Numerical investigation of adhesively bonded metal structures subjected to impact loads using Ls-Dyna

Abstract

Studies carried out in the defense industry (aviation studies, land vehicle developments, development of marine and submarine vehicles, etc.) have revealed that there are requirements such as reducing the weight of structural systems, increasing impact resistance and the ability to use different materials together, it has been observed that traditional mechanical connection methods such as rivets, bolts, welds, etc. do not provide the necessary flexibility and possibilities in this regard and prevent the designs made with some limitations. For example, when two dissimilar metals are to be used together, welding is not feasible, while solutions such as bolts and rivets cause discontinuity in the structure of the materials, making the structure favorable for crack initiation, and the use of conventional connections requires special connection design (e.g. leaving space for the use of hand tools according to the type of connection selected, etc.). In addition to such limitations, traditional methods used in industry often cause localized stress concentrations, crack initiation points and maintenance difficulties; they show limited energy absorption capacity, especially under dynamic loads. In this study, a series of impact scenarios were simulated to investigate the behavior of adhesively bonded metallic structures under varying impact velocities and angles. A hemispherical-headed projectile, 35 mm in length and with a head diameter of 10 mm, was modeled to impact the bonded structure at 90° and 45° angles with velocities of 10, 20, 30, 40, 100, and 215 m/s, respectively. The target structure consisted of Al2024-T3 and Ti-6Al-4V (Ti64) alloy plates, each measuring 250 mm × 100 mm × 3 mm, bonded together with an adhesive layer forming a 100 mm × 100 mm bonding area. Through these simulations, the dynamic response of the adhesively bonded structure under different impact energies and angles was numerically investigated using LS-DYNA. There are many different material models available for modeling metals in the software program. In the literature review, existing mathematical models were examined and it was decided to use the Johnson and Cook material and damage models. In the Ls-Dyna/Explicit software, there are 10 material models based on the Johnson and Cook mathematical model. MAT_015 JOHNSON_COOK and MAT_107 The use of the MODIFIED_JOHNSON_COOK material model was considered suitable because it effectively represents the strain rate and temperature-dependent behavior of metals under impact loading. The material properties required in the models were quoted from the literature. To validate the material models, the numerical analyses presented in previous studies were reproduced and the obtained results were compared with the corresponding experimental data. Thanks to the agreement obtained, the performance of the bonded joints was analyzed under the impact scenarios created for this thesis using the material properties in question. The findings of this study indicate that adhesively bonded joints play a crucial role in defense applications. According to the results obtained in the Ls-Dyna/Explicit environment in line with the parameters verified by using existing sources in the literature. Bonded joint technologies provide an insight into the performance of structures to be developed against impact loads that can cause high deformation rates; Simultaneously, it delivers a computationally efficient and accurate basis for engineers engaged in the structural design of defense systems. Future studies are recommended to address topics such as the behavior of different metal types, temperature effects, hybrid connection solutions and multiaxial loading scenarios.