An efficient reduced simulation of residual stresses in composite forming processes

An efficient simulation of thermal and mechanical models involved in thermosetting composites forming needs to overcome some numerical difficulties related to: (i) the multi-scale behaviour; (ii) the complex geometries involved needing too many degrees of freedom; (iii) the large time intervals where the solution has to be computed; (iv) the non-linearity of the involved evolution equations; (v) the numerous couplings… In this work, an efficient strategy based on a separated representation is proposed. This method enables to avoid the use of an incremental strategy and can lead to impressive computing time savings especially when the model involves fine meshes and very small time steps. The local non-linear chemical kinetics and its coupling with the global heat balance equation are naturally introduced in the separated representation algorithm. Moreover, the dependence of the thermal conductivity and the specific heat on the temperature and on the reaction advancement degree are also taken into account. Knowing the history of the temperature field, the separated representation is again used to solve the thermo-mechanical problem in order to determine the residual stresses.     

Effect of anodization voltage on the formation of phase pure anatase nanotubes with doped carbon

Carbon doped titania nanotubes were prepared by anodization of titanium in a fluoride containing ethylene glycol based electrolyte. Anatase crystallization temperature of the nanotubes varied with respect to anodization voltage. A detailed characterization study and mechanistic analysis of formation and stability of anatase phase of the nanotubes is reported. The findings suggest useful heat treatment parameters for obtaining pure anatase phases of the carbon doped titania nanotubes synthesized by anodization at 40 and 60 V.     

Dynamically loaded light-frame wood stud walls: experimental verification of an analytical model

Light-frame wood structures may deform well beyond the elastic limit when loaded by dynamic forces such as earthquakes and sea wave impacts. This paper reports the results of an investigation into the response effects of structural modeling assumptions typically made in the design of light-frame wood structures. Two dimensional and three dimensional models based on previous research were developed to simulate such responses and examine the validity of such models. The models utilize the finite-element method and include options of nonlinear connection properties, elastic constitutive laws of wood material, large deformations, contact forces, and inertial forces. The models were subjected to an estimate of the impact load imparted by a rapidly moving sea wave. To validate the models, the results of a wave-channel experiment of a full-scale wall were used wherein the wall was instrumented with reaction load cells, displacement transducers, and strain gauges on plywood sheathing and wood framing. A closed-loop hydraulic system utilizing a time varying loading function generated the wave trains. The resulting reactions, deformations, and strains were recorded as functions of time while high-speed cameras visually recorded the failure modes and wall behavior. Material tests were conducted before and after testing to record both the observed member properties and the localized section properties. Connection tests were conducted to provide the ultimate strengths for input in the finite element model. Reasonable agreement between the experimental and analytical results over the duration of the analysis depended on the model and model assumptions as well as the result of interest. The three dimensional model captured observed failure modes including rigid-body motions after connection failures and may reliably be used to analyze similar nonlinear systems loaded well beyond the elastic limit.     

Establishment of traceability for strain measuring data acquisition system in terms of voltage

This paper emphasizes on establishment of traceability for the strain measuring data acquisition system in terms of voltage. If this amplifier’s output voltage is not calibrated then traceability chain breaks. To complete the traceability chain, the amplifier’s output voltage has been calibrated for corresponding strain. The sensitivity is calculated using calibration results and further used to feed in data acquisition system to display the result in terms of force/strain.     

Design of Semi-composite Pressure Vessel using Fuzzy and FEM

The present study attempts to present a new method to design a semi-composite pressure vessel (known as hoop-wrapped composite cylinder) using fuzzy decision making and finite element method. A metal-composite vessel was designed based on ISO criteria and then the weight of the vessel was optimized for various fibers of carbon, glass and Kevlar in the cylindrical vessel. Failure criteria of von-Mises and Hoffman were respectively employed for the steel liner and the composite reinforcement to characterize the yielding/ buckling of the cylindrical pressure vessel. The fuzzy decision maker was used to estimate the thickness of the steel liner and the number of composite layers. The ratio of stresses on the composite fibers and the working pressure as well as the ratio of stresses on the composite fibers and the burst (failure) pressure were assessed. ANSYS nonlinear finite element solver was used to analyze the residual stress in the steel liner induced due to an auto-frettage process. Result of analysis verified that carbon fibers are the most suitable reinforcement to increase strength of cylinder while the weight stayed appreciably low.     

Optimal heat exchanger network synthesis using particle swarm optimization

Heat exchanger network (HEN) synthesis has been a well-studied subject over the past decades. Many studies and methodologies were proposed to make possible the energy recovery, minimizing the utilities consumption and the number of heat transfer equipment.     

Flow Rate Limitation of Steady Convective Dominated Open Capillary Channel Flows Through a Groove

An open capillary channel is a structure that establishes a liquid flow path when the capillary pressure caused by surface tension forces dominates in comparison to the hydrostatic pressure induced by gravitational or residual accelerations. To maintain a steady flow through the channel the capillary pressure of the free surface has to balance the pressure difference between the liquid and the surrounding constant pressure gas phase. Due to convective and viscous momentum transport the pressure along the flow path of the liquid decreases and causes the free surface to bend inwards. The maximum flow rate through the channel is reached when the free surface collapses and gas ingestion occurs near the outlet. This stability limit depends on the geometry of the channel and the properties of the liquid. In this paper we present an experimental setup which is used in the low-gravity environment of the Bremen Drop Tower. Experiments with convective dominated systems have been performed where the flow rate was increased up to the maximum value. In comparison to this we present a one-dimensional theoretical model to determine important characteristics of the flow, such as the free surface shape and the limiting flow rate. Furthermore we present an explanation for the mechanism of flow rate limitation for these flow conditions which is similar to the choking problem for compressible gas flows.     

Influence of Si:Al ratio on the microstructural and mechanical properties of a fine-limestone aggregate alkali-activated slag concrete

Three series of fine limestone aggregate, alkali-activated blast furnace slag (AAS) concretes were fabricated and tested; two through activation with waterglass/NaOH solution, of which one included NaCl as a retarding agent, and one activated by Na₂CO₃. Each of these series was made up of three formulae containing different amounts of Al₂O₃. The compressive strengths of the series activated by waterglass/NaOH after 28 days were ≈65 ± 5.3 MPa, a 22% increase compared to previously reported formulae containing no additional Al₂O₃. Increasing the amount of Al₂O₃ did not further increase strength, however. The Na₂CO₃-activated formulae had strengths of ≈35 ± 3 MPa after 28 days, representing no increase in strength over formulae not containing Al₂O₃ previously reported. X-ray diffraction showed the main binding phase to be calcium silicate hydrate (C–S–H) gel, as is commonly found in ordinary Portland cement (OPC). Fourier transform infrared spectroscopy showed little difference from the previously reported results for formulae not containing Al₂O₃ and strongly resemble the spectra reported elsewhere for C–S–H. Electron microscopy, coupled with energy dispersive spectroscopy, showed the cementing phase to be a single homogenous phase—not a mixed system of geopolymer and C–S–H gel—with a lower volume fraction of unreacted slag than formulae without Al₂O₃. The reason for the increase in strength of Al₂O₃-containing formulae is unclear, but is unlikely to be ascribed to the formation of large amounts of ‘geopolymers’ and may be related to a possible increase in reaction temperature of between 2 and 5°C, depending on amount of additive.     

Modeling Steady Acoustic Fields Bounded in Cavities with Geometrical Imperfections

A mathematical method is derived within the framework of classical Lagrangian field theory, which is suitable for the determination of the eigenstates of acoustic resonators of nearly spherical shape. The method is based on the expansion of the Helmholtz differential operator and the boundary condition in a power series of a small geometrical perturbation parameter e{epsilon} . The method extends to orders higher than e²{epsilon^2} the calculation of the perturbed acoustic eigenvalues, which was previously limited by the use of variational formalism and the methods of Morse and Ingard. A specific example is worked out for radial modes of a prolate spheroid, with the frequency perturbation calculated to order e³{epsilon^3} . A possible strategy to tackle the problem of calculating the acoustic eigenvalues for cavities presenting non-smooth geometrical imperfections is also described.     

Structural investigation of PEG-fibrinogen conjugates

Controllable bio-synthetic polymeric hydrogels made from fibrinogen-poly(ethylene glycol) adducts have been successfully employed in tissue engineering. The structural consequences of PEG conjugation to fibrinogen (i.e., PEGylation) in such a hydrogel network are not fully understood. The current investigation details the structural alterations caused to the reduced fibrinogen polypeptides by the covalent attachment of linear or branched PEG chains. The structure of PEGylated fibrinogen polypeptides were comprehensively characterized using small angle X-ray scattering, light scattering, and cryo-transmission electron microscopy. These characterizations concur that the bio-synthetic hybrids self-assemble into elongated objects, having a protein core of about 50 Å in diameter decorated with multiple PEG chains. Conjugates with branched PEG chains were shorter, and have lower average molecular weight compared to conjugates with linear chains. The diameter of the protein core of both samples was similar, suggesting a tail-to-head aggregation of the PEGylated fibrinogen polypeptide. A more complete understanding of this unique structural arrangement can provide further insight into the full extent of biofunctional accessibility in a biomaterial that combines the advantages of synthetic polymers with bioactive proteins.