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As bonded components of engineering structures inevitably experience fatigue loading conditions during their service life, it is significant to find ways to enhance their endurance. Also, adding nanoparticles to the adhesive can be introduced as an approach to design more durable bonded joints. In this way, it is important to determine a nanoparticle dispersion method which can lead to the longest fatigue life. Accordingly, this paper aims to investigate the influence of various nanoparticle dispersion treatments on static and fatigue responses of aluminum‐to‐composite bonded joints under four‐point bending. For this purpose, four dispersion techniques of mechanical stirring, bath‐sonication, low‐power and high‐power probe‐sonication were used to disperse nanoparticles into the adhesive. Also, four specimen groups of neat (with no additive particles), graphene nano platelet (GNP)‐reinforced, nano silica‐reinforced, and hybrid‐reinforced (including GNP + nano silica) were prepared. Results indicated that, for the joints including GNPs, the longest fatigue life was achieved for the specimens prepared by low‐power sonication method, while for hybrid‐type reinforcements, using high‐power method led to the highest endurance. Moreover, for 0.5 and 1.0 wt.% of nano silica, the endurance of bath‐sonicated specimens was 12.77% and 9.28% longer than low and high‐power probe‐sonicated joints, respectively. Using the backface strain (BFS) measurement technique, the influence of dispersion methods was studied on extending the crack initiation life (CIL) of each joint group. It was revealed that, for 0.5 wt.% and 1.0 wt.% of nano silica, the CIL is independent of the dispersion method, while, for 1.5 wt.%, probe sonicated specimens had the longest CIL. The microstructural characterization of each dispersion method and major reinforcing mechanisms were interpreted by scanning electron microscopy (SEM). For future researches, using X‐ray tomography and health monitoring methods is recommended to detect size and location of damage for nanoparticle reinforced composite structures.

In recent years, varied industrial users such as the automotive and electronic manufacturers, have greatly expanded the application of technical polymers, exploring the lower weight, improved moldability of complex parts and good mechanical performance that these materials can provide, especially when reinforced with fibers. Among these materials, polybutylene terephthalate reinforced with 30% glass fiber, designated as PBT GF30, is highly interesting, since it combines excellent mechanical properties with watertightness, allowing PBT GF30 to be used in the encapsulation of sensitive electronic elements. However, to maintain access, PBT GF30 products always require the use of joints, which are often created using laser welding. This work presents a detailed characterization of the thermal, optical, mechanical, and morphological characteristics of PBT‐GF30 suitable for laser welding, supported by a numerical analysis. This process allowed to determine the influence of thermal energy on the behavior of the material and thus fully understand the mechanical response of the material after laser welding. Testing of the PBT GF30 in the as received state confirmed a fusion temperature of 225°C and large energy absorption for wavelengths around 1000 nm. Exposure to large temperatures leads to increased fiber exposure and matrix degradation, with a deleterious effect on the mechanical properties. When treated at the highest temperature under consideration, the material exhibited a reduction of 66% in its ultimate tensile stress, 67% in the yield at failure, 45% in the Young's modulus and 44% in the stress intensity factor. Hardness was less affected by the temperature increase. From the numerical model for the tensile and the compact tension tests, it was possible to find a good degree of convergence. This material was generally found suitable for laser welding processes and the determined useful to support the modeling the behavior of laser welded joints.

The strength and durability of adhesive joints are significantly influenced by environmental conditions. Humidity absorption can cause deleterious effects on the adhesive joint's performance. The current study investigates the tensile properties of an epoxy‐based adhesive using Arcan joints (which is a kind of butt joint) subjected to different aging levels and loading conditions. To this end, joints with different aging times, as well as reference‐dried samples, were subjected to both the static and cyclic loading conditions. To construct the S–N curves, different cyclic load levels were applied to the joints. The static results showed that the mechanical properties, such as tensile strength of the joints decreased with an increase of the aging time. The fatigue strength and the fatigue lifetime were significantly decreased by the increase of aging levels, mainly due to an interfacial aging phenomenon. The water diffusion in interfacial aging is faster than that of the adhesive aging, which resulted in a premature failure of the joints for both the static and fatigue conditions. Based on the experimental results, the interfacial diffusion coefficient was calculated using an inverse method. According to the results, the rate of water uptake along the interface is more than 30 times higher than that which occurs in the adhesive.