PLASTIC LIMIT ANALYSIS OF DUCTILE COMPOSITE STRUCTURES FROM MICRO-TO MACRO-MECHANICAL ANALYSIS

The load-bearing capacity of ductile composite structures comprised of periodic composites is studied by a combined micro/macromechanicai approach. Firstly, on the microscopic level, a representative volume element （RVE） is selected to reflect the microstructures of the composite materials and the constituents are assumed to be elastic perfectly-plastic. Based on the homogenization theory and the static limit theorem, an optimization formulation to directly calculate the macroscopic strength domain of the RVE is obtained. The finite element modeling of the static limit analysis is formulated as a nonlinear mathematical programming and solved by the sequential quadratic programming method, where the temperature parameter method is used to construct the self-stress field. Secondly, Hill＇s yield criterion is adopted to connect the micromechanicai and macromechanical analyses. And the limit loads of composite structures are worked out on the macroscopic scale. Finally, some examples and comparisons are shown.

Modeling cochlear micromechanics: hypotheses and models

The cochlea plays an important role in the mammalian auditory system.Sound-induced cell motion in the cochlea is transformed into electrical signals that are then sent to primary auditory neurons.The most significant feature of the cochlea is the active and nonlinear amplification of faint sounds.This active process cannot be explained via a simple hydromechanical representation of the cochlea,that is,a macromechanic explanation.Although the mechanisms of this amplification are not well understood,cochlear micromechanical behavior is thought to play a significant role.The measurement of in vivo cochlea micromechanical responses is challenging and restricted by technical limitations.Modeling the micromechanics of the cochlea,however,can facilitate the interpretation of experimental observations.In this paper,we reviewed studies in which researchers modeled the cochlear micromechanics,and we discussed various modeling hypotheses,outcomes,and expectations.

Effects of a polyamine inhibitor on the microstructure and macromechanical properties of hydrated shale

China is rich in shale gas resources,however,wellbores in shale gas reservoirs are frequently unstable.This has a serious impact on the shale gas drilling cycle.Polyamine,a common additive in water-based shale drilling fluids,can effectively inhibit shale hydration.However,there is a lack of quantitative research on the effect of polyamine inhibitors on the microstructure and macromechanical properties of shale.Therefore,this study investigated those issues via a systematic hydration experiment carried out on shale from the Longmaxi Formation.The results show that microfractures are created and expand during shale hydration,that they also connect to form a complex microfracture network,and that 3%polyamine inhibitors(polyamine solution with volume fraction of 3%)can effectively inhibit their evolution.The ultrasonic velocities and UCS of the Longmaxi shale are significantly anisotropic;the former first increases and then decreases with the laminae angle,reaching its maximum when the laminae angle is 30°.The UCS of the shale is highest and lowest,respectively,when the laminae angles are 0°or 90°and 30°.In general,these UCS appear as a"U"pattern,high on two sides with a dip in the center.Polyamines can effectively inhibit both the expansion of shale and the reduction of P-wave and S-wave velocities,the UCS,and elastic modulus.The UCS of a shale sample was reduced by 28%e40%after immersion for 96 h in water,compared to 2%e20%after immersion in a 3%polyamine inhibitor for the same amount of time.The inhibiting effect of the polyamine was remarkable.