Island‐bridge architecture represents a widely used structural design strategy in the field of stretchable inorganic electronics, where flexible serpentine interconnects function as bridges to accommodate most of the deformation, while the islands residing functional devices exhibit minimal deformation. The mismatch of Young's modulus between the elastic substrate and the rigid islands usually leads to stress concentration, which is named the island effect. This phenomenon can significantly increase the risk of interfacial damage, such as debonding and tearing failure near the island. In this work, the mechanical model of the island effect under equal biaxial stretching is developed based on theoretical analysis, simulation, and experimental measurement. The scaling law of the displacement and strain distributions on the substrate surface illustrates that the ratio of the island radius to the substrate length is the main controlling parameter of the island effect, proved by the experimental and numerical results. The criterion distinguishing whether the island effect problem is axisymmetric is derived from this. Further, the deformation field in periodic array structure is predicted based on the theoretical model, demonstrating its potential for application in flexible electronic devices.

This study investigated the axial tensile performance of adhesively bonded T700/C204 carbon fiber composite and TC4 titanium alloy tubular single-lap joints under three distinct temperature conditions: room temperature, low temperature (−65 °C), and room–low–room-temperature cycling. Two configurations of adhesively bonded joints—composite–composite and composite–titanium—were tested. Specimens were designed to evaluate the influence of spew-fillet and perfect lap configurations on uniaxial tensile bonding strength across varying temperature environments. Analysis of the final failure morphology, stress concentration locations, ultimate failure loads, and load-displacement curves revealed that stress concentration and peeling stress were most pronounced at the ends of the bonded region, which served as the initiation points for failure. The adhesively bonded joints exhibited two distinct failure modes, strongly correlated with material properties and environmental temperature. The titanium alloy tubular joints predominantly experienced adhesive layer failure, while the carbon fiber three-way tubular joints were primarily characterized by fiber-tear failure. Environmental temperature significantly influenced the strength of the adhesively bonded joints. Specifically, the tensile failure limit of the bonded specimens subjected to low-temperature cycling (25~−65~25 °C) was approximately 61% higher than that observed under the room or low-temperature conditions. Furthermore, the experimental results demonstrated that a maximum failure load of 27.522 kN and a shear strength of 10.956 MPa were achieved. Notably, the presence of adhesive spew-fillet had a negligible impact on the bonding strength of the joints.

Pre-embedded metal inserts provide a direct load-introduction path for filament-wound composite tubes without cutting the load-carrying fibers. This study evaluates the room-temperature axial tensile response of T700 carbon-fiber/TDE86 epoxy tubes containing grooved, internally threaded TC4 titanium-alloy inserts after one programmed low-temperature conditioning cycle and separately examines a small ambient end-enlarged configuration. Twenty-one destructive test records were analyzed: nine ambient constant-section (“equal-section”) specimens, nine independent equal-section specimens after a 25 → −70 → 25 °C chamber-setpoint cycle followed by 24 h at room temperature, and three ambient end-enlarged specimens. At 1 mm/min, the three cohorts had mean peak loads of 81.39, 81.31, and 88.26 kN and coefficients of variation of 14.04%, 8.70%, and 7.85%, respectively. The −0.07 kN difference between the two independent equal-section cohort means does not establish equivalence or absence of a conditioning effect, and the three-specimen end-enlarged comparison does not isolate a causal geometry effect. Macroscopic failure was dominated by insert pull-out accompanied by visible adhesive/interfacial separation, laminate-layer damage, attached fragments, and local splitting. Because local slip, bond-line deformation, and system compliance were not measured, equilibrium and competing limit states are used only as a qualitative framework. The results concern post-conditioning room-temperature response, not in situ performance at −70 °C.