Flash sintering is a nonlinear phenomenon characterized by a sharp increase in the conductivity of the sample and concomitant rapid densification under an electric field in low temperatures in a ...matter of seconds. Since it is a transient phenomenon, the power dissipation on the sample is not uniform during the process. Thus, a transient analysis is needed to estimate the temperature of the sample during flash sintering due to Joule heating. In this work, the Finite Element Method on a coupled electrothermal nonlinear analysis was used in order to obtain the specimen temperature of 8YSZ after 5 s of flashing. The results agree with the experimental data obtained by the flashing of dense samples and with previous literature.
In this paper the densification of ceramics under flash sintering is modelled using an approach based on the heat equation coupled with a apparent activation energy kinetic equation for ...densification, leading to a system of nonlinear differential equations. Methods to analyse the system either by numerical solutions or via bifurcation theory are presented. Measurements needed to estimate sintering kinetic parameters are executed. The model shown explains the two main features of flash sintering: A characteristic electrical field threshold independent on the temperature, and an incubation time to flash sintering. The results are in agreement with experimental results obtained for Yttria Stabilzed Zirconia and for nanosized BaTiO3. It confirms that the critical condition for the Flash phenomenon is rather the temperature dependent resistivity than the sintering kinetics.
•A research on the rheological-mechanical behavior of high modulus dense asphalt mix is carried out.•All the materials, parameters and models to formulate the asphalt mix tested are defined.•Complex ...modulus, fatigue resistance and numerical simulations are the main evaluation scopes.•Critical energy dissipation temperature is a decisive parameter to design asphalt pavements.
The main aim of this paper is to evaluate the influence of temperature on mechanical-rheological behavior and design of high modulus dense asphalt mix. Analytical procedures were conceived based on the French rational methodology. The asphalt mix formulated was tested through two point bending complex modulus and fatigue tests. Numerical simulations using Huet-Sayegh viscoelastic linear model and computerized tools Viscoanalyse and Viscoroute were proceeded to design asphalt pavement structures. The results obtained indicate the critical energy dissipation temperature verified in complex plan has decisive influence on the asphalt mix behavior and must be analyzed particularly for designing asphalt pavement structures.
Purpose - The purpose of this paper is to investigate the application of the element-free Galerkin (EFG) method to the simulation of metal forming processes and to propose a strategy to deal with ...volumetric locking problem in this context.Design methodology approach - The J2 elastoplastic material model, employed in the work, assumes a multiplicative decomposition of the deformation gradient into an elastic and a plastic part and incorporates a non-linear isotropic hardening response. The constitutive model is written in terms of the rotated Kirchhoff stress and the logarithmic strain measure. A Total Lagrangian formulation of the problem is considered in order to improve the computational performance of the proposed algorithm. The imposition of the essential boundary conditions and also of the unilateral contact with friction condition are made by the application of the Augmented Lagrangian method. Here, aspects related to the volumetric locking are investigated and an F-bar approach is applied.Findings - The results show that the proposed approach presents no volumetric locking phenomenon when using the mean dilation approach. Moreover, differently from finite element approximations, no hour-glass instabilities in the deformation pattern are observed, avoiding in this way the need to devise additional stabilization procedures in the proposed procedure.Originality value - This paper demonstrates the implementation and validation of the mean dilation approach, in the scope of the EFG, which was successful in coping with the volumetric locking phenomena and presented no hour-glass instabilities in the problem cases considered in this work.
Despite many studies on the subject, brake squeal remains a major concern for the automotive industry. Much progress was made toward understanding and preventing this issue, focusing on the dynamic ...behavior of the brake. However, the problem is far from fully understood. Among many friction material ingredients, abrasives are extensively used to regulate friction and wear and are recognized as the main contributors to brake noise. This work investigates the correlation between characteristics of abrasives and squeal noise occurrence determined through the SAE J2521 dynamometer test procedure, FESEM, EDS, nanoindentation, and roughness profiling analyses. The particle size, hardness, Young's modulus, and resistance to elastic deformation of 13 different grades of abrasives were measured. The correlation between these characteristics and squeal noise occurrence was determined through statistical analysis. Spearman's rank correlation coefficient (ρ) showed that squeal noise strongly correlated with hardness and resistance to elastic deformation (ρ = 0.61 and ρ = 0.56, respectively) of abrasive materials and exhibited a poor correlation with their particle size (ρ = −0.099). However, considering groups of samples of the abrasive type, particle size is a characteristic that should be regarded in analyzing squeal noise propensity. In the case of SiC, coarser particles (D90 = 196.70 μm) showed a significant reduction in squeal noise compared to finer particles (D90 = 6.30 μm). On the other hand, coarse particles markedly increased the mass loss of the brake pad and brake disk.
•Dynamometer was used to evaluate the squeal noise response of thirteen abrasives.•Abrasives hardness affects squeal noise occurrence, friction, and disk wear.•Squeal noise correlates with elastic deformation parameters of abrasive particles.•Squeal noise and wear of friction materials are influenced by tribofilm nature.
Measuring and Modeling the Plasticity of Clays de, Andrade F A; Al-Qureshi, H A; Hotza, D
Materials research (São Carlos, São Paulo, Brazil),
09/2010, Letnik:
13, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The measurement of plasticity in clay bodies is crucial in order to get products free of defects and with less processing time. However, tests which simulate the behaviour of the clay during ...processing and the mathematical modelling of some of its characteristics, particularly the plasticity, are difficult because many variables are involved and there is no consensus on the choice of method to be used. This study aimed to develop a mathematical model based on a compression test to evaluate the plasticity of clays. Three types of clay were studied with different levels of moisture and their indices of plasticity were characterised by the Atterberg's and Pfefferkorn's methods. The experimental data were well fitted by the theoretical curves for a wide range of clay plasticity. It was possible to observe a correlation between effective stress of compression and paste moisture within each group of clay.
Annual cement production has surpassed 4 billion tonnes worldwide, strongly contributing to carbon footprint. However, more sustainable and efficient cement based materials have been achieved by ...incorporating cellulose into the mixture. More specifically, cellulose nanocrystals (CNC), nanorods of pure crystalline cellulose, not only present excellent mechanical properties, but also, influence cement hydration by a process termed short circuit diffusion, due to great interaction with water. Therefore, cement pastes prepared with varying contents of CNC, along with a polycarboxilate superplasticizer (SP) were tested with the Impulse Excitation Technique, a nondestructive testing, which allows replicability over time. Hence, to explore the effects of both CNC and SP on the early hydration, tests were conducted on 3, 5, 7, 14 and 28 hydration days for a complete scenario. For a complementary analysis, the degree of hydration, dry and bulk densities and the volume of permeable pores were determined at 7 hydration days. It was found that lower contents of CNC positively affect cement hydration at early ages, resulting in higher dynamic modulus of elasticity (Ed) and lower porosity. Nevertheless, at 28 hydration days, CNC seems to have no greater influence over the SP effect, and all mixtures presented similar Ed.
•Cement-based pastes nanocomposites with varying CNC content and superplasticizer were prepared.•Early hydration moduli were assessed by the IET.•CNC has a greater influence in early cement hydration.
The behavior of ceramic-metal protection against a projectile impact is modeled. The model takes into account the mass and velocity for each stage of the phenomenon. A former model was modified ...considering more realistic parameters such as geometries and deformation profile. To analyze the model, simulations on different parameters have been run. The impact results of different ballistic projectiles were simulated, and the movement was plotted. In addition, a deterministic simulation on the mechanical properties of the back metal plate properties was done.
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