S. Lech, W. Polkowski, A. Polkowska, G. Cempura, A. Kruk
Abstract Ni-Fe-Cr-Al alloy has been subjected to 2 hours aging treatment between 600-900°C, which influenced the mechanical properties and resulted in discontinuous precipitation at the grain boundaries. In this study, SEM, TEM and STEM-EDXS were applied to explore the relationship between the occurring grain boundary precipitation phenomena and mechanical behavior. Within the discontinuous precipitation zone, three different phases were recognized, namely γ solid solution with lamellar M23C6 carbides and elongated γ’ precipitates at the reaction front. Coherency of the discontinuous precipitates was identified as they have shown a cube-on-cube orientation relationship. Furthermore, the development of multiple discontinuous reactions was discussed.
{"title":"Multimodal Discontinuous Rection in Ni-Fe-Cr-Al Alloy","authors":"S. Lech, W. Polkowski, A. Polkowska, G. Cempura, A. Kruk","doi":"10.2139/ssrn.3708722","DOIUrl":"https://doi.org/10.2139/ssrn.3708722","url":null,"abstract":"Abstract Ni-Fe-Cr-Al alloy has been subjected to 2 hours aging treatment between 600-900°C, which influenced the mechanical properties and resulted in discontinuous precipitation at the grain boundaries. In this study, SEM, TEM and STEM-EDXS were applied to explore the relationship between the occurring grain boundary precipitation phenomena and mechanical behavior. Within the discontinuous precipitation zone, three different phases were recognized, namely γ solid solution with lamellar M23C6 carbides and elongated γ’ precipitates at the reaction front. Coherency of the discontinuous precipitates was identified as they have shown a cube-on-cube orientation relationship. Furthermore, the development of multiple discontinuous reactions was discussed.","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"511 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78145125","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Sharma, P. Singh, T. Kirk, V. Levitas, P. Liaw, G. Balasubramanian, R. Arróyave, Duane D. Johnson
Phase diagrams supported by density functional theory methods can be crucial for designing high-entropy alloys (HEAs). We present phase and property analysis of refractory quinary (MoW)xZry(TaTi)1-x-y HEAs from combined Calculation of Phase Diagram (CALPHAD) and density-functional theory results, supplemented by molecular dynamics (MD) simulations. Our analysis indicates a Mo-W-rich region of this quinary system has a stable single-phase body-centered-cubic (bcc). The (MoW)85Zr7.5(TaTi)7.5 was down-selected based on temperature-dependent CALPHAD phase diagram analysis and MD predicted elastic behavior that reveals twinning-assisted pseudoelastic behavior in this refractory HEA. While mostly unexplored in bcc crystals, twinning is a fundamental deformation mechanism that competes against dislocation slip in crystalline solids. This alloy shows identical cyclic deformation characteristics during uniaxial <100> loading, i.e., the pseudoelasticity is isotropic in loading direction. Additionally, a temperature increase from 77 to 1,500 K enhances the elastic strain recovery in load-unload cycles, offering possibly control to tune the pseudoelastic behavior.
{"title":"Pseudoelastic Deformation in Refractory (MoW) 85 Zr 7.5(TaTi) 7.5 High-Entropy Alloy","authors":"A. Sharma, P. Singh, T. Kirk, V. Levitas, P. Liaw, G. Balasubramanian, R. Arróyave, Duane D. Johnson","doi":"10.2139/ssrn.3802817","DOIUrl":"https://doi.org/10.2139/ssrn.3802817","url":null,"abstract":"Phase diagrams supported by density functional theory methods can be crucial for designing high-entropy alloys (HEAs). We present phase and property analysis of refractory quinary (MoW)<sub>x</sub>Zr<sub>y</sub>(TaTi)<sub>1-x-y</sub> HEAs from combined Calculation of Phase Diagram (CALPHAD) and density-functional theory results, supplemented by molecular dynamics (MD) simulations. Our analysis indicates a Mo-W-rich region of this quinary system has a stable single-phase body-centered-cubic (bcc). The (MoW)<sub>85</sub>Zr<sub>7.5</sub>(TaTi)<sub>7.5</sub> was down-selected based on temperature-dependent CALPHAD phase diagram analysis and MD predicted elastic behavior that reveals twinning-assisted pseudoelastic behavior in this refractory HEA. While mostly unexplored in bcc crystals, twinning is a fundamental deformation mechanism that competes against dislocation slip in crystalline solids. This alloy shows identical cyclic deformation characteristics during uniaxial <100> loading, i.e., the pseudoelasticity is isotropic in loading direction. Additionally, a temperature increase from 77 to 1,500 K enhances the elastic strain recovery in load-unload cycles, offering possibly control to tune the pseudoelastic behavior.","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"61 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76107047","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xin Cai, Xiaoqiang Hu, Leigang Zheng, Dianzhong Li
The redistribution of C and N interstitial atoms i n a martensitic stainless steel combined alloying with 0.3 wt.% C and 0.5 wt.% N after cryogenic treatment was investigated by the transition electronic microscope (TEM), X-ray diffractometer (XRD), and atom probe tomography (APT). C atoms accumulated to form clusters which were enhanced by the decrease of cryogenic temperature. N atoms as Mo-N and Cr-N pairs were found when the cryogenic temperature was deep to -190 o C. It seems that the redistribution behavior of C and N atoms is considerably different, and these interstitial atoms migrated more strenuously despite of the cryogenic temperature decreasing. The migration of interstitial atoms is supposed to associate with the microstructure evolution combining the increase of dislocation density and the martensite transformation from the retained austenite during cryogenic treatment.
{"title":"C and N Atom Redistribution Behaviors in 0.30C-15.0Cr-1.0Mo-0.50N Martensitic Stainless Steel During Cryogenic Treatment","authors":"Xin Cai, Xiaoqiang Hu, Leigang Zheng, Dianzhong Li","doi":"10.2139/ssrn.3797410","DOIUrl":"https://doi.org/10.2139/ssrn.3797410","url":null,"abstract":"The redistribution of C and N interstitial atoms i n a martensitic stainless steel combined alloying with 0.3 wt.% C and 0.5 wt.% N after cryogenic treatment was investigated by the transition electronic microscope (TEM), X-ray diffractometer (XRD), and atom probe tomography (APT). C atoms accumulated to form clusters which were enhanced by the decrease of cryogenic temperature. N atoms as Mo-N and Cr-N pairs were found when the cryogenic temperature was deep to -190 o C. It seems that the redistribution behavior of C and N atoms is considerably different, and these interstitial atoms migrated more strenuously despite of the cryogenic temperature decreasing. The migration of interstitial atoms is supposed to associate with the microstructure evolution combining the increase of dislocation density and the martensite transformation from the retained austenite during cryogenic treatment.","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76349812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
N. Koutná, Alexander W. Brenner, D. Holec, P. Mayrhofer
Abstract Superlattices—alternating coherently grown materials of nm thicknesses—proved their potential for enhancing typically antagonistic properties of ceramics: ductility, hardness, and fracture toughness. Material selection, however, is far from trivial, as superlattice films do not simply combine mechanical properties of their layer components. Here we employ high-throughput density functional theory calculations to develop design guidelines for nanolaminates combining cubic transition metal nitride and/or carbide ceramics. Out of 153 MX/M*X* superlattices (M, M* = Al, Ti, Zr, Hf, Nb, V, Ta, Mo, W, and X, X* = C, N) 145 are chemically and mechanically stable and most often contain vacancies on the non-metallic sublattice. Superior ductility together with moderate-to-high fracture toughness and interface strength (above that of the cubic TiN) narrow the set of perspective candidates. Key ingredients promoting the interface-induced enhancement of hardness and/or fracture toughness are lattices parameter and shear modulus mismatch of the layer components. Adding the requirement of phonon stability yields MoN/M*N, M* = Nb, Ta, Ti; TiN/WN (nitrides); HfC/M*N, M* = Mo, W; NbC/M*N, M* = Mo, W; TaC/M*N, M* = Mo, W; VC/M*N, M* = Hf, Ta, Zr (carbonitrides); as the top candidates for novel superlattice films.
{"title":"High-Throughput First-Principles Search for Ceramic Superlattices with Improved Ductility and Fracture Resistance","authors":"N. Koutná, Alexander W. Brenner, D. Holec, P. Mayrhofer","doi":"10.2139/ssrn.3683517","DOIUrl":"https://doi.org/10.2139/ssrn.3683517","url":null,"abstract":"Abstract Superlattices—alternating coherently grown materials of nm thicknesses—proved their potential for enhancing typically antagonistic properties of ceramics: ductility, hardness, and fracture toughness. Material selection, however, is far from trivial, as superlattice films do not simply combine mechanical properties of their layer components. Here we employ high-throughput density functional theory calculations to develop design guidelines for nanolaminates combining cubic transition metal nitride and/or carbide ceramics. Out of 153 MX/M*X* superlattices (M, M* = Al, Ti, Zr, Hf, Nb, V, Ta, Mo, W, and X, X* = C, N) 145 are chemically and mechanically stable and most often contain vacancies on the non-metallic sublattice. Superior ductility together with moderate-to-high fracture toughness and interface strength (above that of the cubic TiN) narrow the set of perspective candidates. Key ingredients promoting the interface-induced enhancement of hardness and/or fracture toughness are lattices parameter and shear modulus mismatch of the layer components. Adding the requirement of phonon stability yields MoN/M*N, M* = Nb, Ta, Ti; TiN/WN (nitrides); HfC/M*N, M* = Mo, W; NbC/M*N, M* = Mo, W; TaC/M*N, M* = Mo, W; VC/M*N, M* = Hf, Ta, Zr (carbonitrides); as the top candidates for novel superlattice films.","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"58 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84863774","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents the variations of surface roughness and geometrical precision of Direct Metal Laser Sintering (DMLS) parts depending on their positions on the building platform of EOS M290. A distinctive design was created to measure and compare the surface quality, dimensional accuracy, and geometrical precision. This design was built on various positions of the building platform using constant parameters. Surface roughness (Ra) measurements and imaging were carried out. Platform position was found to be an important parameter affecting the surface quality of horizontal and inclined surfaces as well as the dimensional accuracy of the fine geometric details.
{"title":"Effect of Building Platform Position on the Surface Quality, Dimensional Accuracy, and Geometrical Precision of Direct Metal Laser Sintering (DMLS) Parts","authors":"Z. Oter, M. Coskun","doi":"10.2139/ssrn.3785856","DOIUrl":"https://doi.org/10.2139/ssrn.3785856","url":null,"abstract":"This paper presents the variations of surface roughness and geometrical precision of Direct Metal Laser Sintering (DMLS) parts depending on their positions on the building platform of EOS M290. A distinctive design was created to measure and compare the surface quality, dimensional accuracy, and geometrical precision. This design was built on various positions of the building platform using constant parameters. Surface roughness (Ra) measurements and imaging were carried out. Platform position was found to be an important parameter affecting the surface quality of horizontal and inclined surfaces as well as the dimensional accuracy of the fine geometric details.","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"395 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76455962","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
P. Moser, G. Wiechers, Sandra Schmidt, J. Monteiro, E. Goetheer, C. Charalambous, Ahmed Saleh, Mijndert van der Spek, S. García
After a 13,000-hour test campaign with aqueous 30 wt% MEA (2-aminoethanol) solvent at the CO2 capture pilot plant at Niederaussem, another long-term test was carried out as part of the ALING-CCUS project. This test ran for more than 12,275 hours with aqueous AMP/PZ (2-Amino-2-methyl-1-propanol/piperazine) solvent, named CESAR1 (3.0 molar AMP (~ 26.74 wt%) and 1.5 molar PZ (~ 12.92 wt. %)). A minimum specific reboiler duty of 2,970 MJ/tCO2 was identified for the capture plant operation with four active absorber beds (total 16 m packing height). Neither a lower desorber pressure of 1.5 bar(a), instead of 1.75 bar(a), nor a change of the different positions of intercooling had a significant effect on energy consumption. Reduction of the active packing height to three beds (i.e., 12 m), resulted in a moderately higher specific energy demand (+100 MJ/tCO2). Tests with CO2 capture rates between 90 and 98% showed only a small increase of the specific energy demand at 95% (+20 MJ/tCO2) and four active packings (98%: + 250 MJ/tCO2). The average solvent consumption of CESAR1 during 400 days of operation was 0.45 kg/tCO2 and is lower than for MEA if the phase of accelerated non-linear degradation of MEA is taken into account. CESAR1 follows a slow-progressing linear degradation behavior; neither a critical metal ion concentration threshold value could be found that triggers fast degradation nor a correlation between accumulated trace components or metal ion concentrations in the solvent and the degradation rate was observed. Highly transient tests were conducted to investigate the dynamic behavior of the capture plant and subsequently special settings were chosen to stimulate high emissions for the investigation of aerosol-based emissions, connected with performance tests of several emission mitigation measures: single water wash, double water wash, acid wash, dry bed, wet electric precipitator and flue gas pre-treatment. When applying the dry bed configuration, emissions of AMP between 15 - 20 mg/Nm3, PZ between 3 - 7 mg/Nm3, and NH3 below 3 mg/Nm3 were achieved.
{"title":"ALIGN-CCUS: Results of the 18-Month Test with Aqueous AMP/PZ Solvent at the Pilot Plant at Niederaussem – Solvent Management, Emissions and Dynamic Behavior","authors":"P. Moser, G. Wiechers, Sandra Schmidt, J. Monteiro, E. Goetheer, C. Charalambous, Ahmed Saleh, Mijndert van der Spek, S. García","doi":"10.2139/ssrn.3812132","DOIUrl":"https://doi.org/10.2139/ssrn.3812132","url":null,"abstract":"After a 13,000-hour test campaign with aqueous 30 wt% MEA (2-aminoethanol) solvent at the CO2 capture pilot plant at Niederaussem, another long-term test was carried out as part of the ALING-CCUS project. This test ran for more than 12,275 hours with aqueous AMP/PZ (2-Amino-2-methyl-1-propanol/piperazine) solvent, named CESAR1 (3.0 molar AMP (~ 26.74 wt%) and 1.5 molar PZ (~ 12.92 wt. %)). A minimum specific reboiler duty of 2,970 MJ/tCO2 was identified for the capture plant operation with four active absorber beds (total 16 m packing height). Neither a lower desorber pressure of 1.5 bar(a), instead of 1.75 bar(a), nor a change of the different positions of intercooling had a significant effect on energy consumption. Reduction of the active packing height to three beds (i.e., 12 m), resulted in a moderately higher specific energy demand (+100 MJ/tCO2). Tests with CO2 capture rates between 90 and 98% showed only a small increase of the specific energy demand at 95% (+20 MJ/tCO2) and four active packings (98%: + 250 MJ/tCO2). The average solvent consumption of CESAR1 during 400 days of operation was 0.45 kg/tCO2 and is lower than for MEA if the phase of accelerated non-linear degradation of MEA is taken into account. CESAR1 follows a slow-progressing linear degradation behavior; neither a critical metal ion concentration threshold value could be found that triggers fast degradation nor a correlation between accumulated trace components or metal ion concentrations in the solvent and the degradation rate was observed. Highly transient tests were conducted to investigate the dynamic behavior of the capture plant and subsequently special settings were chosen to stimulate high emissions for the investigation of aerosol-based emissions, connected with performance tests of several emission mitigation measures: single water wash, double water wash, acid wash, dry bed, wet electric precipitator and flue gas pre-treatment. When applying the dry bed configuration, emissions of AMP between 15 - 20 mg/Nm3, PZ between 3 - 7 mg/Nm3, and NH3 below 3 mg/Nm3 were achieved.","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"41 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85963875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
W. Xiao, Boyu Xue, Xue Wang, Zhongnan Xie, Lu Sun, Jianwei Wang, Hui Yang, H. Guo, Ligen Wang
Copper/diamond composites with various diamond contents are a prototype of thermal management materials and are widely used in many industrial fields due to their excellent thermo-physical properties. It is well known that the carriers of heat in diamond and copper are phonons and electrons, respectively. Scattering and phonon-electron interactions at the interface play a pivotal role on determining the interface thermal conductance. By using this model material the mechanisms of the interface thermal conductance are investigated by experiments and first-principles calculations. The boron addition can promote the thermal conductivity from 261 W/(mK) to 647 W/(mK) or increase the thermal conductivity by 2.5 times for the copper/diamond composite with 60% diamond. The increase of thermal conductivity may be explained by the formation of B4C and Cu-B solid solution at the interface. First-principles calculations show that the interface thermal resistance is mainly attributed to the phonon frequency mismatch and electronic transfer. The B4C phase formed at the interface assists the phonon conductance because the phonon spectrum of the B4C phase spreads across the range of Cu and diamond phonon spectra. The calculated results also show that boron can diffuse toward the interface region with an energy barrier of 0.87 eV and are energetically favorable to form the B4C phase. The present study provides valuable insight into the understanding of atomic mechanisms of thermal conductance at interfaces and a basis for exploring practical applications of the copper/diamond composites.
{"title":"Enhanced Interface Phonon Thermal Conductance via Boron Addition in Copper/Diamond Composites","authors":"W. Xiao, Boyu Xue, Xue Wang, Zhongnan Xie, Lu Sun, Jianwei Wang, Hui Yang, H. Guo, Ligen Wang","doi":"10.2139/ssrn.3774508","DOIUrl":"https://doi.org/10.2139/ssrn.3774508","url":null,"abstract":"Copper/diamond composites with various diamond contents are a prototype of thermal management materials and are widely used in many industrial fields due to their excellent thermo-physical properties. It is well known that the carriers of heat in diamond and copper are phonons and electrons, respectively. Scattering and phonon-electron interactions at the interface play a pivotal role on determining the interface thermal conductance. By using this model material the mechanisms of the interface thermal conductance are investigated by experiments and first-principles calculations. The boron addition can promote the thermal conductivity from 261 W/(mK) to 647 W/(mK) or increase the thermal conductivity by 2.5 times for the copper/diamond composite with 60% diamond. The increase of thermal conductivity may be explained by the formation of B4C and Cu-B solid solution at the interface. First-principles calculations show that the interface thermal resistance is mainly attributed to the phonon frequency mismatch and electronic transfer. The B4C phase formed at the interface assists the phonon conductance because the phonon spectrum of the B4C phase spreads across the range of Cu and diamond phonon spectra. The calculated results also show that boron can diffuse toward the interface region with an energy barrier of 0.87 eV and are energetically favorable to form the B4C phase. The present study provides valuable insight into the understanding of atomic mechanisms of thermal conductance at interfaces and a basis for exploring practical applications of the copper/diamond composites.","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"83 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81279273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. Ghezelbash, A. Eskandari, A. Shirazi-Adl, M. Kazempour, J. Tavakoli, M. Baghani, J. Costi
Collagen fibers within the annulus fibrosus (AF) lamellae are unidirectionally aligned with alternating orientations between adjacent layers. AF constitutive models often combine two adjacent lamellae into a single equivalent layer containing two fiber networks with a crisscross pattern. Additionally, AF models overlook the inter-lamellar matrix (ILM) as well as elastic fiber networks in between lamellae. We developed a nonhomogenous micromechanical model as well as two coarser homogenous hyperelastic and microplane models of the human AF, and compared their performances against measurements (tissue level uniaxial and biaxial tests as well as whole disc experiments) and seven published hyperelastic models. The micromechanical model had a realistic non-homogenous distribution of collagen fiber networks within each lamella and elastic fiber network in the ILM. For small matrix linear moduli (<0.2 MPa), the ILM showed substantial anisotropy (>10%) due to the elastic fiber network. However, at moduli >0.2 MPa, the effects of the elastic fiber network on differences in stress-strain responses at different directions disappeared (<10%). Variations in sample geometry and boundary conditions (due to uncertainty) markedly affected stress-strain responses of the tissue in uniaxial and biaxial tests (up to 16 times). In tissue level tests, therefore, simulations should represent testing conditions (e.g., boundary conditions, specimen geometry, preloads) as closely as possible. Stress/strain fields estimated from the single equivalent layer approach (conventional method) yielded different results from those predicted by the anatomically more accurate apparoach (i.e., layerwise). In addition, in a disc under a compressive force (symmetric loading), asymmetric stress-strain distributions were computed when using a layerwise simulation. Although all selected AF models predicted gross compression-displacement responses of the whole disc within the range of measured data, some showed excessively stiff or compliant responses under tissue-level uniaxial/biaxial tests. This study emphasizes, when constructing and validating constitutive models of AF, the importance of the proper simulation of individual lamellae as distinct layers, and testing parameters (sample geometric dimensions/loading/boundary conditions).
{"title":"Modeling of Human Intervertebral Disc Annulus Fibrosus with Complex Multi-Fiber Networks","authors":"F. Ghezelbash, A. Eskandari, A. Shirazi-Adl, M. Kazempour, J. Tavakoli, M. Baghani, J. Costi","doi":"10.2139/ssrn.3677348","DOIUrl":"https://doi.org/10.2139/ssrn.3677348","url":null,"abstract":"Collagen fibers within the annulus fibrosus (AF) lamellae are unidirectionally aligned with alternating orientations between adjacent layers. AF constitutive models often combine two adjacent lamellae into a single equivalent layer containing two fiber networks with a crisscross pattern. Additionally, AF models overlook the inter-lamellar matrix (ILM) as well as elastic fiber networks in between lamellae. We developed a nonhomogenous micromechanical model as well as two coarser homogenous hyperelastic and microplane models of the human AF, and compared their performances against measurements (tissue level uniaxial and biaxial tests as well as whole disc experiments) and seven published hyperelastic models. The micromechanical model had a realistic non-homogenous distribution of collagen fiber networks within each lamella and elastic fiber network in the ILM. For small matrix linear moduli (<0.2 MPa), the ILM showed substantial anisotropy (>10%) due to the elastic fiber network. However, at moduli >0.2 MPa, the effects of the elastic fiber network on differences in stress-strain responses at different directions disappeared (<10%). Variations in sample geometry and boundary conditions (due to uncertainty) markedly affected stress-strain responses of the tissue in uniaxial and biaxial tests (up to 16 times). In tissue level tests, therefore, simulations should represent testing conditions (e.g., boundary conditions, specimen geometry, preloads) as closely as possible. Stress/strain fields estimated from the single equivalent layer approach (conventional method) yielded different results from those predicted by the anatomically more accurate apparoach (i.e., layerwise). In addition, in a disc under a compressive force (symmetric loading), asymmetric stress-strain distributions were computed when using a layerwise simulation. Although all selected AF models predicted gross compression-displacement responses of the whole disc within the range of measured data, some showed excessively stiff or compliant responses under tissue-level uniaxial/biaxial tests. This study emphasizes, when constructing and validating constitutive models of AF, the importance of the proper simulation of individual lamellae as distinct layers, and testing parameters (sample geometric dimensions/loading/boundary conditions).","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87672730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hydrogel scaffolds are widely used in cartilage tissue engineering as a natural stem cell niche. In particular, hydrogels based on multiple biological signals can guide behaviors of mesenchymal stem cells (MSCs) during neo-chondrogenesis. In the first phase of this study, we showed that functionalized hydrogels with grafted arginine-glycine-aspartate (RGD) peptides and lower degree of crosslinking can promote the proliferation of human mesenchymal stem cells (hMSCs) and upregulate the expression of cell receptor proteins. Moreover, grafted RGD and histidine-alanine-valine (HAV) peptides in hydrogel scaffolds can regulate the adhesion of the intercellular at an early stage. In the second phase, we confirmed that simultaneous use of HAV and RGD peptides led to greater chondrogenic differentiation compared to the blank control and single-peptide groups. Furthermore, the controlled release of kartogenin (KGN) can better facilitate cell chondrogenesis compared to other groups. Interestingly, with longer culture time, cell condensation was clearly observed in the groups with RGD and HAV peptide. In all groups with RGD peptide, significant matrix deposition was observed, accompanied by glycosaminoglycan (GAG) and collagen (Coll) production. Through in vitro and in vivo experiments, this study confirmed that our hydrogel system can sequentially promote the proliferation, adhesion, condensation, chondrogenic differentiation of hMSCs, by mimicking the cell microenvironment during neo-chondrogenesis.
{"title":"A Chondrogenesis Induction System Based on Functionalized Hyaluronic Acid Hydrogel Sequentially Promoting hMSC Proliferation, Condensation, and Differentiation and Matrix Deposition","authors":"Binhong Teng, Siqi Zhang, Jijia Pan, Ziqian Zeng, Yang Chen, Yu Hei, Xiaoming Fu, Qian Li, Mingyuan Ma, Yi Sui, Shicheng Wei","doi":"10.2139/ssrn.3711241","DOIUrl":"https://doi.org/10.2139/ssrn.3711241","url":null,"abstract":"Hydrogel scaffolds are widely used in cartilage tissue engineering as a natural stem cell niche. In particular, hydrogels based on multiple biological signals can guide behaviors of mesenchymal stem cells (MSCs) during neo-chondrogenesis. In the first phase of this study, we showed that functionalized hydrogels with grafted arginine-glycine-aspartate (RGD) peptides and lower degree of crosslinking can promote the proliferation of human mesenchymal stem cells (hMSCs) and upregulate the expression of cell receptor proteins. Moreover, grafted RGD and histidine-alanine-valine (HAV) peptides in hydrogel scaffolds can regulate the adhesion of the intercellular at an early stage. In the second phase, we confirmed that simultaneous use of HAV and RGD peptides led to greater chondrogenic differentiation compared to the blank control and single-peptide groups. Furthermore, the controlled release of kartogenin (KGN) can better facilitate cell chondrogenesis compared to other groups. Interestingly, with longer culture time, cell condensation was clearly observed in the groups with RGD and HAV peptide. In all groups with RGD peptide, significant matrix deposition was observed, accompanied by glycosaminoglycan (GAG) and collagen (Coll) production. Through in vitro and in vivo experiments, this study confirmed that our hydrogel system can sequentially promote the proliferation, adhesion, condensation, chondrogenic differentiation of hMSCs, by mimicking the cell microenvironment during neo-chondrogenesis.","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83449596","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Symmetrically packed TiO2 nanotubes (TNTs) were fabricated in fluorine free perchloric acid medium by electrochemical anodization method. During anodization interconnected pores developed by forming amorphous/ hydroxides of titanium film. On increasing anodization, thickness of film increased and pores tend to become aligned providing surface layer of nanotubes on the electrode material. The 1-D charge carrier transport property of the tubular geometry have attracted scientists attention in using TNTs for TiO2 photovoltaic and photo catalysis applications. By controlling the anodization process, the length, diameter and wall thickness of TNTs can be tailored. The iron and chromium doped highly ordered 1-D TNTs obtained during anodization are superior photoanodes for dye-sensitized solar cells because of its reduced inter tube connections, vertical electron transport, suppressed electron recombination and enhanced current density, efficiency in power conversion and light scattering. The morphological characteristics and microstructure of TNTs were investigated by SEM and X-ray diffraction analysis. Diffusion electron spectroscopy has been used to analyze the amount absorption of the dye on the surface of the various TNT, which acknowledges the direct co relation between the dye absorption and morphology of the sample.
{"title":"Highly Ordered Nanotube Arrays as Photo-Anodes for Dye-Sensitized Solar Cells by Electrochemical Method","authors":"D. Behera, P. Nayak, Tapash Ranjan Rautray","doi":"10.2139/ssrn.3762312","DOIUrl":"https://doi.org/10.2139/ssrn.3762312","url":null,"abstract":"Symmetrically packed TiO2 nanotubes (TNTs) were fabricated in fluorine free perchloric acid medium by electrochemical anodization method. During anodization interconnected pores developed by forming amorphous/ hydroxides of titanium film. On increasing anodization, thickness of film increased and pores tend to become aligned providing surface layer of nanotubes on the electrode material. The 1-D charge carrier transport property of the tubular geometry have attracted scientists attention in using TNTs for TiO2 photovoltaic and photo catalysis applications. By controlling the anodization process, the length, diameter and wall thickness of TNTs can be tailored. The iron and chromium doped highly ordered 1-D TNTs obtained during anodization are superior photoanodes for dye-sensitized solar cells because of its reduced inter tube connections, vertical electron transport, suppressed electron recombination and enhanced current density, efficiency in power conversion and light scattering. The morphological characteristics and microstructure of TNTs were investigated by SEM and X-ray diffraction analysis. Diffusion electron spectroscopy has been used to analyze the amount absorption of the dye on the surface of the various TNT, which acknowledges the direct co relation between the dye absorption and morphology of the sample.","PeriodicalId":18268,"journal":{"name":"Materials Engineering eJournal","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76605280","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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