Shape optimization of single-pin reinforcement in metal-composite joints

Purpose Utilizing through-the-thickness pin reinforcement in metal-to-composite joints can significantly increase the joint mechanical properties, enabling the introduction to a whole new field of applications in joining technology. However, with the rise of advanced pin manufacturing techniques – such as additive layer manufacturing, little research has been performed on the pin shape optimization and its behavior. The paper aims to discuss this issue. Design/methodology/approach In this study, a numerical shape optimization algorithm is used to produce optimized pin shapes for several initial pin dimension parameters, having as objective to achieve a more uniform stress distribution along the surface of the pin, enhancing the pin strength and joint integrity. Findings Results showed that pin shape is a crucial factor in the mechanical response of the pin. In Mode I, the presence of an undercut feature on the pin head can increase the ultimate load of the pin by +250 percent, while in Mode II, the base diameter is the dominant feature in the joint ultimate strength. Originality/value With these results, the paper aims to utilize commercial available numerical software to explore optimization capabilities in joints strength. These optimization capabilities show that it could be used for the enhancement of metal-to-composite joints response.

Mechanical performance of polyester pin-reinforced foam filled honeycomb sandwich panels

Honeycomb sandwich panels entice continuously enhanced attention due to its excellent mechanical properties and multi-functional applications. However, the principal problem of sandwich panels is failure by face/core debond. Novel lightweight sandwich panels with hybrid core made of honeycomb, foam and through-thickness pin was developed. Reinforcing polyester pins between faces and core is an effectual way to strengthen the core and enhance the interfacial strength between the face/core to improve the structural performance of sandwich panels. To provide feasibility for pin reinforcement, honeycomb core was pre-filled with foam. Mechanical properties enhancement due to polyester pinning were investigated experimentally under flatwise compression, edgewise compression and flexural test. The experimental investigations were carried out for both “foam filled honeycomb sandwich panels” (FHS) and “polyester pin-reinforced foam filled honeycomb sandwich panels” (PFHS). The results show that polyester pin reinforcement in foam filled honeycomb sandwich panel enhanced the flatwise, edgewise compression and flexural properties considerably. Moreover, increasing the pin diameter has a larger effect on the flexural rigidity of PFHS panels. PFHS panels have inconsequential increase in weight but appreciably improved their structural performance.

Study on Tensile Mechanical Behavior of Composite T-Joints

Based on three kinds of composite T-joints with different connection way for tension test outside the plane, it was obtained contrastively that how the ordinary adhesive, Z-pin reinforcement and stitching reinforcement three different fitting influence tensile strength, damage failure process and failure mode of composite T-joints. The test results showed that compared with ordinary adhesive connection mode, tensile strength of the Z-pin reinforcement and stitching reinforcement T-joints increased by 13.6% and 11.4%, respectively; and the largest deformation increased by 19.2% and 15.1%, respectively. After reaching maximum load condition, the ordinary adhesive T-joints had brittle failures, but Z-pin reinforcement and stitching reinforcement T-joints all showed that the ductile damage behavior, corresponding to the load-displacement curve appeared saw-tooth wave platform. Obviously, the Z-pin reinforcement T-joints had the most significant reinforcement effect on tensile properties of composite laminates T-joints.

Composite-Composite Joining with through the Thickness Reinforcements for Enhanced Damage Tolerance

A novel composite-composite joining technology based on metal pins oriented in through thickness direction of the composites is presented. A defined pin geometry, which is capable of establishing a through-thickness form-fit connection between composites and the metal reinforcement, is created on thin metal sheets in an automated pin production process. Based on numerical simulations of the fracture of unreinforced single lap shear (SLS) composite specimens, optimum locations for the pin reinforcement were found. Tests on reinforced SLS specimens proved that an enhanced damage tolerance can be achieved by the use of cold metal transfer welded pins (CMT pins) as through-the-thickness reinforcement of the joint area. This paper investigates the mechanisms responsible for the load transfer and failure of such through-the-thickness reinforced composite-composite joints during monotonic loading.