Investigation of micro-scale shear response of sand–rubber granule mixture in terms of particle shape and grain scale deformability effects

In this study,the effects of particle shape of rigid sand and soft rubber materials on macro-scale shear response were reasoned based on micro-scale parameters.For this purpose,first,the shape properties of three different sand and two different rubber samples were quantified using image processing techniques,and the contact model parameters were calibrated through physical experiments.The direct shear test was simulated in a two-dimensional discrete element software with realistic particle forms.The soft nature of rubber particles was reflected using body-centered cubic packing with a linear-parallel bond contact model.As a result,coordination number,distribution of contact forces(i.e.,strong contact,and fabric anisotropy),and contact sliding were derived by the numerical analyses.It has been observed that the particle shape leads to distinctive micro-scale responses due to the variations in the stiffness of the contacts.

Effect of mechanical degradation of laminated elastomeric bearings and shear keys upon seismic behaviors of small-to-medium-span highway bridges in transverse direction

Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations（PGA）. The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.

Elastic strain response in the modified phase-field-crystal model

To understand and develop new nanostructure materials with specific mechanical properties, a good knowledge of the elastic strain response is mandatory. Here we investigate the linear elasticity response in the modified phase-field-crystal（MPFC） model. The results show that two different propagation modes control the elastic interaction length and time, which determine whether the density waves can propagate or not. By quantitatively calculating the strain field, we find that the strain distribution is indeed extremely uniform in case of elasticity. Further, we present a detailed theoretical analysis for the orientation dependence and temperature dependence of shear modulus. The simulation results show that the shear modulus reveals strong anisotropy and the one-mode analysis provides a good guideline for determining elastic shear constants until the system temperature falls below a certain value.

Supramolecular Semi-convertible Hydrogel Enabled Self-Healing Responsive Lubrication Under Dynamic Shearing

Cartilage-inspired hydrogel has attracted great interest due to its tunable mechanics and low friction.However,it is incapable of self-healing under a complex dynamic shearing environment.In this work,a self-healing semi-convertible hydrogel(SHSCH)is developed,which can recover its unique active lubricating function under shearing.Based on the cooperating strategy of noncovalent and covalent bonding,the SHSCH is composed of three interpenetrated networks including:(1)shearresponsive N-fluorenylmethoxycarbonyl-L-tryptophan(FT)supramolecular network,(2)self-healing polyhydroxyethyl acrylamide(PHEAA)network,and(3)rigid polyvinyl alcohol(PVA)covalent network.The shearresponsive lubricating function and mechanical property can be self-healed under a shearing environment through the noncovalent hydrogen-bonding assembly of PHEAA associated by theπ–πassembly of FT.The asdeveloped SCH provides a self-healing model comparable with traditional self-healing lubricating materials through encapsulating lubricant microcapsules or infusing lubricants onto surfaces.We demonstrated a proofof-concept of the self-healing lubrication of a simplified artificial worn cartilage model under a dynamic shearing condition.This study will offer a potential strategy on designing the self-healing soft devices under dynamic stimuli far beyond the lubricating materials.

Recent developments in seismically isolated buildings in Japan

The Building Standard Law of Japan and related Enforcement Order and Notifications have been substantially revised since the year 2000 to introduce a performance-based regulatory and deregulation system for building control systems. Up to then,time-history analyses were mandatory for isolated buildings and had to be specially approved by the Minster of the Ministry of Construction (MOC).Simplified design procedures based on the equivalent linear method for seismically isolated buildings have been issued as'Notification 2009-Structnral calculation procedure for buildings with seismic isolation'from MOC,and are now integrated into the Ministry of Land,Infrastructure,and Transportation (MLIT).Along with Notification 2009,'Notification 1446 of year 2000-Standard for specifications and test methods for seismic isolation devices'was also issued.Buildings with heights equal to or less than 60m and that are designed according to these Notifications,including base isolated buildings,only need approval from local building officials,and no longer require the special approval of the Minister of MLIT.This paper summarizes:1) some statistics related to buildings with seismic isolation completed up to the end of 2001; 2) simplified design procedures required by Notification 2009 of year 2000;and 3) performance of seismic isolation devices required by Notification 1446 of year 2000.