Ensuring the connection strength between extruded fiberglass board and metal components requires a comprehensive solution built from four dimensions: material property adaptation, connection process optimization, structural design innovation, and a quality inspection system. Extruded fiberglass board boasts lightweight, high strength, and corrosion resistance as its core advantages; however, its brittleness differs significantly from the ductility of metals. Improper connection processes can easily lead to stress concentration or delamination failure, thus necessitating targeted connection design.
Mechanical fastening is one of the most mature connection methods in the automotive industry, but the issue of damage to extruded fiberglass board openings needs to be addressed. Traditional bolt connections require pre-drilling, which easily leads to fiber breakage and stress concentration around the hole, resulting in joint strength degradation. To mitigate this problem, increasing the preload can reduce the relative slippage between the bolt and the composite material by increasing the coefficient of friction, thereby reducing the stress value at the opening. Simultaneously, optimizing the layup angle design and introducing a 45° fiber layer can disperse the load path and avoid stress concentration caused by a single layup. Furthermore, interference fits exacerbate damage at the opening, while clearance fits have a smaller impact; therefore, strict control of fit tolerances is essential.
Adhesive bonding technology, with its advantages of lightweight, sealing, and fatigue resistance, has become an important supplement to the connection between extended fiberglass board and metal. Structural adhesives such as epoxy resin and polyurethane can fill the tiny gaps between the metal and the extended fiberglass board, forming a high-strength bond through intermolecular forces. The bonding process requires careful attention to surface treatment; sandblasting or chemical etching can be used to increase the surface roughness of the metal to enhance the mechanical anchoring effect; the surface of the extended fiberglass board needs to be polished to remove weak boundary layers and improve adhesive wettability. To address the impact of humid and hot environments on bond strength, two-component epoxy adhesives can be used, which have low curing shrinkage, excellent weather resistance, and can maintain connection stability over a long period.
Composite connection processes further enhance connection reliability through the synergistic effect of mechanical fastening and bonding. For example, on the basis of bolted connections, structural adhesives can be applied to the joint area, utilizing the bolts to bear the main load while the adhesive layer disperses stress, preventing localized overload. This "hybrid connection" method is widely used in automotive body structures, especially suitable for components subjected to dynamic loads, such as the connection between chassis brackets and fiberglass reinforced floors. Furthermore, rivetless riveting technology uses the plastic deformation of metal rivets to create mechanical interlocking, eliminating the need for pre-drilling and reducing damage to the extruded fiberglass board. However, riveting parameters need to be optimized to avoid interlayer delamination of the composite material.
The connection structure design must fully consider the load transfer path and stress distribution. For the connection between the extruded fiberglass board and the metal frame, a "sandwich structure" design can be adopted, embedding a lightweight foam core material between them. The deformation of the core material absorbs impact energy, reducing joint stress. Simultaneously, optimizing the geometry of the connection area, avoiding right-angle transitions, and using rounded chamfers can reduce stress concentration. In critical components such as electric vehicle battery boxes, the connection between the extruded fiberglass board and the metal frame must meet high rigidity requirements. In this case, a "frame reinforcement + bolt array" structure can be used. The reinforcement increases local rigidity, and the bolt array distributes the load, ensuring connection strength.
A quality inspection system is the last line of defense to ensure connection strength. A comprehensive standard covering material properties, connection processes, and finished product testing needs to be established. For example, ultrasonic testing can be used to assess the presence of bubbles or debonding defects in the adhesive layer; X-ray diffraction can be used to analyze the stress distribution in the mechanical connection area; and tensile and shear tests and fatigue tests can be performed on the finished product to verify whether the connection strength meets the design requirements. Furthermore, strict process specifications must be established, such as controlling parameters like bolt tightening torque, adhesive curing temperature, and time, to ensure that each connection node achieves the expected performance.
