Key Engineering Materials Vol. 1036

Abstract: Single-lap bonded joints are widely used in aerospace, shipbuilding, and other fields due to their advantages, such as light weight, high specific strength, and no stress concentration caused by hole-making or spot-welding. However, the traditional methods of increasing geometric parameters, such as lap length to improve strength, have limitations in scenarios where the bonding area is restricted. To solve this problem, in this study, it is assumed that carbon fibers with a volume fraction of 10% were introduced into the epoxy adhesive layer and arranged in a 45° orientation. The mechanical non-reciprocity was achieved by utilizing the difference in tensile and compressive moduli. A non-reciprocal cohesive fracture mechanics model of the composite single-lap joint structure based on the User-defined Element (UEL) was established to explore the effect of non-reciprocity on the bonding strength. The results show that the non-reciprocal adhesive layer effectively suppresses the peeling stress concentration at the cohesive failure interface of the adhesive layer, increasing the tensile strength of the single-lap bonded joint by approximately 6.27% compared to the traditional homogeneous adhesive layer, verifying the effectiveness of the model. This research breaks through the limitations of traditional geometric parameter optimization. It can specifically regulate the interfacial stress distribution without changing the bonding area, providing a new material design idea for strength optimization in scenarios where the bonding area is restricted, such as in aerospace. It has important theoretical significance and engineering application prospects.

Abstract: This study investigates the stress intensity factors (SIFs) in cylindrical pressure vessels with nozzles, focusing on the effect of nozzle offset on crack behavior. Cracks are positioned on the inner wall of the cylinder at the nozzle intersection, and their location remains constant while the nozzle is systematically offset on the cylindrical surface. The analysis aims to determine how varying nozzle positions influence the SIFs, providing critical insights into structural integrity under different loading conditions. The study employs finite element analysis (FEA) to model the stress distribution and crack propagation behavior for various nozzle offset scenarios. Results highlight the sensitivity of SIFs to nozzle displacement and emphasize the importance of precise positioning in pressure vessel design to prevent crack propagation and failure. These findings offer practical implications for optimizing pressure vessel and nozzle designs in industrial applications, ensuring enhanced safety and reliability.

Abstract: Additive manufacturing (AM), particularly fused deposition modelling (FDM), enables fabricating polymeric structures with complex geometries and functional capabilities. However, the mechanical reliability of FDM components is hindered by process-induced defects and anisotropy, which complicate damage initiation and propagation mechanisms. This paper summarises the damage behaviour of FDM-printed polymers through an integrated experimental–numerical approach. Static and fatigue tests reveal that interlayer bonding quality, infill orientation, and thermal exposure significantly influence stiffness, fracture resistance, and fatigue life. Microstructural features such as void morphology and crack propagation patterns are shown to govern failure modes more than intrinsic material properties. Tribological analyses further demonstrate the sensitivity of wear performance to surface orientation and process parameters, while dynamic response studies establish vibration-based indicators for early-stage damage detection. The implementation of bioinspired self-healing capsules and surface-engineered self-cleaning layers reflects the trend towards multifunctional damage mitigation strategies. Future research directions are outlined, including the need for damage modelling considering multi-loading conditions and different printing parameters.

Abstract: Research purpose is in establishment of dependencies for parameters of a stress-strain state of a layered composite material with an arbitrary but finite amount of layers and a local breakage in continuity of the outermost layer. Research methodology is in construction of a mathematical model of interaction of hard and soft layers considering given arbitrary amount of layers and with a damaged hard layer and analytical solution of the model using methods of mechanics of composite materials. A character of stress redistribution in layers of a composite material with a local breakage of the outermost layer is established. A breakage in continuity of a hard layer leads to distortion of cross-sections of a sample. The damaged layer has larger displacements than the other ones. The uniform distribution of external loads among the layers is disturbed. Disturbance of a stress-strain state is localized both along the sample and along its thickness. Damage to the outermost layer leads to an increase in the tensile load of the adjacent layer by more than 60 % of the average load on layers. The two layers closest to the damaged one are loaded with a force that exceeds their average total load by almost 80 %. The breakage of the middle layer leads to smaller disturbances. The nature of local stress disturbances also depends on the amount of layers in a sample. As the total amount of layers increases, the extreme forces occurring in a sample with a damaged layer decrease to almost constant values if the amount of layers is at least ten. Scientific novelty is in establishing the dependencies for stress-strain state indicators on structural parameters of a composite tractive element with a local breakage of the outermost layer. The linear formulation of the problem and the principle of superposition make it possible to use the obtained dependencies in a case of applying force to one layer and fixing others. The obtained solutions allow determining a stress-strain state of a sample of layered structure and create conditions for implementing justified solutions regarding the conditions and permissibility of using belts of layered structure with layers damaged during operation, thus ensuring the safety of their use and making the most of their technical resource.