Mode III interlaminar fracture of carbon/epoxy laminates using the edge crack torsion (ECT) test

Abstract

The mode III interlaminar fracture of carbon/epoxy laminates was evaluated with the edge crack torsion (ECT) test. Three-dimensional finite element analyses were performed in order to select two specimen geometries and an experimental data reduction scheme. Test results showed considerable non-linearity before the maximum load point and a significant R-curve effect. These features prevented an accurate definition of the initiation point. Nevertheless, analyses of non-linearity zones showed two likely initiation points corresponding to G IIIc values between 850 and 1100 J/m 2 for both specimen geometries. Although any of these values is realistic, the range is too broad, thus showing the limitations of the ECT test and the need for further research.

Experimental Methods of Determining Fracture Toughness of Fiber Reinforced Polymer Composites under Various Loading Conditions

“…Extensive work on Mode I and Mode II fracture is reported in the literature, but less work has been reported on Mode III despite its importance in edge delamination [20,21]. Donaldson [22] has reported that split cantilever beam (SCB) tests can be used to measure the Mode III fracture energy G IIIC .…”

“…The Mode III fracture toughness is calculated by Irwin-Kies relation [7,20] CLT torsional shear moduli of the uncracked and cracked parts of the specimen, respectively, derived by Lee [25].…”

Investigation of push-out delamination using cohesive zone modelling and acoustic emission technique

“…The experimental work was carried out on the epoxy resin reinforced by the E-glass unidirectional and woven fiber with the density of 1.46 g/cm 3 , 500 g/m 2 and 303 g/m 2 , respectively. The laminates were provided by hand lay-up with compression molding.…”

“…Delamination is an insidious failure mode that is frequently present within the composite and it may easily escape detection [3]. Passive methods, such as AE, may improve the reliability and confidence of delamination detection [4][5][6][7][8].…”

Test methods for measuring pure mode III delamination toughness of composite

“…Mode II component can be reduced to a reasonable level with an appropriate choice of the specimen geometry [18e20,22]. It is not satisfactory to apply the data reduction schema based on experimental CC method for determining G IIIC because a large number of specimens with different initial crack lengths had to be used, and the value of G IIIC was found to increase with the crack length [22]. Moreover, small initial crack lengths for ECT specimens should be preferable for measuring G IIIC [26], but too small initial crack lengths would decrease the accuracy because of the uncertainty in the real crack length measurement.…”