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Showing papers in "Key Engineering Materials in 2012"


Journal ArticleDOI
TL;DR: A comprehensive review of the current theories of bonding in cold spraying based on numerical modelling of impact and experimental work is provided in this paper. But, precisely how this high strain rate deformation behavior of material promotes bonding is still unclear and requires further investigations.
Abstract: Cold gas dynamic spraying (CGDS) is a relatively new branch of surface engineering that involves modification of the surface of substrates to provide specific engineering advantages, which the substrate alone cannot provide. Cold spraying, as a metal deposition technique, involves spraying of typically 10-40 μm particles which are accelerated by a propellant gas to 300-1200 m/s at a temperature well below the melting point of material, and upon impact deform and adhere to the substrate. The deposition process in cold spraying occurs in a solid state which results in reduced oxidation and absence of phase changes; whereas, in thermal spraying deposition occurs of molten or semi molten particles. Over the last decade the interest in cold spraying has increased substantially. Considerable effort has been invested in process developments and optimization of coatings like copper. However, bonding in cold spraying is still a matter of some debate. The most prevalent theory is that when a particle travels at a minimum required velocity the particle deforms at a very high strain rate upon impact and during this deformation thermal softening dominates over work hardening in impact zone and a material jet is produced. This material jet removes oxides from the surface of the materials and the metal-to-metal contact is established between the freshly exposed surfaces. However, precisely how this high strain rate deformation behaviour of material promotes bonding is still unclear and requires further investigations. This article provides a comprehensive review of the current theories of bonding in cold spraying based on numerical modelling of impact and experimental work. The numerical modelling of the impact section reviews adiabatic shear instability phenomena, critical velocity, critical particle diameter, window of deposition of particles, particle impact on various substrates and the role of adhesion and rebound energy. The review of the experimental section describes the shear lip formation, crater formation on the substrates, role of surface oxides, characterization of bond formation, role of substrate preparations, coating build up mechanisms and contributions of mechanical and metallurgical components in bonding. Cold spraying of copper and aluminium has been widely explored in the last decade, now it is of growing interest to the scientific and engineering communities to explore the potential of titanium and its alloys. Titanium and its alloys are widely utilized in many demanding environments such as aerospace, petrochemical, biomedical etc. Titanium components are very expensive to manufacture because of the costly extraction process of titanium and their difficult to machine properties. Therefore, additive manufacturing from powder and repair of titanium components are of great interest to the aerospace industry using technologies such as cold gas spraying. Titanium coating as a barrier layer has a great potential for corrosion resistant applications. Cold spraying has a great potential to produce oxygen-sensitive materials, such as titanium, without significant chemical degradation of the powder. In-flight oxidation of materials can be avoided to a great extent in cold spraying unlike thermal spraying. This review article provides a critical overview of deposition efficiency of titanium powder particles, critical velocity, bond strength, porosity, microhardness, microstructural features including microstrain and residual stress, mechanical properties reported by various research groups. A summary of the competitor warm sprayed titanium coating is also presented in this article.

92 citations


Journal ArticleDOI
TL;DR: In this article, the thermal conductivity of metal powders with different particle diameters and their mixture was analyzed using a theoretically verified method, and its relation to porosity was elaborated.
Abstract: Selective Laser Melting (SLM) is a direct fabrication of part through layer by layer powder deposition and successive laser beam irradiation based on Computer Aided Design (CAD) data. One of the important properties in SLM is thermal conductivity of metal powder. This is because the ability of metal powder to conduct heat will affect the consolidation process during SLM. In this paper, thermal conductivity of metal powders with different particle diameters and their mixture was analysed. Other than that, thermal conductivity of consolidated materials fabricated via SLM process was also studied. In order to measure the thermal conductivity of metal powder, a theoretically verified method which was previously developed by the authors was used. Determination of thermal conductivity of consolidated material was analysed using laser flash technique. It was found that the thermal conductivity of powder metal was influenced by bulk density and particle diameter of metal powder. In this study also, metal powders of different particle diameters were mixed with various volume ratios, and its effect was discussed. Thermal conductivity of the consolidated materials was also examined, and its relation to porosity was elaborated.

80 citations


Journal ArticleDOI
TL;DR: The use of hemp-lime as a construction technique is a novel approach which combines renewable low carbon materials with exceptional hygrothermal performance as mentioned in this paper, making it very efficient in the use of time and material resources.
Abstract: The use of hemp-lime as a construction technique is a novel approach which combines renewable low carbon materials with exceptional hygrothermal performance. The hemp plant can grow up to 4m over a four month period, with a low fertilizer and irrigation demand, making it very efficient in the use of time and material resources. All parts of the plant can be used the seed for food stuffs, the fibre surrounding the stem for paper, clothing and resin reinforcement, and the woody core of the stem as animal bedding and aggregate in hemp-lime construction. The unique pore structure of the woody core (shiv) confers low thermal conductivity and thermal and hygric buffering to hemp-lime. The construction technique promotes good air tightness and minimal thermal bridging within the building envelope. All these factors combine to produce low carbon, hygrothermally efficient buildings which are low energy both in construction and in use, and offer opportunities for recycling at end of life. This paper reports on the hygrothermal performance of an experimental hemp-lime building, and on the development of a computerized environmental model which takes account of the phase change effects seen in hemp-lime.

69 citations


Journal ArticleDOI
TL;DR: In this article, the impurity elements (oxygen, chlorine, carbon) and their conditions on the powder particle surface, as well as the surface processes and gases emitted from powders upon heating, have been analyzed by means of surface science techniques.
Abstract: The powder metallurgy (PM) approach is widely used for cost-effective production of titanium alloys and articles. In the PM approach the large specific surface of starting powders heightens the risk of excessive impurity presence and, hence, degradation of final alloy properties. The present study analyzes the opportunity to produce sintered commercially pure titanium (CP-Ti) with acceptable impurity content from powder materials. Starting titanium and titanium hydride powders were comparatively examined. The impurity elements (oxygen, chlorine, carbon) and their conditions on the powder particle surface, as well as the surface processes and gases emitted from powders upon heating, have been analyzed by means of surface science techniques. The role of hydrogen emitted from titanium hydride in material purification has been discussed. The opportunity to produce titanium materials with final admissible content of interstitials (O, C, Cl, and H) using starting titanium hydride powder has been demonstrated.

54 citations


Journal ArticleDOI
TL;DR: In this article, a numerical model of the selective laser melting (SLM) process was investigated to simulate the genesis of residual stresses, based upon a double meshing with a multi-step birth and death technique of manufactured part.
Abstract: Selective laser melting (SLM) first developed for rapid prototyping (RP) is now used for rapid manufacturing of parts with inner complex shapes that cannot be made by more conventional routes. For example, production of injection moulds with cooling channels is of special interest. In this paper, a numerical model of SLM process was investigated to simulate the genesis of residual stresses. The proposed numerical modelling is based upon a double meshing with a multi step birth and death technique of manufactured part. The influence of the mesh size is analysed with element as small as the powder layer thickness for 2D and 3D geometries of simple parts. Comparisons between plane stress, plane strain, and 3D analysis are presented in order to propose a simplified approach.

46 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate examples related to structural health monitoring using noncontact optical/laser measuring techniques in many engineering applications, such as strain, vibration and ultrasound measurements.
Abstract: Non-contact optical/laser measuring techniques are very attractive in many engineering applications The paper demonstrates examples related to structural health monitoring Various methods based on strain, vibration and ultrasound measurements are presented together with relevant references Applications examples utilise in-plane and out-of-plane measurements taken by 1-D and 3-D laser Doppler vibrometers

45 citations


Journal ArticleDOI
TL;DR: In this article, a warm incremental forming of magnesium alloys is investigated, where hot fluid is used as heating media to obtain a homogeneous temperature in the forming areas, and final microstructures are related to the possible deformation mechanism.
Abstract: Industrial application of magnesium alloys is increasing in the last decade due to the very high mechanical strength to weight ratio they present. Typical applications are aeronautic parts but their use in the automotive industry is also growing. The bigger the reduction of the vehicle weight is, which can be obtain using these alloys, the bigger the energy saving will be in the near future. However, the formability of these alloys is poor and they are very difficult to be formed at room temperature. Several works have been presented by different authors on the positive influence the temperature increase has to form magnesium alloys. Normal process temperature is about 200-250°C. In this paper warm incremental forming of magnesium alloys is investigated. The work focuses in the formability limits of the alloys and the identification of the optimal process parameters. Aiming to obtain a homogeneous temperature in the forming areas, hot fluid is used as heating media. Experimental results for different temperatures are presented and final microstructures are related to the possible deformation mechanism.

44 citations


Journal ArticleDOI
TL;DR: Both these Functionalized Carbon Nanomaterials are Ideal Carriers for Drug Delivery and Covalently Functionalized Multiwalled Carbon Nanotubes and Graphene Oxide with Highly Hydrophilic and Biocompatible Excipients in order to increase their Aqueous Solubility and BiOCompatibility.
Abstract: Carbon Nanotubes (CNTs) and Graphene Have Attracted Tremendous Attention as the Most Promising Carbon Nanomaterials in the 21st Century for a Variety of Applications such as Electronics, Biomedical Engineering, Tissue Engineering, Neuroengineering, Gene Therapy and Biosensor Technology. For the Biomedical Applications, Cnts Have Been Utilized over Existing Drug Delivery Vectors due to their Ability to Cross Cell Membranes Easily and their High Aspect Ratio as Well as High Surface Area, which Provides Multiple Attachment Sites for Drug Targeting. Besides, it Has Also Been Proved that the Functionalization of CNTs May Remarkably Reduce their Cytotoxic Effects and at the Same Time Increase their Biocompatibility. So, the Functionalized CNTs Are Safer than Pristine or Purified CNTs, Thus Offering the Potential Exploitation of Nanotubes for Drug Administration. On the other Hand, More Recently Graphene and its Derivatives Have Been Enormously Investigated in the Biological Applications because of their Biocompatibility, Unique Conjugated Structure, Relatively Low Cost and Availability on both Sides of a Single Sheet for Drug Binding. In Our Study, we Have Covalently Functionalized Multiwalled Carbon Nanotubes (MWCNTs) and Graphene Oxide (GO) with Highly Hydrophilic and Biocompatible Excipients in Order to Increase their Aqueous Solubility and Biocompatibility. Various Excipients Used Were Polyvinyl Alcohol, Pluronic F38, Tween 80 and Maltodextrin. The Poorly Water-Soluble Anticancer Drugs such as, Camptothecin and Ellagic Acid, Were Loaded onto the Functionalized MWCNTs and GO via Non-Covalent Interactions. Furthermore, Drug Loading and Cytotoxic Activity of Drugs Incorporated with the Functionalized MWCNTs and GO as Nanocarriers Were Also Investigated. Drugs Loaded on both Carbon Nanocarriers Exhibited a Higher Cytotoxic Activity than Free Drug. On the other Hand, No Significant Toxicity Was Found even at Higher Concentrations when the Cells Were Incubated with the Functionalized Mwcnts and GO. Therefore, both these Functionalized Carbon Nanomaterials Are Ideal Carriers for Drug Delivery.

43 citations


Journal ArticleDOI
TL;DR: In this article, the effect of laser point distance on density and mechanical properties of the SLM-produced parts has not been widely studied, and the results of using SLM to produce biomedical beta Ti-24Nb-4Zr-8Sn components were presented.
Abstract: As many complex processing parameters are involved in Selective Laser Melting (SLM), an understanding of the scientific and technical aspects of the production route on the microstructural evolution during SLM process is required in order to obtain parts with near full density and desirable surface finish. Although the effects of the various processing parameters on the density of parts have been well documented, the effect of laser point distance on density and mechanical properties of the SLM-produced parts has not been widely studied. In this paper, we present the results of using SLM to produce biomedical beta Ti-24Nb-4Zr-8Sn components. Both the density and hardness of the material increases with increasing incident laser energy and reaches a near full density value of >99% without any post-processing. When the laser energy density input is high enough to fully melt powder, the laser point distance has no influence on the density or hardness of the samples. In contrast, at low energy densities, large point distances have been shown to be detrimental.

42 citations


Journal ArticleDOI
TL;DR: In this paper, a special brass wire technology for cutting Ni-based super alloys was developed to meet the requirements of fir tree production concerning aspects of surface integrity and geometry, and destructive analyses in terms of cross section polishing for showing thermal influenced rim zones have been prepared.
Abstract: This paper deals with developments of Wire-EDM technologies for fir tree slot production. The aim of these developments is to substitute certain conventional processes within turbine manufacturing that have been identified as non-optimal like the critical broaching process. Thereby the negative characteristics like inflexible manufacturing processes, high machine tool investment costs and huge energy consumption can be abolished. The objective targets of the conducted research are to meet all safety requirements of the critical components and get an economic manufacturing process. In the first step a special brass wire technology for cutting Ni-based super alloys was developed. Main focus was to meet the requirements of fir tree production concerning aspects of surface integrity and geometry. To measure these aspects on the one hand non-destructive analyses have been performed to guarantee surface roughness and accuracy. On the other hand destructive analyses in terms of cross section polishing for showing thermal influenced rim zones have been prepared. A capable Wire-EDM process is presented.

39 citations


Journal ArticleDOI
TL;DR: In this paper, basic requirements in terms of raw materials, facilities and processing in order to produce high performance components are presented for metal injection molding (MIM) for the processing of titanium and titanium alloys.
Abstract: Metal injection moulding (MIM) attracts growing interest as an economic net-shape manufacturing technique for the processing of titanium and titanium alloys. Even for titanium-aluminides, intended for high-temperature applications, MIM is seen as a reasonable technique to overcome processing problems with conventional methods. In this paper, basic requirements in terms of raw materials, facilities and processing in order to produce high performance components are presented. Main focus is laid on the well-known Ti-6Al-4V alloy. It is shown that the tensile properties of specimens after MIM processing can exceed the requirements given by ASTM standards even without performing an additional HIP process. For an oxygen content ranging from 0.15 to 0.33 wt% plastic elongation yields excellent 14%. Fatigue measurements performed by means of 4-point-bending tests show that grain size is more important than residual porosity in order to achieve a high endurance limit. This is shown by addition of boron powder which refines the microstructure dramatically. The modified alloy Ti-6Al-4V-0.5B yields an endurance limit of 640 MPa compared to 450 MPa of MIM parts made from standard alloy powder. Sintered components from Ti-45Al-5Nb-0.2B-0.2C (at%) powder made by inert gas atomising (EIGA technique) and processed by MIM exhibit a residual porosity of only 0.2% and tensile properties comparable to cast material.

Journal ArticleDOI
TL;DR: This communication shows the results of the Project MOON (asseMbly Oriented authOring augmeNted reality) developed by AIRBUS Military, which uses 3D information from the industrial Digital Mock-Up to generate assembly instructions and their deployment by applying Augmented Reality technology.
Abstract: The assembly of components in the aerospace industry is currently supported by procedures based on work instructions. This documentation describes both the sequence of operations to be performed by operators and fundamental parameters of operation. However, sometimes difficulties arise, either by the difficulty of interpreting the information or because the process is too complex. This communication shows the results of the Project MOON (asseMbly Oriented authOring augmeNted reality) developed by AIRBUS Military. MOON uses 3D information from the industrial Digital Mock-Up to generate assembly instructions and their deployment by applying Augmented Reality technology. A prototype was developed for the electrical harness routing in the frame 36 of the AIRBUS A400M.

Journal ArticleDOI
TL;DR: A new continuous process for the direct production of CP titanium powder is being developed at CSIRO as mentioned in this paper, which has two major steps: the first step is conducted in a fluidised bed where titanium tetrachloride and magnesium powder react to form small (1.5 µm) titanium metal particles uniformly dispersed inside larger spheroidal magnesium chloride particles with an average particle size of 350 µm.
Abstract: A new continuous process for the direct production of CP titanium powder is being developed at CSIRO. The TiRO™ process has two major steps. The first step is conducted in a fluidised bed where titanium tetrachloride and magnesium powder react to form small (1.5 µm) titanium metal particles uniformly dispersed inside larger spheroidal magnesium chloride particles with an average particle size of 350 µm. The second step involves vacuum distillation in which the magnesium chloride is removed from the titanium. During vacuum distillation the magnesium chloride is volatilised and the micron sized titanium particles come together to form partially sintered predominantly spheroidal porous particles with a similar shape to the starting particle, some which appeared to be hollow. A mechanism for their formation is proposed. The spheroidal particles are all lightly sintered together. The vacuum distilled product was very lightly ground to liberate the spheroidal particles which had an average particle size of about 200 µm. With further grinding an angular Ti powder was produced. The ground titanium was free flowing and had a tap density of 2.4 g/cm3.

Journal ArticleDOI
TL;DR: In this paper, a scheme based on MEMS is proposed to solve the problem of noise due to the inconsistency and asymmetry of electrodes of electrochemical accelerometer. But, traditional fabrication process of EAM is rather complex and can’t eliminate the noise.
Abstract: Petroleum prospecting and early warning of some geological disaster increasingly depend on the accelerometers which can detect vibrate of frequency below 1Hz, but it’s embarrassing that accelerometers based on Si or SiO2 structure make an awful performance in this frequency range. Electrochemical accelerometers were developed in 1990s. With fluidics to be inertial mass, electrochemical accelerometer not only show an excellent property in low frequency, but also has a wide dynamic range. However, traditional fabrication process of electrochemical accelerometer is rather complex and can’t eliminate the noise due to the inconsistency and asymmetry of electrodes. To solve these problems, a scheme based on MEMS is proposed here, including design, fabrication and package. Properties of electrochemical accelerometer (EAM) are tested in two conditions at last.

Journal ArticleDOI
TL;DR: In this article, a set of processes were assembled by selecting individual unit processes that when combined synergistically could offer the optimum performance to cost ratio for Ti manufacturing, including using low cost powders, using automatable near-net-shape compaction techniques, and using sintering.
Abstract: Powder Metallurgy (PM) Titanium has great potentials as low-cost alternative for Ti manufacturing, but the use of conventional PM processes for producing Ti products is also limited due to reasons related to either that the properties are not as satisfactory as that of equivalent wrought materials, or the cost advantage is not as significant as it was expected. Therefore, the main challenge of developing PM Ti is to increase performance to cost ratio. Reduction of costs and improvement of final products must involve every step of the entire process. This article attempts to assemble a set of processes by selecting individual unit processes that when combined synergistically could offer the optimum performance to cost ratio. This set of processes include using low cost powders, using automatable near-net-shape compaction techniques, and using sintering using sintering technologies that can produce parts with very fine grain sizes, thus satisfactory mechanical properties, in as-sintered state.

Journal ArticleDOI
TL;DR: In this article, the effect of sugar cane bagasse fibres (SCF) on extruded cementitious composite performance was evaluated, using cellulose pulp as secondary micro-reinforcement to improve the resistance to the appearance of microcracks.
Abstract: The extrusion process can produce composites with high-density matrix and fibre packing, low permeability and fibre matrix bond strengthening. This process is also compatible with the use of vegetable fibres as raw materials in the production of cost-effective construction elements such as ceiling panels. Sugar cane bagasse fibres (SCF), one of the largest cellulosic agroindustrial by-products of sugar and alcohol industry available in Brazil, are a renewable resource usually used as a biomass fuel for the boilers. The remaining bagasse is still a source of contamination to the environment, so there is a great interest on exploiting novel applications to sugar cane bagasse fibres. In this work, the effect of SCF on extruded cementitious composite performance was evaluated. Three different contents of SCF were considered, using cellulose pulp as secondary micro-reinforcement to improve the resistance to the appearance of microcracks. Composites were prepared using a laboratory Auger extruder with vacuum chamber and were tested after 28 days of water curing and after 200 accelerated ageing cycles. Modulus of rupture (MOR) and Tenacity (TE) of extruded composites were assessed by four point bending test. Water absorption and apparent volume were determined by water immersion. Microstructure behavior was evaluated by mercury intrusion porosimetry and scanning electron microscopy (SEM). Results indicated that the introduction of larger fibres increased tenacity (TE) at 28 days and favored a higher amount of macropores (0.1 to 1 mm); SEM observations confirmed that fibre degradation occurred after 200 cycles.

Journal ArticleDOI
TL;DR: In this paper, the authors presented a structural health monitoring (SHM) system, dedicated to marine structures, based on the fiber optic technique with Fibre Bragg Grating (FBG) sensors.
Abstract: The paper presents structural health monitoring (SHM) system, dedicated to marine structures. The considered system is based on the fibre optic technique with Fibre Bragg Grating (FBG) sensors. The aim of this research is recognition of possible practical applications of the fibre optic techniques in selected elements of marine structures. SHM and damage detection techniques have a great importance (economical, human safety and environment protection) in the wide range of marine structures, especially for ships and offshore platforms. In the paper monitoring system of the Horyzont II and Dar Mlodziezy ships and offshore oil platform is presented. Practical implementation of safety system based on optical sensors meets several difficulties. There has been installed the FBG system and its measurement results have been compared with classical techniques, e.g. piezoelectric accelerometers. The investigations have been performed for undamaged and damaged structure. Different types of failures have been modelled and tested. Damage detection ability has been specifying on the base of static and dynamic structural characteristics.

Journal ArticleDOI
TL;DR: In this paper, the sisal fibers were treated with methane plasma generated by direct electric current during 10, 20 and 30 min with gas flow of 5 cm3/s and current of 0.10 A.
Abstract: One of the main problems in using vegetable fibers as reinforcement in aggressive cement matrix is the penetration of alkaline products in the porous structure of the filaments, making them very fragile with the time. In this sense a series of physical and chemical methods of surface modification has been used in order to improve its characteristics. The plasma surface modification technique is a physical method surface modification that utilizes ionized gas at low pressure to change the chemical nature and the substrate surface morphology of both organic and inorganic materials without changing their intrinsic properties. This is considered an environmentally friendly process without generation of contamination and has a low operating cost compared to some chemical (such as silane based) treatments. In the present study, the sisal fibers were treated with methane plasma generated by direct electric current during 10, 20 and 30 min with gas flow of 5 cm3/s and current of 0.10 A. The study presents some mechanical, physics and chemical characteristics of sisal fiber after being subjected to treatment with methane cold plasma. The results presented indicate that treatment with methane cold plasma induced changes in sisal fibers at all times of exposure to treatment (10, 20 and 30 min). However, the major changes in structural and mechanical components may be seen in fibers treated with 10 min of exposure to plasma.

Journal ArticleDOI
TL;DR: In this article, a composite panel is built from a chiral honeycomb and two composite skins, and the panel is used for impact damage detection using nonlinear acoustics, which involves combined vibro-acoustic interaction of high-frequency ultrasonic wave and low-frequency vibration excitation.
Abstract: This paper demonstrates impact damage detection in a composite sandwich panel. The panel is built from a chiral honeycomb and two composite skins. Chiral structures are a subset of auxetic solids exhibiting counterintuitive deformation mechanism and rotative but not reflective symmetry. Damage detection is performed using nonlinear acoustics,involves combined vibro-acoustic interaction of high-frequency ultrasonic wave and low-frequency vibration excitation. High-and low-frequency excitations are introduced to the panel using a low-profile piezoceramic transducer and an electromagnetic shaker, respectively. Vibro-acoustic modulated responses are measured using laser vibrometry. The methods used for impact damage detection clearly reveal de-bonding in the composite panel. The high-frequency weak ultrasonic wave is also modulated by the low-frequency strong vibration wave when nonlinear acoustics is used for damage detection. As a result frequency sidebands can be observed around the main acoustic harmonic in the spectrum of the ultrasonic signal.

Journal ArticleDOI
TL;DR: In this paper, a standardized test to receive typical workpiece material removal properties according to its electrochemical machinability is introduced and the experimental setup of this test is described in detail.
Abstract: In this paper technological and economical capabilities of manufacturing titanium- and nickel-based alloys via unpulsed Electrochemical Machining (ECM) are presented. A standardized test to receive typical workpiece material removal properties according to its electrochemical machinability is introduced. First of all the experimental setup of this test is described in detail. The test results for the materials Ti-6Al-4V and Inconel 718 are presented and discussed. Here the feed rate – current density- and surface roughness – current density curves are in focus. With help of these two functions as an example out of many possible applications the capability of blisk manufacturing by electrochemical machining is quantified. Therefore the theoretical machining times for both materials of substituted blisk geometry are calculated. Finally on this basis an economical comparison between ECM and milling as rough estimation is executed.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the effect of local adapted tribological conditions on the material flow in sheet-bulk metal forming (SBMF) processes and developed a masking technique based on the FE-simulation.
Abstract: Innovative trends like increasing component functionality, the demand for automotive lightweight constructions and the economic issue to optimize existing process chains, require new ways in manufacturing. Today, the traditional sheet metal and bulk metal forming processes are often reaching their limits if closely-tolerated complex functional components with variants have to be produced. A promising approach is the direct forming of high-precision shapes starting from blanks. Thus, classic sheet metal forming operations, such as deep drawing, are combined with bulk metal forming operations like extrusion of complex variants as for example teeth. This combination of sheet and bulk metal forming operations leads to a side by side situation of different tribological conditions according to the locally varying load situations within the same forming process. This new class of forming processes is defined as sheet-bulk metal forming (SBMF). The tribological conditions in sheet-bulk metal forming processes are of major importance for the process realization, its stability and for the quality of the produced part. The objective of this paper is the investigation of material flow in SBMF in general and the attempt to improve the material flow by local adapted tribological conditions. First the material flow was analyzed by FE-simulation of a model geometry that is typical for SBMF. The investigations with FE-simulation have shown, locally adapted tribological conditions are leading to an improvement in material flow and thus to an increased mould filling. As frictional conditions are directly connected to the topography of workpiece and tool, the modification of the workpiece topography is leading to an alteration in friction values. For the modification of workpiece topography grit blasting was used. The increase in friction of grit blasted surface towards untreated surface was investigates by using the laboratory friction tests. To manufacture specimens with locally adapted topographies for forming tests a masking technique has been developed. The masks are designed after the preliminary findings determined by FE-simulation.

Journal ArticleDOI
TL;DR: In this paper, a direct comparison of the springback in both processes was performed using six samples of automotive steels in a conventional roll forming line where the transverse springback is measured.
Abstract: Bending in a V-die has been used to indicate the outcome of bending in cold roll forming, although little direct correlation has been performed. In this work direct comparison of the springback in both processes was performed using six samples of automotive steels in a conventional roll forming line where the transverse springback is measured. A bend of similar radius was formed in a V-die and the springback determined. In general, the springback in V-die forming was greater than in roll forming, in some cases by a factor of 2. The theoretical springback angle was determined for all steels using a simple and approximate analytical equation and compared to the experimental roll forming and bending results. While for the roll forming process good agreement was achieved the theoretical values significantly underestimated springback in the V-bending process.

Journal ArticleDOI
TL;DR: In this article, the powder phase of vaterite and dicalcium phosphate anhydrous (DCPA) was mixed with 0.8 mol/L of NaH2PO4, Na2HPO4, and Na3PO4 aqueous solution, respectively, with liquid to powder ratio (L/P ratio) of 0.45, 0.55, and 0.65.
Abstract: The aim of the present study is to fabricate bone cement that could transform to carbonate apatite (CO3Ap) completely at body temperature. The powder phase of vaterite and dicalcium phosphate anhydrous (DCPA) was mixed with 0.8 mol/L of NaH2PO4, Na2HPO4, and Na3PO4 aqueous solution, respectively, with liquid to powder ratio (L/P ratio) of 0.45, 0.55, and 0.65. The paste was packed into split stainless steel mold, covered with the glass slide and kept at 37°C and 100% relative humidity for up to 96 hours (h). XRD analysis revealed that the cement became pure CO3Ap within 24 h for Na3PO4, 72 h for Na2HPO4, and 96 h for NaH2PO4, respectively. FT-IR results showed that all of the obtained specimens could be assigned to B-type CO3Ap. CHN analysis showed the carbonate content of the specimen were 10.4 ± 0.3% for NaH2PO4, 11.3 ± 0.7% for Na2HPO4, and 11.8 ± 0.4% for Na3PO4, respectively. Diametral tensile strength of the set CO3Ap cement was 1.95 ± 0.42 MPa for NaH2PO4, 2.53 ± 0.53 MPa for Na2HPO4, and 3.45 ± 1.53 MPa for Na3PO4, respectively. The set CO3Ap cement had low crystallinity similar to bone apatite since it was synthesized at body temperature. We concluded, therefore, that CO3Ap cement prepared from the present method has higher possibility to be used as an ideal bone replacement.

Journal ArticleDOI
TL;DR: In this article, the conditions of the arc transition from one phase to another are formulated in terms of the above characteristics and increasing of gas ionization level, and the results of calculation and experimental data enable us to conclude that in short arc length, which is characterized by material transfer from the anode to the cathode, the erosion of contacts is considerably small than erosion of contact both for resistive and inductive circuits, while in gaseous arc phase (long arc length) with opposite material transfer the rate of erosion depends on the inductance.
Abstract: Investigation of transition phenomena accompanying the evolution of metallic phase of electric arc into gaseous phase is very important for the further progress in such fields as plasma technologies, electrical apparatus, plasmatrons and other technical applications. Some aspects of this transition are considered in presented paper on the base of mathematical model described dynamics of phenomena in the arc column, near-electrode zones, anode and cathode solids. Cathode and anode phenomena such as ion bombardment, thermionic emission, inverse electron flux, evaporation, radiation, heat conduction etc. are considered in dependence on time, current, opening velocity, parameters of the gas and contact materials. The conditions of the arc transition from one phase to another are formulated in terms of above characteristics and increasing of gas ionization level. Special experiments with two contacts materials, and have been carried to verify the mathematical model. The results of calculation and experimental data enables us to conclude that in metallic arc phase (short arc length), which is characterized by material transfer from the anode to the cathode, the erosion of contacts is considerably small than erosion of contacts both for resistive and inductive circuits, while in gaseous arc phase (long arc length) with opposite material transfer the rate of erosion depends on the inductance. If the inductance, then contacts have smaller erosion in comparison with contacts, however for inductive circuits situation is quite different, thus use of contacts in the case of long arcs burning in gaseous phase is more preferable. It was found also that the addition of niobium diselenide (1%) and tantalum (5%) into silver contact material which are sublimating into arc plasma enables to change ionization potential, that leads to decreasing of the arc temperature, arc duration and contact erosion.

Journal ArticleDOI
TL;DR: In this paper, a steel disc of hardness 40 HRC was put in contact with a steel pin of hardness 64 HRC with spherical end, and wear tests were conducted using a pin-on-disc tester.
Abstract: Wear tests were conducted using a pin-on-disc tester. In the experiment, a steel disc of hardness 40 HRC was put in contact with a steel pin of hardness 64 HRC with spherical end. Disc samples were prepared in order to obtain very similar values of the Sq parameter of one-process and two-process isotropic surfaces. Height of one–process disc surfaces, characterized by the Sq parameter was in the range 0.5 – 6 µm, but of two-process textures 1- 4.5 µm. Dry and lubricated tests, using different contact conditions were carried out. During testing, the friction force was monitored as a function of time. Wear of disc was measured after the test using white light interferometer. Tests under boundary lubrication condition were done using L-AN 46 oil.

Journal ArticleDOI
TL;DR: In this article, two forming limit curves (FLC) are numerically computed to characterize two moments: when damage becomes pronounced and when the final failure is triggered by the accumulation of damage.
Abstract: For modern high strength steels, instead of metal instability, ductile damage triggered by the formation of microvoids or microcracks resulting from the complex material microstructure, has become the key factor responsible for the final failure in the forming process of such steels. The target of this study is to describe the initiation and evolution of damage in a dual-phase (DP) steel (DP600). By applying a newly proposed approach that is able to indicate the onset of damage in an engineering sense and quantify the subsequent damage evolution, to predict the forming limits for DP600 are predicted by simulating Nakajima test. Accordingly, two forming limit curves (FLC) are numerically computed to characterize two moments: when damage becomes pronounced and when the final failure is triggered by the accumulation of damage. Comparing with the conventional experimentally calibrated FLC at necking, the limit at crack initiation predicted by modeling gives a lower but defect-free forming boundary. The forming limit at final fracture is well captured by allowing the subsequent damage evolution to a critical value.

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TL;DR: The concept of the distributed diagnostic system capable of monitoring the technical state of critical elements of large infrastructure objects like steel trusses, supermarket buildings, exposition halls, bridges etc. is discussed.
Abstract: The complexity and diversity of civil engineering structures impose requirements on the monitoring systems, which are difficult to be satisfied. In the paper the concept of the distributed diagnostic system capable of monitoring the technical state of critical elements of large infrastructure objects like steel trusses, supermarket buildings, exposition halls, bridges etc. is discussed. Adaptation of such systems is essential for online assessment of technical state of the infrastructure objects and could limit the possibility of catastrophic disasters with loss of people. As a source of information data from strain gauges, passive magnetic field sensors and acceleration sensors applied to the construction are considered. For the process of selection of sensors and diagnostic methods the mathematical model of the construction and the physical test stand were used.

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TL;DR: In this paper, the authors proposed to change the focus from the cement production optimization to optimization of concrete production industry, responsible for most of cement consumption, and discussed the limits of clinker substitution by mineral admixtures, comparing the expected cement demand increase versus the availability of these alternative materials, concluding that despite the importance of this strategy, it is actually not capable for mitigating cement CO2 emissions in a satisfactory way.
Abstract: Cement industry is under stress for mitigating CO2 emissions: it is responsible for around 5-7% of total global emissions due to the production that went over 2x109 tones in 2006. And this prospect will aggravate since it is expected, for 2050, an increase of 2.5 times, which will make cement industry guilty for more than 30% of CO2 emissions. Main actions for decreasing emissions are: energy efficiency in kilns, use of alternative fuels and clinker substitution. These, however, are not capable to decrease emissions in a satisfactory way. CO2 capture is expensive and could increase cement costs. The pressure, which is increasing all over the world, will certainly strike concrete producers. The optimization of cement use in concrete is an undeveloped strategy that can provide a huge contribution. For its development an international and cooperative effort is crucial. This paper proposes to change the focus from the cement production optimization to optimization of concrete production industry, responsible for most of cement consumption. It is discussed the limits of clinker substitution by mineral admixtures, comparing the expected cement demand increase versus the availability of these alternative materials, concluding that, despite the importance of this strategy, it is actually not capable for mitigating cement CO2 emissions in a satisfactory way. It is discussed and assessed technical possibilities and limits of optimization of cement content in concrete, based on literature data analysis using two new environmental indicators Binder Intensity and CO2 Intensity. There is a potential to reduce significantly the cement content on concrete, being possible to increase concrete production without increasing cement production and CO2 generation. This can impact significantly on concrete environmental load to global warming and also in its cost, making possible to increase popular habitations construction mainly in some developing countries which have a lack of different sort of infrastructure where concrete technology is still dominant.

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TL;DR: In this paper, the effects of rare earth elements (La and Y) on the densification behaviors, mechanical properties and high temperature oxidation resistance of PM Ti alloys are reviewed and compared.
Abstract: To lower the cost, Ti alloys fabricated by elemental powder metallurgy have been widely studied. High contents of oxygen and residual porosities are usually inevitable in as-sintered Ti alloys. Thus, rare earth elements are added to PM Ti alloys for scavenging of oxygen, increasing sintered density and strengthening the matrix. This paper reviews recent studies on the effects of rare earth elements (La and Y) on the densification behaviours, mechanical properties and high temperature oxidation resistance of PM Ti alloys. The improvement of room temperature ductility of PM Ti alloys through the addition of rare earth elements has been extensively confirmed. However, other benefits from rare earth additions depend largely on alloy compositions, processing parameters and environmental conditions.

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TL;DR: A case study on a recently built holiday house is presented illustrating the architectural, structural, environmental and technical performance of a Guadua building as mentioned in this paper, highlighting the need for similar assessments.
Abstract: Guadua Angustifolia Kunth (Guadua) is a tropical species of bamboo endemic to South and Central America and widely used as a mainstream material for construction in Colombia Its rapid rate of biomass production, renewability, high level of CO2 fixation and storage, wide diameter, long-length, and durability are distinctive and highly desirable features which can benefit the new built environment Research interest in Guadua construction increased significantly after many Guadua-constructed buildings withstood or suffered only minor damage during an earthquake which reached 62 on the Richter scale in 1999, resulting in the standardization of Guadua in the seismic-resistant Colombian code (NSR, 2010) However, Guadua buildings constructed in the Americas and other parts of the world, whilst considered to be sustainable, are not fully characterised in terms of the preparation, use and disposal of Guadua Furthermore, workability, building durability and the construction process have not been specifically documented and evaluated The structure, properties and availability of Guadua are described in this paper A case study on a recently built holiday house is presented illustrating the architectural, structural, environmental and technical performance of a Guadua building This paper presents the construction process, discusses difficulties encountered during the building life cycle and highlights the need for similar assessments It is concluded that with the aim of achieving a low carbon construction system using Guadua bamboo, challenges regarding manufacture, bio-deterioration, integration with conventional systems, and environmental impacts must be addressed