Effects of stochastic tow waviness on stiffness and strength of plain-weave ceramic matrix composites

This article presents the development of a finite element model, which considers stochastic tow waviness using a Markov Chain algorithm and non-linear material properties using Binary Model, to predict the stress–strain and fracture behaviour of plain-weave ceramic matrix composites under uniaxial extension. The stochastic waviness is described by fluctuations in the centroid coordinates of tow positioning. The tow deviations are generated by marching sequentially from one grid point to next along a tow path. The deviations depend only on the deviation of the previous point using a probability transition matrix. A non-linear orthotropic constitutive model was implemented in a commercial finite element code Abaqus using a user-defined subroutine. Two 2 × 2 unit cell models of a plain-weave ceramic matrix composite laminate are created using stochastic tow elements generated by the virtual specimen generator, which was developed on the basis of the Markov Chain algorithm. A comparison has been made between the systematic and stochastic models to assess the effects of stochastic tow waviness on the stiffness and strength of the laminate. The numerical results have been validated by the comparison of predictions with the experimental data. The stochastic model which considers random waviness correlates well with the experimental data

Can China’s Growth be Sustained? A Productivity Perspective

China’s gradual approach to economic transition has resulted in sustained high growth. However, in recent years Chinese economists have increasingly referred to the growth pattern as “extensive,” generated mainly through the expansion of inputs. Our investigation of the Chinese economy during the reform period finds that reform measures often resulted in one-time level effects on total factor productivity (TFP). China now needs to adjust its reform program toward sustained increases in productivity. Market and ownership reforms, and open door policies have improved the conditions under which Chinese firms operate, but further institutional reforms are required to consolidate China’s move to a full-fledged market economy

The Effect of Slag on the Mechanical Properties of Coralline-Activated Materials and the Formation and Transformation of Mineral Crystals

In this study, coralline-activated materials were prepared using ball-milled coral powder as cementitious material and coral sand as fine aggregate. XRF (X-ray fluorescence) and chemical dissolution tests were carried out to determine the content and reactivity of various elements in coral powder. The compressive strength of the developed composites was evaluated at different ages, and the formation and transformation of mineral crystals in coralline-activated samples were further analyzed by XRD (X-ray diffractometer). The results show that the calcium content in coral powder was as high as 89.5% (loss on ignition). However, only 56% of the active calcium could participate in the polymerization reaction. The silicon and aluminum content was too low, and the slag addition could improve the deficiency of silicon and aluminum in coral powder. With the increase in slag content (from 0% to 50%), the compressive strength of the composites increases significantly. Nevertheless, the enhancement is not pronounced when the slag content exceeds 50%. The increase in slag amount can stimulate the transformation of calcium minerals, e.g., aragonite and calcite, into hydrated calcium silicate and calcium aluminosilicate gels, which significantly enhances the resulting compressive strength

Binder polymer influence on the electrical and UV response of organic field-effect transistors

The use of blends of small molecule organic semiconductors (OSCs) with insulating binding polymers has been shown to be a promising route to facilitate the processing of OSCs over large areas using printing techniques. Here we fabricated organic field-effect transistors (OFETs) and phototransistors using the benchmark OSC 7-decyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) and blends of this material with polystyrene (PS), poly(pentafluorostyrene) (PFS) and poly(methyl methacrylate) (PMMA). We show that the nature of the binding polymer has a significant impact on the device performance. The OFETs showing the best performance are the ones based on blends of PS since they reveal less interfacial traps, leading to devices with higher mobility, threshold voltage close to zero and high bias stress stability. The lowest OFET performance is found in the devices based on PMMA blends due to the higher density of majority charge carrier (i.e., holes) traps. On the other hand, regarding the response of the devices to UV light, the PFS and pristine films exhibited the highest photoresponse, which was attributed to the higher density of minority charge carrier (i.e., electrons) traps. Therefore, this work demonstrates that the binding polymer is a useful tool to optimise the OFET electrical characteristics as well as its photoresponsivity.This work was funded by the projects GENESIS PID2019-111682RB-I0 and Severo Ochoa FUNFUTURE CEX2019-000917-S from MCINN/AEI/10.13039/501100011033/and by the Generalitat de Catalunya (2017-SGR-918). J. L. acknowledges funding from the Chinese Scholarship Council (CSC). J. L. is enrolled in the UAB Materials Science PhD program. S.R-G. acknowledges support from the Marie Skłodowska Curie Cofund, Beatriu de Pinós Fellowship (AGAUR-2019 BP 00200). R. P. acknowledges support from the Ramón y Cajal Fellowship (Ref. RyC2019-028474-I).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Schematic diagram of Hooke’s law for plane stress state.

<p>Schematic diagram of Hooke’s law for plane stress state.</p

Typical model and response on 20μm×20μm domain (100 samples, actin filament relative density: 0.15%, actin filament length: 5μm±2μm, segment length 0.3μm±0.06μm, and maximum cross-linker length: 0.3 μm) (a) layout of a selected sample (20μm×20μm) (b) histogram of elastic moduli, E¯=3.09kPa, std(E)=0.24kPa.

<p>Typical model and response on 20μm×20μm domain (100 samples, actin filament relative density: 0.15%, actin filament length: 5μm±2μm, segment length 0.3μm±0.06μm, and maximum cross-linker length: 0.3 μm) (a) layout of a selected sample (20μm×20μm) (b) histogram of elastic moduli, </p><p></p><p></p><p><mi>E</mi><mo>¯</mo></p><p></p><p></p>=3.09kPa, std(E)=0.24kPa.<p></p

Variation of network stiffness as a function of average filament length.

<p>Variation of network stiffness as a function of average filament length.</p

Variation of average stiffness of networks with relative density of actin filaments.

<p>Variation of average stiffness of networks with relative density of actin filaments.</p

Layouts of selected samples with different actin filament relative densities.

<p>(a) 0.15% (b) 0.20% (c) 0.25% (d) 0.30%.</p