Numerical Study on the Dynamic Fracture Energy of Concrete Based on a Rate-Dependent Cohesive Model

As an important parameter for concrete, fracture energy is difficult to accurately measure in high loading rate tests due to the limitations of experimental devices and methods. Therefore, the utilization of numerical methods to study the dynamic fracture energy of concrete is a simple and promising choice. This paper presents a numerical investigation on the influence of loading rate on concrete fracture energy and cracking behaviors. A novel rate-dependent cohesive model, which was programmed as a user subroutine in the commercial explicit finite element solver LS-DYNA, is first proposed. After conducting mesh sensitivity analysis, the proposed model is calibrated against representative experimental data. Then, the underlying mechanisms of the increase in fracture energy due to a high strain rate are determined. The results illustrate that the higher fracture energy during dynamic tension loading is caused by the wider region of the damage zone and the increase in real fracture energy. As the loading rate increases, the wider region of the damage zone plays a leading role in increasing fracture energy. In addition, as the strain rate increases, the number of microcracks whose fracture mode is mixed mode increases, which has an obvious effect on the change in real fracture energy.

A cohesive model of predicting tax evasion from the perspective of fraudulent financial reporting amongst small and medium sized enterprises

Purpose The issue of tax evasion through fraudulent financial reporting committed by companies is a major concern facing the tax authority in Malaysia. As such, the purpose of this study is to propose a cohesive model of predicting tax evasion from the perspective of fraudulent financial reporting amongst small- and medium-sized enterprise (SME) taxpayers. Design/methodology/approach The proposed model for this study is designed to explore the extent of the relationships between the independent variables: family ownership firms, company size, presence of tax professionals, company’s duration in business and frequency of tax audits and the moderating variable, i.e. tax audit officers’ level of competence; and the dependent variable, i.e. tax evasion from the perspective of fraudulent financial reporting. This study is grounded on four theories: agency theory, political cost theory, economic deterrence theory and competency theory. Data will be gathered from actual audit cases resolved by the Inland Revenue Board of Malaysia. Ordinary least square regression analysis is proposed for the investigation. Findings This study anticipates that family ownership firms, company size, presence of tax professionals, company’s duration in business and frequency of tax audits could be associated with tax evasion amongst SMEs in Malaysia. This study further proposes that highly competent tax audit officers could mitigate the relationship between frequency of tax audits and tax evasion practices amongst SMEs in Malaysia. Originality/value This study should be able to provide a cohesive model of predicting tax evasion from the perspective of fraudulent financial reporting amongst SMEs in Malaysia. Research on fraudulent financial reporting amongst SMEs is very limited, especially involving the level of competence of the tax audit officers; therefore, this study should contribute to the tax evasion literature by providing a comprehensive model of predicting tax evasion through fraudulent financial reporting using a Malaysian tax setting.

Molecular Dynamics Modeling of Mechanical Properties of Polymer Nanocomposites Reinforced by C7N6 Nanosheet

Carbon-nitride nanosheets have attracted remarkable attention in recent years due to their outstanding physical properties. C7N6 is one of the hotspot nanosheets which possesses excellent mechanical, electrical, and optical properties. In this study, the coupled thermo-mechanical properties of the single nanosheet C7N6 are systematically investigated. Although temperature effects have a strong influence on the mechanical properties of C7N6 monolayer, thermal effects were not fully analyzed for carbon-nitride nanosheet and still an open topic. To this end, the presented contribution aims to highlight this important aspect and investigate the temperature influence on the mechanical stress-strain response. By using molecular dynamics (MD) simulation, we have found out that the C7N6 monolayer’s maximum strength decreases as the temperature increase from 300 K to 1100 K. In the current contribution, 5% to 15% volume fractions of C7N6/P3HT composite were employed to investigate the C7N6 reinforcing ability. Significantly, the uniaxial tensile of C7N6/P3HT composite reveals that 10%C7N6 can enhance the maximum strength of the composite to 121.80 MPa which is 23.51% higher than the pure P3HT matrix. Moreover, to better understand the enhanced mechanism, we proposed a cohesive model to investigate the interface strength between the C7N6 nanosheet and P3HT matrix. This systematic study provides not only a sufficient method to understand the C7N6 thermo-mechanical properties, but also the reinforce mechanism of the C7N6 reinforced nanocomposite. Thus, this work provides a valuable method for the later investigation of the C7N6 nanosheet.

The Numerical Analysis of the In-Plane Constraint Influence on the Behavior of the Crack Subjected to Cyclic Loading

The paper presents the influence of in-plane constraints defined by T-stress on the behavior of a crack subjected to cyclic loading. In the analysis, a modified boundary layer model approach was used in which the cohesive model was introduced. In the simulations, the constant maximum value of the stress intensity factor and four levels of T-stress were defined. The model was subjected to ten repeated stress cycles. Based on the results obtained, an analysis of the effect of the in-plane constraint on selected aspects of crack behavior was made. The strong influence of in-plane constraint applied in the model on the crack closure and the fatigue crack growth rate was proven. Since the in-plane constraint described the influence of geometry on the stress field surrounding the fatigue crack tip in real geometry, the results suggested that it is possible to create precise formulae connecting the level of the in-plane constraint with the effective stress intensity factor range and to incorporate the T-stress or Q-stress level in the Paris law.

Thermal Delamination Modelling and Evaluation of Aluminium–Glass Fibre-Reinforced Polymer Hybrid

This paper aims to propose a temperature-dependent cohesive model to predict the delamination of dissimilar metal–composite material hybrid under Mode-I and Mode-II delamination. Commercial nonlinear finite element (FE) code LS-DYNA was used to simulate the material and cohesive model of hybrid aluminium–glass fibre-reinforced polymer (GFRP) laminate. For an accurate representation of the Mode-I and Mode-II delamination between aluminium and GFRP laminates, cohesive zone modelling with bilinear traction separation law was implemented. Cohesive zone properties at different temperatures were obtained by applying trends of experimental results from double cantilever beam and end notched flexural tests. Results from experimental tests were compared with simulation results at 30, 70 and 110 °C to verify the validity of the model. Mode-I and Mode-II FE models compared to experimental tests show a good correlation of 5.73% and 7.26% discrepancy, respectively. Crack front stress distribution at 30 °C is characterised by a smooth gradual decrease in Mode-I stress from the centre to the edge of the specimen. At 70 °C, the entire crack front reaches the maximum Mode-I stress with the exception of much lower stress build-up at the specimen’s edge. On the other hand, the Mode-II stress increases progressively from the centre to the edge at 30 °C. At 70 °C, uniform low stress is built up along the crack front with the exception of significantly higher stress concentrated only at the free edge. At 110 °C, the stress distribution for both modes transforms back to the similar profile, as observed in the 30 °C case.

Getting Your Neutrophil: Neutrophil Transepithelial Migration in the Lung

Neutrophil transepithelial migration is a fundamental process that facilitates the rapid trafficking of neutrophils to inflammatory foci and occurs across a diverse range of tissues. For decades there has been widespread interest in understanding the mechanisms that drive this migratory process in response to different pathogens and organ systems. This has led to the successful integration of key findings on neutrophil transepithelial migration from the intestines, lungs, liver, genitourinary tract, and other tissues into a single, cohesive model. However, recent studies have identified organ specific differences in neutrophil transepithelial migration. These findings support a model where the tissue in concert with the pro-inflammatory stimuli dictate a unique collection of signals that drive neutrophil trafficking. This review focuses on the mechanisms that drive neutrophil transepithelial migration in response to microbial infection of a single organ, the lung. Herein we provide a detailed analysis of the adhesion molecules and chemoattractants that contribute to the recruitment of neutrophil into the airways. We also highlight important advances in experimental models for studying neutrophil transepithelial migration in the lung over the last decade.