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Metals, Volume 5, Issue 2 (June 2015), Pages 484-1126

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Open AccessArticle Study on Dual Modification of Al-17%Si Alloys by Structural Heredity
Metals 2015, 5(2), 1112-1126; https://doi.org/10.3390/met5021112
Received: 30 April 2015 / Revised: 10 June 2015 / Accepted: 13 June 2015 / Published: 22 June 2015
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Abstract
In this study, Al-17%Si alloys were dual modified by fine-grained structural materials (FSM) according to structural heredity. Microstructure and thermal analyses were undertaken to study the modification effect of the FSM master alloy on primary and eutectic Si. Primary Si is refined to
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In this study, Al-17%Si alloys were dual modified by fine-grained structural materials (FSM) according to structural heredity. Microstructure and thermal analyses were undertaken to study the modification effect of the FSM master alloy on primary and eutectic Si. Primary Si is refined to a smaller size and eutectic Si is modified from needle-like to fibrous shape after FSM master alloy addition. The optimal content of FSM master alloy is 20% and the holding time is 15min. Finer FSM master alloy leads to finer Al-17%Si alloy microstructure and more area percentage of α-Al. DSC analyses results show that FSM master alloy can raise the precipitation temperatures of primary and eutectic Si, meanwhile it can reduce the latent heat of Si solidification process. Full article
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Open AccessReview Mechanical Relaxation of Metallic Glasses: An Overview of Experimental Data and Theoretical Models
Metals 2015, 5(2), 1073-1111; https://doi.org/10.3390/met5021073
Received: 20 May 2015 / Revised: 11 June 2015 / Accepted: 12 June 2015 / Published: 19 June 2015
Cited by 19 | PDF Full-text (1945 KB) | HTML Full-text | XML Full-text
Abstract
Relaxation phenomena in glasses are a subject of utmost interest, as they are deeply connected with their structure and dynamics. From a theoretical point of view, mechanical relaxation allows one to get insight into the different atomic-scale processes taking place in the glassy
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Relaxation phenomena in glasses are a subject of utmost interest, as they are deeply connected with their structure and dynamics. From a theoretical point of view, mechanical relaxation allows one to get insight into the different atomic-scale processes taking place in the glassy state. Focusing on their possible applications, relaxation behavior influences the mechanical properties of metallic glasses. This paper reviews the present knowledge on mechanical relaxation of metallic glasses. The features of primary and secondary relaxations are reviewed. Experimental data in the time and frequency domain is presented, as well as the different models used to describe the measured relaxation spectra. Extended attention is paid to dynamic mechanical analysis, as it is the most important technique allowing one to access the mechanical relaxation behavior. Finally, the relevance of the relaxation behavior in the mechanical properties of metallic glasses is discussed. Full article
(This article belongs to the Special Issue Metallic Glasses) Printed Edition available
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Open AccessArticle Synergic Role of Self-Interstitials and Vacancies in Indium Melting
Metals 2015, 5(2), 1061-1072; https://doi.org/10.3390/met5021061
Received: 21 April 2015 / Accepted: 11 June 2015 / Published: 16 June 2015
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Abstract
Precursor effects of indium melting have been investigated by means of Mechanical Spectroscopy (MS) and High Temperature X-ray Diffraction (HT-XRD). MS tests evidenced a sharp drop of dynamic modulus in the temperature range between 418 K and 429 K (melting point). At 429
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Precursor effects of indium melting have been investigated by means of Mechanical Spectroscopy (MS) and High Temperature X-ray Diffraction (HT-XRD). MS tests evidenced a sharp drop of dynamic modulus in the temperature range between 418 K and 429 K (melting point). At 429 K, HT-XRD showed partial grain re-orientation, peak profile broadening, in particular in the lower part, and peak shift towards lower angles. Experimental results are consistent with density increase of self-interstitials and vacancies in the crystal lattice before melting. Self-interstitials and vacancies play a synergic role in the solid–liquid (S-L) transformation. The increase of self-interstitials over a temperature range of about 10 K before melting has the effect of weakening interatomic bonds (modulus drop) that favors the successive vacancy formation. Finally, the huge increase of vacancy concentration above 428 K leads to the collapse of crystal lattice (melting). Full article
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Open AccessArticle Submicron Particles during Macro- and Micro-Weldings Procedures in Industrial Indoor Environments and Health Implications for Welding Operators
Metals 2015, 5(2), 1045-1060; https://doi.org/10.3390/met5021045
Received: 29 April 2015 / Revised: 26 May 2015 / Accepted: 3 June 2015 / Published: 9 June 2015
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Abstract
One of the emerging risks in the engineering and electronic industries is the exposure of workers to ultrafine particles during (micro-)welding operations, i.e., processes used for joining two metal parts heated locally, which constitute the base metal, with or without addition of
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One of the emerging risks in the engineering and electronic industries is the exposure of workers to ultrafine particles during (micro-)welding operations, i.e., processes used for joining two metal parts heated locally, which constitute the base metal, with or without addition of another metal which is the filler metal, melted between the edges to be joined. The process is accompanied by formation of metallic fumes arising from the molten metal as well as by the emission of metal fumes of variable composition depending on the alloys welded and fused. The aim of this paper is to investigate the number, concentration and size distribution of submicron particles produced by (micro-)welding processes. Particle number size distribution is continuously measured during (micro-)welding operations by means of two instruments, i.e., Fast Mobility Particle Sizer and Nanoparticle Surface Area Monitor. The temporal variation of the particle number size distribution across the peaks evidences the strong and fast-evolving contribution of nucleation mode particles: peak values are maintained for less than 10 s. The implication of such contribution on human health is linked to the high deposition efficiency of submicronic particles in the alveolar interstitial region of the human respiratory system, where gas exchange occurs. Full article
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Open AccessArticle On the Stability of the Melt Jet Stream during Casting of Metallic Glass Wires
Metals 2015, 5(2), 1029-1044; https://doi.org/10.3390/met5021029
Received: 19 May 2015 / Revised: 31 May 2015 / Accepted: 2 June 2015 / Published: 8 June 2015
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Abstract
The factors that affect the stability of the melt stream during the casting of wire directly from the melt have been investigated. It is shown that the criticality of process parameters centres mostly on the forces imposed on the melt stream at confluence
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The factors that affect the stability of the melt stream during the casting of wire directly from the melt have been investigated. It is shown that the criticality of process parameters centres mostly on the forces imposed on the melt stream at confluence with the cooling water. The analysis of these forces indicated that the shear component of the disturbance is dependent on the ratio of the velocity of the melt stream (vm) to that of the cooling water (vw) in accord with results obtained from previous experiments. The role of oxide-forming elements in widening the process parameters range is attributed to the increased stability of the melt stream due to the additional shear force resistance offered by the solid oxide layer. The roles of Cr and Si oxides in stabilising the melt stream are confirmed by X-ray photoelectron spectroscopy (XPS) of wire indicating the presence of these oxides on fresh as-cast wires. Melt superheat and nozzle clearance distance are not strictly stream stability factors, but rather their role in glass formation prescribes optimal limits for fully amorphous wire. Full article
(This article belongs to the Special Issue Metallic Glasses) Printed Edition available
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Open AccessArticle Structure and Mössbauer Analysis of Melt-Spun Fe-Pd Ribbons Containing Ni and Co
Metals 2015, 5(2), 1020-1028; https://doi.org/10.3390/met5021020
Received: 15 April 2015 / Accepted: 25 May 2015 / Published: 5 June 2015
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Abstract
Fe68.45Pd28.21Co1.66Ni1.66 alloy in ribbon geometry was produced by melt spinning. The microstructure of the samples was examined using scanning electron microscopy. The structural identification of the as-spun ribbon sample and the annealed ones was performed by
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Fe68.45Pd28.21Co1.66Ni1.66 alloy in ribbon geometry was produced by melt spinning. The microstructure of the samples was examined using scanning electron microscopy. The structural identification of the as-spun ribbon sample and the annealed ones was performed by means of X-ray diffraction. All the Bragg peaks were indexed based on an fcc type structure of (γ-Fe, Pd) phase with a lattice parameter a = 3.742 (3) Å. This result was proved by Mössbauer technique. The annealed ribbon at 600 °C shows an L10 ordered fct structure. An endothermic reaction at T = 358 °C followed by an exothermic one at 390 °C were observed on heating. These reactions were attributed to the Curie temperature of nickel and to the annihilation of an excess of quenched-in vacancies, respectively. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2014)
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Open AccessArticle On Thermal Expansion and Density of CGI and SGI Cast Irons
Metals 2015, 5(2), 1000-1019; https://doi.org/10.3390/met5021000
Received: 30 April 2015 / Revised: 18 May 2015 / Accepted: 26 May 2015 / Published: 4 June 2015
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Abstract
The thermal expansion and density of Compacted Graphite Iron (CGI) and Spheroidal Graphite Iron (SGI) were measured in the temperature range of 25–500 °C using push-rod type dilatometer. The coefficient of the thermal expansion (CTE) of cast iron can be expressed by the
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The thermal expansion and density of Compacted Graphite Iron (CGI) and Spheroidal Graphite Iron (SGI) were measured in the temperature range of 25–500 °C using push-rod type dilatometer. The coefficient of the thermal expansion (CTE) of cast iron can be expressed by the following equation: CTE = 1.38 × 10−5 + 5.38 × 10−8 N − 5.85 × 10−7 G + 1.85 × 10−8 T − 2.41 × 10−6 RP/F − 1.28 × 10−8 NG − 2.97 × 10−7 GRP/F + 4.65 × 10−9 TRP/F + 1.08 × 10−7 G2 − 4.80 × 10−11 T2 (N: Nodularity, G: Area fraction of graphite (%), T: Temperature (°C), RP/F: Pearlite/Ferrite ratio in the matrix). Full article
(This article belongs to the Special Issue Casting Alloy Design and Modification)
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Open AccessArticle Hot Ductility Behavior of a Peritectic Steel during Continuous Casting
Metals 2015, 5(2), 986-999; https://doi.org/10.3390/met5020986
Received: 15 May 2015 / Revised: 25 May 2015 / Accepted: 27 May 2015 / Published: 3 June 2015
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Abstract
Hot ductility properties of a peritectic steel for welded gas cylinders during continuous casting were studied by performing hot tensile tests at certain temperatures ranging from 1200 to 700 °C for some cooling rates by using Gleeble-3500 thermo-mechanical test and simulation machine in
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Hot ductility properties of a peritectic steel for welded gas cylinders during continuous casting were studied by performing hot tensile tests at certain temperatures ranging from 1200 to 700 °C for some cooling rates by using Gleeble-3500 thermo-mechanical test and simulation machine in this study. The effects of cooling rate and strain rate on hot ductility were investigated and continuous casting process map (time-temperature-ductility) were plotted for this material. Reduction of area (RA) decreases and cracking susceptibility increases during cooling from solidification between certain temperatures depending on the cooling rate. Although the temperatures which fracture behavior change upon cooling during continuous casting may vary for different materials, it was found that the type of fracture was ductile at 1100 and 1050 °C; semi-ductile at 1000 °C, and brittle at 800 °C for the steel P245NB. There is a ductility trough between 1000 and 725 °C. The ductility trough gets slightly narrower as the cooling rate decreases. Full article
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Open AccessCommunication Mechanical Behavior of Ultrafine Gradient Grain Structures Produced via Ambient and Cryogenic Surface Mechanical Attrition Treatment in Iron
Metals 2015, 5(2), 976-985; https://doi.org/10.3390/met5020976
Received: 31 March 2015 / Revised: 19 May 2015 / Accepted: 21 May 2015 / Published: 3 June 2015
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Abstract
Ambient and cryogenic surface mechanical attrition treatments (SMAT) are applied to bcc iron plate. Both processes result in significant surface grain refinement down to the ultrafine-grained regime; the cryogenic treatment results in a 45% greater grain size reduction. However, the refined region is
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Ambient and cryogenic surface mechanical attrition treatments (SMAT) are applied to bcc iron plate. Both processes result in significant surface grain refinement down to the ultrafine-grained regime; the cryogenic treatment results in a 45% greater grain size reduction. However, the refined region is shallower in the cryogenic SMAT process. The tensile ductility of the grain size gradient remains low (<10%), in line with the expected behavior of the refined surface grains. Good tensile ductility in a grain size gradient requires the continuation of the gradient into an undeformed region. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
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Open AccessReview Nanotoxicology of Metal Oxide Nanoparticles
Metals 2015, 5(2), 934-975; https://doi.org/10.3390/met5020934
Received: 8 April 2015 / Revised: 18 May 2015 / Accepted: 26 May 2015 / Published: 3 June 2015
Cited by 28 | PDF Full-text (1465 KB) | HTML Full-text | XML Full-text
Abstract
This review discusses recent advances in the synthesis, characterization and toxicity of metal oxide nanoparticles obtained mainly through biogenic (green) processes. The in vitro and in vivo toxicities of these oxides are discussed including a consideration of the factors important for safe use
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This review discusses recent advances in the synthesis, characterization and toxicity of metal oxide nanoparticles obtained mainly through biogenic (green) processes. The in vitro and in vivo toxicities of these oxides are discussed including a consideration of the factors important for safe use of these nanomaterials. The toxicities of different metal oxide nanoparticles are compared. The importance of biogenic synthesized metal oxide nanoparticles has been increasing in recent years; however, more studies aimed at better characterizing the potent toxicity of these nanoparticles are still necessary for nanosafely considerations and environmental perspectives. In this context, this review aims to inspire new research in the design of green approaches to obtain metal oxide nanoparticles for biomedical and technological applications and to highlight the critical need to fully investigate the nanotoxicity of these particles. Full article
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Open AccessArticle Mechanical and Structural Investigation of Porous Bulk Metallic Glasses
Metals 2015, 5(2), 920-933; https://doi.org/10.3390/met5020920
Received: 28 April 2015 / Revised: 20 May 2015 / Accepted: 25 May 2015 / Published: 2 June 2015
Cited by 8 | PDF Full-text (2959 KB) | HTML Full-text | XML Full-text
Abstract
The intrinsic properties of advanced alloy systems can be altered by changing their microstructural features. Here, we present a highly efficient method to produce and characterize structures with systematically-designed pores embedded inside. The fabrication stage involves a combination of photolithography and deep reactive
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The intrinsic properties of advanced alloy systems can be altered by changing their microstructural features. Here, we present a highly efficient method to produce and characterize structures with systematically-designed pores embedded inside. The fabrication stage involves a combination of photolithography and deep reactive ion etching of a Si template replicated using the concept of thermoplastic forming. Pt- and Zr-based bulk metallic glasses (BMGs) were evaluated through uniaxial tensile test, followed by scanning electron microscope (SEM) fractographic and shear band analysis. Compositional investigation of the fracture surface performed via energy dispersive X-ray spectroscopy (EDX), as well as Auger spectroscopy (AES) shows a moderate amount of interdiffusion (5 at.% maximum) of the constituent elements between the deformed and undeformed regions. Furthermore, length-scale effects on the mechanical behavior of porous BMGs were explored through molecular dynamics (MD) simulations, where shear band formation is observed for a material width of 18 nm. Full article
(This article belongs to the Special Issue Metallic Glasses) Printed Edition available
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Open AccessArticle Epitaxial Growth of Hard Ferrimagnetic Mn3Ge Film on Rhodium Buffer Layer
Metals 2015, 5(2), 910-919; https://doi.org/10.3390/met5020910
Received: 23 April 2015 / Revised: 15 May 2015 / Accepted: 21 May 2015 / Published: 2 June 2015
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Abstract
Mn\(_3\)Ge has a tetragonal Heusler-like D0\(_{22}\) crystal structure, exhibiting a large uniaxial magnetic anisotropy and small saturation magnetization due to its ferrimagnetic spin structure; thus, it is a hard ferrimagnet. In this report, epitaxial growth of a Mn\(_3\)Ge film on a Rh buffer
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Mn\(_3\)Ge has a tetragonal Heusler-like D0\(_{22}\) crystal structure, exhibiting a large uniaxial magnetic anisotropy and small saturation magnetization due to its ferrimagnetic spin structure; thus, it is a hard ferrimagnet. In this report, epitaxial growth of a Mn\(_3\)Ge film on a Rh buffer layer was investigated for comparison with that of a film on a Cr buffer layer in terms of the lattice mismatch between Mn\(_3\)Ge and the buffer layer. The film grown on Rh had much better crystalline quality than that grown on Cr, which can be attributed to the small lattice mismatch. Epitaxial films of Mn\(_3\)Ge on Rh show somewhat small coercivity (\(H_{\rm c}\) = 12.6 kOe) and a large perpendicular magnetic anisotropy (\(K_{\rm u}\) = 11.6 Merg/cm\(^3\)), comparable to that of the film grown on Cr. Full article
(This article belongs to the Special Issue Manganese-based Permanent Magnets)
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Open AccessArticle Fatigue Behavior of Ultrafine-Grained Medium Carbon Steel with Different Carbide Morphologies Processed by High Pressure Torsion
Metals 2015, 5(2), 891-909; https://doi.org/10.3390/met5020891
Received: 21 March 2015 / Revised: 21 May 2015 / Accepted: 25 May 2015 / Published: 29 May 2015
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Abstract
The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect
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The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect of different carbide morphologies in the initial microstructure on the fatigue behavior after high pressure torsion (HPT) treatment of SAE 1045 steels. The two initial carbide morphologies are spheroidized as well as tempered states. The HPT processing increased the hardness of the spheroidized and tempered states from 169 HV and 388 HV to a maximum of 511 HV and 758 HV, respectively. The endurance limit increased linearly with hardness up to about 500 HV independent of the carbide morphology. The fracture surfaces revealed mostly flat fatigue fracture surfaces with crack initiation at the surface or, more often, at non-metallic inclusions. Morphology and crack initiation mechanisms were changed by the severe plastic deformation. The residual fracture surface of specimens with spheroidal initial microstructures showed well-defined dimple structures also after HPT at high fatigue limits and high hardness values. In contrast, the specimens with a tempered initial microstructure showed rather brittle and rough residual fracture surfaces after HPT. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
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Open AccessArticle Twinning-Detwinning Behavior during Cyclic Deformation of Magnesium Alloy
Metals 2015, 5(2), 881-890; https://doi.org/10.3390/met5020881
Received: 20 April 2015 / Revised: 12 May 2015 / Accepted: 18 May 2015 / Published: 26 May 2015
Cited by 7 | PDF Full-text (1101 KB) | HTML Full-text | XML Full-text
Abstract
In situ neutron diffraction has been used to examine the deformation mechanisms of a precipitation-hardened and extruded Mg-8.5wt.%Al alloy subjected to (i) compression followed by reverse tension (texture T1) and (ii) tension followed by reverse compression (texture T2). Two starting textures are used:
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In situ neutron diffraction has been used to examine the deformation mechanisms of a precipitation-hardened and extruded Mg-8.5wt.%Al alloy subjected to (i) compression followed by reverse tension (texture T1) and (ii) tension followed by reverse compression (texture T2). Two starting textures are used: (1) as-extruded texture, T1, in which the basal pole of most grains is normal to the extrusion axis and a small portion of grains are oriented with the basal pole parallel to the extrusion axis; (2) a reoriented texture, T2, in which the basal pole of most grains is parallel to the extrusion axis. For texture T1, the onset of extension twinning corresponds well with the macroscopic elastic-plastic transition during the initial compression stage. The non-linear macroscopic stress/strain behavior during unloading after compression is more significant than during unloading after tension. For texture T2, little detwinning occurs after the initial tension stage, but almost all of the twinned volumes are detwinned during loading in reverse compression. Full article
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Open AccessArticle Analysis of Magneto-Piezoelastic Anisotropic Materials
Metals 2015, 5(2), 863-880; https://doi.org/10.3390/met5020863
Received: 15 December 2014 / Accepted: 14 May 2015 / Published: 26 May 2015
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Abstract
The paper is concerned with the analysis of magneto-piezoelastic anistropic materials. Analytical modeling of magneto-piezoelastic materials is essential for the design and applications in the smart composite structures incorporating them as actuating and sensing constituents. It is shown that Green’s function method is
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The paper is concerned with the analysis of magneto-piezoelastic anistropic materials. Analytical modeling of magneto-piezoelastic materials is essential for the design and applications in the smart composite structures incorporating them as actuating and sensing constituents. It is shown that Green’s function method is applicable to time harmonic magneto-elastic-piezoelectricity problems using the boundary integral technique, and the exact analytical solutions are obtained. As an application, a two-dimensional static plane-strain problem is considered to investigate the effect of magnetic field on piezoelectric materials. The closed-form analytical solutions are obtained for a number of boundary conditions for all components of the magneto-piezoelectric field. As a special case, numerical results are presented for two-dimensional static magneto-electroelastic field of a piezoelectric solid subjected to a concentrated line load and an electric charge. The numerical solutions are obtained for three different piezoelectric materials and they demonstrate a substantial dependence of the stress and electric field distribution on the constitutive properties and magnetic flux. Full article
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