Strain evolution in the single point incremental forming process: digital image correlation measurement and finite element prediction

Incremental Sheet Forming (ISF) is a relatively new class of sheet forming processes that allow the manufacture of complex geometries based on computer-controlled forming tools in replacement (at least partially) of dedicated tooling. This paper studies the straining behaviour in the Single Point Incremental Forming (SPIF) variant (in which no dedicated tooling at all is required), both on experimental basis using Digital Image Correlation (DIC) and on numerical basis by the Finite Element (FE) method. The aim of the paper is to increase understanding of the deformation mechanisms inherent to SPIF, which is an important issue for the understanding of the high formability observed in this process and also for future strategies to improve the geometrical accuracy. Two distinct large-strain FE formulations, based on shell and first-order reduced integration brick elements, are used to model the sheet during the SPIF processing into the form of a truncated cone. The prediction of the surface strains on the outer surface of the cone is compared to experimentally obtained strains using the DIC technique. It is emphasised that the strain history as calculated from the DIC displacement field depends on the scale of the strain definition. On the modelling side, it is shown that the mesh density in the FE models plays a similar role on the surface strain predictions. A good qualitative agreement has been obtained for the surface strain components. One significant exception has however been found, which concerns the circumferential strain evolution directly under the forming tool. The qualitative discrepancy is explained through a mechanism of through-thickness shear in the experiment, which is not fully captured by the present FE modelling since it shows a bending-dominant accommodation mechanism. The effect of different material constitutive behaviours on strain prediction has also been investigated, the parameters of which were determined by inverse modelling using a specially designed sheet forming test. Isotropic and anisotropic yield criteria are considered, combined with either isotropic or kinematic hardening. The adopted constitutive law has only a limited influence on the surface strains. Finally, the experimental surface strain evolution is compared between two cones with different forming parameters. It is concluded that the way the plastic zone under the forming tool accommodates the moving tool (i.e. by through-thickness shear or rather by bending) depends on the process parameters. The identification of the most determining forming parameter that controls the relative importance of either mechanism is an interesting topic for future research.     

Compaction and shearing behaviour study of recycled aggregates

The aggregates resulting from the recycling of the products of demolition lie within the scope of local materials replacement and this study contributes to their valorisation in the field of the civil engineering, particularly in roads. After having sorted and selected the recycled aggregates, their characterization will bear on the comparison of the physical and mechanical behaviour of the recycled aggregates and natural materials (sand and gravel). In order to study their mechanical response and determine their mechanical characteristics the proctor test, the CBR test and the shearing test have been carried out. The result obtained showed that their characteristics are lower than those of the natural aggregates. Then, we tried to improve them by the following additions (sand, cement and brick). The combination of these materials two to two enabled us to improve some of their physical and mechanical characteristics and bring them near to the natural aggregates. Moreover, repeated shearing of the same sample, in each initial state of stress, highlighted the durability of the aggregates, and particularly their crushing phenomenon.     

Electrochemical investigation of Ni−P autocatalytic deposition in ammoniacal solutions

The kinetics of Ni–P autocatalytic deposition in ammoniacal solutions was investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy. The effect of the solution constituents (hypophosphite, nickel salt and pH) was examined. Strong interactions between the cathodic and anodic processes occur. The metal discharge is enhanced by the oxidation of hypophosphite, which is the predominant reaction in this process. The nickel deposition also affects the anodic process. With increasing pH the nickel discharge is progressively inhibited due to the change in the nature of the Ni(II) complexes. In contrast, in the presence of Ni(II) species, due to the opposite effect of the two partial processes, the plating rate increases for pH values up to 9 and then decreases for higher pH values.     

Accident prediction models for roads with minor junctions

The purpose of this study was to develop and validate a method for predicting expected accidents on main roads with minor junctions where traffic counts on the minor approaches are not available. The study was based on data for some 3800 km of highway in the U.K. including more than 5000 minor junctions. The highways consisted of both single and dual-carriageway roads in urban and rural areas. Generalized linear modelling was used to develop regression estimates of expected accidents for six highway categories and an empirical Bayes procedure was used to improve these estimates by combining them with accident counts. Accidents on highway sections were shown to be a non-linear function of exposure and minor junction frequency. For the purposes of estimating expected accidents, while the regression model estimates were shown to be preferable to accident counts, the best results were obtained using the empirical Bayes method. The latter was the only method that produced unbiased estimates of expected accidents for high-risk sites.     

Contribution à l’étude du mouvement de terrain de la ville de Tigzirt (Algérie)

This article is a contribution to the study of the causes, characterization, and numerical modeling, using finite elements, of the landslide affecting the coastal slope at the edge of the Mediterranean Sea near the city center of Tigzirt (Algeria). This slope is characterized by a relatively low inclination (13°–15°) and composed of two main geological formations (marly bedrock overlain by recent Quaternary deposits). Several factors have acted jointly and explain the activity of Tigzirt landslide: it is the effect of geological, morphological, and hydrogeological site contexts combined to triggering factors of various origins (human, climatic, and seismic). The landslide is characterized by a planar failure surface, which involves a global translational deformation towards the sea.     

Robust geocast routing protocols for safety and comfort applications in VANETs

Routing in cooperative vehicular networks is a challenging task because of high mobility of vehicles and difficulty of localization. In this paper, we study the geocast routing problem in Vehicular Ad‐hoc NETworks (VANETs), which aims at delivering data to a specific group of mobile vehicles identified by their geographical location. Although many geocast routing protocols have been proposed, only partial inherent constraints of VANETs (such as mobility, internal network fragmentation problem, external network fragmentation problem, and overload) are taken into account. Therefore, we propose two novel and robust geocast routing protocols: the first one, called Robust Geocast Routing Protocol for Safety Applications (RGRP‐SA), is dedicated to road safety applications, while the second, namely, Robust Geocast Routing Protocol for Comfort Applications (RGRP‐CA), is designed for comfort applications. Simulations conducted in NS‐2 demonstrate that our safety‐oriented RGRP‐SA protocol outperforms Inter‐Vehicle Geocast protocol and Mobicast Routing Protocol in VANETs by sending up to 25% more packets, cutting the end‐to‐end delay in half, and solving the internal network fragmentation problem. Besides, it is also shown that our comfort‐oriented RGRP‐CA protocol serves well comfort applications with only light overhead by solving internal and external network fragmentation problems and providing more reliable data delivery (with a 25% higher packet delivery ratio) and higher network throughput utilization in comparison with Mobicast with Carry‐and‐Forward protocol. Copyright © 2015 John Wiley & Sons, Ltd.     

FE analysis of the behaviour of microcracks in the cement mantle of reconstructed acetabulum in the total hip prosthesis

Cracking of cement mantle of joint arthoplasties is one possible factor in the loosening of cemented replacements. The analysis of the fracture behaviour of cement in such case can be an effective means being able to contribute to the prediction of the lifespan of the various types of cemented prostheses. In this study, the three-dimensional finite element method was used to analyse the fracture behaviour of cement of reconstructed acetabulum by computing the stress intensity factor along the crack front. The obtained results show that the risk of crack propagation by opening effect is more important than the sliding and the tearing ones when the crack is located at the free edge of the cement mantle. The sliding effect is dominant when the crack is inclined at 45° from the free edge of the cement mantle.     

Preamble sampling MAC protocols with persistent receivers in wireless sensor networks

We provide an analytical framework for preamble sampling techniques for MAC protocols in wireless sensor networks, from which we derive closed-form formulas for lifetime and reliability calculations. In addition to take into account transmitter behavior that controls the form and the content of the transmitted preamble, our model also considers receiver behavior that controls the duration of preamble reception in case of successful and failed reception. Along with both transmitter and receiver behavior, our model considers a non-perfect channel and thus takes into account the impacts of transmission errors and retransmissions on lifetime and reliability of preamble sampling protocols. Numerical results show that no protocol is universally optimal; that is, each protocol has its own optimal operation point that depends on the given channel and load conditions.     

Effect of oxygen dissolved in metal on the strength of Silver-Alumina junctions formed in the solid state

In this study, the strength of the junctions formed by thermal compression of solid silver and alumina is measured using an indirect tensile test. The essential role of the oxygen content in solid solution of metal on the adherence force is particularly highlighted. Our results are analyzed starting from the surfactant effect of oxygen, in solid solution of metal at the interface Ag/Al₂O₃. It’s clearly shown that an unfavourable couple (weak energy of adhesion) can have an interesting behaviour if the beneficial role of certain elements of additions is taken into account. It is also shown that strong junctions can be obtained while exploiting the initial preparation of metal.     

Effect of gamma irradiation and sodium hydroxide treatment on the debittering of olive (Olea europaea) fruits

The effect of gamma irradiation and sodium hydroxide (NaOH) treatment on the debittering of olive (Olea europaea, var Surrany) fruits was investigated. Fruits were treated with 1, 2 or 3 kGy of gamma irradiation at a dose rate of 669 Gy h^?1. Irradiated and unirradiated fruits were processed with NaOH solution (11 g l^?1) for 3 or 6 h and washed once per day for 3 days. The fruits were then immersed in brine (56 g l^?1 sodium chloride) and stored for 12 months at room temperature. Dissolved organic and inorganic solids, Na⁺, K⁺ and Ca²⁺ contents, pH and electrical conductivity values were determined in the debittering solutions (lye, rinse and washing waters) and brines. Gamma irradiation significantly (p < 0.05) increased the dissolved organic and inorganic solids and the Na⁺ and K⁺ concentrations in the debittering solutions when the fruits were treated with NaOH for 3 h. On the other hand, gamma irradiation had no significant effect on these parameters, except for an increase in K⁺ concentration, when using NaOH solution for 6 h. Gamma irradiation with NaOH treatment for 3 h decreased the concentration of Ca²⁺ in the debittering solutions, whereas irradiation and treatment with NaOH solution for 6 h increased its concentration. © 2003 Society of Chemical Industry