An energy approach for predicting springback of metal sheets after double-curvature forming, Part I: axisymmetric stamping

In our previous study (Xue P, Yu TX, Shu E. International Journal of Materials Processing Technology 1999; 89-90:65-71.), based on the membrane theory of shells of revolution and an energy method a mechanics model and corresponding analytical procedure have been proposed to predict springback of circular and square metal sheets after a double-curvature forming operation. The strain hardening of the material is incorporated into the mechanics model. In the present paper, the method is extended to the cases, in which bending effect, as well as bending-and-unbending effect are taken into account. It is shown that the procedure developed is capable of quantitatively predicting the strain distribution and springback of metal sheets after axisymmetric stamping with a relatively minor effort of calculation and a good accuracy. The effect of stretching force applied at the edge of the plate on springback is also considered. Excellent agreement is found between the theoretical prediction of springback and experiment results.     

Automated Compositional Abstraction Refinement for Concurrent C Programs: A Two-Level Approach

The state space explosion problem in model checking remains the chief obstacle to the practical verification of real-world distributed systems. We attempt to address this problem in the context of verifying concurrent (message-passing) C programs against safety specifications. More specifically, we present a fully automated compositional framework which combines two orthogonal abstraction techniques (operating respectively on data and events) within a counterexample-guided abstraction refinement (CEGAR) scheme. In this way, our algorithm incrementally increases the granularity of the abstractions until the specification is either established or refuted. Our explicit use of compositionality delays the onset of state space explosion for as long as possible. To our knowledge, this is the first compositional use of CEGAR in the context of model checking concurrent C programs. We describe our approach in detail, and report on some very encouraging preliminary experimental results obtained with our tool MAGIC.     

Influence of intracrystalline diffusion in shape selective catalytic test reactions

Molecular dynamics simulations are used to measure the self diffusion constant D of linear decane and n-methylnonanes (n = 2, 3, 4, and 5) at a catalytically relevant temperature in seven 10 member ring zeolites. Two general behaviors are observed in D as the branch position is moved towards the center of the alkane chain. For three of the zeolites (MEL, MFI, and MTT), D decreases monotonically as expected based on a consideration of the bulkiness of the different isomers. For the other four, alkane diffusion is considered anamolous as D is not a monotonic function of branch position. For n-methylnonanes in three zeolites D shows a minimum at either n = 2 (FER), 3 (EUO), or 4 (TON). In AEL, D has a local maximum for n = 3. Alkane diffusion is anamolous in these zeolites because they have structural features that provide a unique hindrance to molecular motion along the main diffusion channel. The ability of the zeolite to hinder motion depends on the molecular structure of the isoparaffin, resulting in the anamolous behavior observed. The 10 member ring zeolites selected for this study represent the entire group for which known structures exist and values of the modified constraint index have been published. The diffusion data presented indicates that product shape selectivity may play some part in determining the modified constraint index. This revised version was published online in July 2006 with corrections to the Cover Date.     

Profile Scaling of Miniature Centrifugal Fans

This paper addresses issues that relate to downscaling the height of centrifugal fans for application in low profile technologies, such as the cooling of portable power electronics. The parameters studied include flow rate, pressure rise, and power consumption characteristics. The former two of these are measured using a fan characterization rig and the latter by directly measuring the power supplied to the fan. These are studied for fan diameters ranging from 15 to 30 mm with numerous profile heights between 0.3 mm and 15 mm. It is found that all of the phenomena encountered are best described in terms of fan aspect ratio. The results show that the conventional scaling laws cannot be accurately applied when blade profile alone is scaled. Indeed, the only parameter reasonably well predicted was the pressure rise attainable, but that was only accurate for fan aspect ratios greater than 0.17. Below this, the pressure rise generated reduces logarithmically toward zero. The study also reveals that no advantage is gained by using fans of aspect ratio greater than 0.3, as the maximum flow rate attainable decreases slightly above this. Overall, the scaling phenomena reported herein provide invaluable information for the future design of efficient low-profile cooling solutions that are to incorporate such fans.     

Esters from castor oil functionalized with aromatic amines as a potential lubricant

Vegetable oils are very promising alternatives to fossil lubricants due to their abundance, low cost, excellent performance, and environmental friendliness. Due to its multifunctional structure, castor oil is an excellent precursor in the synthesis of new biolubricants. However, it showed poor thermal-oxidative stability and a higher pour point. This study used castor oil fatty acids prepared by transesterification (EHRO), epoxidation (TEPO), and oxirane ring opening with the aromatic amines aniline (ANIL) and p-anisidine (ANIS). The chemical structure of these oils was verified by ¹H and ¹³C NMR analysis, and mass spectrometry. Measurements show that the presence of an aromatic amine increases the viscosity resulting in 172 (ANIL) and 199 (ANIS) cSt at 40°C, but reduces viscosity index to 16 and 1, respectively. In addition, the amine groups can scavenge radicals increasing their thermal and oxidative stability. These products do not oxidize copper, and tribological analysis reveals that ANIS has the lowest torque with wear equivalent to commercial mineral lubricant NH-140.     

Editorial: Journal of Scheduling (2022)

Journal of Scheduling -     

3D optical coherence tomography as new tool for microscopic investigations of nucleate boiling on heated surfaces

Boiling phenomena are an important aspect in security and efficiency for technical applications with high heat flux like nuclear reactors. This study presents optical coherence tomography (OCT) as a novel modality for three-dimensional and two-dimensional time resolved imaging of nucleate boiling on heated surfaces on a microscopic scale with high spatial (<10 μm) and temporal (>25 frames per second) resolution. Within this study, a borosilicate glass plate coated with an optically transparent and electrically conductive indium tin oxide (ITO) layer with a thickness of approximately 100 nm was used as heating surface. The combination of these two properties allows optical inspection of the nucleate boiling from the backside by OCT focused on the formation, growth and detachment of single bubbles. We demonstrated for the first time that OCT is an excellent tool to acquire two-dimensional and three-dimensional images of the base of vapor bubbles from the backside of the heated surface. The acquired images allow for instance the temporally resolved measurement of the bubble diameter, diameter of the bubble base and the contact angle. Exploiting the phase information of the acquired OCT signal stacks allows imaging the movement of the bubble surrounding fluid. We think that OCT will provide many new insights into the boiling phenomena at the bubble base. The recent enhancement of the acquisition rates of OCT systems will facilitate four-dimensional imaging of single bubble evaporation procedures in the nearer future.