Dynamic properties of pultruded natural fibre reinforced composites using Split Hopkinson Pressure Bar technique

The paper presents results on dynamic mechanical properties of jute, and kenaf fibre reinforced composites at various strain rates using compression Split Hopkinson Pressure Bar technique. The stress–strain curves for both pultruded natural fibre reinforced composites at strain rates of nearly 1400 s⁻¹ are illustrated and then compared with statically determines stress–strain curve (1.0 × 10⁻³ s⁻¹). Results show that the strain rate does affect the value of dynamic compressive properties of both pultruded natural fibre composites. Higher dynamic compression modulus and 2.5% flow stress were recorded for higher strain rates as compared to lower strain rate over the range of strain rates investigated. Under dynamic loading, jute fibre reinforced composites recorded the highest value of dynamic response in terms of compression modulus, 2.5% flow stress and compressive strength than that of kenaf fibre reinforced composites. In addition, kenaf fibre reinforced composites is more severely damaged as compared to jute fibre reinforced composites for all tested strain rate.     

MapReduce scheduling algorithms: a review

Recent trends in big data have shown that the amount of data continues to increase at an exponential rate. This trend has inspired many researchers over the past few years to explore new research direction of studies related to multiple areas of big data. The widespread popularity of big data processing platforms using MapReduce framework is the growing demand to further optimize their performance for various purposes. In particular, enhancing resources and jobs scheduling are becoming critical since they fundamentally determine whether the applications can achieve the performance goals in different use cases. Scheduling plays an important role in big data, mainly in reducing the execution time and cost of processing. This paper aims to survey the research undertaken in the field of scheduling in big data platforms. Moreover, this paper analyzed scheduling in MapReduce on two aspects: taxonomy and performance evaluation. The research progress in MapReduce scheduling algorithms is also discussed. The limitations of existing MapReduce scheduling algorithms and exploit future research opportunities are pointed out in the paper for easy identification by researchers. Our study can serve as the benchmark to expert researchers for proposing a novel MapReduce scheduling algorithm. However, for novice researchers, the study can be used as a starting point.

     

Thermal properties of nanocellulose-reinforced composites: A review

Nanocellulose has received increasing attention in science and industry in recent years as a nanoscale material for the reinforcement of polymer matrix composites due to its superior mechanical properties, renewability, and biodegradability. New nanocellulose sources, modifications, and treatments are under development to reduce the high energy required during production and to create a more suitable industrial-scale production process. Thus, this paper reviews plant-based nanocellulose composites and their properties, with a focus on their thermal-related characteristics. The purpose of this review is to establish for readers the impact of the incorporation of nanocellulose on the thermal and dynamic mechanical properties of nanocellulose composites. Understanding of the thermal properties is important for researchers to assess the suitability of the nanocomposites for a variety of applications in response to new and evolving societal requirements. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48544.     

Corrosion Behavior of Sn-3.0Ag-0.5Cu Lead-Free Solder in Potassium Hydroxide Electrolyte

The corrosion behavior of Sn-3.0Ag-0.5Cu (SAC305) solder alloy in 6?M potassium hydroxide electrolyte was investigated using polarization analysis. The results revealed that SAC305 is susceptible to corrosion because of the dissolution of the Sn phase. The corrosion potential (E _corr) and corrosion current density (i _corr) obtained from the sample was ?C1.108?V vs Hg/HgO and 1.795?×?10^?4?A cm^?2, respectively. In addition, microstructural and elemental characterization revealed the presence of tin oxide, Cu, and/or Ag-containing corrosion product on the surface of the corroded sample. The morphology of the samples was also observed to contain several pits, cracks, and pore-like structures.     

On the longitudinal vibrations of a bar with viscous boundaries: Super-stability,super-instability,and loss of damping

This paper presents the investigation of the longitudinal motions of a bar subjected to viscous boundary conditions at each end. These viscous boundary conditions can also be thought of in terms of boundary feedback control. The system is not self-adjoint and for certain parameter regimes exhibits super-stable, super-unstable, and undamped behavior. Closed form solutions to the response of the system subjected to initial conditions and external excitation are obtained. The physical origins of the super-stable and super-unstable behavior are investigated and their intricate connectedness with the continuum model used to understand the dynamics is explained. The issue of discretization of the continuous system is discussed and it is shown that the continuum assumption bestows certain features to the response of the system that no finite dimensional approximation can qualitatively capture. Computational results corroborating the theoretical analysis are presented.     

Time-Delayed Positive Velocity Feedback Control Design for Active Control of Structures

In this paper we present and propose a design methodology that uses intentional time delays for the active control of structures. We use here positive velocity-feedback, time-delayed control and show that its performance is, in general, superior to the previously developed methodology of using time delayed, negative velocity-feedback control. A detailed study carried out in this paper of the nonsystem poles and their interaction with the system poles reveals the reasons for this. Analytical results related to performance and stability of the new method are presented. We apply the time delayed positive velocity feedback active control methodology to a multidegree-of-freedom system subjected to the S00E component of ground acceleration recorded during the El Centro 1940 earthquake. The excellent behavior in terms of stability, performance, and control efficiency that is demonstrated by our time-delayed control design as well as its facile implementation makes it attractive for earthquake hazard mitigation in a practical sense.     

Electrodeposition of BiVO4 with needle-like flower architecture for high performance photoelectrochemical splitting of water

Photoelectrochemical (PEC) water splitting is a green and sustainable approach capable of driving mass hydrogen production in the future. To realize this vision, development of a well-performing photoelectrode is highly demanded. In this comprehensive study, electrodeposition technique was applied for fabricating BiVO₄ films by regulating the deposition time from 1 min until 9 min. Interestingly, the morphology, crystallinity, chemical structure, and optical properties of BiVO₄ films depend strongly on the deposition time. It is found that BiVO₄ layer deposited for 7 min with a cross-section thickness of around 321.1–326.5 nm showed the optimum performance, whereby the photocurrent reached up to ~0.32 mA/cm^?2 at 1.23 V vs. RHE. The deposited BiVO₄ represents tiny and long petals, similar to “needle” nanostructures, which is embedded closely into compact agglomerates. Such morphology enables the BiVO₄ films to perform efficiently as photoanode in PEC cells. Besides, high crystallinity is detected from the sharp peaks of XRD and Raman analysis, as well as good light absorption capability that are the main contributors to the enhancement of PEC performance. In addition to the facile fabrication offered by electrodeposition method, the non-toxic attributes and the impressive PEC performance of the optimum BiVO₄ layer could serve as an interesting option for other applications such as gas sensors, solar cells, degradation of pollutants and photocatalytic water splitting.     

Measurement and prediction of compressive properties of polymers at high strain rate loading

Strain-rate effect is widely recognized as a crucial factor that influences the mechanical properties of material. Despite the acknowledge importance, the understanding of how such factor interact with the sensitivity of the polymers in terms of mechanical properties is still less reported. In this study, an experimental technique, based on the compression split Hopkinson pressure bar, was introduced to perform high strain rate testing, whereas, a conventional universal testing machine was used to perform static compression testing, to experimentally investigate the independent and interactive effects of strain rates towards mechanical properties of various polymers. Based on the experimental results, we parameterized two equation models, which were used to predict the yield behavior of tested polymer samplings. The experimental results indicate that, the yield stress, compression modulus, compressive strength, strain rate sensitivity and strain energy increased significantly with increasing strain rates for all tested polymers. Meanwhile, the yield strain and the thermal activation volume exhibit contrary trend to the increasing strain rates. Interestingly, the proposed constitutive models were almost agreed well with experimental results over a wide range of strain rate investigated. Of the three polymers, polypropylene shows the highest strain rate sensitivity at static and quasi-static region. On the other hand, at dynamic region, polycarbonate shows the highest strain rate sensitivity than that of polypropylene and polyethylene. Overall, both experimental and numerical models proved that the mechanical properties of polymer show significant sensitivity and dependency towards applied strain rates up to certain extent.     

Development and material properties of new hybrid medium density fibreboard from empty fruit bunch and rubberwood

In this research, new hybrid medium density fibreboard (MDF) was produced by using rubberwood (RW) and empty fruit bunch (EFB) based on oven-dried weight. There are two different ratios of hybrid MDF from rubberwood and EFB were produced which are EFB:RW, 20:80 and EFB:RW, 50:50 at 65% and 93% relative humidity (RH). The effect of storage time and relative humidity on the mechanical and physical properties of new hybrid MDF was studied. It was found that at 93% relative humidity, new hybrid MDF exhibited a highest effect on the mechanical and physical properties of panel after 10 weeks storage time. It observed that, hybrid MDF with ratio of EFB:RW, 20:80 exhibited the highest mechanical (flexure test and internal bonding) and physical properties [moisture content (MC), thickness swelling (TS), water absorption (WA)] as compared to hybrid MDF produced from EFB:RW, 50:50. Thus, the result showed that addition of higher amount of EFB fibres in hybrid MDF will decreased the composites properties. The property of composites decreases with increase of relative humidity and storage time. The result showed that, at 65% humidity new hybrid MDF exhibited lower effect on mechanical and physical properties of the panel.