Research Papers

J. Eng. Mater. Technol. 2016;138(4):041001-041001-6. doi:10.1115/1.4033576.

A relatively low-temperature carbon nanotube (CNT) synthesis technique, graphitic structure by design (GSD), was utilized to grow CNTs over glass fibers. Composite laminates based on the hybrid CNTs–glass fibers were fabricated and examined for their electromagnetic interfering (EMI) shielding effectiveness (SE), in-plane and out-of-plane electrical conductivities and mechanical properties. Despite degrading the strength and strain-to-failure, improvements in the elastic modulus, electrical conductivities, and EMI SE of the glass fiber reinforced polymer (GFRP) composites were observed.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041002-041002-6. doi:10.1115/1.4033465.

The desirability of using the KOBO extrusion process for AZ91 magnesium alloy preceding its further plastic processing has been experimentally verified. Importantly, during the conducted experiments, heat treatment (e.g., homogenization) was applied either before or after direct KOBO extrusion, which if used might have affected the properties of the alloy. The products of the cold KOBO process take the form of tapes with different cross sections. They were pressed (deep drawing), or, alternatively, subjected to conventional indirect extrusion in order to acquire the desired spatial geometry of the product. Due to the need for relatively wide strips, a variant of the KOBO extrusion with lateral outflow was used, since the press structure, providing reversibly oscillating die, strongly limited the cross sections of directly extruded products. The research procedure, involving plastic deformation with cyclic changes of the deformation path, allowed to obtain results indicating new potential properties of metallic materials crucial for their applicability.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041003-041003-8. doi:10.1115/1.4033374.

The manufacturing parameters such as curing process cause residual stresses in polymeric laminated composites. Therefore, an accurate method of measurement of residual stresses is essential for the design and analysis of composites structures. The slitting method is recently used for measurement of the residual stresses in laminated composites. However, this method has some drawbacks such as high sensitivity to noise of measurements and high scattering in the final results, which necessitate using of normalization techniques. Moreover, the form of polynomials, used in the conventional slitting method for calculation of the stiffness matrix, has a significant effect on final results. In this paper, it is shown that the major reason of the drawbacks of the slitting method in calculating the residual stresses is a direct use of the elastic released strains recorded by strain gages. In the present study, instead of direct calculation of residual stresses from the elastic released strains, eigen strain distribution as a constant and invariant field has been calculated from the recorded elastic strains. Then, by using the calculated eigen strain field in a finite-element model, the residual stress filed was obtained. Also, instead of using polynomials to calculate the compliance, a superposition method was used. The results show that the new method decreases the sensitivity of the final results to noise and scattering of the experimental data. It means that the normalization methods are not needed any more.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041004-041004-14. doi:10.1115/1.4033559.

Microstructurally informed macroscopic impact response of a high-manganese austenitic steel was modeled through incorporation of the viscoplastic self-consistent (VPSC) crystal plasticity model into the ansys ls-dyna nonlinear explicit finite-element (FE) frame. Voce hardening flow rule, capable of modeling plastic anisotropy in microstructures, was utilized in the VPSC crystal plasticity model to predict the micromechanical response of the material, which was calibrated based on experimentally measured quasi-static uniaxial tensile deformation response and initially measured textures. Specifically, hiring calibrated Voce parameters in VPSC, a modified material response was predicted employing local velocity gradient tensors obtained from the initial FE analyses as a new boundary condition for loading state. The updated micromechanical response of the material was then integrated into the macroscale material model by calibrating the Johnson–Cook (JC) constitutive relationship and the corresponding damage parameters. Consequently, we demonstrate the role of geometrically necessary multi-axial stress state for proper modeling of the impact response of polycrystalline metals and validate the presented approach by experimentally and numerically analyzing the deformation response of the Hadfield steel (HS) under impact loading.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041005-041005-6. doi:10.1115/1.4033577.

As an important surface treatment method, shot peening (SP) can improve the surface properties effectively. In this work, after multiple SP treatments, the uniformity of the residual stress distribution and the domain size distribution on the surface of Ti–6Al–4 V have been investigated via an X-ray diffraction method. Compared with traditional SP treatments, the multiple SP can increase the surface residual stresses and make the stress distribution more uniform. In terms of the domain size, the multiple SP treatments mainly influence its uniform distribution, and there is no obvious effect to the values, which is due to the saturation status of SP process. In addition, the effects of multiple SP on the surface roughness and hardness have been studied. The results show that the multiple SP can reduce the surface roughness and increase the hardness in a certain extent comparing with the effect of traditional SP, which are ascribed to the smaller shot balls and the more homogeneous deformation during the process of multiple SP. Therefore, an appropriate multiple SP can improve the surface properties of Ti–6Al–4 V effectively.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041006-041006-5. doi:10.1115/1.4033466.

The fatigue properties of high-pressure die-casting (HPDC) magnesium (Mg) alloys AZ91 exhibit a high variability, due primarily to the porosity that is inherent in the injection process. In the 94% of the studied samples, the porosity in which crack nucleation originates is at the surface or adjacent to the surface. The threshold stress intensity factor amplitude and the limit of fatigue have been calculated following the classical models of parameterization of defects. A new set of samples were prepared by machining the surface slightly, in order to conserve the microstructure, and the fatigue behavior at low level of stress was improved. All the samples were produced in molds with the final shape by HPDC process, which allowed a realistic study of the surface effect and the influence of grain size variation from the edge to the center of the samples.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041007-041007-15. doi:10.1115/1.4033488.

Simulation plays a critical role in the development and evaluation of critical components that are regularly subjected to mechanical loads at elevated temperatures. The cost, applicability, and accuracy of either numerical or analytical simulations are largely dependent on the material model chosen for the application. A noninteraction (NI) model derived from individual elastic, plastic, and creep components is developed in this study. The candidate material under examination for this application is 2.25Cr–1Mo, a low-alloy ferritic steel commonly used in chemical processing, nuclear reactors, pressure vessels, and power generation. Data acquired from prior research over a range of temperatures up to 650 °C are used to calibrate the creep and plastic components described using constitutive models generally native to general-purpose fea. Traditional methods invoked to generate constitutive modeling coefficients employ numerical fittings of hysteresis data, which result in values that are neither repeatable nor display reasonable temperature dependence. By extrapolating simplifications commonly used for reduced-order model approximations, an extension utilizing only the cyclic Ramberg–Osgood (RO) coefficients has been developed. This method is used to identify the nonlinear kinematic hardening (NLKH) constants needed at each temperature. Single-element simulations are conducted to verify the accuracy of the approach. Results are compared with isothermal and nonisothermal literature data.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041008-041008-16. doi:10.1115/1.4033634.

A new peridynamic (PD) formulation is developed for cubic polycrystalline materials. The new approach can be a good alternative to traditional techniques such as finite element method (FEM) and boundary element method (BEM). The formulation is validated by considering a polycrystal subjected to tension-loading condition and comparing the displacement field obtained from both PDs and FEM. Both static and dynamic loading conditions for initially damaged and undamaged structures are considered and the results of plane stress and plane strain configurations are compared. Finally, the effect of grain boundary strength, grain size, fracture toughness, and grain orientation on time-to-failure, crack speed, fracture behavior, and fracture morphology are investigated and the expected transgranular and intergranular failure modes are successfully captured. To the best of the authors' knowledge, this is the first time that a PD material model for cubic crystals is given in detail.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041009-041009-7. doi:10.1115/1.4033635.

The influences of pulse electric currents at energy density levels of 0.105 J/mm3 and 0.150 J/mm3 on AA5754's flow stress and elongation are investigated. Different combinations of current density and pulse duration are carried out for each energy density. The non-Joule heating effects in electrically assisted forming (EAF) are revealed since the temperatures generated by the electric currents of the same energy density are identical. It is observed that a pulse current helps reduce AA5754's flow stress and increase its elongation. At the same level of energy density, as the current density increases, the instant drop of stress increases as well as the elongation, although the maximum flow stress remains almost unchanged. A theoretical model is proposed that can predict the stress drop during electrically assisted forming. The fracture surfaces of AA5754 subject to pulse currents are observed and analyzed. The dimples of fracture continue to decrease until they completely disappear as the density of pulse current increases. The suppression of voids nucleation and growth by a pulse current leads to the increase of total elongation.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041010-041010-9. doi:10.1115/1.4033632.

A subregular solution thermodynamic model was employed to calculate the stacking fault energy (SFE) in Fe–Mn–Al–C–Si steels with contents of carbon 0.2–1.6 wt.%, manganese 1–35 wt.%, aluminum 1–10 wt.%, and silicon 0.5–4 wt.%. Based on these calculations, temperature-dependent and composition-dependent diagrams were developed in the mentioned composition range. Also, the effect of the austenite grain size (from 1 to 300 μm) on SFEs was analyzed. Furthermore, some results of SFE obtained with this model were compared with the experimental results reported in the literature. In summary, the present model introduces new changes that shows a better correlation with the experimental results and also allows to expand the ranges of temperatures, compositions, grain sizes, and also the SFE maps available in the literature to support the design of Fe–Mn–Al–C–Si steels as a function of the SFE.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041011-041011-7. doi:10.1115/1.4033636.

Currently, available results for the large deflection of circular isotropic membranes are valid for Poisson's ratio of 0.2, 0.3, and 0.4 only. This paper explores the deflection of circular membranes when the membrane material is auxetic, i.e., when they possess negative Poisson's ratio and compared against conventional ones. Due to the multistage calculations involved in the exact method, a generic semi-empirical model is proposed to facilitate convenient and direct computation of the membrane deflection as a function of the radial distance; additionally, a specific semi-empirical model is given to provide a more accurate maximum deflection. Comparison of deflection distributions verifies the validity of the semi-empirical model vis-à-vis the exact model. The deflection of circular membrane increases with the diminishing effect as the Poisson's ratio of the membrane material becomes more negative.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041012-041012-9. doi:10.1115/1.4033908.

The present work incorporates a modified Q-state Monte Carlo (Potts) model to evaluate two-dimensional annealing of representative paramagnetic and diamagnetic polycrystalline materials in the presence of a magnetic field. Anisotropies in grain boundary energy, caused by differences in grain orientation (texturing), and the presence of an external magnetic field are examined in detail. In the former case, the Read–Shockley equations are used, in which grain boundary energies are computed using a low-angle misorientation approximation. In the latter case, magnetic anisotropy is simulated based on the relative orientation between the principal grain axis and the external magnetic field vector. Among other findings, the results of texture development subject to a magnetic field showed an increasing orientation distribution function (ODF) asymmetry over time, with higher intensities favoring the grains with principal axes most closely aligned with the magnetic field direction. The magnetic field also tended to increase the average grain size, which was accompanied by a corresponding decrease in the total grain boundary energy.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041013-041013-7. doi:10.1115/1.4033898.

Increasing interest in using aluminum as the structural component of light-weight structures, mechanical devices, and ships necessitates further investigations on fatigue life of aluminum alloys. The investigation reported here focuses on characterizing the performance of cruciform-shaped weldments made of 5083 aluminum alloys in thickness of 9.53 mm (3/8 in.) under constant, random, and bilevel amplitude loadings. The results are presented as S/N curves that show cyclic stress amplitude versus the number of cycles to failure. Statistical procedures show good agreements between test results and predicted fatigue life of aluminum weldments. Moreover, the results are compared to the results obtained from previous experiments on aluminum specimens with thicknesses of 12.7 mm (1/2 in.) and 6.35 mm (1/4 in.).

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041014-041014-8. doi:10.1115/1.4033909.

Measurement of transient temperature and heat flux has attained enormous importance with the recent advancement in technology. Certain situations demand transient measurements to be performed for extremely short durations (approximately few seconds) which in turn call for sensors capable of responding within microseconds or even less. Thin-film gauges (TFGs), a particular class of resistance temperature detectors (RTDs), are such kind of sensors which are suitable for above requirements due to their quick and precise measurements in transient environments. The present work aims at designing an in-house fabrication and calibration of fast response TFG prepared by depositing nanocarbon layer on silver films as a laminated composite topping to enhance thermal and electrical properties. A significant improvement in the thermal and electrical conductivity of the composite sensor is observed when compared to gauges made from pure metals.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041015-041015-9. doi:10.1115/1.4033910.

In this study, we developed a physically based mesoscale model for dislocation dynamics systems to predict the deformation and spontaneous formation of spatio-temporal dislocation patterns over microscopic space and time. Dislocations and dislocation patterns are emblematic of plastic deformation, a nonlinear, dissipative process involving the dynamics of underlying dislocations as carriers of plastic deformation. The mesoscale model includes a set of nonlinear partial differential equations of reaction–diffusion type. Here, we consider the equations within a one-dimensional framework and analyze the stability of steady-state solutions for these equations to elucidate the associated patterns with their intrinsic length scale. The numerical solution to the model yields the spatial distribution of dislocation patterns over time and provides respective stress–strain curves. Finally, we compare the stress–strain curves associated with the dislocation patterns with the experimental results noted in the literature.

Topics: Dislocations
Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041016-041016-8. doi:10.1115/1.4033911.

Layered structures typically used in applications such as windshields, thermal protection systems, heavy armor, etc., have property jumps at the layer interfaces. Present study focuses on understanding crack initiation and propagation in such systems under dynamic loading particularly when the property jumps are across the crack front. Layered plates were fabricated by joining polymethylmethacrylate (PMMA) and epoxy sheets using an epoxy-based adhesive (Araldite). Single-edge notched (SEN) specimens were subjected to dynamic loading using a modified Hopkinson bar setup. High-speed imaging coupled with dynamic photoelasticity was used to record the crack-tip isochromatic fringes from which the stress intensity factor (SIF) history was obtained. In selected experiments, a pair of strain gages installed on surfaces of specimen was used to record the strain history in the layers, from which the SIF in each layer was obtained. The results indicated that, prior to crack extension, the strain in both layers was identical. The crack tips in the layers start extending at different time instants with the one in the relatively brittle epoxy layer extending first followed by the one in the PMMA layer. At low impact velocity, the delay obtained was significantly higher than that at high impact velocity. The speed of epoxy crack was lower initially due to the bridging of the crack by the uncracked portion of the PMMA layer till initiation of the crack in the PMMA layer. This effect reduced at higher impact velocity for which the delay was much lower and the cracks propagated at a higher-speed.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041017-041017-7. doi:10.1115/1.4034075.

Cobalt-based Tribaloy alloys are strengthened mainly by a hard, intermetallic Laves phase consisting of Co3Mo2Si or/and CoMoSi; therefore, silicon content plays a large role in the microstructure and performance of these materials. In this research, the microstructures of two cobalt-based Tribaloy alloys that are largely different in Si content are studied using scanning electron microscopy (SEM) with an EDAX energy dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD), fatigue strength under rotating-bending test, mechanical behavior under nanoindentation, and hardness at room and elevated temperatures using a microindentation tester. It is revealed that with higher silicon content (2.6 wt. %), T-400 has a hypereutectic microstructure with Laves phase as primary phase, whereas with lower silicon content (1.2 wt. %), T-401 has a hypoeutectic microstructure with solid solution as primary phase. T-400, containing lager volume fraction of Laves phase, exhibits better fatigue strength, in particular, at high stresses, while T-401, with less volume fraction of Laves phase, has improved ductility, exhibiting better resistance to fatigue at low stresses. The hardness of both alloys decreases with temperature, and T-401 shows higher reduction rate. T-400 is harder than T-401.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041018-041018-9. doi:10.1115/1.4034095.

Design of high-performance power lines with advanced materials is indispensable to effectively eliminate losses in electrical power transmission and distribution (T&D) lines. In this study, aluminum conductor composite core with carbon nanostructure (ACCC–CNS) coating in a multilayered architecture is considered as a novel design alternative to conventional aluminum conductor steel-reinforced (ACSR) transmission line. In the multiphysics approach presented herein, first, electrothermal finite element analysis (FEA) of the ACSR line is performed to obtain its steady-state temperature for a given current. Subsequently, the sag of the ACSR line due to self-weight and thermal expansion is determined by performing thermostructural analysis employing an analytical model. The results are then verified with those obtained from the FEA of the ACSR line. The electrothermal finite element (FE) model and the thermostructural analytical model are then extended to the ACCC–CNS line. The results indicate that the ACCC–CNS line has higher current-carrying capacity (CCC) and lower sag compared to those of the ACSR line. Motivated by the improved performance of the ACCC–CNS line, a systematic parametric study is conducted in order to determine the optimum ampacity, core diameter, and span length. The findings of this study would provide insights into the optimal design of high-performance overhead power lines.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2016;138(4):041019-041019-10. doi:10.1115/1.4034204.

The use of lightweight materials in the automotive industry for structural parts has been increasing in recent years in order to reduce the overall vehicle's weight. New innovative lighter materials are being developed nowadays to accomplish that objective. In order to keep or even increase passenger's safety, structural parts made of these materials need to withstand static and impact loads within a range of different temperatures along the vehicle's life. The effect of these conditions when joining these dissimilar lighter materials is a critical issue to be considered when designing the car's body. In this paper, the strength under real car conditions of single lap joints (SLP) made of aluminum alloy (AA) bonded to carbon fiber reinforced polymer (CFRP) adherends was studied. A new crash-resistant epoxy adhesive was used to bond these lightweight materials and an extended characterization of its cohesive properties was carried out. The single lap joints were tested at temperatures of −30, +23, and +80 °C under quasi-static and impact loading. The data obtained was used to perform simple numerical models of the single lap joints under static and impact loads. The experimental results showed an expected increase of the joints strength with the strain rate. The joints behavior was highly influenced by the adherends, especially by the aluminum yielding at high and room temperatures. Delamination of the composite was obtained at low and room temperatures, which explained the strain rate dependence of the failure load. The numerical models predicted with good accuracy the strength of the joints under both static and impact loads.

Commentary by Dr. Valentin Fuster

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