The distribution of reinforcing fibers in a resin wheel has a crucial influence on its impact resistance. This influence stems from the synergistic effects of the interfacial bonding between the fibers and the resin matrix, the stress transfer efficiency of fiber orientation, and the energy absorption of the fiber stacking pattern. Uniform fiber dispersion is fundamental to ensuring impact resistance. When the fibers are evenly distributed within the resin matrix, each fiber forms a good interfacial bond with the resin. This bond not only strengthens the adhesion between the fibers and the matrix but also evenly transfers stress to the fiber network through the interface during impact, preventing localized stress concentration and crack propagation. If the fibers are clumped or unevenly distributed, the interfacial bonding between the fibers and the matrix is weakened in the agglomerated areas, where impact energy is easily concentrated, triggering crack initiation and rapid propagation, significantly reducing the impact resistance of the resin wheel.
The matching of fiber orientation with the impact direction directly affects stress transfer efficiency. In a resin wheel with unidirectional fiber distribution, when the impact direction is parallel to the fiber orientation, the fibers' high modulus effectively supports the impact load, absorbing significant energy through axial stretching, resulting in optimal impact resistance. However, when the impact direction is perpendicular to the fiber orientation, the fibers primarily experience shear stress, while the resin matrix has a low shear strength, which can easily lead to debonding at the fiber-matrix interface and rapid crack propagation perpendicularly, significantly reducing impact resistance. Therefore, optimizing the fiber orientation to align with the expected impact direction can significantly improve the impact resistance of the resin wheel.
The fiber stacking sequence has a hierarchical effect on the impact resistance of the resin wheel. In a hybrid interlayer structure, the alternating stacking of different fiber types (such as carbon fiber and aramid fiber) creates a "soft-hard" synergistic effect: when an impact occurs, the high-modulus fibers (such as carbon fiber) in the surface layer preferentially bear the impact load, absorbing some of the energy through elastic deformation. The high-tenacity fibers (such as aramid fiber) in the inner layer further absorb the remaining energy through plastic deformation and fiber pullout, while preventing crack propagation deeper into the wheel. This hierarchical energy absorption mechanism significantly enhances the overall impact resistance of the resin wheel. In contrast, laminated structures composed of a single fiber type are prone to catastrophic fracture under impact and have weak impact resistance.
Fiber blending optimizes impact resistance through synergistic effects. When high-modulus fibers (such as carbon fibers) are blended with high-tenacity fibers (such as aramid fibers), the former provides strength support while the latter enhances energy absorption, complementing each other's strengths. For example, in an intra-layer blended structure, carbon fibers and aramid fibers are randomly distributed within the same layer. During an impact, the carbon fibers absorb energy through fracture, while the aramid fibers further dissipate energy through fiber pullout and plastic deformation. The synergistic effect of the two fibers delays crack propagation and improves the impact damage tolerance of the resin wheel. This blending method has been widely used in impact-resistant and energy-absorbing structures such as helmets and body armor.
The fiber volume fraction and distribution must be optimized in tandem. Within a certain range, increasing the fiber volume fraction can improve the impact resistance of a resin wheel, but this requires uniform fiber dispersion. If the fiber content is too high and the distribution is uneven, insufficient resin impregnation can occur, resulting in defects such as pores, which in turn reduces impact resistance. Therefore, process control (such as molding temperature, pressure, and dwell time) is required to ensure uniform fiber dispersion within the resin matrix, while optimizing the fiber volume fraction to maximize impact resistance.
The fiber surface condition indirectly regulates impact resistance by influencing interfacial bonding strength. Factors such as fiber surface roughness and the type and content of functional groups determine its interfacial bonding ability with the resin matrix. For example, carbon fibers have a smooth surface and lack polar groups, resulting in weak interfacial bonding with the resin matrix and prone to debonding under impact. Oxidation treatment or coupling agent coating can increase fiber surface roughness and the presence of active functional groups, improving interfacial bonding strength and thus enhancing the impact resistance of the resin wheel. Therefore, fiber surface modification is an important means of optimizing impact resistance.
