Four-dimensional (4D) printing enables additively manufactured components to undergo programmed shape change, yet applications remain limited by the trade-off between shape-memory behavior and mechanical strength. In the study, we compare shape-memory PETG (SMP-PETG) and carbon fiber–reinforced PETG (CF-PETG), the latter containing a manufacturer- reported 10–15% chopped carbon fiber region localized within the filament core. We fabricated specimens by fused deposition modeling (FDM) using different nozzle temperatures and layer heights, and performed tensile, thermal and cyclic shape recovery tests to establish structure–property–function relationships within the PETG family. DSC showed predominantly amorphous behavior in CF-PETG, whereas SMP-PETG exhibited cold crystallization and melting features consistent with a crystallizable fraction in that commercial formulation. CF-PETG also showed a higher glass transition temperature than SMPPETG, indicating different thermal activation windows for the two materials. SMP-PETG exhibited ductile tensile behavior, with a peak strength of 25.69 MPa at 255°C and a layer height of 0.3 mm, and retained more stable shape recovery, with about 10–15% degradation over 50 cycles. In contrast, CF-PETG showed a steeper tensile response and higher strength, approaching 29 MPa, but less stable recovery, with losses of about 20–25% over the same cycle range. These findings characterize the combined effects of commercial formulation, reinforcement and processing; isolating the specific influence of core-localized reinforcement architecture will require comparisons with compositionally matched neat PETG and uniformly reinforced CF-PETG.

This study investigates the effects of renewable chopped cellulose fiber (CCleF) on the physical and mechanical properties, oil resistance, and thermal-oxidative aging behavior of acrylonitrile-butadiene rubber (NBR), aiming to determine the optimal filler content. CCleF/NBR composites with varying CCleF loadings were prepared and systematically characterized through analyses of vulcanization behavior, three-dimensional morphology, mechanical properties, thermal-oxidative aging, and oil resistance. The results indicate that the composite with 3 phr CCleF exhibits uniform fiber dispersion and optimal overall performance, showing enhanced processability, a reduced vulcanization time, and improved physical and mechanical properties. After thermal-oxygen aging, the composite demonstrated superior stability: the percentage change in tensile modulus, rebound resilience, and DIN abrasion decreased significantly by 13.73, 49.82, and 74.9%, respectively, while the aging coefficient reached 0.86. Notably, this composite also exhibited excellent oil resistance, with a volume expansion rate of 7.24%, which is 13.1% lower than that of unfilled NBR. Correspondingly, the tensile product’s retention rate decreased by 37.72%, while rebound resilience and abrasion resistance improved. This study demonstrates that incorporating 3 phr CCleF is a practical approach to achieving high-performance NBR, providing a material basis for its use in demanding environments such as the petrochemical industry.

The main purpose of structural health monitoring (SHM) is to detect damage at its earliest possible stage to prevent severe deterioration and reduce subsequent repair costs. Carbon nanotubes (CNTs) buckypaper (BP) was embedded into different cross-ply glass fibre composites to monitor the curing process and impact damage as an in situ sensor in this research. BP sensor can capture the four stages of the curing process, the gel point of the resin and residual stresses of the composite structure can be achieved by analysing the change of the resistance curve. Numerical and experimental analyses were performed to predict the damage in composite structures subjected to low-velocity impact. BP sensors’ electrical resistance increases with repeated impact loading; composite structure elastic deformation and damage evolution can be identified from resistance change. Experiment results show that structure monitoring based on the BP sensors cannot only detect small, barely visible impact damage flaws and the damage evaluation of composite structures subjected to impact, but also provide a new method to monitor the curing process through the analysis of results. This work makes some constructive contributions to monitoring the manufacturing process of composites and long-term SHM to evaluate impact resistance and damage prediction of composite structures.

Adding heterogeneous fillers with high thermal conductivity (TC) to polymer has been recognized as an effective way to increase the effective thermal conductivity (ETC) of polymer composites. Extensive researches have been conducted on the ETC of composites with heterogeneous fillers. However, the heat transfer enhancement mechanism of heterogeneous fillers remains unknown, and the combined effects of filler size, filler contact, interface thermal resistance (R_c) and other parameters on the ETC have not been explored. In this study, above combined effects are investigated. The results show that the filler contact and R_c are the key factors determining the ETC. The ETC of composite with filler contacts reaches 2.35 at filler content of 25%, which is 11.9% higher than that without filler contacts. The ETC also strongly depends on the R^*_c (dimensionless form of R_c) ratio (R^*_c1/R^*_c2) between two fillers, with it becoming asymmetrical when the amount of R^*_c(R^*_c1 + R^*_c2) is larger. The ETCs decrease with the increase of R^*_c1/R^*_c2 when the R^*_c1/R^*_c2<1, while they increase with R^*_c1/R^*_c2 when the R^*_c1/R^*_c2>1. When R^*_c1 + R^*_c2 is a constant, the ETC increases with the competing effects of R^*_c. The models with filler contacts exhibit higher accuracy than other classical models in calculating the ETC across the entire range of filler content.