An efficient methodology for the experimental characterization of mode II delamination growth under fatigue loading

Abstract

Crack growth rate curves provide information about the delamination resistance of composite materials under cyclic loading. The existing methodologies for mode II fatigue testing using three-point bending end-notched flexure (3-ENF) under constant cyclic displacement conditions yield discontinuous delamination growth rate curves, therefore requiring a batch of several specimens to be tested under different severity conditions in order to fully characterize the crack growth. This work describes a variable cyclic displacement test procedure that, in combination with the real time monitoring of the specimen's compliance, allows the crack growth rate to be measured for the desired range of severities with a single specimen, thus avoiding any human intervention during the tes

A simulation method for fatigue-driven delamination in layered structures involving non-negligible fracture process zones and arbitrarily shaped crack fronts

“…Crack growth rate curves under mode I loading conditions were obtained using the multi-specimen testing methodology described in [54] with R = 0.1 and R = 0.5. Under mode II and mixed-mode loading conditions, the methodology described in [55] and [56] was used instead. This consisted of varying the applied cyclic displacement in order to increase the energy release rate range covered by a single test.…”

“…The input parameters pI and AI are obtained from the Paris' law-based fitting of the experimental data listed in Table 4. Figure 6: Comparison between the experimentally obtained mode II crack growth rate curves [55] and the results from the 2D simulations. The input parameters pII and AII are obtained from the Paris' law-based fitting of the experimental data listed in Table 4.…”

A computationally-efficient micromechanical model for the fatigue life of unidirectional composites under tension-tension loading

“…c) The Paris law constants of the interface (C II int and m II int ) have an important effect on the composite S-N curves predicted by the model. Despite the lack of experimental results to determine these constants for interfacial debonding, an estimation of these parameters was made (see Table 4) based on values found in the literature [16,[23][24][25][26][27] for mode-II delamination propagation. This motivated the parametric study presented in Section 3.3 to demonstrate the sensitivity of the model to these parameters.…”

“…The growth rate of matrix cracks and interfacial debonds can be modelled by a Paris power law [17][18][19][20], and is affected by the quality of the bonding between the fibres and the matrix, which is often controlled by surface treatments on the fibres [6,21,22]. Determining the Paris law constants for crack propagation along the fibre-matrix interface is a challenging task: in the literature, a wide scatter of data can be found for the values of Paris law constants for mode-II debonding/delamination in composite materials [16,[23][24][25][26][27]; moreover, there are also only a few experimental studies for the Paris law constants for interfacial debonding around individual fibres [28] and no experimental data for debonding around small bundles of fibres.…”

Comparison of static and fatigue interlaminar testing methods for continuous fiber reinforced polymer composites

“…In the case of short beam shear, delamination forms and propagates during the bending test of a relatively thick specimen in the three-point bending setup, while in the case of the double-notched interlaminar shear test, interlaminar stress is introduced by the compressive or tensile loading parallel to the interface. Fatigue properties are mostly characterized with the ENF [17][18][19] test, which is similar to the short beam shear method used in the static setup, but delamination does not start at the free edge of the specimen but at an artificial initial delamination front. Since artificial delamination has to be introduced and compliance calibration has to be performed, the ENF test is complex.…”