Additive manufacturing processes have become commercially available and are particularly interesting for the production of free-formed parts. Selective laser melting allows to manufacture components by localized melting of successive layers of metal powder. In order to be able to describe and to understand the complex dynamics of selective laser melting processes more accurately, online measurements using ultrasound have been performed for the first time. In this contribution, we report on the integration of the measurement technique into the manufacturing facility and on a variety of promising monitoring results
Selective Laser Melting (SLM) is a 3D-printing-process which provides the possibility to construct complex geometries by layered manufacturing of components with metallic powder. At MTU Aero Engines the optical tomography (OT) was developed as an Online Process Monitoring system which documents the complete welding process during the SLM fabrication procedure. Some details of the camera-system are shown. To create probability of detection (POD) curves, different specimens are investigated with digital radiography. To detect the small lack of fusion defects the specimens were plastified in order to increase the volume of the defects. Results of plastified specimens are presented.
Subduction initiation often takes advantage of previously weakened lithosphere and may preferentially nucleate along pre-existing plate boundaries. To evaluate how past tectonic regimes and inherited lithospheric structure might lead to self-sustaining subduction, we present an analysis of the Puysegur Trench, a young subduction zone with a rapidly evolving tectonic history. The Puysegur margin, south of New Zealand, has experienced a transformation from rifting to seafloor spreading to strikeslip, and most recently to incipient subduction, all in the last ∼45 million years. Here we present deeppenetrating multichannel reflection and ocean-bottom seismometer tomographic images to document crustal structures along the margin. Our images reveal that the overriding Pacific Plate beneath the Solander Basin contains stretched continental crust with magmatic intrusions, which formed from Eocene-Oligocene rifting between the Campbell and Challenger plateaus. Rifting was more advanced to the south, yet never proceeded to breakup and seafloor spreading in the Solander Basin as previously thought. Subsequent strike-slip deformation translated continental crust northward causing an oblique collisional zone, with trailing ∼10 Myr old oceanic lithosphere. Incipient subduction transpired as oceanic lithosphere from the south forcibly underthrust the continent-collision zone. We suggest that subduction initiation at the Puysegur Trench was assisted by inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of continental rifting and strike-slip along the plate boundary. The Puysegur margin demonstrates that forced nucleation along a strike-slip boundary is a viable subduction initiation scenario and should be considered throughout Earth's history.Plain Language Summary Subduction zones, where one plate underthrusts another, are the principal driver of tectonic plate motions on Earth; however, the origin of these convergent margins remains unsolved. Geoscientists have proposed that the process of forming a new subduction zone takes advantage of weaknesses such as buoyancy contrasts and re-using older weak plate boundaries. To test these ideas, we use new seismic images to document tectonic structures at the Puysegur margin, an incipient subduction zone south of New Zealand. Our images reveal that the upper plate of the Puysegur margin consists mostly of stretched continental lithosphere that formed during an Eocene-Oligocene extension phase. Following extension, a translational phase juxtaposed thin and high-density oceanic lithosphere against thick and low-density continental lithosphere in a wide damage zone. Convergence across this zone led to underthrusting of the Australian Plate beneath the Pacific Plate and the development of the newly established Puysegur subduction zone. Our results demonstrate that subduction initiation was aided by lithospheric buoyancy contrasts and weak zones inherited from earlier phases of tectonic activity. Our findings argue that pre-...
A survey of the major structures technology developments that have in uenced modern aircraft design is presented. The authors' perspectives on the key materials and design concepts that are presently driving U.S. Air Force and Navy military airframes are presented. The current focus of research and development (R&D) structural development resources and the reasons for this focus are addressed. Some thoughts on how to approach future designs are provided, and the structures technologies that are expected to be the focus of future R&D efforts are identi ed.
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