Partners

Abstract:
During hot stamping of titanium alloys, insufficient forming temperatures result in limited material formability, whereas temperatures approaching the β phase transus also result in reduced formability due to phase transformation, grain coarsening and oxidation during the long-time heating. To solve this problem, Fast light Alloys Stamping Technology (FAST) is proposed in this paper, where fast heating is employed. Effects of heating parameters on the formability and post-form strength were studied by tensile tests. Forming of a wing stiffener was performed to validate this new process. Results show that microstructure of TC4 alloy after fast heating was in nonequilibrium state, which could enhance ductility significantly compared with the equilibrium state. When TC4 alloy was first heated to 950 °C with heating rate of 100 °C/s and then cooled to 700 °C, the elongation at 700 °C was more than 3 times that of a slow heating rate with soaking. Nano-scaled martensite with high dislocation density transformed from β phase was observed under fast heating condition. A complex shaped wing stiffener was successfully formed from TC4 titanium alloy in less than 70 s including heating, transfer and forming, and the post-form strength was almost the same with the initial blank.

Keywords:
titanium alloys, fast heating, hot stamping, formability, post-form strength

Abstract:
The growing use of 3D-printed (additively manufactured) structural components implies the need to develop effective methods of damage assessment. This study focuses on guided wave propagation and its interaction with structural damage. The waves were excited using a laser scanning system which allows for easy excitation of the waves at various points at the surface. Also, the excitation is broadband, giving the ability to excite more guided wave modes at once. The combined laser scanning with a single piezoelectric measurement transducer takes advantage of reciprocity to reconstruct the full propagating wavefield. The investigated sample was printed from an aluminum alloy. The first set of measurements was realized for an intact (healthy) sample. Next, an artificial damage was introduced in order to study the wave interaction with it. Machine learning-based signal process algorithms were developed to analyze the wave interaction with the damaged plate. The obtained results show a good potential of guided wave-based techniques for the structural health monitoring of 3D-printed structures. © 2024, The Society for Experimental Mechanics, Inc.

Keywords:
3D printing; Guided waves; k-means clustering; Laser ultrasonics; Nondestructive evaluation; Principal component analysis