The Si_(3)N_(4)/SiC gradient material with a gradient composition structure was prepared by a hot pressing sintering.The sinterability,distribution of residual stress and the effect of residual stress on mechanical pr...The Si_(3)N_(4)/SiC gradient material with a gradient composition structure was prepared by a hot pressing sintering.The sinterability,distribution of residual stress and the effect of residual stress on mechanical properties of Si_(3)N_(4)/SiC gradient materials were studied.The research results show that,at 1750℃,Si_(3)N_(4)/SiC gradient materials with different ratios can achieve co-sintering,and the overall relative density of the sample reaches 98.5%.Interestingly,the flexural strength of Si_(3)N_(4)/SiC gradient material is related to its loading surface.The flexural strength of SiC as the loading surface is about 35%higher than that of Si_(3)N_(4)as the loading surface.The analysis of the residual stress of the material in the gradient structure shows that the gradient stress distribution between the two phases is a vital factor affecting the mechanical properties of the material.With the increase of SiC content in the gradient direction,the fracture toughness of each layer of Si_(3)N_(4)/SiC gradient materials gradually decreases.The surface hardness of the pure SiC side is lower than that reported in other literature.展开更多
Quantitative damage identification of surrounding rock is important to assess the current condition and residual strength of underground tunnels.In this work,an underground tunnel model with marble-like cementitious m...Quantitative damage identification of surrounding rock is important to assess the current condition and residual strength of underground tunnels.In this work,an underground tunnel model with marble-like cementitious materials was first fabricated using the three-dimensional(3D)printing technique and then loaded to simulate its failure mode in the laboratory.Lead zirconate titanate piezoelectric(PZT)transducers were embedded in the surrounding rock around the tunnel in the process of 3D printing.A 3D monitoring network was formed to locate damage areas and evaluate damage extent during loading.Results show that as the load increased,main cracks firstly appeared above the tunnel roof and below the floor,and then they coalesced into the tunnel boundary.Finally,the tunnel model was broken into several parts.The resonant frequency and the peak of the conductance signature firstly shifted rightwards with loading due to the sealing of microcracks,and then shifted backwards after new cracks appeared.An overall increase in the root-mean-square deviation(RMSD)calculated from conductance signatures of all the PZT transducers was observed as the load(damage)increased.Damage-dependent equivalent stiffness parameters(ESPs)were calculated from the real and imaginary signatures of each PZT at different damage states.Satisfactory agreement between equivalent and experimental ESP values was achieved.Also,the relationship between the change of the ESP and the residual strength was obtained.The method paves the way for damage identification and residual strength estimation of other 3D printed structures in civil engineering.展开更多
To investigate the impact of dietary supplementation of different omega-3 polyunsaturated fatty acids (n-3 PUFAs) resources on PUFAs enrichment in hen eggs, two supplemental materials, flaxseed and oil-extracted micro...To investigate the impact of dietary supplementation of different omega-3 polyunsaturated fatty acids (n-3 PUFAs) resources on PUFAs enrichment in hen eggs, two supplemental materials, flaxseed and oil-extracted microalgal residue of heterotrophic Schizochytrium, were added to the diet of laying hens in 3 groups. Results showed that supplementation with flaxseed and Schizochytrium residue gave rise to the increased, but different n-3 PUFAs levels in egg yolk, mainly α-linolenic acid (ALA) and docosahexaenoic acid (DHA). The ratio of n-6/n-3 PUFAs was reduced in all groups. After 14 days feeding of supplied PUFAs resources, n-3 PUFAs contents reached a plateau, and then remained constant during further supplementation in 3 experimental groups. Both the highest ALA level and DHA level were achieved in flaxseed group and microalgae group, reaching up to 353.69 (±68.15) mg/egg and 301.41 (± 26.76) mg/egg respectively. Moreover, the n-3 PUFAs enrichment efficiency was relatively low in flaxseed group when compared to other 2 groups. Laying rates of hens before entering peak production period could be improved by adding flaxseed but was not obviously affected by Schizochytrium residue. The egg weight, on the other hand, had no relationship with dietary supplementation. Thus, supplementation of flaxseed or Schizochytrium residue into standard feed offers an alternative choice for the production of n-3 PUFAs enriched eggs.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.43190311,43200301 and 631800611)。
文摘The Si_(3)N_(4)/SiC gradient material with a gradient composition structure was prepared by a hot pressing sintering.The sinterability,distribution of residual stress and the effect of residual stress on mechanical properties of Si_(3)N_(4)/SiC gradient materials were studied.The research results show that,at 1750℃,Si_(3)N_(4)/SiC gradient materials with different ratios can achieve co-sintering,and the overall relative density of the sample reaches 98.5%.Interestingly,the flexural strength of Si_(3)N_(4)/SiC gradient material is related to its loading surface.The flexural strength of SiC as the loading surface is about 35%higher than that of Si_(3)N_(4)as the loading surface.The analysis of the residual stress of the material in the gradient structure shows that the gradient stress distribution between the two phases is a vital factor affecting the mechanical properties of the material.With the increase of SiC content in the gradient direction,the fracture toughness of each layer of Si_(3)N_(4)/SiC gradient materials gradually decreases.The surface hardness of the pure SiC side is lower than that reported in other literature.
基金The study is financially supported by the National Major Research Instrument Development Project of the National Natural Science Foundation of China(Grant No.51627812)the National Natural Science Foundation of China(Grant No.52078181)the Natural Science Foundation of Hebei Province,China(Grant No.E2019202484)。
文摘Quantitative damage identification of surrounding rock is important to assess the current condition and residual strength of underground tunnels.In this work,an underground tunnel model with marble-like cementitious materials was first fabricated using the three-dimensional(3D)printing technique and then loaded to simulate its failure mode in the laboratory.Lead zirconate titanate piezoelectric(PZT)transducers were embedded in the surrounding rock around the tunnel in the process of 3D printing.A 3D monitoring network was formed to locate damage areas and evaluate damage extent during loading.Results show that as the load increased,main cracks firstly appeared above the tunnel roof and below the floor,and then they coalesced into the tunnel boundary.Finally,the tunnel model was broken into several parts.The resonant frequency and the peak of the conductance signature firstly shifted rightwards with loading due to the sealing of microcracks,and then shifted backwards after new cracks appeared.An overall increase in the root-mean-square deviation(RMSD)calculated from conductance signatures of all the PZT transducers was observed as the load(damage)increased.Damage-dependent equivalent stiffness parameters(ESPs)were calculated from the real and imaginary signatures of each PZT at different damage states.Satisfactory agreement between equivalent and experimental ESP values was achieved.Also,the relationship between the change of the ESP and the residual strength was obtained.The method paves the way for damage identification and residual strength estimation of other 3D printed structures in civil engineering.
文摘To investigate the impact of dietary supplementation of different omega-3 polyunsaturated fatty acids (n-3 PUFAs) resources on PUFAs enrichment in hen eggs, two supplemental materials, flaxseed and oil-extracted microalgal residue of heterotrophic Schizochytrium, were added to the diet of laying hens in 3 groups. Results showed that supplementation with flaxseed and Schizochytrium residue gave rise to the increased, but different n-3 PUFAs levels in egg yolk, mainly α-linolenic acid (ALA) and docosahexaenoic acid (DHA). The ratio of n-6/n-3 PUFAs was reduced in all groups. After 14 days feeding of supplied PUFAs resources, n-3 PUFAs contents reached a plateau, and then remained constant during further supplementation in 3 experimental groups. Both the highest ALA level and DHA level were achieved in flaxseed group and microalgae group, reaching up to 353.69 (±68.15) mg/egg and 301.41 (± 26.76) mg/egg respectively. Moreover, the n-3 PUFAs enrichment efficiency was relatively low in flaxseed group when compared to other 2 groups. Laying rates of hens before entering peak production period could be improved by adding flaxseed but was not obviously affected by Schizochytrium residue. The egg weight, on the other hand, had no relationship with dietary supplementation. Thus, supplementation of flaxseed or Schizochytrium residue into standard feed offers an alternative choice for the production of n-3 PUFAs enriched eggs.
