A mode II fracture specimen—finite element analysis

A series of studies which demonstrate the potential of a proposed mode II fracture specimen are reported. First, previously obtained photoelastic results[1–3] are reviewed so that this paper will be self-contained. Then, a finite element analysis is presented in order not only to corroborate the experimental results but also to calibrate the specimen for $\text{K}{}_{\mathrm{IIC}}$ measurements. Finally, a preliminary $\text{K}{}_{\mathrm{IIC}}$ test performed on a brittle steel specimen is described.     

Micromechanical modeling of particulate-filled composites using micro-CT to create representative volume elements

International Journal of Mechanics and Materials in Design - A method based on X-ray micro-CT was introduced to create realistic representative volume elements (RVE) for particulate-filled...     

Interplay of Particle Shape and Surface Roughness to Reach Maximum Flotation Efficiencies Depending on Collector Concentration

Particle–particle and bubble–particle-interactions in flotation systems are governed by physico-chemical and hydrodynamic conditions of pulp. Shape factor and roughness of particles significantly affect these interactions, and hence both grade and recovery in flotation. Although many studies have been conducted to understand morphological features of particles, the underlying mechanism of their effect on flotation recovery have not been clearly shown. Towards this aim, acombination of grinding and abrasion processes was applied to mimic grinding in terms of shape and roughness in order to get their corresponding flotation recoveries at different collector levels. For this purpose, glass beads representing smooth spherical particles of –150+106 µm in size along with ground and abraded glass particles of different shapes and roughness were used to evaluate the flotation efficiency of these particles in the absence and presence of amine collector. The dependence of the shape and roughness on the flotation recoveries at different hydrophobicities as monitored by different amine collector concentrations is demonstrated. Finally, the results are discussed to see if morphology ofparticles can be tuned through grinding to achieve maximum flotation efficiencies.     

Performances of hill-type and neural network muscle models-toward a myosignal-based exoskeleton.

Muscle models are the essential components of any musculoskeletal simulation. In addition, muscle models which are incorporated in neural-based prosthetic and orthotic devices may significantly improve their performance. The aim of the study was to compare the performances of two types of muscle models in terms of predicting the moments developed at the human elbow joint complex based on joint kinematics and neuromuscular activity. The performance evaluation of the muscle models was required to implement them in a powered myosignal-driven exoskeleton (orthotic device). The experimental setup included a passive exoskeleton capable of measuring the joint kinematics and dynamics in addition to the muscle myosignal activity (EMG). Two types of models were developed and analyzed: (i) a Hill-based model and (ii) a neural network. The task, which was selected for evaluating the muscle models performance, was the flexion-extension movement of the forearm with a hand-held weight. For this task the muscle model inputs were the normalized neural activation levels of the four main flexor-extensor muscles of the elbow joint, and the elbow joint angle and angular velocity. Using this inputs, the muscle model predicted the moment applied on the elbow joint during the movement. Results indicated a good performance of the Hill model, although the neural network predictions appeared to be superior. Relative advantages and shortcomings of both approaches were presented and discussed.     

Multi-parameter acoustic imaging of uniform objects in inhomogeneous soft tissue

The problem studied in this paper is ultrasound image reconstruction from frequency-domain measurements of the scattered field from an object with contrast in attenuation and sound speed. The case in which the object has uniform but unknown contrast in these properties relative to the background is considered. Background clutter is taken into account in a physically realistic manner by considering an exact scattering model for randomly located small scatterers that vary in sound speed. The resulting statistical characteristics of the interference are incorporated into the imaging solution, which includes application of a total-variation minimization-based approach in which the relative effect of perturbation in sound speed to attenuation is included as a parameter. Convex optimization methods provide the basis for the reconstruction algorithm. Numerical data for inversion examples are generated by solving the discretized Lippman-Schwinger equation for the object and speckle-forming scatterers in the background. A statistical model based on the Born approximation is used for reconstruction of the object profile. Results are presented for a two-dimensional problem in terms of classification performance and compared with minimum-l2-norm reconstruction. Classification using the proposed method is shown to be robust down to a signal-to-clutter ratio of less than 1 dB.     

Second-Law Analysis for an Inclined Channel Containing Porous-Clear Fluid Layers by Using the Differential Transform Method

In this study, convection in a porous medium for a laminar, incompressible, non-Darcy model flow in an inclined channel has been investigated. The flow field considered is composed of porous and clear viscous layers. The solutions are carried out for both clear fluid and porous regions by using the differential transform method (DTM). For the solutions of governing equations, constant values for some parameters such as angle of inclination (φ), porous parameter (σ), and the ratio of the heights of two layers (h) are assigned. In order to verify the applied solution technique, the results obtained are compared to the already existing ones evaluated by perturbation method. It is noticed that the results by two methods are in agreement for small values of Brinkman number (Br). However, for higher values of Br, the solutions carried out by perturbation method lose accuracy but the results of the DTM are still valid. The entropy generation number (N _s ) is derived and plotted by using dimensionless velocity and temperature profiles. One of the advantages of this study to similar studies is to give an open form series solution, which gives a tractable and easily applicable recurative form of nonlinear field equations. In similar studies, it is said that the equations are solved; however, neither solution technique nor accuracy or applicability of given technique are clear. In this work, these are well documented.     

Antioxidant activity of protein extracts from heat-treated or thermally processed chickpeas and white beans

In this study, antioxidant activities of water-soluble protein extracts from chickpeas and white beans were investigated. The area under the curve (AUC) values of lyophilized crude protein extracts (dialyzed or undialyzed) from thermally processed (121 °C for 20 min) or heat-treated (90 °C for 20 min) chickpeas (73–91 μmol trolox/g) and white beans (39–67 μmol trolox/g) indicated a higher free radical-scavenging capacity and thermostability for chickpea proteins than for white bean proteins. The thermal processing also increased the Fe⁺²-chelating capacity of lyophilized chickpea crude protein extracts 1.8-fold whereas it caused a 2.3-fold reduction in the Fe⁺²-chelating capacity of lyophilized white bean crude protein extracts. Dialysis increased the protein content of lyophilized chickpea extracts 1.5–2-fold but it did not affect the protein content of lyophilized white bean extracts significantly. Ammonium sulfate precipitation was not effective for selective precipitation of antioxidant proteins. However, it improved the free radical-scavenging capacity of lyophilized protein extracts from thermally processed chickpeas and white beans by almost 25% and 100%, respectively. DEAE-cellulose chromatography, indicated the presence of five (A₁–A₅) and three (B₁–B₃) antioxidant protein fractions in heat-treated and thermally processed chickpea protein extracts, respectively, and can be used for the partial purification of antioxidant proteins. The results of this study showed the good potential of chickpea proteins as thermostable natural food antioxidants.     

Performance evaluation of a mercury‐steam combined–energy‐generation system (MES)

In this study, exergy and thermo‐ecology–based performance analyses of a mercury‐steam combined–energy‐generation system are comprehensively presented. Performance characteristics such as net‐power output, net‐power density, exergy efficiency, exergy destruction, and ecological coefficient of performance have been obtained by developing a novel numerical model. The impacts of the pressures of open feed water heater and steam turbines, temperatures of mercury boiler, and mercury turbines on the performance characteristics have been investigated. The results indicated that the performance characteristics of the system have been remarkably affected by the pressure and temperature variations of the system components.     

Performance analysis of a novel eco‐friendly internal combustion engine cycle

The Miller cycle applications have been performed to diminish NO_x released from internal combustion engines (ICEs), in recent years. The Miller cycle provides decreased compression ratio and enhanced expansion ratio; hereby, maximum in‐cylinder combustion temperatures diminish, and NO_x formations slow down remarkably. Another less‐known method is Takemura cycle application, which provides heat addition into engine cylinder at constant combustion temperatures. In this study, a novel cycle including the Miller cycle and the Takemura cycle has been developed by using novel numerical models and computing methods with seven processes and a novel way to decrease NO_x emissions at higher levels compared with the single applications of known cycles. A comprehensive performance examination of the proposed cycle engine in terms of performance characteristics such as effective power (EFP), effective power density (EFPD), exergy destruction (X), exergy efficiency (ε), and ecological coefficient of performance (ECOP) has been conducted. The impacts of engine operating and design parameters on the performance characteristics have been computationally examined. Furthermore, irreversibilities depending on incomplete combustion loss (INCL), exhaust output loss (EXOL), heat transfer loss (HTRL), and friction loss (FRL) have been considered in the performance simulations. The minimum exergy destruction and maximum performance specifications have been observed with 30 of the compression ratio. Maximum effective power values have been obtained at range between 1 and 1.2 of equivalence ratio. The optimum range for exergy efficiency is between 0.8 and 1 of equivalence ratio. Increasing engine speed has provided enhancing effective power. However, an optimum range has been found for the exergy efficiency that is interval of 3000 to 4000 rpm. The results obtained can be assessed by researchers studying on modeling of the engine systems and designs.