Simulation of distortion due to machining of thin-walled components

The distortion of components is strongly related to the residual stress state induced by manufacturing processes like heat treatment, forming or machining. Each process step affects the initial stress state of the following process step. When removing material during machining, the component establishes a new stress equilibrium. Stresses are redistributed causing the component geometry to adjust. Especially for thin-walled components distortion potential is high. Gaining knowledge about the influence of initial loads and the release of distortion during machining processes helps to increase product quality and efficiency. The influences of different initial stress states and different machining parameters on the amount of distortion are examined using both FEM simulations and experiments. A thin-walled T-profile made of aluminum alloy Al 7075-T6 serves as test specimen. A bending process applies a load to initialize a repeatable and defined residual stress state. A groove was machined afterwards into the plastically deformed work piece to trigger stress redistribution and a release of distortion. Different loads with 35 to 45 kN and two different geometries of a groove were used. The amount of initial stress has a significant effect on the distortion potential which could be quantified in the study. Simulations show the same behavior as the experiments and the results match very well especially for a high load

Biophysical characterization of the inactivation of E. coli transketolase by aqueous co-solvents

Transketolase (TK) has been previously engineered, using semi-rational directed evolution and substrate walking, to accept increasingly aliphatic, cyclic, and then aromatic substrates. This has ultimately led to the poor water solubility of new substrates, as a potential bottleneck to further exploitation of this enzyme in biocatalysis. Here we used a range of biophysical studies to characterise the response of both E. coli apo- and holo-TK activity and structure to a range of polar organic co-solvents: acetonitrile (AcCN), n-butanol (nBuOH), ethyl acetate (EtOAc), isopropanol (iPrOH), and tetrahydrofuran (THF). The mechanism of enzyme deactivation was found to be predominantly via solvent-induced local unfolding. Holo-TK is thermodynamically more stable than apo-TK and yet for four of the five co-solvents it retained less activity than apo-TK after exposure to organic solvents, indicating that solvent tolerance was not simply correlated to global conformational stability. The co-solvent concentrations required for complete enzyme inactivation was inversely proportional to co-solvent log(P), while the unfolding rate was directly proportional, indicating that the solvents interact with and partially unfold the enzyme through hydrophobic contacts. Small amounts of aggregate formed in some cases, but this was not sufficient to explain the enzyme inactivation. TK was found to be tolerant to 15% (v/v) iPrOH, 10% (v/v) AcCN, or 6% (v/v) nBuOH over 3 h. This work indicates that future attempts to engineer the enzyme to better tolerate co-solvents should focus on increasing the stability of the protein to local unfolding, particularly in and around the cofactor-binding loops

A sensibility analysis to geometric and cutting conditions using the particle finite element method (PFEM)

The (PFEM) is employed to simulate orthogonal metal cutting of 42CD4 steel. The objectives of this work are mainly three: The first one is to validate PFEM strategies as an efficient tool for numerical simulation of metal cutting processes by a detailed comparison (forces, stresses, strains, temperature, etc.) with results provided by commercial finite element software (Abaqus, AdvantEdge, Deform) and experimental results. The second is to carry out a sensibility analysis to geometric and cutting conditions using PFEM by means of a Design of Experiments (DoE) methodology. And the third one is to identify the advantages and drawbacks of PFEM over FEM and meshless strategies. Also, this work identifies some advantages of PFEM that directly apply to the numerical simulation of machining processes: (i) allows the separation of chip and workpiece without using a physical or geometrical criterion (ii) presents negligible numerical diffusion of state variables due to continuous triangulation, (iii) is an efficient numerical scheme in comparison with FEM

Evolution of residual stresses induced by machining in a Nickel based alloy under static loading at room temperature

Tensile residual stresses are very often generated on the surface when machining nickel alloys. In order to determine their influence on the final mechanical behaviour of the component residual stress stability should be considered. In the present work the evolution of residual stresses induced by machining in Inconel 718 under static loading at room temperature has been studied. An Inconel 718 disc has been face turned and specimens for tensile tests have been extracted from the disc. Then surface residual stresses have been measured by X-ray diffraction for initial state and different loading levels. Finally, a finite element model has been fitted to experimental results and the study has been extended for more loading conditions. For the studied case, it has been observed that tensile residual stresses remain stable when applying elastic loads but they increase at higher loads close to the yield stress of the material

Initial exploration of the genetic structure of domestic pig (Sus scrofa domestica) in Sampués, Sucre, Colombia, using microsatellites

El objetivo de la presente investigación fue evaluar la variabilidad genética de una población de cerdo doméstico (Sus scrofa domestica) en Sampués, Sucre, Colombia, para determinar su situación genética. Se estudiaron 50 muestras de la población. Se utilizaron 20 microsatélites, cinco pertenecientes a la lista de los recomendados por la FAO/ISAG para estudios de biodiversidad porcina y los restantes representan la mayor parte del genoma porcino. Se pudo precisar que los microsatélites utilizados resultaron polimórficos, detectándose entre 3 (SW2019) y 14 (SW957) alelos, con un número medio de alelos de 6 y un total de 120. La heterocigosidad media esperada fue de 0.5465 y la heterocigosidad media observada fue de 0.5203. Los valores del contenido de información polimórfica (PIC) oscilaron entre 0.2823 y 0.7252 para los loci SW1041 y SW957, respectivamente. Los resultados muestran a la población de cerdos estudiada como un grupo con alto grado de diversidad genética.The aim of this research was to evaluate the genetic variability of a population of domestic pigs (Sus scrofa domestica) in Sampués, Sucre, Colombia to determine their genetic status. Fifty samples were studied. Twenty microsatellites were used where five of them were from the list of those recommended by FAO/ISAG for studies of swine biodiversity and the remaining represent most of the pig genome. The microsatellites used were polymorphic, detecting between 3 (SW2019) to 14 (SW957) alleles with an average 6 and a total of 120. The mean expected heterozygosity was 0.5465 and the mean observed heterozygosity was 0.5203. The polymorphism information content (PIC) ranged between 0.2823 and 0.7252 for SW1041 and SW957 loci respectively. The results showed that the studied population as a group with a high degree of genetic diversity

Relationships between Body Composition and Game Day Training Load in Ice Hockey Players

Body composition can impact physical activities and exercise performance. However, relationships between body composition and workload during ice hockey games remain unknown. PURPOSE: To examine relationships between body composition and game day training load in ice hockey players. METHODS: Eleven highly-trained ice hockey players (10 males, 1 female; mean ± standard deviation; age, 21.73 ± 1.34 yrs.; height, 179.93 ± 8.49 cm; body mass, 76.87 ± 14.38 kg, body fat percentage [BFP]: 18.0 ± 7.9% [mean ± SD]; fat-free mass index [FFMI]: 19.8 ± 2.2 kg/m2) participated in the study. First, participants visited the laboratory to assess their body composition by dual-energy X-ray absorptiometry and 3-dimensional optical imaging. Then, participants wore a player tracking device to monitor training load during an entire ice hockey game. Pearson correlations were utilized to assess relationships between selected body composition (body fat percentage [BFP], fat-free mass index [FFMI]) and training load metrics (average heart rate [HR], training impulse [TRIMP]). RESULTS: No statistically significant correlations between the selected body composition and training load variables were observed. Correlation coefficients were negative for the relationship between BFP and TRIMP (r = -0.46, p = 0.15) and between BFP and HR (r = -0.49, p = 0.12). In contrast, correlation coefficients were positive for the relationship between FFMI and TRIMP (r = 0.57, p = 0.07) and between FFMI and HR (r = 0.49, p = 0.12). CONCLUSION: With no statistically significant associations between training load and body composition, BFP and FFM might not impact workload in the ice hockey players during the game. However, further investigation will be necessary to establish this finding more definitively, due to the utilization of a single game’s training load and a modest sample of players

Impact of cofactor-binding loop mutations on thermotolerance and activity of E. coli transketolase

Improvement of thermostability in engineered enzymes can allow biocatalysis on substrates with poor aqueous solubility. Denaturation of the cofactor-binding loops of Escherichia coli transketolase (TK) was previously linked to the loss of enzyme activity under conditions of high pH or urea. Incubation at temperatures just below the thermal melting transition, above which the protein aggregates, was also found to anneal the enzyme to give an increased specific activity. The potential role of cofactor-binding loop instability in this process remained unclear. In this work, the two cofactor-binding loops (residues 185–192 and 382–392) were progressively mutated towards the equivalent sequence from the thermostable Thermus thermophilus TK and variants assessed for their impact on both thermostability and activity. Cofactor-binding loop 2 variants had detrimental effects on specific activity at elevated temperatures, whereas the H192P mutation in cofactor-binding loop 1 resulted in a two-fold improved stability to inactivation at elevated temperatures, and increased the critical onset temperature for aggregation. The specific activity of H192P was 3-fold and 19-fold higher than that for wild-type at 60 °C and 65 °C respectively, and also remained 2.7-4 fold higher after re-cooling from pre-incubations at either 55 °C or 60 °C for 1 h. Interestingly, H192P was also 2-times more active than wild-type TK at 25 °C. Optimal activity was achieved at 60 °C for H192P compared to 55 °C for wild type. These results show that cofactor-binding loop 1, plays a pivotal role in partial denaturation and aggregation at elevated temperatures. Furthermore, a single rigidifying mutation within this loop can significantly improve the enzyme specific activity, as well as the stability to thermal denaturation and aggregation, to give an increased temperature optimum for activity

Ti6Al4V metal cutting chip formation experiments and modelling over a wide range of cutting speeds

Measured forces, chip geometry and tool temperatures from machining a mill annealed Ti6Al4V at cutting speeds mainly from 1 to 100 m/min, but in some cases down to 0.1 m/min, are reported, as well as mechanical testing of the material. Finite element simulations with inputs the measured flow stress, and subsequently a small high temperature strain hardening recovery correction, and a failure model calibrated from the cutting tests at speeds from 1 to 10 m/min, give satisfactory agreement with the higher speed tests once surface strain hardening and damage from the previous pass of the tool are taken into account. This paper’s originality is firstly to show that more complicated flow stress models involving large strain softening are not needed provided shear failure is included; and secondly its failure model: this proposes a non-zero failed shear stress depending on local pressure and temperature. The simulations provide relations between tool mechanical and thermal loading and cutting conditions to aid process improvement

Do cognitive patterns of brain magnetic activity correlate with hippocampal atrophy in Alzheimer’s disease

Background: Many reports support the clinical validity of volumetric MRI measurements in Alzheimer's disease. Objective: To integrate functional brain imaging data derived from magnetoencephalography (MEG) and volumetric data in patients with Alzheimer's disease and in age matched controls. Methods: MEG data were obtained in the context of a probe-letter memory task. Volumetric measurements were obtained for lateral and mesial temporal lobe regions. Results: As expected, Alzheimer's disease patients showed greater hippocampal atrophy than controls bilaterally. MEG derived indices of the degree of activation in left parietal and temporal lobe areas, occurring after 400 ms from stimulus onset, correlated significantly with the relative volume of lateral and mesial temporal regions. In addition, the size of the right hippocampus accounted for a significant portion of the variance in cognitive scores independently of brain activity measures. Conclusions: These data support the view that there is a relation between hippocampal atrophy and the degree of neurophysiological activity in the left temporal lobe