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The mechanical property of advanced ceramics by additive manufacturing through layer‐by‐layer processing and subsequent sintering has been employed as a key basis for optimizing the processing and developing future application. 3Y‐TZP ceramic was fabricated by stereolithography‐based additive manufacturing, and the mechanical properties were investigated by nanoindentation and microscratch testing. The microscopic mechanism and evolution of surface deformation and damage induced by scratching were revealed by scanning electron microscopy and surface interferometer. Results showed that the nanoindentation hardness and elastic modulus were comparable to those of conventional process. With the increase in the applied normal load, the scratch‐induced damage followed three sequential stages, that is, plastic plowing, microcracking and surface spalling. The magnitude of the microcracks nucleated during scratching depended on the applied normal load. Concerning the homogeneity and integrity with the sintered parts without delaminated cracks and pores, the evolution of surface damage was discussed in different stages. It was concluded that the layer‐by‐layer process did not affect the characteristic of microcracking evolution. [ABSTRACT FROM AUTHOR]

Multi-ply woven fabric consists of many layers and can be used to form three-dimensional shapes, which finds its application in a variety of end-uses. One of the advantages is that this type of products requires no seams or cuts. This paper presents a novel method to facilitate the design of 3D rectangular box-shaped fabrics made of multi-ply weaves. A preliminary folding-down process is a must for fabric manufacture and two folding approaches were developed accordingly. Approach A has been found to be more suitable for boxes with X ≥ 2Z. The elimination of quadruple-layer fabric region simplifies the design and weaving process. In this regard, plain weave was used sections form box body and basket weave was employed for bound-layer regions so that fabric recoiling could be avoided. The diagonal lines connecting the bound-layer and double-layer regions is required to have an angle of 45°, and hence a Jaquard loom was in use for manufacturing. As the fabric is formed by different parts, thread density varies, leading to uneven yarn tension. This problem can be solved using additional warp beams. Approach B requires the two side planes to be folded in, the design process of which is similar to that of approach A. Theoretically, boxes with multiple cells could also be designed using this technique. Approach A has been found to be able to deal with boxes of various geometrical parameters. One problem of the 3D fabric is the soft edges, which requires further investigations. [ABSTRACT FROM AUTHOR]

Periodicity frequently occurs in hard disk drives (HDDs) whose servo systems with periodic phenomena can be usually modeled as linear periodically time-varying (LPTV) systems. This paper discusses optimal H\infty control synthesis for discrete-time LPTV systems via discrete Riccati equations. First, an explicit minimum entropy H\infty controller for general time-varying systems is obtained. Subsequently, the developed control synthesis algorithm is applied to LPTV systems and it is shown that the resulting controllers are periodic. The proposed control synthesis technique is evaluated through both single and multirate optimal H\infty track-following control designs. The single-rate servo design shows that our proposed control synthesis technique is more numerically robust in calculating optimal H\infty controllers for discrete-time linear time-invariant systems than the MATLAB function of “hinfsyn,” while the multirate servo design validates its ability of synthesizing multirate controllers to achieve the robust performance of a desired error-rejection function. Moreover, an experimental study—in which the developed control synthesis algorithm on a real HDD with missing position error signal sampling data is implemented—further demonstrates its effectiveness in handling LPTV systems with a large period and attaining desirable disturbance attenuation. [ABSTRACT FROM PUBLISHER]

Missing position error signal sampling data in hard disk drives (HDDs) results in their servo systems having irregular sampling rates (ISRs). With the natural periodicity of HDDs, which is related to the disk rotation, HDD servo systems with ISRs can be modeled as linear periodically time-varying systems. Based on our previous results, an explicit minimum entropy H\infty controller for HDD servos with ISRs via discrete Riccati equations is first obtained. The resulting controller is subsequently demonstrated to be periodically time-varying and implementable. Simulation and experimental studies, which have been carried out on a set of hard disk drives, demonstrate that the proposed control synthesis technique is able to handle ISRs and can be used to conveniently design a loop-shaping track-following servo that achieves the robust performance of a desired error rejection function for disturbance attenuation. Experimental results on ten actual 2.5" hard disk drives show around 27% improvement of the 3\sigma PES was obtained by the proposed control algorithm. [ABSTRACT FROM PUBLISHER]

This paper considers two novel controller synthesis methodologies using a feedforward control structure for performing concentric self-servo track writing in hard disk drives. In the first methodology, it is assumed that a conventional causal track-following controller has been designed and a non-causal feedforward controller, which utilizes the stored error signal from writing the previous track, is designed using standard H\infty control synthesis techniques, in order to prevent the track errors from propagating and to achieve good disturbance attenuation. In the second methodology, both the track-following feedback controller and the feedforward controller are simultaneously designed via a mixed H2/H\infty control scheme, which involves the solution of a set of linear matrix inequalities and achieves good disturbance attenuation while preventing the propagation of track errors from the previous tracks. Simulation results confirm that the two proposed control synthesis methodologies prevent error propagation from the previously written tracks and significantly improve concentric self-servo track writing performance. [ABSTRACT FROM AUTHOR]

This article presents a simplified method, known as a fractional formula description, to describe the angle-interlock woven fabric construction. According to the interweaving between warp and weft yarns in multi-layered angle-interlock fabric, the construction of the angle-interlock fabric is represented by a fractional formula to illustrate the interweave rule of a warp yarn in a unit cell. Furthermore, this article also gives an extended method to apply the fractional formula to the multilayered angle-interlock fabric design. From the discussion of the fractional formula description method, it is proven that the description method is more efficient and valid for the representation and design of angle-interlock woven fabric construction and fabric design, especially for the computer-aided design (CAD) of multilayered angle-interlock woven fabric. [ABSTRACT FROM AUTHOR]

The nanoscale plasticity phenomena in zirconia-toughened alumina (ZTA) ceramics with yttria-stabilized zirconia (YSZ) addition of 10% and 30% fabricated by additive manufacturing based on a stereolithography technique were explored in detail by nanoindentation and scanning electron microscopy. It was demonstrated that the initiation of nanoscale plasticity was attributed to the combined contributions from the generation of nanoscale shear deformation bands and localized microcracking at the indentations. Such localized plastic behavior underneath the nanoindenter was interpreted by maximum shear stress analysis. The response of the phase boundary during indentation was emphasized through crack propagation paths, and optimization of alumina–YSZ adaptation through component design and SL processing was expected. [ABSTRACT FROM AUTHOR]