In this article, the impact of laser-induced thermal damage on the static strength properties of consolidated continuous carbon fibre reinforced thermoplastics induced by high-power laser cutting is presented. Organic sheets based on a polyphenylene sulphide matrix are machined using a fibre laser providing a maximum output power of 6000 W. In this context, the influence of the applied laser power and the feed rate on the cut quality as well as the resulting tensile strength is discussed. In order to analyse the laser cutting edge through a quantitative evaluation of the damaged areas due to laser impact, optical micrographs are prepared. The results of tensile strength tests are compared with those measured from the specimens that were generated by a conventional processing technique (milling). A linear dependency between a specific part of the heat-influenced zone and the corresponding maximum tensile load is found. A reduced load bearing area, as a consequence of a modified fibre-matrix-structure due to laser impact, is identified as the responsible factor for reduced tensile strengths, especially for low feed rates.
Abstract. In consequence of an increased interest in using endless carbon fibre reinforced thermoplastic composites (TPC), automated and highly productive processing technologies for cutting and trimming steps of consolidated materials are sought. In this paper, the influence on the thermal effect caused by laser cutting with respect to static strength properties of TPC based on a polyphenylene sulfide (PPS) matrix is studied. For the cutting experiments, consolidated TPC laminates at varying thicknesses up to s = 3.1 mm and a disc laser emitting at a wavelength of ! = 1030 nm at a maximum output power of P L = 2 kW are used. For the first time, the resulting magnitude of the heat affected zone (HAZ) at the cutting edge of the composite material is correlated with interlaminar shear strength tests. The results are compared to specimens prepared by milling and abrasive water jet cutting. Depending on the laminate thickness, the laser treated TPC samples show comparable properties to those of conventionally processed specimens. A reduced load bearing area, as a consequence of damaged fibre-matrix-adhesion due to laser impact, is identified as main factor for the reduction of interlaminar shear strengths for higher laminate thicknesses.
Abstract. The growing energy consumption of data centers has become an area of research interest lately. For this reason, the research focus has broadened from a solely performance-oriented system evaluation to an exploration where energy efficiency is considered as well. The Transaction Processing Performance Council (TPC) has also reflected this shift by introducing the TPC-Energy benchmark. In this paper, we recommend extensions, refinements, and variations for such benchmarks. For this purpose, we present performance measurements of real-world DB servers and show that their mean utilization is far from peak and, thus, benchmarking results, even in conjunction with TPC-Energy, lead to inadequate assessment decisions, e.g., when a database server has to be purchased. Therefore, we propose a new kind of benchmarking paradigm that includes more realistic power measures. Our proposal will enable appraisals of database servers based on broader requirement profiles instead of focusing on sole performance. Furthermore, our energy-centric benchmarks will encourage the design and development of energy-proportional hardware and the evolution of energy-aware DBMSs.
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