Applied Mechanics and Materials Vol. 146

Abstract: Railway networks are subjected to more and more severe loading conditions requiring the use of steels with a high resistance to wear and good fatigue behaviour. The surveys carried out on out of use equipment, such as rails or switches, show that these equipments fail by wear after quite a long period of use, but they can fail by fatigue in a substantially shorter time. In service, crossings are submitted to rolling, impact and sliding stresses. The impact-sliding is the result of the wheel transition from rail wing to crossing nose. Very high contact forces act on the crossing nose while such wheels are passing over it. These large contact forces between wheel and crossing can cause severe damage at crossing nose and wing rail. The influence of contact parameters on the damage of the crossing alloy (Hadfield steel GX120Mn13) in comparison with rail steel (R260) was investigated by impact and impact-sliding tests. The results are described and discussed using weight loss and microhardness measurements, optical and scanning electron microscopy observations of the contact surface. Examination of the results shows large plastic deformation in surface and subsurface of samples. In comparison with impact tests, sliding produces a change in size and shape of the contact area, a higher weight loss and lower hardening. A better impact–sliding wear resistance of Hadfield steel has been confirmed.

Abstract: We report new experimental and theoretical study of mechanical property of aligned and nonaligned (entangled) single walled carbon nanotubes (SWCNTs), and their effect on nanostructures. Experimentally, the contact mode atomic force microscopy cantilever tip is used to measure the Young’s modulus of aligned and nonaligned SWCNTs. The measured Young's modulus of aligned SWCNT bundles ranged between 1100 GPa (1.1 TPa) and 1300 GPa (1.3 TPa) with a relative uncertainty of 5 % whereas that of the entangled SWCNT bundles ranged between 500 GPa and 700 GPa. Young’s modulus increase with aligned SWCNT bundles and then increase their performance in nanostructure comparing with entangled SWCNT bundles. We put emphasis on the combination of physical modeling and reliability based design optimization of nanomaterials. After investigation, we could make suggestions such as how to improve the reliability of nanodevices and nanosystems, and how to reduce cost and economic rates.

Abstract: This paper presents a nanoactuator device as new model of the nanocomposite application. The carbon nanotube was incorporated in the polyvinylidne fluoride and trifluoroethylene P(VDF-TrFE) copolymer matrix. The P(VDF-TrFE) was chosen for its three characteristics which is ferroelectric, piezoelectric and pyroelectric to convert directly the electrical excitation to the mechanical motion (deflection). The SWCNT/P(VDF-TrFE) nanocomposite nanostructure is proposed as nanomaterial challenge to build a nanoactuator and drive systems in nanometer scale size. A deflection the SWCNT of about 10 picometer was found using the atomic force microscopy technique combined with lock-in-amplifier. And in this paper, we present a new method based on Optimal Safety Factors (OSF) in the context of the Reliability-Based Design Optimization (RBDO) analysis of of Carbon Nanotubes in Nanoactuator. We will underline also the different methods of the RBDO analysis and we highlight the advantage of our approach. Numerical results are given to illustrate the proposed method.

Abstract: Carbon nanotubes with polymers offers great advantages in improving material for both mechanical and electrical nanostructures. Design and fabrication have to consider that a local change in each compound accounts to the total change of physical properties in nanocomposite materials. This paper presents two parts of study. A model of strain nanosensor has been developed by using the polyvinylidne fluoride and trifluoroethylene P(VDF-TrFE) copolymer and carbon nanotubes in sandwich nanostructure [P(VDF-TrFE)/SWCNTs/ P(VDF-TrFE)] as a new application in nanotechnology domain. The experimental strain sensing was about 10^-4. On the other hand, reliability-based optimization is assessed for an efficient tool to consider this nanosensors nanodevice. We put emphasis on the combination of physical modeling and reliability based design optimization of nanomaterials. After investigation, we could make suggestions such as how to improve the reliability of nanodevices and nanosystems, and how to reduce cost and economic rates.

Abstract: The costs associated with the provision and maintenance of drinking water and wastewater infrastructure represents a significant financial demand worldwide. Maintenance costs are disproportionately high, indicating a lack of adequate durability. The aim of this paper is to study the degradation mode and the responsible factors of deterioration concrete pipe, used in the sewage’s city of Rennes (France). Thus, samples taken from different areas of the pipe (Raft, medium and roof) were analyzed using investigation methods in order to illustrate the internal and external rate of damage, caused by effluents and ground. In addition, chemical and mineralogical changes recorded were identified using scanning electron micrographs (SEM). In this research program, chemical and mechanical studies were performed by measuring the compressive and splitting tensile strengths. A phenolphthalein indicator solution is applied to a concrete specimen on a fresh fracture surface to determine the corrosion of steel reinforcement and the diseases advancement (pathologies depth). This study clearly shows the important anisotropy of both, internal and external damage. Finally, recommendations are proposed in line with the environment and possible approaches to sustainability assessment are also imposed.

Abstract: The paper deals with the rheological properties of epoxy resin additivated with organically modified montmorillonites, carbon nanotubes and nanocarbon. The paper also presents the influence of nanoadditives over composites mechanical properties. The epoxy polymer is diglycidyl ether of bisphenol A (DGEBA) and the curing agent is an aliphatic tetraamine. Organically modified montmorillonites Cloisite 30B and Cloisite 93A, MWCNTs and laser synthesized nanocarbon were used to synthesize nanocomposites by dispersing each in an epoxy resin. The dispersion was achieved through mechanical and sonic methods. The epoxy resin additivated with nanosized fillers was rheologically tested to study the dispersion influence. The sonic dispersion of nanoadditives is observed to drastically influence the rheological behavior of the suspensions. Newtonian fluid behavior disappears as the additive loading increases. The work mentions the influence of nanoadditives on the manufacturing process of epoxy /glass fibre and epoxy/ carbon fibre laminated composites.

Abstract: We currently notice a substantial growth in the wind energy sector worldwide. This growth is expected to be even faster in the coming years. This means that a massive number of wind turbine blades will be produced in the forthcoming years. There is a large potential for materials savings in these blades. The analysis of designed blade is done in dynamic loading. Five types of spars cross-section are taken in this work. The blade and spar are of composite material. The Finite element modal analysis of designed blade is done in ABAQUS. The scope of the present work is to investigate the structural modal analysis of full-scale 48m fiberglass composite wind turbine blades for 5MW horizontal axis wind turbine and through this to assess the potential for materials savings and consequent reductions of the rotor weight. The entire wind turbine can benefit from such weight reductions through decreased dynamics loads and thus leave room for further optimization. A numerical work has been used to address the most adequate spar shape and to get an understanding of the complex structural behavior of wind turbine blades. Five different types of structural reinforcements helping to prevent undesired structural elastic mechanisms are presented. Comparisons of the eigenfrequencies observed in the full-scale tests are presented and conclusions are drawn based on the mechanisms found.

Abstract: The work of this study concerns the fine modelling of the thermomechanical and metallurgical behavior of interface ceramic-metal in order to determine the residual mechanical state of the structures during brazing process. For these cases, difficulties mainly arise in the modelling of the solid-solid phase transformations as well as in the modelling of the mechanical behavior of the multiphasic material. Within an original theoretical framework - generalized standard materials with internal constraints – we proposed models for the behavior of multiphasic material. The design of joints in engineering structures and the optimisation of the industrial brazing process require determining and analysing such a phenomenon. In this way, the present work aims at predicting the thermally induced stresses (localisation and level) through numerical simulations and then, at defining the main parameters which influence their development

Abstract: Brittle materials in general and particularly glass are very sensitive to dynamic particles impacts of different nature. The ancient objects in glass (building, monuments) and some precious objects are subjected to atmospheric aggressions such as humidity, sand particles, hail,…etc.). Their surfaces are however, often exposed to severe climatic conditions in an environment where the sand wind is a daily phenomenon or beach wind. Many degradation processes due to erosion affect significantly surfaces of buildings that are part of the Cultural Heritage.

Abstract: The aim of this work is to study the effects of hydrogen absorption on mechanical properties of pipe API 5L X70 steel. This study is conducted in special soil solution NS4 with pH 6.7 It show that the tensile properties like yield stress, ultimate strength and elongation at failure reduced under hydrogen embrittlement. Several fatigue tests (three (03) points bending tests) on roman tile specimens with notch are performed. Fatigue initiation is detected by acoustic emission. A comparison between specimens electrolytically charged with hydrogen and specimens without hydrogen absorption is made and it has been noted that fatigue initiation time is reduced when hydrogen embrittlement occurs. The field of elastoplastic stresses near the notch is computed by the finite-element method with the Abaqus software package. Effective distance and stress are calculated with the volumetric approach and the Notch intensity Factor of the roman tile specimen is determined for each loading value used in our tests.