A series of YAG:Ce,Mn transparent ceramics were prepared via a solid-state reaction-vacuum sintering method. The effects of various Mn 2+-Si 4+ pair doping levels on the structure, transmittance, and luminescence properties were systematically investigated. These transparent ceramics have average grain sizes of 10-16 μm, clean grain boundaries, and excellent transmittance up to 83.4% at 800 nm. Under the excitation of 460 nm, three obvious emission peaks appear at 533, 590, and 745 nm, which can be assigned to the transition 5d→4f of Ce 3+ and 4 T 1 → 6 A 1 of Mn 2+. Thus, the Mn 2+-Si 4+ pairs can effectively modulate the emission spectrum by compensating broad orange-red and red spectrum component to yield high quality warm white light. After the optimized YAG:Ce,Mn transparent ceramic packaged with blue light-emitting diode (LED) chips, correlated color temperature (CCT) as low as 3723 K and luminous efficiency (LE) as high as 96.54 lm/W were achieved, implying a very promising candidate for application in white light-emitting diodes (WLEDs) industry.
A novel in situ tensile device with a large output load–volume ratio was developed for testing the mechanical properties of bulk materials. A major characteristic of the device was the modular non-standard layout, as the specimen was placed on the top plane of the device to approach the lens of an optical microscope or the electron gun of a scanning electron microscope. Accordingly, to investigate the effects of non-standard layout on tensile properties, displacement and load correction methods were given by formulas based on theoretical calculations to describe the specimen's actual tensile displacement and load. Based on in situ observation, the feasibility of the correction method was verified by comparing it with the data from metallographic microscope images. The bending effects on the specimen's vertical displacements and tensile load due to the installation mode were also discussed. This paper presents a modularized correction method for a horizontal-type tensile device with a non-standard layout design.
Adhesive bonding community shows a continued interest in using bridging mechanisms to toughen the interface of secondary bonded joints, especially in the case of laminated composites. Due to snap-back instability that occurs during fracture, confusions may exist when identifying the toughening effect experimentally. The true toughening effect may be overestimated by lumping all energy contributions (kinetic energy included) in an overall effective toughness. Here, fundamentals for bridging to enhance fracture resistance are explored through the theoretical analysis of the delamination of a composite double cantilever beam (DCB) with bridging. Specifically, we establish a theoretical framework on the basis of Timoshenko beam theory and linear elastic fracture mechanics to solve the fracture response of DCB in the presence of discrete bridging phases. We elucidate the crack trapping and the snap-back instability in structural response during the crack propagation. We identify the contribution to the overall toughness observed numerically/experimentally of both the physical fracture energy and other types of dissipation.The associated toughening mechanisms are then unveiled. Furthermore, we study the effects of property of the bridging phases on the snap-back instability, based on which, we propose a dimensionless quantity that can be deployed as an indicator of the intensity of snap-back instability. Finally, we identify the role of geometrical properties, i.e. the substrate thickness and the arrangement spacing of the bridging phases, in the snap-back instability and the macroscopic fracture toughness of a DCB. This work provides, from a theoretical point of view, an essential insight into the physics related to the structural response of DCB with discrete toughening elements.
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