Small-sized structural elements such as beams, plates, and shells are usually used as nanomechanical resonators, nanoscale mass sensors, nanoelectromechanical actuators, and nanoenergy harvesters. At the nanoscale, the structures usually possess a high surface area-to-bulk volume ratio, leading to the free energy related to surface atoms becoming considerable compared to that of the bulk part. Earlier reports indicated several physical reasons for size-dependent phenomena, e.g., nonlocal stress, surface energy, and couple stress. To provide an in-depth insight into the mechanical behavior of small-scale structures, size-dependent continuum models including two or more physical factors have attracted the attention of the academic community. This research analyzes the thermal buckling and postbuckling characteristics of functionally graded carbon nanotube-reinforced (FG-CNTR) nanobeams with a tri-parameter, nonlinear elastic foundation and subjected to a uniform temperature rise. Chen-Yao’s surface energy theory and Yang’s symmetrical couple stress theory are combined to capture two types of size effects in nanobeams. The postbuckling model is formulated based on the Euler–Bernoulli deformation hypothesis and Euler–Lagrange equation. Using a two-step perturbation technique, the related postbuckling equilibrium path is determined. In numerical analysis, the impacts of surface energy, couple stress, elastic foundation, boundary conditions, geometric factor, layout type, and volume fraction of CNTs on the thermal buckling and postbuckling behaviors of nanobeams are revealed. It is indicated that considering couple stress or surface energy can lead to a significant increase in the postbuckling stability of nanobeams compared to the case in which it is not considered. In addition, there is a reverse competition between couple stress or surface energy effects on the thermal buckling responses of nanobeams. As the temperature rise will cause the material elastic moduli softening, the thermal buckling load–deflection curves of nanobeams with the temperature-independent case are much higher than those with the temperature-dependent cases.

This study presents a new GFRP pipe structure fabricated by a combination of continuous and spacing arrangement of filament winding, where the latter was used to form the stiffened part and the former to form the structural part. Results of comparative analysis through a series of flatwise compression tests indicate that, with the same material consumptions, up to 38.7% increase in ring stiffness was achieved by the stiffened outer pipes with diameter of 400 mm, compared with the plain ones. The failure mode of this proposed pipe is ductile fracture during the loading process, and its bearing capacity did not decrease rapidly after fiber failure. The stiffened inner pipes with diameter of 500 mm exhibited an average of 16.7% increase in ring stiffness compared with the plain ones, while both types of specimens showed the same failure mode with delamination occurring between the stiffened layer and outer structural layer. From the experimental investigation, it is concluded that suitable geometric shape can significantly improve the ring stiffness of the specimens, which provides a guidance for structural design of pipelines and their geometric optimization.