An analysis of microband orientation in hot deformed aluminium alloy AA5052 using forward and reverse torsion

The effects of strain path reversal on the macroscopic orientation of microbands in AA5052 have been studied using high resolution electron backscatter diffraction. Deformation was carried using two equal steps of forward/forward or forward/reverse torsion at a temperature of 300°C and strain rate of 1s-1 to a total equivalent tensile strain of 0.5. In both cases microbands were found in the majority of grains examined with many having more than one set. The microbands appear to cluster at specific angles to the macroscopic deformation. For the forward/forward condition microbands clustered around -20° and +45° to the maximum principle stress direction and at ± 30-35° to the principal strain direction. For the forward/reverse condition significantly more spread in microband angle was observed though peaks were visible at ±35° with respect to principal stress direction and at -40° and +30° with respect to the principal strain direction of the reverse torsion. This suggests the microbands formed in the forward deformation have or are dissolving and any new microbands formed are related to the deformation conditions of the final strain path.

A heuristic model selection scheme for representing hot flow data using the hot torsion test results

The problem of "model selection" for expressing a wide range of constitutive behaviour adequately using hot torsion test data was considered here using a heuristic approach. A model library including several nested parametric linear and non-linear models was considered and applied to a set of hot torsion test data for API-X 70 micro-alloyed steel with a range of strain rates and temperatures. A cost function comprising the modelled hot strength data and that of the measured data were utilized in a heuristic model selection scheme to identify the optimum models. It was shown that a non-linear rational model including ten parameters is an optimum model that can accurately express the multiple regimes of hardening and softening for the entire range of the experiment. The parameters for the optimum model were estimated and used for determining variations of hot strength of the samples with deformation.

Post processing of the hot torsion test results using a multi-dimensional modelling approach

A model selection scheme was extended to a multi-dimensional representation of the hot torsion test torque, twist and twist rate data to calculate partial derivatives of the torque data with respect to twist and twist rate. These enabled calculation of the instantaneous strain and strain rate hardening indices in the Fields and Backofen method. The concept of an iso-parametric shape function has been borrowed from the finite element method for adding twist rate as a dependant variable to the torque-twist models identified by the model selection scheme. Expressions to calculate the hardening indices, when employing a rational model of torsion data, were derived and presented. Subsequently, the models were used for post processing the data and determining hot strength behaviour, taking into account variations of strain and strain rate hardening indices during the deformation. To substantiate the technique, the hot flow behaviour of API-X70 micro-alloyed steel was determined using a range of hot torsion test data for the material. The flow stress obtained using the instantaneous hardening indices were compared with that obtained by the orthodox technique. For the investigated cases, the onset of dynamic recrystallization (DRX) predicted by the presented technique deviated considerably from those obtained when the average indices were used.

Development and physiology of gastric dilation air sacculitis in Chinook salmon, Oncorhynchus tshawytscha (Walbaum)

The syndrome known as gastric dilation air sacculitis (GDAS) has previously been shown to affect Chinook salmon, Oncorhynchus tshawytscha, in seawater (SW) aquaculture. Feed and osmoregulatory stress have been implicated as potential epidemiological co-factors. The development and physiology of GDAS was investigated in SW and freshwater (FW) adapted smolts. Diet A (low-cohesion pellets) and diet B (high-cohesion pellets) were fed to both FW- and SW-adapted fish. GDAS was induced only in the SW trial on feeding diet A. Stimulated gastro-intestinal (GI) smooth muscle contractility, and fluid transport by the pyloric caeca were different in GDAS-affected fish, which also showed osmoregulatory dysfunction. Cardiac stomach (CS) smooth muscle contractility in response to acetylcholine and potassium chloride (KCl) was significantly reduced in fish fed diet A relative to controls from weeks 3–5. In contrast, maximal pyloric sphincter (PS) circular smooth muscle contraction in response to KCl was significantly elevated in fish fed diet A in weeks 4 and 5. Serum osmolality was elevated in GDAS-affected fish from week 2 of the SW trial. Fluid transport from the mucosal to serosal surface of isolated pyloric caeca was significantly reduced in weeks 3, 4 and 5 in SW fish fed diet A. Gastric evacuation from the stomach of healthy fish was shown to be significantly different when diets of low- and high-cohesion were fed. The results are consistent with the intestinal brake playing a role in the development of the disease.

Motivation, readiness to change, and weight loss following adjustable gastric band surgery

High levels of readiness to change (RTC) are considered critical to the long-term success of weight management programs including bariatric surgery. However, there are no data to support this assertion. We hypothesize that RTC level will not influence weight outcomes following surgery. In 227 consecutive patients undergoing adjustable gastric banding surgery, we recorded reasons for seeking surgery, and RTC measured with the University of Rhode Island Change Assessment. Scores were blinded until study completion. The primary outcome measure was percentage of excess BMI loss at 2 years (%EBMIL-2); others included compliance and surgical complications. Of 227 subjects, 204 (90%) had weight measurement at 2 years. There was no significant correlation between RTC score and %EBMIL-2 (r = 0.047, P = 0.5). Using the median split for RTC score the lowest 102 subjects mean %EBMIL-2 was 52.9 ± 26.9% and the highest 52.2 ± 28.3%, P = 0.869. There was no weight loss difference between highest and lowest quartiles, or a nonlinear relationship between weight loss and RTC score. There was no significant relationship between RCT score and compliance, or likelihood of complications. Those motivated by appearance were more likely to be younger women who lost more weight at 2 years. Poor attendance at follow-up visits was associated with less weight loss, especially in men. Measures of RTC did not predict weight loss, compliance, or surgical complications. Caution is advised when using assessments of RTC to predict outcomes of bariatric surgery.

Orientation dependence of the substructure characteristics in a Ni- 30%Fe austenitic alloy deformed in hot torsion

The present work examines the microstructure and texture evolution in a Ni-30wt.%Fe austenitic model alloy deformed in torsion at 1000 °C, with a particular emphasis on the orientation dependence of the substructure characteristics within the deformed original grains. Texture of these grains was principally consistent with that expected for simple shear and comprised the main A, B and C components. The deformation substructure within the main texture component grains was characterised by "organised" arrays of parallel microbands with systematically alternating misorientations, locally accompanied by micro-shear bands within the C grains. With increasing strain, the mean subgrain size gradually decreased and the mean misorientation angle concurrently increased towards the saturation. The stored deformation energy within the main texture component grains was principally consistent with the respective Taylor factor values. The microband boundaries corresponded to the expected single slip {111} plane for the A oriented grains while these boundaries for the C oriented grains represented a variety of planes even for a single grain.

Surface wrinkling of the twinning induced plasticity steel during the tensile and torsion tests

'Heterogeneous twinning' is defined as plastic deformation due to the formation and progress of twins resulting in surface wrinkles on the deforming part when the initial grain size is relatively large compared to the typical size of the part. In the case of a Twinning Induced Plasticity (TWIP) steel with an initial grain size of ~160. m, the heterogeneous twinning generated visible wrinkles, an orange peel effect, under medium uni-axial strains. The heterogeneous twinning did not occur in the material subjected to high shear strains. The complications resulting from this phenomenon on strain hardening characterization of the TWIP steels using two commonly used mechanical tests, tensile and torsion are discussed along with some experimental aspects of heterogeneous twinning. © 2014.