Showing papers in "Journal of the mechanical behavior of materials in 2017"

A review on mechanical and water absorption properties of polyvinyl alcohol based composites/films

Abstract: Abstract Polyvinyl alcohol (PVA) is a nontoxic and thermoplastic polymer which is completely biodegradable. PVA shows excellent mechanical and thermal properties due to better interfacial adhesion with reinforcing material such as fibers, particles or flakes because of which it can be used for fabrication of composite. PVA based fiber or particle reinforcing composites have gained interest in many applications in different fields. This paper reviews the mechanical and water absorption properties studied by different researcher and some of them were discussed here. The article also focused on the effect on the mechanical properties on PVA based composites with particle or fiber used as reinforcing material at nano/micro level and different polymers used to prepare PVA blend films. The major disadvantage of PVA based composites/films is higher water uptake or solubility in water. To over this negative aspect, many researchers studied crosslinking of PVA based composites/films, which are also discussed in the article. This review concludes that PVA has the potential for use in the synthesis of composites/films with their abundant applications.

Temperature-dependent vibration analysis of a FG viscoelastic cylindrical microshell under various thermal distribution via modified length scale parameter: a numerical solution

Abstract: Abstract In this article, the vibrational analysis of temperature-dependent cylindrical functionally graded (FG) microshells surrounded by viscoelastic a foundation is investigated by means of the modified couple stress theory (MCST). MCST is applied to this model to be productive in design and analysis of micro actuators and micro sensors. The modeled cylindrical FG microshell, its equations of motion and boundary conditions are derived by Hamilton’s principle and the first-order shear deformation theory (FSDT). For the first time, in the present study, functionally graded length scale parameter which changes along the thickness has been considered in the temperature-dependent cylindrical FG microshell. The accuracy of the present model is verified with previous studies and also with those obtained by analytical Navier method. The novelty of the current study is consideration of viscoelastic foundation, various thermal loadings and size effect as well as satisfying various boundary conditions implemented on the temperature-dependent cylindrical FG microshell using MCST. Generalized differential quadrature method (GDQM) is applied to discretize the equations of motion. Then, some factors are investigated such as the influence of length to radius ratio, damping, Winkler and Pasternak foundations, different temperature changes, circumferential wave numbers, and boundary conditions on natural frequency of the cylindrical FG microshell. The results have many applications such as modeling of microrobots and biomedical microsystems.

Diffraction, microstructure and thermal stability analysis in a double phase nanocrystalline Al20Mg20Ni20Cr20Ti20 high entropy alloy

Abstract: Abstract An effort has been made to develop a new composition of AlMgNiCrTi high entropy alloy (HEA) with a distinct properties includes squat density, intense strength and hardness, superior corrosion resistance, better oxidation resistance, high temperature resistance, fatigue load and crack resistance to congregate the necessity of aircraft applications. The equivalent atomic percentage for the above defined composition is established using analytical correlation for molar and atom renovation by trial and error method. The alloy is synthesized by powder metallurgy technique through mechanical alloying. Succeeding to mechanical alloying it is elucidated that the metal powder is primarily composed of single BCC solid solution with crystallite magnitude <10 nm. It is also observed that the alloy is thermally stable at prominent temperature about 800°C as it is retained its nanostructure which was revealed using differential scanning caloriemetry (DSC). This alloy powder was consolidated and sintered using spark plasma sintering at 800°C with 50 Mpa pressure to a density of 98.83%. Subsequent to sintering, Titanium carbide FCC phase evolved along with the BCC phase. The alloying behavior and phase transformation were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM). The homogeneity of the composition is confirmed by energy dispersive spectroscopy (EDS). The hardness of the alloy is found to be 710±20 HV. The evolutions of the phases and hardness imply that this alloy is apposite for both high strength and high temperature applications.

Fractional vector calculus and fluid mechanics

Abstract: Abstract Basic fluid mechanics equations are studied and revised under the prism of fractional continuum mechanics (FCM), a very promising research field that satisfies both experimental and theoretical demands. The geometry of the fractional differential has been clarified corrected and the geometry of the fractional tangent spaces of a manifold has been studied in Lazopoulos and Lazopoulos (Lazopoulos KA, Lazopoulos AK. Progr. Fract. Differ. Appl. 2016, 2, 85–104), providing the bases of the missing fractional differential geometry. Therefore, a lot can be contributed to fractional hydrodynamics: the basic fractional fluid equations (Navier Stokes, Euler and Bernoulli) are derived and fractional Darcy’s flow in porous media is studied.

Review on effect of chemical, thermal, additive treatment on mechanical properties of basalt fiber and their composites

Abstract: Abstract Basalt fiber is emerging out the new reinforcing material for composites. To overcome some of the disadvantages of fibers such as poor bonding to polymers, low thermal stability and high moisture absorption fiber characteristics are modified with chemical, thermal and additive treatments. Chemical treatment corrosive resistance to alkali and acid were investigated which were used to clean and modify the surface of fiber for higher bonding with resins. To improve the thermal stability and reduce moisture uptake thermal treatment such as plasma and non thermal plasma were used which increased the surface roughness and change the chemical composition of surface of basalt fiber. Additive treatment is used to improve the mechanical properties of fibers, in basalt fiber additive treatment was done with SiO2 additive because of its chemical composition which contains major content of SiO2. In present investigation review on the effect of different treatment such as chemical, thermal and additive were studied. Effect of these treatment on chemical composition of the surface of basalt fiber and corrosion to acidic and alkali solution were studied with their effect on mechanical properties of basalt fiber and their composite.

Modeling of inter- and transgranular stress corrosion crack propagation in polycrystalline material by using phase field method

Abstract: A coupled multiphysics phase field framework is proposed to model anodic dissolution induced by stress corrosion fracture growth at microstructual level. The effects of electrochemical-mechanical processes (including crystal anisotropy) are all taken into account. This new model is based upon: (i) an anisotropic phase transformation model based on a variational formulation to describe material dissolution along preferential directions; (ii) an efficient description of grain boundaries as a smeared cohesive zone; (iii) an explicit approximation to model the different electrochemical behaviors between grain boundary and grain interior. Both intergranular and transgranular stress corrosion cracking is simulated in an efficient manner. The abilities of the proposed model are illustrated through several numerical examples involving a full prediction of complex crack network growth induced by stress corrosion cracking within 2D polycrystaline models.

Multi-objective optimization of a functionally graded sandwich panel under mechanical loading in the presence of stress constraint

Abstract: Abstract A method was presented for multi-objective optimization of material distribution of simply supported functionally graded (FG) sandwich panel, and sensitivity analyses of optimal designs were also conducted based on design variables and objective functions. The material composition was assumed to vary only in the thickness direction. Piecewise cubic interpolation of volume fractions was used to calculate volume fractions of constituent material phases at a point; these fractions were defined at a limited number of evenly spaced control points. The effective material properties of the panel were obtained by applying the linear rule of mixtures. The behavior of FG sandwich panel was predicted by Reddy’s assumptions of third-order shear deformation theory. Exact solutions for deflections and stresses of simply supported sandwich panel were presented using the Navier-type solution technique. The volume fractions at control points, material, and thickness of the faces which were selected as decision variables were optimized by a multi-objective evolutionary algorithm known as the fast and elitist multi-objective genetic algorithm (NSGA-II). The mass and deflection of the model were considered the objective functions to be minimized with stress constraints. This model was optimized to verify the capability and efficiency of the proposed model under mechanical loading. The framework proposed for designing FG sandwich panel under pure mechanical conditions was furnished by the results.

Interfacial characteristics of hybrid nanocomposite under thermomechanical loading

Abstract: Abstract In this work, an improved shear lag model was developed to investigate the interfacial characteristics of three-phase hybrid nanocomposite which is reinforced with microscale fibers augmented with carbon nanotubes on their circumferential surfaces. The shear lag model accounts for (i) radial and axial deformations of different transversely isotropic constituents, (ii) thermomechanical loads on the representative volume element (RVE), and (iii) staggering effect of adjacent RVEs. The results from the current newly developed shear lag model are validated with the finite element simulations and found to be in good agreement. This study reveals that the reduction in the maximum value of the axial stress in the fiber and the interfacial shear stress along its length become more pronounced in the presence of applied thermomechanical loads on the staggered RVEs. The existence of shear tractions along the RVE length plays a significant role in the interfacial characteristics and cannot be ignored.

Complexity theory, time series analysis and Tsallis q-entropy principle part one: theoretical aspects

Abstract: Abstract In this study, we present the highlights of complexity theory (Part I) and significant experimental verifications (Part II) and we try to give a synoptic description of complexity theory both at the microscopic and at the macroscopic level of the physical reality. Also, we propose that the self-organization observed macroscopically is a phenomenon that reveals the strong unifying character of the complex dynamics which includes thermodynamical and dynamical characteristics in all levels of the physical reality. From this point of view, macroscopical deterministic and stochastic processes are closely related to the microscopical chaos and self-organization. The scientific work of scientists such as Wilson, Nicolis, Prigogine, Hooft, Nottale, El Naschie, Castro, Tsallis, Chang and others is used for the development of a unified physical comprehension of complex dynamics from the microscopic to the macroscopic level. Finally, we provide a comprehensive description of the novel concepts included in the complexity theory from microscopic to macroscopic level. Some of the modern concepts that can be used for a unified description of complex systems and for the understanding of modern complexity theory, as it is manifested at the macroscopic and the microscopic level, are the fractal geometry and fractal space-time, scale invariance and scale relativity, phase transition and self-organization, path integral amplitudes, renormalization group theory, stochastic and chaotic quantization and E-infinite theory, etc.

Optimizing the laser parameters to attain maximum hardness in nickel based hardfacing surfaces

Abstract: Abstract In this investigation, an attempt has been made to optimize the laser hardfacing (LH) parameters such as power, powder feed rate (PFR), travel speed and defocusing distance to maximize hardness of Ni-based hardfacing surfaces. Statistical tools such as the design of experiments (DoE), analysis of variance (ANOVA) are used to develop the empirical relationship to predict the hardness of the deposits at the 95% confidence level. Response graphs and contour plots are constructed using response surface methodology (RSM) concept. From this investigation, it is found that the maximum hardness of 820.48 HV could be achieved for the deposit made using a power of 1314 W, PFR of 9 g/min, a travel speed of 366 mm/min, and a defocusing distance of 32 mm.

FSW between Al alloy and Mg Alloy: the comparative study

Abstract: Abstract It is difficult to fusion weld Al alloy to Mg alloy, so by experimental optimization procedure (EOP) optimum parameters for FSW between Al alloy and Mg alloy were determined and experiment conducted using these parameters resulted in not only sound weld but also highest strength weld for 5 mm thickness of the alloys plates. One can arrive to optimum parameters by following the EOP in case of similar and dissimilar materials FSW, such as Al alloy and Mg alloy FSW. It has observed that tensile sample having least thickness intermetallics (IMs) layer has highest strength compared to sample with larger thickness of intermetallics layer and also it has observed that weld of lesser thickness plates have strength higher than welds of larger thickness plates. It has observed that, Vickers hardness in WN i.e. on the region containing layers of IMs is considerably higher, which leads to emerge of new type of laminated composite materials. It has observed that, it is the least thickness IMs layers in the weld are responsible for higher strength of weld not the ductility of the IMs formed owing to the insertion of intermediate material in the weld. It has found that coefficient of friction is =0.25, in case of bead on plate welding of Mg alloy.

Experimental study of wood shaving addition in mortar and statistical modeling on selected effects

Abstract: Abstract In the frame of an extended research program dealing with wood shavings utilization in mortar, a set of procedures were developed for verifying effects of wood shavings addition to specific mortar properties. Mixes containing wood shavings replacing fine aggregates by 0, 30, 50 and 70% of their volume were made. Workability, fresh mortar unit weight, ultrasonic pulse velocity (UPV) and flexural and compressive strength were determined, based on measurements, at various curing ages. Measurement results and analysis suggest that compressive strength reduction caused by wood shavings addition could be predicted. The outcome was standardized in the form of a multifactorial sigmoidal model. It was also made evident that the mix proportion of cement increases when wood shavings are used as a by volume replacement of conventional fine aggregates, due to the low value of specific gravity of wood compared to conventional aggregates. Another procedure is suggested based on mass and volume measurements aiming at the verification of the mix proportions in the final mortar mixture.

Propagation of Rayleigh waves in an incompressible rotating orthotropic elastic solid half-space with impedance boundary conditions

Abstract: Abstract In this paper, the governing equations of an incompressible rotating orthotropic elastic medium are formulated and are solved to obtain Rayleigh surface wave solutions in a particular half-space. The surface of half-space is subjected to impedance boundary conditions, in which normal and tangential stresses are proportional to frequency times normal and tangential displacement components, respectively. A secular equation for Rayleigh surface wave is obtained. With the help of MATLAB, the secular equation is solved numerically to obtain non-dimensional wave speed. The dependence of non-dimensional wave speed on non-dimensional material constant, rotation parameter and impedance parameters is shown graphically.

A semianalytical approach for determining the nonclassical mechanical properties of materials

Abstract: In this article, a semianalytical approach for demonstrating elastic waves propagation in nanostructures has been presented based on the modified couple-stress theory including acceleration gradients. Using the experimental results and atomic simulations, the static and dynamic length scales were calculated for several materials, zinc oxide (ZnO), silicon (Si), silicon carbide (SiC), indium antimonide (InSb), and diamond. To evaluate the predicted static and dynamic length scales as well as the presented model, the natural frequencies of a beam in addition to the phase velocity and group velocity of Si were studied and compared with the available static length scales, estimated using strain-gradient theory without considering acceleration gradients. These three criteria, natural frequency, phase velocity, and group velocity, show that the presented model is dynamically stable even for larger wavevector values. Furthermore, it is explained why the previous works, which all are based on the strain-gradient theory without acceleration gradients, predicted very small values for the static length scale in the longitudinal direction rather than the static length scale in the transverse directions.

Evaluating stress corrosion cracking behaviour of high strength AA7075-T651 aluminium alloy

Abstract: Abstract The objective of the present study is to determine the threshold stress level of stress corrosion cracking (SCC) in AA7075-T651 aluminium alloy by suitable experimentation. The test was carried out using a circumferential notch specimen in a horizontal-type constant load SCC setup in a 3.5 wt.% NaCl solution. The time to failure by SCC was determined at various loading conditions. The threshold stress of AA7075-T651 alloy was found to be 242 MPa in a 3.5 wt.% NaCl solution. The various regions of the fractured surface specimen such as machined notch, SCC region and final overload fracture area were examined using scanning electron microscopy (SEM) in order to identify the SCC mechanism.

"Pop-in" and "pop-out" effect in monocrystalline silicon. A statistical investigation

Abstract: Abstract Pop-in and pop-out effects in silicon (Si) have long been known. They were evidenced in the indentation loading-unloading curves as a sudden displacement discontinuity. They consist in a sudden contraction (pop-in) or a sudden expansion (pop-out) of the material underneath the indenter in a short period of time and are attributed to Si phase transformations that take place during the nanoindentation procedure. In this paper, first we provide a statistic analysis of such pop-in/pop-out events depending on the maximum indentation load and second we examine the dependence of their appearance on the indentation loading-unloading rate.

Strain field determination in III–V heteroepitaxy coupling finite elements with experimental and theoretical techniques at the nanoscale

Abstract: Abstract We are briefly reviewing the current status of elastic strain field determination in III–V heteroepitaxial nanostructures, linking finite elements (FE) calculations with quantitative nanoscale imaging and atomistic calculation techniques. III–V semiconductor nanostructure systems of various dimensions are evaluated in terms of their importance in photonic and microelectronic devices. As elastic strain distribution inside nano-heterostructures has a significant impact on the alloy composition, and thus their electronic properties, it is important to accurately map its components both at the interface plane and along the growth direction. Therefore, we focus on the determination of the stress-strain fields in III–V heteroepitaxial nanostructures by experimental and theoretical methods with emphasis on the numerical FE method by means of anisotropic continuum elasticity (CE) approximation. Subsequently, we present our contribution to the field by coupling FE simulations on InAs quantum dots (QDs) grown on (211)B GaAs substrate, either uncapped or buried, and GaAs/AlGaAs core-shell nanowires (NWs) grown on (111) Si, with quantitative high-resolution transmission electron microscopy (HRTEM) methods and atomistic molecular dynamics (MD) calculations. Full determination of the elastic strain distribution can be exploited for band gap tailoring of the heterostructures by controlling the content of the active elements, and thus influence the emitted radiation.

The combined theoretical and experimental approach to arrive at optimum parameters in friction stir welding

Abstract: Abstract Even though friction stir welding was invented long back (1991) by TWI England, till now there has no method or procedure or approach developed, which helps to obtain quickly optimum or exact parameters yielding good or sound weld. An approach has developed in which an equation has been derived, by which approximate rpm can be obtained and by setting range of rpm ±100 or 50 rpm over approximate rpm and by setting welding speed equal to 60 mm/min or 50 mm/min one can conduct FSW experiment to reach optimum parameters; one can reach quickly to optimum parameters, i.e. desired rpm, and welding speed, which yield sound weld by the approach. This approach can be effectively used to obtain sound welds for all similar and dissimilar combinations of materials such as Steel, Al, Mg, Ti, etc.