Specific damping capacity calculation of composite plates with delamination based on higher-order Zig-Zag theory

Damping is focused in a mass of engineering applications at present. In this paper a new laminate element rests on the higher-order zig-zag theory for composite plates were presented. And then, viscoelasticity damping and frictional damping models in delaminated composites were established. The damping changes of delaminated composites with different boundary conditions were investigated via the laminate element, the effects of area and location on damping were also researched. The results revealed that viscoelasticity damping and frictional damping are in the same order of magnitude even delamination area is small, and frictional damping increase significantly when delamination area enlarged, frictional damping is needed to be considered in the damping research of delaminated composites

A cognitive evaluation and equity-based perspective of pay for performance on job performance: A meta-analysis and path model

Pay for performance, as one of the most important means of motivating employees, has attracted the attention of many scholars and managers. However, controversy has continued regarding whether it promotes or undermines job performance. Drawing on a meta-analysis of 108 independent samples (N = 71,438) from 100 articles, we found that pay for performance was positively related to job performance. That pay for performance had a more substantial positive effect on task performance than contextual performance in workplace settings. From the cognitive evaluation perspective, we found that pay for performance enhanced employees' task performance and contextual performance by enhancing intrinsic motivation and weakened task performance and contextual performance by increasing employee pressure. From the equity perspective, our results indicated that the relationship between pay for performance and task performance was partially mediated by employee perceptions of distributive justice and procedural justice, with distributive justice having a more substantial mediating effect than procedural justice. However, the relationship between pay for performance and contextual performance was only partially mediated by procedural justice. Further tests of moderating effects indicated that the varying impacts of pay for performance are contingent on measures of pay for performance and national culture. The findings contributed to understanding the complex mechanisms and boundary conditions of pay-for-performance's effects on job performance, which provided insights for organizations to maximize its positive effects

Tuning crystal-phase of bimetallic single-nanoparticle for catalytic hydrogenation

Bimetallic nanoparticles afford geometric variation and electron redistribution via strong metal-metal interactions that substantially promote the activity and selectivity in catalysis. Quantitatively describing the atomic configuration of the catalytically active sites, however, is experimentally challenged by the averaging ensemble effect that is caused by the interplay between particle size and crystal-phase at elevated temperatures and under reactive gases. Here, we report that the intrinsic activity of the body-centered cubic PdCu nanoparticle, for acetylene hydrogenation, is one order of magnitude greater than that of the face-centered cubic one. This finding is based on precisely identifying the atomic structures of the active sites over the same-sized but crystal-phase-varied single-particles. The densely-populated Pd-Cu bond on the chemically ordered nanoparticle possesses isolated Pd site with a lower coordination number and a high-lying valence d-band center, and thus greatly expedites the dissociation of H$_2$ over Pd atom and efficiently accommodates the activated H atoms on the particle top/subsurfaces

RNA-binding protein RALY reprogrammes mitochondrial metabolism via mediating miRNA processing in colorectal cancer

Objective: Dysregulated cellular metabolism is a distinct hallmark of human colorectal cancer (CRC). However, metabolic programme rewiring during tumour progression has yet to be fully understood. Design: We analysed altered gene signatures during colorectal tumour progression, and used a complex of molecular and metabolic assays to study the regulation of metabolism in CRC cell lines, human patient-derived xenograft mouse models and tumour organoid models. Results: We identified a novel RNA-binding protein, RALY (also known as hnRNPCL2), that is highly associated with colorectal tumour aggressiveness. RALY acts as a key regulatory component in the Drosha complex, and promotes the post-transcriptional processing of a specific subset of miRNAs (miR-483, miR-676 and miR-877). These miRNAs systematically downregulate the expression of the metabolism-associated genes (ATP5I, ATP5G1, ATP5G3 and CYC1) and thereby reprogramme mitochondrial metabolism in the cancer cell. Analysis of The Cancer Genome Atlas (TCGA) reveals that increased levels of RALY are associated with poor prognosis in the patients with CRC expressing low levels of mitochondrion-associated genes. Mechanistically, induced processing of these miRNAs is facilitated by their N6-methyladenosine switch under reactive oxygen species (ROS) stress. Inhibition of the m6A methylation abolishes the RALY recognition of the terminal loop of the pri-miRNAs. Knockdown of RALY inhibits colorectal tumour growth and progression in vivo and in organoid models. Conclusions: Collectively, our results reveal a critical metabolism-centric role of RALY in tumour progression, which may lead to cancer therapeutics targeting RALY for treating CRC

Numerical Study on the Rebound of Low-Velocity Impact-Induced Indentation in Composite Laminate

Indentation is an effective indication of LVI damage in PMCs. However, indentation can rebound partly with time. Thus, a good understanding of the rebound behavior of the impacted pit is helpful in damage assessment for composites. In this paper, a transverse isotropic viscoelastic model and a viscoelastic cohesive interface model are proposed to represent the viscoelastic properties of ply and the interface between adjacent plies, respectively. In these models, we implement the in-plane 3D Hashin failure criterion to simulate ply level failures and the stress-based quadratic failure criterion and linear softening mixed-mode BK law to simulate cohesive interface failure initiation and propagation, respectively. LVI testing was performed on specimens at different impact energies (30 J, 40 J, and 50 J). Dents induced by impact will eventually rebound due to the viscoelastic behavior of plies and cohesive interfaces. This results in a decrease in depth with time. This indentation and its rebound phenomenon were simulated in ABAQUS by considering viscoelasticity with user-defined material subroutines. The simulation results show good agreement with the experimental observations and are validated accurately in terms of the indentation’s initial depth upon impact and its final rebound with time. From experiments, it was observed that the decrease in the original depth of indentation initially becomes faster with time after impact; then, it slows down with time and eventually stops due to viscoelasticity. While this decrease in the original depth of indentation remains invariable with time in simulation, it has a different rebound path

Numerical Study on the Rebound of Low-Velocity Impact-Induced Indentation in Composite Laminate

Indentation is an effective indication of LVI damage in PMCs. However, indentation can rebound partly with time. Thus, a good understanding of the rebound behavior of the impacted pit is helpful in damage assessment for composites. In this paper, a transverse isotropic viscoelastic model and a viscoelastic cohesive interface model are proposed to represent the viscoelastic properties of ply and the interface between adjacent plies, respectively. In these models, we implement the in-plane 3D Hashin failure criterion to simulate ply level failures and the stress-based quadratic failure criterion and linear softening mixed-mode BK law to simulate cohesive interface failure initiation and propagation, respectively. LVI testing was performed on specimens at different impact energies (30 J, 40 J, and 50 J). Dents induced by impact will eventually rebound due to the viscoelastic behavior of plies and cohesive interfaces. This results in a decrease in depth with time. This indentation and its rebound phenomenon were simulated in ABAQUS by considering viscoelasticity with user-defined material subroutines. The simulation results show good agreement with the experimental observations and are validated accurately in terms of the indentation’s initial depth upon impact and its final rebound with time. From experiments, it was observed that the decrease in the original depth of indentation initially becomes faster with time after impact; then, it slows down with time and eventually stops due to viscoelasticity. While this decrease in the original depth of indentation remains invariable with time in simulation, it has a different rebound path

TWO-SCALE NUMERICAL SIMULATION OF PROGRESSIVE TENSILE FAILURE OF HYBRID COMPOSITES

Two 3D finite element approaches for unidirectional hybrid composites were built to represent failure process in scales of individual fiber and fiber tow,respectively. The first scale approach was defined as iso-type fibers and epoxy composed fiber tow in which micro damages concerned including failures of individual fiber,matrix and fiber / matrix interface. The second scale approach assembled with different type fiber tows. In this scale,failure regularities of tow and interface between adjacent tows were considered and the former was obtained from first scale model. Cohesive zone model was used to simulate the damage and failure of component materials,this method could reflect the distribution and propagation of the crack in composites. Explicit FEM was used for both the two scale models to characterize the impaction of energy released from the broken fiber or tow. Weibull type distribution was used to describe strengths of fiber and fiber tow in the two scale approaches for charactering the randomness of failures. The two scale approaches were employed to simulate the progressive failure of carbon / glass fiber hybrid unidirectional composites under tensile load. Two distribution patterns of carbon tow in hybrid composites,i. e. coaxial and dispersed were taken into account,meanwhile for each pattern different volume ratio of carbon fiber and glass fiber was considered. The study reveals that when volume fraction of carbon tows is equal or less than 10% the second damage phenomenon is obvious,meanwhile the critical elongation and strength for coaxial hybrid composited are slightly bigger than those for dispersed one. Otherwise,the two patterns hybrid composites behave in brittle way and little discrepancy between their strengths has been found

Numerical Study of the Hygrothermal Effects on Low Velocity Impact Induced Indentation and Its Rebound in Composite Laminate

Impact indentation is believed to be an effective indication of low-velocity impact (LVI) damage for polymer matrix composites. However, it has been discovered that an indentation can partially rebound over time. Impact indentation and its rebound behavior over a period of time are significantly affected by hygrothermal conditions, especially moisture absorption. Therefore, a good understanding of the moisture-dependent impact indentation and its rebound behavior is helpful for impact damage assessment for composites. In this paper, moisture effects are considered for both the intra-laminar transverse property model and the interlaminar interface model in the simulation of impact indentation. Then, in these two models, viscosities are introduced to represent the indentation rebound over time. In order to validate the proposed models, LVI experiments with different impact energies were conducted on dry and hygrothermal conditioned carbon fiber/epoxy matrix composite laminates. For the specimens, the initial depths of impact dents and their rebounds over time were measured. The specimens of hygrothermal conditions were found with deeper dents compared with dry ones under the same impact energy; and their rebounds were also more significant. These phenomena were explained by the fact that moisture softens epoxy in composite and meanwhile elevates its viscosity. This indentation and its rebound phenomenon were simulated in ABAQUS by considering the moisture effects and viscoelasticity with user-defined material subroutines. These experiments were simulated using the proposed models, and the numerical predictions conformed well with the experimental observations