Radu Cojocaru

Application of Thermography in Materials Science and Engineering

The chapter presents the main applications of IR thermography in material science and engineering with focus on modern methods for examination of materials and applications in new processing technologies development and to the improvement of existing processing technologies by implementing process control. Beside a synthesis of the applications presented in the existing literature, applications of IR thermography developed by the chapter’s authors are presented. The following subchapters will present various applications of IR thermography in materials science and engineering.

Modeling of Airport Rigid Pavement Structure Made of RCC and Recycled Cement Concrete for Complex Configuration of Landing Gears

This paper presents the results of the research undertaken by the authors in the frame of the postdoctoral program 4D-POSTDOC. After a short introduction on the actual status of structural design of airport pavements including geometrical and loading characteristics of complex loading gears, the modeling and the structural design of airport rigid pavements, constructed with conventional and various recycled materials, using the finite element method, is described. The main objective of this research program was to elaborate a design method which, beside the complex landing gear including six footprint tires, all specific parameters related with the recycled materials and with conventional and reinforce rolled compacted concrete (RCC) technologies are included. Finally, practical design diagrams for structural design of the concrete slabs, including their specific correlation function, used for the construction of the Airbus-A380 runway are presented.

Friction Stir Lap Welding of Light Alloy Sheets

Aluminum alloys are widely used in aerospace, automotive, railway and shipbuilding industry, as materials having remarkable properties for applications in these fields. For this reason, in recent years the interest for friction stir lap welding of sheets from these alloys increased.The behaviour of welding materials from the plastic and mechanic viewpoint are different in case of friction stir lap welding compared to friction stir butt welding.The welding tools for friction stir lap welding can have different configurations and sizes compared to butt welding. The used welding parameters must be reconsidered in order to obtain a proper flow of material for obtaining a friction stir lap welded joint.In addition, it is very important how to prepare the sheets surfaces that come into contact and their placement (relative to each other).The paper presents considerations regarding friction stir lap welding, with examples/concrete results obtained in welding of similar and dissimilar light alloys (alloys of aluminum, magnesium and titanium). It also presents data on the characteristics of obtained welded joints, related with particularities of friction stir lap welding.The obtained results showed that light alloys sheets used in various industrial fields can be joined with respect of basis conditions specific for the friction stir lap welding process.

Microstructural Transformation during Dissimilar Friction Stir Welding (FSW) of Aluminum-Cooper Alloys

This paper presents some results obtained in Friction Stir Welding (FSW) of aluminum and cooper alloys, as a result of joint researches carried out in University Politehnica Timisoara and National R&D Institute for Welding and Material Testing – ISIM Timisoara. Microstructural investigations revealed a nugget zone well defined, in which the two materials are well mixed and adjacent zones (thermos-mechanically affected zones) in which thin vanes from one material is mixed into the other material. SEM and EDX analysis revealed the blending of the two materials which provides good continuity of the welded joint. The tool and welding technology developed during the researches provides a good quality FSW welded joint. which will give the possibility to engineer components with high electric current conductivity and in the same time low weight, needed by the automotive industry in developing the new generation of electric vehicles.

Numerical Modeling of Thermal Field Distribution during Friction Stir Welding (FSW) of Dissimilar Materials

Friction Stir Welding (FSW) is an innovative solid state welding process, relatively new in industry, which allow welding of two or more materials which have very different properties, particularly thermal properties as fusion temperature, thermal expansion coefficient, specific heat and thermal conduction and have a predisposition to form intermetallic brittle phases, neither one of the components to be weld reach to the melting point. Being a solid state welding process temperature field is very important for the quality of the welded joint, and a lot of researches focused on this topic. This paper presents some results in modeling and estimation of thermal field developed during FSW of dissimilar joints, using Finite Element Analysis. Numerical modeling of thermal field allows engineers to predict, in advance, the evolution of temperature and to estimate the behavior of the welded materials during the welding process. This will reduce significantly the time and number of experiments that have to be carried out, in the process of establishing a good FSW technology, as well as reducing significantly the cost of the tests.

Possibilities for Application of Friction Stir Welding Process to Titanium TiGr2

The interest in friction stir welding (FSW) of different categories of light metallic materials, including titanium and its alloys, has growing in recent years.Due to favorable ratio between strength and density, titanium and its alloys have increasingly used in applications in priority areas (e.g. aeronautics and in aerospace). Having the best impact strength and good corrosion resistance, these materials find applications in chemistry, nuclear and military technology.This paper present the results obtained at friction stir butt welding of TiGr2 sheets with thickness 4mm.The experimental program has developed using three categories of welding tools: with smooth cylindrical pin and flat shoulder, with tapered pin and flat shoulder, respectively with tapered pin having four plane chamfers and flat shoulder. The welding experiments have made using combinations of tools and welding parameters.The control of FSW welding process of titanium TiGr2 sheets has done using an innovative method namely infrared thermography technique.The research program has focused on development of some welding tools and welding regimes correlated with obtaining some of better mechanical characteristics for welded joints.Results obtained to the friction stir butt welding of titanium TiGr2, lead to conclusion that welding joints without defects and with good mechanical characteristics can be obtained, if are known and met the specific requests regarding applying of FSW process to this type of material.

Examination of Noxious Emissions of the Welding Process “Cold Metal Transfer (CMT)”

For the examination of noxious emissions, cladding tests were performed according to EN ISO 6847. The filler materials were 1.2 mm diameter wire-electrodes, made of tin bronze, aluminium bronze, austenitic stainless steel, duplex stainless steel and nickel alloy.The low-energy metal transfer welding process, named CMT (cold metal transfer) was examined, on the welding source type Trans Puls Synergic 2700 CMT, of 270 A, produced by the company Fronius, Austria. For sampling welding smoke particles, an Apex type pump was used. For measuring the concentration of gases emitted by welding, a Triple Plus type multi-gas detector was applied.The particulate emission rate is 0.500 mg / m3 in the breathing zone, according to ISO 10882-1. For comparison, the measured emission rate is from 0.877 to 2.513 mg / m3 in the welding zone, according to ISO 15011-1. The concentration of the emitted gases is in the ranges: 0.14 to 0.16% CO2; 0.1-0.2 ppm NO2; 0-15 ppm H2; 0-5 ppm CO. These concentration levels are below the exposure limits (8 hours per day, five days a week): 5% CO2; 1.0 ppm NO2; 30 ppm CO. In conclusion, the emissions from the CMT welding process are without health risk for the welder.

Welding of AA2124/SiC/25p-T4 by FSW at High Welding Speed and Monitoring the Process by Real-Time Control of Infrared Termography and Energy Consumption

The objective of this study is to present the feasibility of welding of AA2124/SiC/25p-T4 metal matrix composite at high welding speed by friction stir welding. We carried out the analysis of the microstructure, microhardness, and tensile test of welded sample from different areas, to evaluate the performance of the weld. The phase structure of AA2124/SiC/25p-T4 metal matrix composite was determined by X-ray diffraction (XRD). The temperature monitoring and measurements in the welding zone, in different areas was made, using infrared thermography to demonstrate that the FSW welds of AA2124/SiC/25p-T4 is below the melting temperature of the base material and to see the temperature distribution during the process. In addition, the monitoring and the control of energy consumption was achieved.

Modelling of Airport Rigid Pavement for Complex Configuration of Landing Gears and for a Large Spectrum of Cement Concrete

The purpose of this paper is to develop new design diagrams in order to complete the actual Romanian standard. This addendum is justified by the fact that the current design diagrams are elaborated for a single value of the E - dynamic elasticity modulus (in Romanian standard E = 30000 MPa) and of the Poisson ratio (in Romanian standard ν = 0.15). Therefore the diagrams from the Romanian standard NP034-99 do not permit the design for other types of concrete cement with improved characteristics with elasticity modulus E 30000 until E = 50000 MPa or of the Rolled Compacted Concrete (RCC) with Poisson ratio ν = 0.25 or of the other concrete types as cement concretes with recycled aggregates or steel fibre reinforced concrete. The first part of the paper presents the stress design methodology based on the finite element software and on the parameters which interfere in the design calculation. In addition to the diagrams from the Romanian standard which apply only to an external load up to a four wheel bogie, the diagrams with loads with six wheel bogie are introduced. Further are shown the differences between the stress calculated with single values from the actual Romanian standard and the stress calculated with the exact values of the considered parameters [E dynamic elasticity modulus and the Poisson ratio]. The study relies on the specific load of modern aircrafts (like Airbus - A380, Boeing - B777) that have six footprints tire in the landing gear structure. In the end, the article brings forward a graphic comparison analysis between the diagrams of the Romanian current standard and the ones conducted in the present study by using FEM (Finite Element Method). Furthermore, a design case study exemplifies the method used to obtain the slab thickness for an airport rigid pavement structure using an external load from a complex landing gear with six footprints tire.