Mixed-mode fracture toughness of co-cured and secondary bonded composite joints

Hygrothermal effects on mode II interlaminar fracture toughness of co‐bonded and secondary bonded composites joints

“…The fracture toughness obtained for SB (RTA condition) is close to those reported in the literature. Blackman et al obtained propagation values of 5,000 J/m 2 (5 N/mm) using ELS setup with T300/924 and an epoxy‐paste adhesive (pre‐cracked in Mode I), while Mohan et al reached values from 3,000 to 7,000 J/m 2 (3–7 N/mm) with 977‐2/HTS and an epoxy‐film adhesive. Moura et al also tested SB joints between unidirectional carbon/epoxy prepregs with Araldite under ENF setup and reported G IIC of 4,600 J/m 2 (4.6 N/mm).…”

“…However, composite parts are still assembled with conventional fasteners, which can compromise the mechanical improvements reached with the wisely designed use of these materials. The main disadvantages from the use of screws and rivets on composites are the high‐stress concentration generated around the holes fiber discontinuity and delamination introduced during the machining process, which might decrease the load‐carrying capacity of the structure .…”

Mode I Interlaminar Fracture Toughness Analysis of Co-Bonded and Secondary Bonded Carbon Fiber Reinforced Composites Joints

“…Such development is due to the advantages the use of these materials brings, like resistance to corrosion, fatigue, impact and thermal stability, besides the more attractive mechanical characteristics in comparison to metallic materials 2 traditionally used. Additionally to composite material itself, the study of alternative bonding techniques has also become a topic of relevance in the industry, taking place of the conventional screws and rivets, which not only increase weight but also deteriorate the components structural capacity because they actuate like a stress concentrator contributing to severe delamination problems 3,4 . In this manner, co-cure, co-bonding and secondary bonding techniques have received special attention in recent years, with emphasis on the last two for allowing more varied project designs, sizes and simpler manufacture 3 , besides lowering or suppressing the stress concentration 5 .…”

“…This difference in glass transition temperature between the bonding technologies can be responsible for the differences that occurred during their mechanical tests. The lower Tg observed for CB adhesive could be explained by the fact that uncured materials contain free and bound water (the first bonds with resin by one single hydrogen bond whereas the second bonds by multiple hydrogen bonds 4,22 ), which is released during cure process. SB has only the water from the adhesive to be released, while CB still has an uncured laminate to be cured.…”

Experimental assessment of an End Notched Flexure test configuration with an inserted roller for analyzing mixed-mode I/II fracture toughness

“…Extensive experiments have been conducted to investigate the mixed-mode fracture of composite laminates using different type of test configurations, as was reviewed by Brunner et al [10], such as Mixed Mode Bending test (MMB) [11][12][13][14], Asymmetric Double Cantilever Beam (ADCB) test [15,16], Single-Leg Four Point Bending test (SLFPB) [17] and Compact Tension Shear specimen (CTS) [18]. Bennati et al [19] developed an enhanced beam-theory model of the MMB test, after a review of the existing models.…”