Radiative deformation

An infinitesimal change δQδQ in heat flux Q is shown, in terms of entropy flux Ψ=Q/T,Ψ=Q/T, to have two parts, δQ=TδΨ+ΨδT.δQ=TδΨ+ΨδT. The first part being the thermal displacement and the second part being the thermal deformation. Only the second part dissipates into internal energy and generates entropy. Thermodynamic arguments are extended to transport phenomena. It is shown that the thermal part of the rate of local entropy generation is related to the local rate of thermal deformation by s′′′=−ψi/T(∂T/∂xi),s′′′=−ψi/T(∂T/∂xi), where ψi=qi/T,ψi=qi/T, ψiψi being the rate of entropy flux vector, and qiqi the rate of heat flux vector. The part of this generation related to radiation is illustrated in terms of an example. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70807/2/JAPIAU-87-6-3093-1.pd

Numerical investigations of planar solidification of an undercooled liquid

We investigate evolution of a planar interface during unstable solidification of a pure undercooled liquid between two parallel plates. The governing equations are solved using a front tracking/finite difference technique that allows discontinuous material properties between the phases and interfacial anisotropy. The simulations produce some of the futures of the dendritic solidification which are in good qualitative agreement with the works of the previous investigators. The effects of the physical parameters on the crystal growth and interface instability are also examined. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87387/2/629_1.pd

On interface dynamics

An intuitive study is presented for unstable interfacial waves. The maximum wavelength obtained for the most rapid unstable growth is shown to have a universal part which also characterizes the isotropic scales of buoyancy-driven turbulence. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70336/2/PHFLE6-12-5-1244-1.pd

Effects of curing conditions on crack bridging response of PVA reinforced cementitious matrix

The effect of the different curing conditions on the response of fiber crack bridging of PVAECC is studied. The self compacting PVA-ECC was cast into the moulds to produce four similar rectangular panels. These panels were kept under different curing conditions for 28 days. The tensile specimens were cut from these panels, and after executing a notch they were tested under tensile loading. The stress versus crack opening relationship for the specimens extracted from panels cured at different conditions is obtained, and the derived results are compared. The dispersion of results, the stress at crack initiation, the maximum fibers bridging stress and the corresponding crack opening, the absorbed energy and the fibers bridging stiffness are the investigated parameters. Also macroscopic images of the fibers in fracture surface are used to interpret the obtained data. As a result of this study a significant influence of different curing conditions on the fiber crack bridging response was observed

Hybrid Composite Plates (HCP) for shear strengthening of RC beams

The potential of a hybrid composite plate (HCP) for the strengthening of reinforced concrete (RC) deep beams is evaluated. HCP are composed of a CFRP sheet that is glued to the external surface of a thin plate made of strain hardening cementitious composite (SHCC). These panels were glued to the lateral faces of RC deep beams. Three groups of shear strengthened RC beams were tested under three-point bending load configuration. CFRP sheet, SHCC plate or HCP were individually applied to the lateral faces of shear deficiently reinforced beams to compare the effectiveness of these different strengthening schemes. The load-mid span deflections of these beams are compared to the response of the control beam. The maximum load carrying capacity and its corresponding mid-span deflection, crack pattern and the initial flexural stiffness are the studied parameters.Fundação para a Ciência e a Tecnologia (FCT

Measurement of depth-dose of linear accelerator and simulation by use of Geant4 computer code

AbstractRadiation therapy is an established method of cancer treatment. New technologies in cancer radiotherapy need a more accurate computation of the dose delivered in the radiotherapy treatment plan. This study presents some results of a Geant4-based application for simulation of the absorbed dose distribution given by a medical linear accelerator (LINAC). The LINAC geometry is accurately described in the Monte Carlo code with use of the accelerator manufacturer's specifications. The capability of the software for evaluating the dose distribution has been verified by comparisons with measurements in a water phantom; the comparisons were performed for percentage depth dose (PDD) and profiles for various field sizes and depths, for a 6-MV electron beam. Experimental and calculated dose values were in good agreement both in PDD and in transverse sections of the water phantom

Materiais de matriz cimentícia de elevado desempenho para o reforço estrutural

No presente trabalho avaliam-se as potencialidades de materiais com endurecimento em tração (designados na bibliografia inglesa por “Strain Hardening Cement Composites-SHCC”) no reforço à flexão de estruturas com comportamento frágil, e no reforço ao corte de vigas de betão armado (BA). No reforço à flexão foi aplicada uma camada de SHCC, de 15 e 20 mm de espessura, na face de tração de vigas de alvenaria formadas por tijolos maciços de argila ligados por argamassa de baixa resistência, tendo-se constatado que esta técnica de reforço, de fácil e rápida execução, permite aumentar significativamente, quer a capacidade de carga como a deformabilidade deste tipo de elementos estruturais. Para o reforço ao corte de vigas de BA foram pré-fabricados painéis de SHCC de 18 mm de espessura, os quais foram aplicados nas faces laterais das vigas a reforçar por intermédio de adesivo epóxi. Um dos grupos de vigas foi reforçado aplicando nas suas faces laterais manta de fibras de carbono (CFRP) segundo a técnica “Externally Bonded Reinforcement-EBR”, sobre a qual foi aplicado o tipo de painel de SHCC anteriormente referido, recorrendo a adesivo epóxi. Os resultados dos ensaios demonstraram que ambas as técnicas, somente com painel de SHCC, e com SHCC mais manta de CFRP, permitem aumentar significativamente a rigidez e a capacidade de carga de vigas de BA, em especial neste último caso, em resultado da adequada sinergia de efeitos dos materiais envolvidos.In the present work the potentialities of strain hardening cement composites (SHCC) are assessed for the flexural strengthening of brittle structural elements, as well as for the shear strengthening of reinforced concrete (RC) beams. For the flexural strengthening, masonry beams, formed by massive clay bricks bonded by low strength mortar, were strengthened with a layer of SHCC of 15 or 20 mm thickness applied in the tensile surface of these beams. The results have evidenced the possibility of increasing significantly the load carrying capacity and the deformability of this quite brittle type of structural elements. For the shear strengthening of RC beams it was explored the potentialities of applying prefabricated panels of 18 mm thickness on the lateral faces of the beams. In one of the groups of beams, a sheet of carbon fibre reinforced polymer (CFRP) was combined with the SHCC. The results demonstrated the capacity of these techniques to increase the load carrying capacity and the stiffness of RC beams failing in shear, mainly when SHCC is combined with CFRP, due to the favorable synergy effect of the ductile character of SHCC and the high tensile strength and elasticity modulus of CFRP.Fundação para a Ciência e a Tecnologia (FCT

Strain hardening fiber reinforced cement composites for the flexural strengthening of masonry elements of ancient structures

To assess the strengthening ability of a strain hardening cementitious composite (SHCC), a layer of SHCC was applied to masonry beams subjected to bending. When compared to the strengthening performance of steel fibre reinforced self-compacting concrete (SFRSCC) layer for this type of brittle beams, the SHCC presented better workability in fresh state, and provided a higher load carrying capacity and deflection ductility even with a smaller layer thickness. By using the data derived from the experimental tests with the constituent materials of the strengthened masonry beams, the behaviour of the tested strengthened masonry beams was numerically simulated with good accuracy.The study presented in this paper is a part of the research Project titled "PrePam - Pre-fabricated thin panels using advanced materials for structural rehabilitation" with reference number of PTDC/ECM/114511/2009 supported by FCT. It is also conducted as part of the MSC-SAHC Master's program supported by the European Commission. The authors also thank the collaboration of the following companies: Sika for providing the sand, Grace for the superplasticizers, Dow for the viscosity modification agents, ENDE-SA Compostilla power station for the fly ash, and SECIL for supplying the cement. The first author acknowledge the PhD grant SFRH/BD/65663/2009 provided by FCT

Development of hybrid composite plate (HCP) for the repair and strengthening of RC elements

Hybrid Composite Plates (HCPs) made of a Strain Hardening Cementitious Composite (SHCC) and reinforced with Carbon Fiber Reinforced Polymer (CFRP) materials are developed by taking the synergetic advantages of SHCC and CFRP for the retrofitting of reinforced concrete (RC) structures. Thanks to the high ductile character of SHCC, this prefabricated plate can be attached to the substrate using a combination of adhesive and chemical anchors to assure an effective transference of forces between these elements, leading to a high mobilization of the tensile capacity of the CFRP. This paper reports the most relevant results of a series of experimental tests performed to assess the effectiveness of this innovative technique for the repair/strengthening of RC elements. Enhancements obtained in both shear and flexural capacity of strengthened RC beams, in shear capacity of a repaired RC beam, as well as in the repair of a severely damaged interior RC beam-column joint, have demonstrated the high effectiveness of this technique.Fundação para a Ciência e a Tecnologia (FCT

Flexural strengthening of masonry members using advanced cementitious materials

Two different cement based fiber reinforced composites for the flexural strengthening of masonry beams under monotonic loading are studied. Steel Fiber Reinforced Self- Compacting Concrete (SFRSCC) with tensile strain-softening behavior, and PVA fiber reinforced cement based mortar (SHCC) with tensile Strain-Hardening were the developed composites. Both composites were applied on the tensile surface of masonry beams and the effectiveness of this technique for the flexural strengthening of these quasi-brittle structural elements was assessed by performing four point beam bending tests. Both materials contributed effectively to increase the load carrying capacity and ultimate deflection ductility of the tested masonry beams, but, higher average values were obtained for these two indicators of the strengthening effectiveness when using a layer thickness of SHCC that is 2/3 of the thickness of SFRSCC. Furthermore, much more homogenous results, in terms of forcedeflection relationship, were obtained with masonry beams strengthened with SHCC than with SFRSCC