An additive manufacturing-based approach for carbon fiber reinforced polymer recycling

The vast Carbon Fiber Reinforced Polymer (CFRP) waste accumulated is pressing for its recycling. A novel recycling approach, which integrated carbon fiber reclamation and composite additive manufacturing, is proposed to process the CFRP waste into three Dimensional (3D) parts. In the experiments, the CFRP waste was recycled by supercritical n-butanol to yield reclaimed Carbon Fibers (rCFs). The rCFs were ground by a ball mill, mixed with Poly-Ether-Ether-Ketone (PEEK) powder and then extruded to the composite filament. The filament was fed to the Fused Deposition Modeling (FDM) printer to fabricate 3D parts. Mechanical and electrical properties of the parts were investigated and compared with that of pure PEEK. The results illustrate that the additive manufacturing-based approach offers a potential strategy to reuse the CFRP waste and rapidly fabricate the rCF reinforced plastics with complex geometry and function.     

Flexural behaviour of RC slabs strengthened with prestressed CFRP strips using different anchorage systems

The Externally Bonded Reinforcement (EBR) technique using Carbon Fiber-Reinforced Polymers (CFRP) has been commonly used to strengthen concrete structures in flexure. The use of prestressed CFRP material offers several advantages well-reported in the literature. Regardless of such as benefits, several studies on different topics are missing. The present work intends to contribute to the knowledge of two commercially available systems that differ on the type of anchorage: (i) the Mechanical Anchorage (MA), and (ii) the Gradient Anchorage (GA). For that purpose, an experimental program was carried out with twelve slabs monotonically tested under displacement control up to failure by using a four-point bending test configuration. The effect of type of anchorage system (MA and GA), prestrain level (0 and 0.4%), width (50 mm and 80 mm) and thickness (1.2 mm and 1.4 mm) of the CFRP laminate, and the surface preparation (grinded and sandblasted) on the flexural response were the main studied parameters. Better performance was observed for the slabs: (i) with prestressed laminates, (ii) for the MA system, and (iii) with sandblasted surface preparation.     

核聚变堆用钨表面超精密抛光的研究现状与趋势

钨作为未来核聚变堆中最有前景的面向等离子体材料,在反应堆工况下将承受高能粒子的辐照冲击。表面质量的好坏会直接影响材料的氢/氦滞留行为和辐照损伤程度,进而影响聚变堆的安全性和可靠性。现阶段,针对钨的抗辐照改性研究主要着眼于材料的成分、结构和组织设计,关于机械加工对材料表面抗辐照改性的研究甚少。文章聚焦前沿科学问题,从机械加工角度分析核材料领域科学问题,结合国内外相关研究成果及核聚变堆用钨(PFM-W)的机械加工现状,阐述了PFM-W表面超精密抛光的必要性。通过对比不同抛光方法,提出了磁流变抛光和力流变抛光是较为适合PFM-W表面超精密加工的观点,并对未来PFM-W表面超精密抛光研究趋势进行了分析,重点在抛光方法的探索以及抛光后材料表面质量对抗辐照性能影响的研究。     

Experiments and simulations of the mechanical performance of repaired panels

Firstly, the compress experiment is undertaken to investigate the efficiency of repaired panels in this paper, and then modeling of the mechanical behavior of the repaired composite panel under compressive static load is conducted by using of the finite element method. The effect of geometric non-linearity on the stress–strain response is considered in the numeric analysis. Fatherly, the user material subroutine (UMAT) is integrated with the ABAQUS package with the geometric non-linearity effect for studying the damage initiation and its progression in the composite structure, and quadrilateral, linear, thick shell elements (S8R) are adopted. Finally, the predicted strain distribution, damage evolution and strength of the laminate are compared with the test results.     

The combustion of kerosene: Experimental results and kinetic modelling using 1- to 3-component surrogate model fuels

The oxidation of kerosene Jet-A1 and that of n-decane have been studied experimentally in a jet-stirred reactor at atmospheric pressure and constant residence time, over the high temperature range 900–1300 K, and for variable equivalence ratio (0.5≤ϕ≤2). Concentration profiles of the reactants, stable intermediates, and final products have been obtained by probe sampling followed by on-line and off-line GC analyses. The oxidation of neat n-decane and of kerosene in these conditions was modeled using a detailed kinetic reaction mechanism (209 species and 1673 reactions, most of them reversible). The present model was successfully used to simulate the structure of a fuel-rich premixed n-decane–oxygen–nitrogen flame. In the modelling, kerosene was represented by four surrogate model fuels: 100% n-decane, n-decane-n-propylbenzene (74%/26% mol), n-decane-n-propylcyclohexane (74%/26% mol), and n-decane-n-propylbenzene-n-propylcyclohexane (74%/15%/11% mol). The 3-component model fuel was the most appropriate for simulating the JSR experiments. It was also successfully used to simulate the structure of a fuel-rich premixed kerosene–oxygen–nitrogen flame.     

Interpretation of the morphology and crystallography of precipitate γ1-Ti4Nb3Al9 in L10-TiAl(Nb)-based intermetallics by invariant line theory

The coherent precipitate γ₁-Ti₄Nb₃Al₉ in the Nb-modified TiAl-based intermetallic compound with a nominal composition of Ti–48 at% Al–10 at% Nb was investigated by transmission electron microscopy. The crystallographic and morphologic characteristics of the precipitating phase have been calculated based on invariant line theory. It is revealed that in the γ-TiAl(Nb)/γ₁-Ti₄Nb₃Al₉ couples, both the morphological and crystallographical characteristics of the precipitate γ₁-Ti₄Nb₃Al₉ could be predicted by the three-dimensional phase transformation invariant line model. The needle direction of [001] at the early stage for coherent precipitate γ₁-Ti₄Nb₃Al₉ and [111] for equilibrium phase γ₁-Ti₄Nb₃Al₉ have both been explained well. The characterization of morphology and crystallography of the precipitate reaction in γ-TiAl/γ₁-Ti₄Nb₃Al₉ system sustain the postulate that precipitates are bounded by unrotated planes (eigenplanes) when three real eigenvalues exist.     

Intelligent tool wear monitoring based on parallel residual and stacked bidirectional long short-term memory network

Effective tool wear monitoring (TWM) is essential for accurately assessing the degree of tool wear and for timely preventive maintenance. Existing data-driven monitoring methods mainly rely on complex feature engineering, which reduces the monitoring efficiency. This paper proposes a novel TWM model based on a parallel residual and stacked bidirectional long short-term memory (PRes–SBiLSTM) network. First, a parallel residual network (PResNet) is used to extract the multi-scale local features of sensor signals adaptively. Subsequently, a stacked bidirectional long short-term memory (SBiLSTM) network is used to obtain the time-series features related to the tool wear characteristics. Finally, the predicted tool wear value is outputted through a fully connected network. A smoothing correction method is applied to improve the prediction accuracy. The proposed model is experimentally verified to have a high prediction accuracy without sacrificing its generalization ability. A TWM system framework based on the PRes–SBiLSTM network is proposed, which has a certain reference value for TWM in actual industrial environments.     

Evaluation of amines for the selective catalytic reduction (SCR) of NOx from diesel engine exhaust

With a view to developing onboard generation of selective reductants for NO_x removal from diesel engine exhaust we compared the performance of a primary, secondary and tertiary amine to NH₃ using a typical mini core NH₃-SCR catalyst. Primary amines with short hydrocarbon chains, e.g. CH₃NH₂ (maximum NO_x conversion, 50%) approached the NO_x conversion obtained using NH₃ (maximum NO_x conversion, 70%). Increasing the amine to NO_x ratio greater than 1 results in NO_x conversions closer to those of NH₃ (maximum NO_x conversion increased to 60%). Secondary and tertiary amines had smaller NO_x conversions as a function of temperature and the drop in NO and NO_x conversion decreased with increasing amine hydrogen substitution. Also, the maximum NO_x conversion for each reductant tends to move to a lower temperature as the degree of substitution increases.Unlike NH₃, the amines can react in the gas phase at temperatures within the range of diesel engine exhaust. Due to this gas phase reactivity the NO_x conversions measured using the mini core SCR catalyst also contain a gas phase conversion component. Gas phase conversions were investigated by replacing the mini core SCR catalyst with an equivalent length of quartz beads. Subtraction of the two results highlighted the differences between the mini core catalytic and gas phase conversions measured in this manner over the temperature range investigated. These differential NO_x conversions for the three amines had maxima at about 375 °C.     

Playing vibrotactile music: A comparison between the Vibrochord and a piano keyboard

A novel vibrotactile musical input device called the Vibrochord, which is designed to deliver patterns of vibration to the skin, not to the ear, through the use of a vibrotactile display called the Emoti-Chair, is evaluated using proposed evaluation frameworks. Findings show that the mixture of frameworks used in this study provided valuable insight into the design of this novel musical device. Results obtained through the implementation of a mixture of these frameworks show that the Vibrochord facilitated an increased accuracy rate over the traditional piano keyboard, when inexperienced vibrotactile musicians tried to repeat vibrotactile patterns or “melodies”.