Search

An investigation is carried out on natural cellulosic fibers which have gained interest in the composite field due to their superior specific properties as well as their eco-friendly environment character and biodegradability. A multi-scale finite element (FE) model of natural fiber composite materials is developed. The study is performed for multiple fibers in hexagonal packings with 10, 20, and 30% of fiber mass fractions. The mechanical behavior of the composite, processed by means of hand lay-up method and examined thanks to scanning electron microscopy (SEM), is simulated at macro-scale as well as mesoscopic scale. In particular, the response to tensile and three-point bending test is studied. Linear material properties are obtained by using pure strain assumptions in the implicit analysis of the composite, while the non-linear behavior and viscoelastic parameters require the explicit dynamic analysis. Simulation is performed thanks to ABAQUS finite element software. Comparison of experimental and FEM tensile and three-point bending strength shows very good agreement. From the results, it has been found that the prepared natural fiber composite materials can be used for structural engineering applications. [ABSTRACT FROM AUTHOR]

Surface roughness is one of the critical parameters that affect the component performance during its working life. To develop any process to its full potential, it is necessary to understand the physics of that process. Abrasive flow finishing (AFF) is one of the advanced finishing processes. In the current research work, an effort is made to understand physics and mechanism of surface roughness improvement during the AFF process. This research paper is divided into two sections. Firstly, the amount of finishing stresses and forces generated during the finishing of microholes fabricated on surgical stainless steel (316L) workpieces are computed by using the finite element method. Finishing stresses are generated in the viscoelastic medium. So, to compute finishing stresses, finite element analysis of the viscoelastic medium is carried out by incorporating its experimentally measured rheological properties. Finishing stresses are calculated along the circumferential direction of the microhole. Later, at the same workpiece surface location, simulated and experimentally measured surface roughness value are compared. Secondly, a new simulation model is proposed to predict the surface roughness on the microhole wall surface for various AFF input parameters. Maximum percentage change in surface roughness error of 8% is observed between simulated and experimental results after AFF process. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation of the laser shock peening (LSP) process using the finite element method. The majority of controlling parameters of the LSP process have been taken into account. The LSP loading has been characterized by the use of a repetitive time Gaussian increment pressure applied uniformly at a circular impacted zone. The utilized model of the treated material behaviour law is the Johnson-Cook’s visco-elastic-plastic coupled with damage. The proposed model leads to determine the LSP surface modifications: (i) the in-depth residual stresses, (ii) the induced plastic strains and (iii) the superficial damage. These modifications can be significantly induced in few cases, particularly when the operating conditions are not well optimized. An application is carried out on the laser peened titanium aero-engine super alloy Ti-6Al-4V. A satisfactory correlation between the computed and experimental results is observed. Also, it is noted that the computed superficial damage values increase with the growth of the maximal peak pressure of the laser spot, which are physically consistent. Otherwise, in order to optimize the laser peening operating conditions, a design of experiments is established. It allows having surface-response relationships between the operating parameters and the three announced induced effects. [ABSTRACT FROM AUTHOR]

Finite element modeling (FEM) of machining has recently become the most attractive computational tool to predict and optimize metal cutting processes. High-speed computers and advanced finite element code have offered the possibility of simulating complex machining processes such as turning, milling, and drilling. The use of an accurate constitutive law is very important in any metal cutting simulation. It is desirable that a constitutive law could completely characterize the thermo-visco-plastic behavior of the machined materials at high strain rate. The most commonly used law is that of Johnson and Cook (JC) which combines the effect of strains, strain rates, and temperatures. Unfortunately, the different coefficients provided in the literature for a given material are not reliable since they affect significantly the predicted results (cutting forces, temperatures, residual stresses, etc.). In the present work, five different sets of JC are determined based on orthogonal machining tests. These five sets are then used in finite element modeling to simulate the machining behavior of Al2024-T3 alloy. The effects of these five different sets of JC constants on the numerically predicted cutting forces, chip morphology, and tool-chip contact length are the subject of a comparative investigation. It is concluded that these predicted cutting parameters are sensitive to the material constants. [ABSTRACT FROM AUTHOR]

In this study, two different thermoforming molds, i.e., male and female, were prepared and used to conduct different tests at various heating times and evacuation powers. High impact polystyrene sheets of 0.5 mm thick were used to produce the cups with two vacuum and drape forming process. The experimental results showed that a more uniform thickness distribution could be obtained by increasing the heating time for the female mold. However, for the male mold, the heating time must be decreased in order to achieve a more uniform thickness distribution. Our findings showed that biaxial stretching was dominant in the vacuum forming, while uniaxial stretching was dominant in the drape forming. A finite element simulation of the vacuum forming process was also conducted to present a simple and accurate study of the forming process. In this work, a hyperviscoelastic constitutive model was used for modeling the high impact polystyrene behavior at forming temperature. The thickness distribution obtained by the finite element analysis is in a good agreement with the experimental results. In addition, the effect of friction coefficient was investigated by finite element analysis on the thickness distribution of the cup. [ABSTRACT FROM AUTHOR]