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    The effects of nanostructure additive on fracture strength in adhesively bonded joints subjected to fully reversed four-point bending fatigue load
    (Elsevier Sci Ltd, 2021) Demir, Kubra; Gavgali, Esma; Yetim, Ali Fatih; Akpinar, Salih
    Structural adhesive joints used in aerospace are usually subjected to fatigue loading rather than static loading. This study experimentally and numerically investigated the static four-point bending loads of adhesively bonded joints after fully reversed four-point bend fatigue loading where nanoadhesives - obtained by adding carbon nanostructures into aerospace grade structural adhesive - were used to bond the joints. Single lap joint specimens were produced using a nanocomposite adhesive obtained by adding 1 wt % graphene, 1 wt % carbon nanotubesCOOH and 1 wt % fullerene C60 nanostructures to a DP460 structural adhesive. AA2024-T3 aluminum alloy and carbon fiber-reinforced composites (CFRCs) with a plain weave fabric (0/90 degrees) were used as adherend materials. First, static four-point bending tests were applied to these joints to obtain their strengths and then fully reversed sinusoidal fatigue tests were applied under a constant load amplitude, a frequency of 20 Hz and a load ratio of R = -1. Fatigue tests were performed over 1,000,000 cycles - accepted as an infinite life - at four different load levels by considering the strengths obtained from the static tensile tests. After obtaining the static four-point bending strengths of the joints to which fatigue loading was applied, the changes in the strengths of joints with and without fatigue testing were examined. The static strengths of aluminum joints bonded with nanoadhesive and subjected to fully reversed fatigue loading significant increased, depending on the nanostructure type added to the adhesive. Moreover, such increases in the strengths of joints are highly dependent on the adherend type (composite with [0/90]6 stacking sequence or AA2024-T3 aluminum).
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    A study on the effects of nanostructure reinforcement on the failure load in adhesively bonded joints after the subjected to fully reversed fatigue load
    (Taylor & Francis Ltd, 2022) Akpinar, Salih; Demir, Kubra; Gavgali, Esma; Yetim, Ali Fatih
    Today, adhesively bonded joints are frequently used in the space and aviation industries. Joints used in these sectors are generally subject to dynamic loads due to environmental factors. This study experimentally and numerically investigated the static tensile loads of adhesively bonded joints after fully reversed (combination of tensile and compressive) fatigue loading where nanoadhesives - obtained by adding carbon nanostructures into aerospace grade structural adhesive - were used to bond the joints. Single lap joint specimens were produced using a nanocomposite adhesive obtained by adding 1 wt. % graphene, 1 wt. % carbon nanotubes-COOH and 1 wt. % fullerene C60 nanostructures to a DP460 structural adhesive. AA2024-T3 aluminum alloy and carbon fiber-reinforced composites (CFRCs) with a plain weave fabric (0/90 degrees) were used as adherend materials. First, static tensile tests were applied to these joints to obtain their failure loads and then fully reversed sinusoidal fatigue tests were applied under a constant load amplitude, a frequency of 20 Hz and a load ratio of R = -1. Considering the failure loads obtained from the static tensile tests, 10(6) fully reversed fatigue loading cycles were applied - which was accepted as an infinite life - at 400 N, 800 N and 1200 N load levels. The static tensile failure loads and energy values absorbed of these joints were obtained and the change in the failure loads and energy values absorbed of the joints subjected to fatigue was investigated. The static failure loads of aluminum joints bonded with nanoadhesive and subjected to fully reversed fatigue loading increased by approximately 5% to 17%, depending on the nanostructure type added to the adhesive. Moreover, it was observed that there was an increase in loading of approximately 3% to 20% for the nanostructure reinforced joints obtained by using CFRCs with [0/90](6) stacking sequence.