A particle breakage has a significant impact on the mechanical behavior of granular materials. In this paper, we present an elasto-plastic model with two yield surfaces to which the influence of particle breakage has ...A particle breakage has a significant impact on the mechanical behavior of granular materials. In this paper, we present an elasto-plastic model with two yield surfaces to which the influence of particle breakage has been introduced. The main feature of this model is to incorporate the change in the critical state line (CSL) consequent to the grain breakage induced by isotropic and deviatoric stresses during loading. For this purpose we propose a breakage function which connects the evolution of the CSL to the energy consumed. Results from earlier studies on drained and undrained compression and extension triaxial tests were used to calibrate and validate the model. Comparison between earlier results and our simulations indicates that the model can reproduce with good accuracy the mechanical behavior of crushable granular materials and predict the evolution of the grain size distribution during loading.展开更多
Bone tissue regeneration in critical-size defects is possible after implantation of a 3D scaffold and can be additionally enhanced once the scaffold is enriched with drugs or other factors supporting bone remodelling ...Bone tissue regeneration in critical-size defects is possible after implantation of a 3D scaffold and can be additionally enhanced once the scaffold is enriched with drugs or other factors supporting bone remodelling and healing.Sodium alendronate(Aln),a widely used anti-osteoporosis drug,exhibits strong inhibitory effect on bone resorption performed by osteoclasts.Thus,we propose a new approach for the treatment of bone defects in craniofacial region combining biocompatible titanium dioxide scaffolds and poly(L-lactide-co-glycolide)microparticles(MPs)loaded with Aln.The MPs were effectively attached to the surface of the scaffolds’pore walls by human recombinant collagen.Drug release from the scaffolds was characterized by initial burst(2466% of the drug released within first 24 h)followed by a sustained release phase(on average 5 mg of Aln released per day from Day 3 to Day 18).In vitro tests evidenced that Aln at concentrations of 5 and 2.5 mg/ml was not cytotoxic for MG-63 osteoblast-like cells(viability between 8166% and 9863% of control),but it prevented RANKL-induced formation of osteoclast-like cells from macrophages derived from peripheral blood mononuclear cells,as shown by reduced fusion capability and decreased tartrateresistant acid phosphatase 5b activity(5665% reduction in comparison to control after 8 days of culture).Results show that it is feasible to design the scaffolds providing required doses of Aln inhibiting osteoclastogenesis,reducing osteoclast activity,but not affecting osteoblast functions,which may be beneficial in the treatment of critical-size bone tissue defects.展开更多
Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils shou...Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils should exist,below which there is a high risk of soil clogging in shield tunneling.To determine the critical particle size,a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents.It was found that the tangential adhesion strength at the soilesteel interface gradually increased linearly with applied normal pressure.When the particle size of the soil specimen was less than 0.15 mm,the interfacial adhesion force first increased and then decreased as the water content gradually increased;otherwise,the soil specimens did not manifest any interfacial adhesion force.The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force,thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling.The critical particle size of soils causing clogging was determined to be 0.15 mm.Finally,the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.展开更多
The equation of phase equilibria in nano-sized crystal of metals has been established in terms of thermodynamic equilibrium. The thermodynamic parameters are calculated and the critical grain size for the stable high-...The equation of phase equilibria in nano-sized crystal of metals has been established in terms of thermodynamic equilibrium. The thermodynamic parameters are calculated and the critical grain size for the stable high-temperature phase at room temperature is obtained. As an example, the critical grain size of β-Co at room temperature is determined at 35nm when the excess volume is 10%. The result agrees well with the experiment of Katakimi et al. The factors affecting the stability of β-Co are also discussed.展开更多
文摘A particle breakage has a significant impact on the mechanical behavior of granular materials. In this paper, we present an elasto-plastic model with two yield surfaces to which the influence of particle breakage has been introduced. The main feature of this model is to incorporate the change in the critical state line (CSL) consequent to the grain breakage induced by isotropic and deviatoric stresses during loading. For this purpose we propose a breakage function which connects the evolution of the CSL to the energy consumed. Results from earlier studies on drained and undrained compression and extension triaxial tests were used to calibrate and validate the model. Comparison between earlier results and our simulations indicates that the model can reproduce with good accuracy the mechanical behavior of crushable granular materials and predict the evolution of the grain size distribution during loading.
基金supported by National Science Centre,Poland(2013/09/N/ST8/00309)Norwegian Research Council(228415)BMBF,Germany(GoBone German-Polish bilateral project 01DS16010A).
文摘Bone tissue regeneration in critical-size defects is possible after implantation of a 3D scaffold and can be additionally enhanced once the scaffold is enriched with drugs or other factors supporting bone remodelling and healing.Sodium alendronate(Aln),a widely used anti-osteoporosis drug,exhibits strong inhibitory effect on bone resorption performed by osteoclasts.Thus,we propose a new approach for the treatment of bone defects in craniofacial region combining biocompatible titanium dioxide scaffolds and poly(L-lactide-co-glycolide)microparticles(MPs)loaded with Aln.The MPs were effectively attached to the surface of the scaffolds’pore walls by human recombinant collagen.Drug release from the scaffolds was characterized by initial burst(2466% of the drug released within first 24 h)followed by a sustained release phase(on average 5 mg of Aln released per day from Day 3 to Day 18).In vitro tests evidenced that Aln at concentrations of 5 and 2.5 mg/ml was not cytotoxic for MG-63 osteoblast-like cells(viability between 8166% and 9863% of control),but it prevented RANKL-induced formation of osteoclast-like cells from macrophages derived from peripheral blood mononuclear cells,as shown by reduced fusion capability and decreased tartrateresistant acid phosphatase 5b activity(5665% reduction in comparison to control after 8 days of culture).Results show that it is feasible to design the scaffolds providing required doses of Aln inhibiting osteoclastogenesis,reducing osteoclast activity,but not affecting osteoblast functions,which may be beneficial in the treatment of critical-size bone tissue defects.
基金The financial support from the National Natural Science Foun-dation of China(Grant Nos.52022112 and 51778637)the Sci-ence and Technology Innovation Program of Hunan Province(Grant No.2021RC3015)are acknowledged and appreciated.
文摘Shield tunneling is easily obstructed by clogging in clayey strata with small soil particles.However,soil clogging rarely occurs in strata with coarse-grained soils.Theoretically,a critical particle size of soils should exist,below which there is a high risk of soil clogging in shield tunneling.To determine the critical particle size,a series of laboratory tests was carried out with a large-scale rotary shear apparatus to measure the tangential adhesion strength of soils with different particle sizes and water contents.It was found that the tangential adhesion strength at the soilesteel interface gradually increased linearly with applied normal pressure.When the particle size of the soil specimen was less than 0.15 mm,the interfacial adhesion force first increased and then decreased as the water content gradually increased;otherwise,the soil specimens did not manifest any interfacial adhesion force.The amount of soil mass adhering to the steel disc was positively correlated with the interfacial adhesion force,thus the interfacial adhesion force was adopted to characterize the soil clogging risk in shield tunneling.The critical particle size of soils causing clogging was determined to be 0.15 mm.Finally,the generation mechanism of interfacial adhesion force was explored for soils with different particle sizes to explain the critical particle size of soil with clogging risk in shield tunneling.
基金This work was supported by the National Natural Science Foundation of China (Grand No. 59971029).
文摘The equation of phase equilibria in nano-sized crystal of metals has been established in terms of thermodynamic equilibrium. The thermodynamic parameters are calculated and the critical grain size for the stable high-temperature phase at room temperature is obtained. As an example, the critical grain size of β-Co at room temperature is determined at 35nm when the excess volume is 10%. The result agrees well with the experiment of Katakimi et al. The factors affecting the stability of β-Co are also discussed.
