Ning Ding

A combined experimental and molecular simulation study was conducted to investigate the effect of hyperbranched epoxy (HPE) grafting on the interfacial and mechanical properties of carbon fiber/epoxy (CF/EP) composites. HPE was chemically grafted onto carbon fiber surfaces to construct an engineered interphase with enhanced physicochemical compatibility toward the epoxy matrix. Surface characterization revealed significantly increased roughness and wettability after HPE grafting. Compared with untreated CF/EP composites, the HPE‐functionalized composites exhibited improvements of 117.2%, 34.2%, and 13.5% in interfacial shear strength, interlaminar shear strength, and flexural strength, respectively, together with enhanced thermal stability. Fracture morphology analysis demonstrated substantially improved fiber/matrix adhesion and suppressed interfacial debonding. Molecular dynamics simulations further revealed increased interfacial interaction energy and reduced mean square displacement and free volume fraction, indicating restricted molecular‐chain mobility and the formation of a more compact interfacial structure. Overall, this work provides multiscale insights into the interfacial reinforcement mechanisms induced by HPE grafting and demonstrates the potential of interphase engineering for the development of high‐performance CF/EP composites.

Carbon fiber reinforced polymers (CFRP) composites, prized for their outstanding mechanical properties, have garnered extensive applications across critical industries including aerospace, transportation, new energy systems, and power infrastructure. However, under increasingly demanding service environments, improving the interlaminar fracture toughness of CFRP composites has become a pivotal challenge to ensure structural integrity and longevity. The present work presents an effective design strategy to address this issue for the carbon fiber/epoxy/core‐shell rubber composite by integrating multi‐scale reinforcements. The mechanical performance of specimens with different compositions was systematically analyzed. Synergistic multi‐scale toughening mechanisms were rigorously elucidated through fracture surface morphology analysis and correlative mechanical data interpretation. The results demonstrate that incorporating short carbon fibers (SCF) into CFRP (i) and adding core‐shell rubber (CSR) to CFRP (ii) both significantly enhance the toughness. CFRP (iii), which contains both SCF and CSR, exhibits an even more pronounced toughening effect. The subsequent grafting of carboxylated multi‐walled carbon nanotubes (MWCNTs‐COOH) onto SCF, resulting in CFRP (iv) with SCF‐CNTs and CSR mixed, demonstrates superior interlaminar fracture toughness compared to CFRP (iii). Specifically, the and of CFRP (iv) increase by 12.89% and 15.46%, respectively, compared to CFRP (iii). This improvement is attributed to the strengthened interfacial bonding between MWCNTs‐COOH and the matrix through mechanical interlocking, which enhances fiber bridging and the effects of core‐shell rubber. This multi‐scale reinforcement paradigm provides critical insights into the design of damage‐tolerant CFRP composites for extreme operational scenarios, advancing their deployment in next‐generation engineering systems subjected to complex mechanical loads.

In this work, polydopamine (PDA) and polyetheramine D230 were selected to construct the PDA-D230 interphase between the carbon fiber (CF) and epoxy matrix. Density functional theory (DFT) and molecular dynamics (MD) simulations were performed to explore the interface enhancement mechanisms of a carbon fiber reinforced polymer (CFRP) with the PDA-D230 interphase from the molecular level. The adsorption characteristics of a PDA molecule on the CF surface were investigated using the DFT method. The results show that stronger π-π stacking interactions are formed due to the structure and orientation preference of the PDA molecule. The interfacial structures and properties of CFRP with the PDA-D230 interphase are derived from MD simulations. The PDA-D230 interphase on the CF surface induces stronger interfacial interaction energy, leading to the better load transfer between the CF and epoxy matrix. The existence of the PDA-D230 interphase on the CF surface can decrease the mean-square displacement (MSD) value and the free volume fraction of CFRP, which restricts the movement of epoxy atoms and inhibits the translational and rotational motion of epoxy chains. Compared with the epoxy using pristine CFs as reinforcement, the interfacial shear stress (ISS) of CFRP with the PDA-D230 interphase is improved by 13.1%. Our results provide valuable insights into the interface characteristics of CFRP with the PDA-D230 interphase, which are of great significance for exploring the strengthening mechanisms for CFRPs with the PDA-D230 interphase.

In this study, molecular dynamics (MD) method was used to systematically investigate the effects of grain boundaries (GBs), degree of cure and temperature on the mechanical properties and thermal stability of epoxy/graphene composites. Uniaxial tensile simulations were performed for pristine graphene and graphene containing GBs reinforced epoxy composites with different degrees of cure. Results show that the yield strength and Young's modulus of epoxy/graphene composites increase with the degree of cure. The behind mechanisms can be attributed to the stronger bonding interaction between epoxy chains. The mechanical properties of epoxy/graphene composites with high degree of cure are more sensitive to GB types. The glass transition temperature (T_g) of pristine graphene and graphene containing GBs reinforced epoxy composites presents an increasing trend with the degree of cure. The introduction of GBs can enhance the T_g of epoxy/graphene composites because of the appropriate wrinkles of GBs in graphene sheets helping to block the slippage of epoxy chains. The MD predicted results of T_g are in good agreement with existing experimental data and the DiBenedetto relationship can be applied using the MD parameters. Both yield strength and Young's modulus of epoxy/graphene composites decrease with temperature, which is mainly due to the weak interface interactions at high temperature and the sufficient energy of atoms at high temperature to overcome the energy barrier. GBs present diverse effects on the yield strength and Young's modulus at different temperatures. This work provides a theoretical basis for the application of epoxy composites reinforced with graphene containing GBs under different conditions.Highlights: The thermomechanical properties of epoxy/graphene composites are studied. The coupling effects of GBs, cure degree, and temperature are evidenced. The existence of GBs can improve the T_g of epoxy/graphene composites. MD predicted T_g agrees well with experimental data using the WLF relationship.

This work presents a molecular dynamics (MD) simulation study on the effect of grain boundaries (GBs) on the mechanical properties of epoxy/graphene composites. Ten types of GB models were constructed and comparisons were made for epoxy/graphene composites containing graphene with GBs. The results showed that the tensile and compressive behaviors, the glass transition temperature (T_g), and the configurations of epoxy/graphene composites were significantly affected by GBs. The tensile yield strength of epoxy/graphene composites could be either enhanced or weakened by GBs under a tensile load parallel to the graphene sheet. The underlying mechanisms may be attributed to multi-factor coupling, including the tensile strength of the reinforcements, the interfacial interaction energy, and the inflection degree of reinforcements. A balance exists among these effect factors, resulting in the diversity in the tensile yield strength of epoxy/graphene composites. The compressive yield strength for epoxy/graphene composites is higher than their counterpart in tension. The tensile/compressive yield strength for the same configuration presents diversity in different directions. Both an excellent interfacial interaction and the appropriate inflection degree of wrinkles for GB configurations restrict the translational and rotational movements of epoxy chains during volume expansion, which eventually improves the overall T_g. Understanding the reinforcing mechanism for graphene with GBs from the atomistic level provides new physical insights to material design for epoxy-based composites containing defective reinforcements.

Honeycomb sandwich composites play an important role in the aviation structural components, especially in aircraft radomes. Due to the multiple production processes, failure of the honeycomb sandwich composite usually occurs. This would affect the working stability of mechanical components made mainly of the honeycomb structural materials. In the present work, collapse failure of the honeycomb sandwich composite in an aircraft radome was investigated. The observation and analysis results show that the failure mode of the honeycomb structure is compression instability failure. There are a lot of pore defects in some local bonding areas of the honeycomb structure, forming a weak bonding area. In the process of curing and pressurization, debonding occurs at the adjacent honeycomb cells near the weak bonding area, forming a cracking band and resulting in the decrease of the stiffness and the instability failure under pressure. The work would provide reference information for the application of honeycomb sandwich composites in mechanical equipment.

Electrical fire accidents occurred frequently all over the world in recent years, which had caused a large number of casualties and property losses. The main cause of electrical fire is electrical wire short circuit fault. Investigations of the characteristic and influence factors of the molten marks play an important role to determine the cause of fire. In the present work, microscopic characteristics of copper wires with short-circuit molten marks in electrical fire were investigated. Primary and secondary short-circuit molten marks (PMMs and SMMs) of copper wires were prepared by simulation test. The micro-morphology, microstructure and chemical composition of molten marks were observed and compared. Based on the quantitative characterization, effects of different overload currents and heating temperatures on the microstructure of molten marks were analyzed. The results would provide fundamental information for cause identification of the electrical fire.