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Intermetallic compounds (IMCs) at the Sn-3.0Ag-0.5Cu/Cu joint interface were prepared through reflow soldering and isothermal aging in a QHL360 SMT fully automatic reflow soldering system and a high-temperature test chamber, respectively. The mechanical properties of IMCs were then studied and characterized by nanoindentation. The mechanical responses of both Cu6Sn5 and Cu3Sn (IMCs) show large dependence on the strain rate during loading. In addition, multiple pop-in events are observed in Cu6Sn5 but not evident in Cu3Sn. During loading, the contact stiffness of IMCs increases almost linearly with the indentation depth under each strain rate. In total, the hardness and elastic modulus of Cu3Sn are larger than those of Cu6Sn5, and the hardness of both Cu6Sn5 and Cu3Sn increase with increasing strain rate. During the holding stage, creep deformations of IMCs increase as loading strain rate increases. Indentation creep displacement-time curves for Cu6Sn5 and Cu3Sn can be well described by the generalized Kelvin model. The lower creep rate sensitivity exponent of Cu3Sn implies its relatively higher creep resistance. [ABSTRACT FROM AUTHOR]

In this paper, nanoindentation tests with CSM technique were conducted on Sn-3.0Ag-0.5Cu(SAC) lead-free solder under different strain rates at room temperature. Results show that the nanomechanical properties of SAC solder depend on the strain rate remarkably. The contact stiffness increases almost linearly with indentation depth. Under different strain rates, contact stiffness and elastic modulus basically remain unchanged, but the hardness increases with increasing strain rate. For the same holding time, creep deformation is more evident under high strain rate. The "bulge" phenomenon for SAC solder weakens as unloading rate increases, residual indentation depth after unloading is larger under high strain rate. [ABSTRACT FROM AUTHOR]

• A novel single curved fiber-metal hybrid lamina composite (FM-HLC) was designed. • The impact resistance of FM-HLC can be enhanced by increasing fiber content. • Decreasing the radius of curvature limits the impact failure region. • The FM-HLC strategy can prevent metal-composite interface failure in FMLs. Fiber-metal hybrid lamina composites (FM-HLCs) are a new kind of fiber-metal composites, which aims at addressing the metal-composite interface failure in conventional fiber-metal laminates. In the current study, the low-velocity impact tests were conducted to examine the dynamic response of single curved FM-HLCs. The influence of weave pattern of fiber-metal hybrid lamina, impact velocity and radius of curvature on the dynamic response is considered in the experiment. The deformation/failure modes, force-time histories and energy absorption were obtained. The high-speed cameras were used to capture the deformation/failure processes of FM-HLCs and the instantaneous images for digital image correlation analysis. The results indicate that the "fiber-metal hybrid lamina" strategy can efficiently help maintain the integrity of FM-HLCs outside the impact region. The increase of fiber content can efficiently decrease the deformation/failure region and permanent deflection of FM-HLCs, thus, enhancing its impact resistance. When the fiber content along circumferential and longitudinal directions is not consistent or the radius of curvature decreases, there forms an elliptical deformation region of FM-HLCs. The current work is expected to be of significance for the follow-up research and the potential applications of FM-HLCs. In addition, it is also a good reference for investigating the dynamic response of orthotropic panels/shells under low-velocity impact. [ABSTRACT FROM AUTHOR]