Fracture mechanics‐based progressive damage modelling of adhesively bonded fibre‐reinforced polymer joints

A quasi‐static progressive damage model for prediction of the fracture behaviour and strength of adhesively bonded fibre‐reinforced polymer joints is introduced in this paper. The model is based on the development of a mixed‐mode failure criterion as a function of a master R‐curve derived from the experimental results obtained from standard fracture mechanics joints. Consequently, the developed failure criterion is crack‐length and mode‐mixity dependent, and it takes into account the contribution of the fibre‐bridging effect. Energy release rate values for adhesively bonded double‐lap joints are obtained by using the virtual crack closure technique method in a finite element model, and the numerically obtained strain energy release rate is compared to the critical strain energy release rate given by the mixed‐mode failure criterion. The entire procedure is implemented in a numerical algorithm, which was successfully used for predicting the strength and R‐curve response of adhesively bonded double‐lap structural joints made of pultruded glass fibre‐reinforced polymers and epoxy adhesives.     

Hydrometallurgical Extraction of Vanadium from Mechanically Milled Oil-Fired Fly Ash: Analytical Process Optimization by Using Taguchi Design Method

In this study, the Taguchi design method was employed to determine the optimum experimental parameters in extraction of vanadium by NaOH leaching of oil-fired fly. Prior to designed experiments, the raw precipitates were mechanicallly milled using a high-energy planetary ball mill. Experimental parameters were investigated as follows: mechanical milling (MM) times (2 and 5?hours), NaOH (1 and 2 molar concentration) as reaction solution (RS), powder to solution (P/S) ratios (100/400 and 100/600?mg/mL), temperature (T) of reaction system (303 K and 333?K [30?°C and 60?°C]), stirring times (ST) of reaction media (4 and 12?hours), stirring speed (SS) being adjusted to 400 and 600?rpm, and rinsing times (RT) of remained filtrates (1 and 3?hours). Statistical analysis of signal-to-noise ratio followed by analysis of variance was performed in order to estimate the optimum levels and their relative contributions. Data analysis is carried out using L₈ orthogonal array consisting of seven parameters each with two levels. The optimum conditions were MM1 (3?hours), RS2 (2 molar NaOH), P/S2 (100/600?mg/mL), T2 (333?K [60?°C]), ST2 (12?hours), SS1 (400?rpm), and RT1 (1?hour). Finally, from environmental and economical points of view, the process is faster and better organized by employing this analytical design method.     

Significant improvement of semi-solid microstructure and mechanical properties of A356 alloy by ARB process

Accumulative roll bonding (ARB) process was used in this study as an effective method for manufacturing high-strength, finely-dispersed and highly-uniform A356 alloy. It was found that when the number of ARB cycles was increased, the uniformity of silicon particles in the aluminum matrix improved, the particles became finer and spheroider and therefore, the tensile strength (TS) and ductility of the samples improved. The microstructure of the manufactured A356 alloy after five ARB cycles indicated a totally modified structure such that it's TS and elongation values reached 269 MPa and 5.3% which were 2.6 and 2.5 times greater than those of the as-cast material, respectively. Also, the hardness value increased from 55.4 (for as-cast sample) to 100.2 HV (after the fifth cycle of ARB), and registered 81% increase.     

A comparative study between gravel and rubber drainage columns for mitigation of liquefaction hazards

Liquefaction is one of the most destructive natural hazards that cause damage to engineering structures during an earthquake. This study aims to examine the effect of rubber and gravel drainage columns on the reduction of liquefaction potential of saturated sandy soils using a shaking table. Experiments were carried out in various conditions such as construction materials, different arrangements and diameters of drainage columns. Effects of the relative density and the input motion on the base test were investigated as well. The results demonstrate that rubber drainage columns have slightly better performance compared to gravel drainage columns at high relative density and high input acceleration. Soil improvement using gravel drainage columns, which leads to reduction in liquefaction effects at moderate input acceleration and low relative density, is a more effective method than that using rubber drainage columns. By increasing the number and diameter of gravel and rubber drainage columns, deformations due to liquefaction are reduced. The drainage rate of gravel drains is higher than that of rubber drains after shaking. Totally, the outcomes indicate that densification is the most important factor controlling liquefaction.     

Low-power highly linear UWB CMOS mixer with simultaneous second- and third-order distortion cancellation

A 3.1-4.8 GHz mode-1 UWB CMOS mixer that utilizes simultaneous second- and third-order distortion cancellation is presented. The scheme is based on a new derivative superposition, employing PMOS as an auxiliary FET to cancel the second- and the third-order nonlinear currents of common-source transconductance in the mixer and gives rise to low-distortion operation for a broad range of gate-source voltage. Full Volterra series analysis of the proposed transconductance is reported to examine the effectiveness of the new technique. Simulations in a 0.13 μm CMOS technology demonstrate that IIP3 and IIP2 of the proposed mixer have 18 and 10 dB improvements, respectively, compared with conventional Gilbert-type mixer with the same power consumption. The robustness of the technique has been verified by Monte Carlo analysis. The mixer has a gain of 12 dB and noise figure of 13 dB, while drawing only 2.5 mA from 1.2 V supply voltage.     

Correlative High‐Resolution Mapping of Strain and Charge Density in a Strained Piezoelectric Multilayer

A key to strain engineering of piezoelectric semiconductor devices is the quantitative assessment of the strain‐charge relationship. This is particularly demanding in current InGaN/GaN‐based light‐emitting diode (LED) designs as piezoelectric effects are known to degrade the device performance. Using the state‐of‐the‐art inline electron holography, we have obtained fully quantitative maps of the two‐dimensional strain tensor and total charge density in conventional blue LEDs and correlated these with sub‐nanometer spatial resolution. We show that the In_0.15Ga_0.85N quantum wells are compressively strained and elongated along the polar growth direction, exerting compressive stress/strain on the GaN quantum barriers. Interface sheet charges arising from a polarization gradient are obtained directly from the strain data and compared with the total charge density map, quantitatively verifying only 60% of the polarization charges are screened by electrons, leaving a substantial piezoelectric field in each In_0.15Ga_0.85N quantum well. The demonstrated capability of inline electron holography provides a technical breakthrough for future strain engineering of piezoelectric optoelectronic devices.     

Microstructural and mechanical properties of friction stir welded Cu–30Zn brass alloy at various feed speeds: Influence of stir bands

In this study, the effect of various feed speeds on microstructure and mechanical properties of friction stir welded Cu–30Zn brass alloy is investigated. Rotation speed was fixed at 950 rpm and feed speed varied in the range of 190–375 mm/min. Examination of the microstructure showed very fine grains with some deformed grains in the stirred zone and some coarser grains in the thermo-mechanically affected zone and base metal. A unique deformation pattern, namely “stir band” in the stirred zone region was identified and its density increased by increase in feed speed. Results showed that the grain size profile was independent of feed speed and the hardness values decreased by increase in feed speed. Increase in feed speed led to a slight improvement of yield strength and ultimate tensile strength, associated to continuous spring-like morphology of stir bands acting as a strengthening structure. However, ductility reduces considerably from 57 to 27%. Moreover, it is observed that during tensile test, fracture cracks originate exactly adjacent to the stir bands.     

Severe pathological changes of parabrachial nucleus in Alzheimer's disease

In the first of a series of studies aimed at mapping brain stem pathological changes in patients with Alzheimer's disease (AD), we report a new finding regarding the parabrachial nucleus (PBN), a unit of paramount importance in the relay and integration of visceral and nociceptive information as well as in homeostatic control. The brains of 20 patients with AD were surveyed. The PBN contained pervasive neuropathological changes in 100% of the brains from those with early-onset dementia and in 80% from those with late-onset dementia. These changes were entirely absent in all 10 normal controls. The pathological changes of PBN, would cause autonomic dysfunction in patients with AD and perhaps contribute to the disproportionate mortality encountered in these patients.