In the realm of optomechanical joints, the roughness of the component frequently limits the bonded joint's stability and dependability. This study investigates the failure mechanisms and interfacial stress transfer characteristics of bonded structures with six controlled roughness levels to elucidate roughness-dependent adhesion behavior. Shear experiments have been carried out to analyze the failure mechanisms of bonded joints. The results indicate that when roughness increases, shear strength first rises and subsequently falls. When the surface roughness of the duralumin alloy is 4.2 ± 0.75 μm, the shear strength reaches its maximum value of 11.97 MPa. After analyzing the surface characteristics of substrates with various degrees of roughness, the results show that increasing surface roughness can significantly change the substrate's surface energy, wettability, and contact area while also greatly changing the bonding quality. The fractographic evaluation identified interfacial debonding and cohesive-adhesive hybrid failure as the predominant fracture mechanisms. Specimens exhibiting hybrid failure demonstrated enhanced interfacial load transfer capability through synergistic contributions from both adhesive-substrate bonding and bulk adhesive deformation. This research offers an important reference for the manufacture and application of epoxy adhesive and duralumin alloy joints. It has a guiding significance for improving the performance and reliability of joints.

As the core load-transfer medium in bonded structures, the adhesive layer critically governs overall reliability, with Mode I fracture representing its dominant failure mechanism under tensile loading. This study systematically compares the eXtended Finite Element Method (XFEM) and its two coupled variants—the XFEM-Cohesive Zone Model (CZM) and XFEM-Virtual Crack Closure Technique (VCCT)—in simulating Mode I fractures of adhesive joints. Key comparisons include predictions of stress distribution, load-transfer evolution, and crack propagation paths, all validated through Double Cantilever Beam (DCB) simulations and experiments. Results show that standard XFEM accurately predicts initial stiffness (error < 8%) but overestimates peak load by 10.7%. XFEM-CZM maintains errors below 8% for both stiffness and peak load, while XFEM-VCCT achieves exceptional peak-load accuracy (error < 1%) but overestimates stiffness. In crack evolution, standard XFEM yields an idealized propagation path, whereas the coupled methods reveal a distinct three-stage process. Stress/strain fields in standard XFEM remain stable during propagation, while the coupled approaches exhibit interfacial irregularities before crack arrival, followed by tip concentration and band-like transfer during stable growth. Each method offers distinct advantages, underscoring that selection should align with specific research objectives and modeling requirements.

To improve the shear strength of the 2A12 aluminum alloy adhesive-bonded joint, two kinds of surface micropatterns, parallel and cross waves, were constructed on the surface of aluminum alloy by a laser engraving machine. The shear strength of two different surface micropatterns at different laser processing distances was investigated. The results show that the surface of the aluminum alloy with a surface micropattern shows excellent hydrophilicity, which is beneficial to forming a mechanical interlock between the adhesive and aluminum alloy. The shear strength of the bonded joint decreases with the increase in laser processing distances for the parallel wavy micropattern. When the laser processing distance is 0.5 mm, the shear strength reaches a maximum of 14.04 MPa. For the cross-wave micropattern, the shear strength of the bonded joint increases first and then decreases with the increase in laser processing distances. When the laser processing distance is 0.75 mm, the shear strength reaches a maximum of 13.74 MPa. The obtained data are important for adhesive aluminum alloys with different surface micropatterns.