Microstructure and mechanical properties of the bonding interface of explosively welded TA2/Q235 composite under dynamic shear loading

Abstract

The strengths of the welded composites are largely influenced by the bonding strengths of the explosive welding interfaces, which generally exhibit a periodic wavy shape. The measurement of the dynamic shear properties of the bonding interface is challenging due to the difficulties in preparing conventional shear specimens arising from the millimeter-sized thickness of the flyer plate. In this paper, small-sized (10 mm × 6 mm × 6 mm) S-shaped specimens were designed and machined to study dynamic shear properties and failure mechanisms of the bonding interface of explosively welded titanium/steel composite. Combined with digital image correlation technique, quasi-static (0.001 s − 1) shear tests were conducted using the Instron MTS universal testing machine and dynamic (5000∼7000 s − 1) shear tests were performed using the split Hopkinson pressure bar apparatus. Besides, microstructure of the bonding interface was characterized by optical microscopy, scanning electron microscopy and energy dispersive spectrometer. According to experimental results, the strength of the bonding interface increased with an increase in strain rate, showing an obvious positive strain rate sensitivity. The fluctuation in shear strengths and failure strains of the bonding interface was due to the presence of non-uniform defects (e g. cavities, cracks and brittle intermetallic etc.). Those defects were discontinuities and may act as stress concentration points leading to degraded mechanical properties. The fracture morphology revealed ductile-brittle mixed fracture patterns under both quasi-static and dynamic strain rates. Failure mainly occurred in the bonding interface near the titanium (TA2) side, which showed microcracks, cleavage plane, tearing ridges, dimples and fragmentation of brittle intermetallic compounds. In addition, the S-shaped specimen was proven to be effective to measure shear properties of the bonding interface of explosively welded composites with small thicknesses.