loading (G II = 34%, 85%) was investigated for 0°//0°, 0°//22.5°, 0°//45°, and 0°//90° interfaces. More recent results of similar investigations can be found, e.g., in [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ], and in [ 19 , 20 , 21 , 22 ] where also R-curves were of interest.…”

An experimental evaluation of cryogenic machining in the drilling of carbon fiber reinforced plastics for aerospace

“…25 Moreover, in aerospace structures, delamination usually appears between plies at different orientations. 26 So, the laminates were created by stacking unidirectional plies under the following configurations: 0/90/45, 30/60 and 0/90. For sample manufacturing, the MTM® 57 series resins from the company CYTEC and the standard modulus carbon fiber T700S from the company Toray were used.…”