非饱和砂浆氯离子传输与pH分布相关性研究

研究了非饱和砂浆在氯盐溶液中持续浸泡、干湿循环作用下的氯离子传输和pH分布,并考虑了碳化作用对氯离子传输的影响,重点分析了氯离子传输与pH分布的相关性。研究结果表明:干燥砂浆在NaCl溶液中持续浸泡不同时间后,氯离子浓度分布与pH分布没有表现出明显的相关性;然而,在干湿循环作用下,非饱和砂浆的氯离子传输与pH分布密切相关,砂浆近表层氯离子浓度的减小与pH下降具有一致性;非饱和预碳化砂浆经干湿循环之后的氯离子浓度分布与pH分布具有相同的特征,均呈"S"型,碳化作用使砂浆的pH分布发生改变,进而影响了氯离子传输行为。

Globularization Mechanism and Near Isotropic Properties in Subcritical Heat‑Treated Ti6Al4V Fabricated by Directed Energy Deposition

Microstructure with globularαphase is desirable as it contributes to preferable comprehensive mechanical properties for titanium alloys.However,titanium alloys fabricated by directed energy deposition(DED)are mainly characterized by the lamellarαphase within the basket-weave microstructure,which often leads to severe anisotropy and inferior low cycle fatigue(LCF)properties.To address this,the subcritical annealing and the cyclic annealing were applied to DED Ti–6Al–4V in order to achieve the transformation from the lamellarαphase to the globularαphase.The microstructural characteristics and the globularization behavior ofαphase during heat treatment were investigated.The results show that the aspect ratio ofαis significantly decreased with the subcritical annealing due to the coarsening of lamellarα.Furthermore,the globularαis obtained with the cyclic annealing as a combination result of the termination dissolution and the side surface growth of the lamellarα.These contribute to a pronounced reduction of 85.4%in the ductility anisotropy,compared with the as-built specimens,and superior comprehensive mechanical properties including LCF are achieved with the formation of globularα.

Analysis of Bone Remodeling Under Piezoelectricity Effects Using Boundary Elements

Piezoelectric materials exhibit a response to mechanical-electrical coupling, which represents an important contribution to the electrical-mechanical interaction in bone remodeling process. Therefore, the study of the piezoelectric effect on bone re- modeling has high interest in applied biomechanics. The effects of mechano-regulation and electrical stimulation on bone healing are explained. The Boundary Element Method （BEM） is used to simulate piezoelectric effects on bones when shearing forces are applied to collagen fibers to make them slip past each other. The piezoelectric fundamental solutions are obtained by using the Radon transform. The Dual Reciprocity Method （DRM） is used to simulate the particular solutions in time-dependent problems. BEM analysis showed the strong influence of electrical stimulation on bone remodeling. The examples discussed in this work showed that, as expected, the electrically loaded bone surfaces improved the bone deposition. BEM results confirmed previous findings obtained by using the Finite Element Method （FEM）. This work opens very promising doors in biomechanics research, showing that mechanical loads can be replaced, in part, by electrical charges that stimulate strengthening bone density. The obtained results herein are in good agreement with those found in literature from experimental testing and/or other simu- lation approaches.

A Preconditioned Implicit Free-Surface Capture Scheme for Large Density Ratio on Tetrahedral Grids

We present a three dimensional preconditioned implicit free-surface capture scheme on tetrahedral grids.The current scheme improves our recently reported method[10]in several aspects.Specifically,we modified the original eigensystem by applying a preconditioning matrix so that the new eigensystem is virtually independent of density ratio,which is typically large for practical two-phase problems.Further,we replaced the explicit multi-stage Runge-Kutta method by a fully implicit Euler integration scheme for the Navier-Stokes(NS)solver and the Volume of Fluids(VOF)equation is now solved with a second order Crank-Nicolson implicit scheme to reduce the numerical diffusion effect.The preconditioned restarted GeneralizedMinimal RESidual method(GMRES)is then employed to solve the resulting linear system.The validation studies show that with these modifications,the method has improved stability and accuracy when dealing with large density ratio two-phase problems.

Drag reduction via turbulent boundary layer flow control

Turbulent boundary layer control(TBLC) for skin-friction drag reduction is a relatively new technology made possible through the advances in computational-simulation capabilities,which have improved the understanding of the flow structures of turbulence.Advances in micro-electronic technology have enabled the fabrication of active device systems able to manipulating these structures.The combination of simulation,understanding and micro-actuation technologies offers new opportunities to significantly decrease drag,and by doing so,to increase fuel efficiency of future aircraft.The literature review that follows shows that the application of active control turbulent skin-friction drag reduction is considered of prime importance by industry,even though it is still at a low technology readiness level(TRL).This review presents the state of the art of different technologies oriented to the active and passive control for turbulent skin-friction drag reduction and contributes to the improvement of these technologies.