Rheological numerical simulation for thermo-hydro-mechanical coupling analysis for rock mass

Under the environment of seepage field, stress field and temperature field interaction and influence, the three fields will not only produce coupling effect, but also have deformation with time due to the rheological behavior of rock mass. In the paper, based on the fundamental theories of rock mass coupling theory and rheological mechanics, the rheological model for fully coupled thermo-hydro-mechanical analysis for rock mass was set up, and the corresponding constitutive relationship, the conservation equation of mass and the conservation equation of energy were given, and the finite element formulas were derived for coupling analysis of rock mass. During establishing governing equations, rock mass was assumed approximately as macro-equivalent continuum medium. The obtained rheological numerical model for fully coupled thermo-hydro-mechanical analysis can be used for analyzing and predicting the long-term stability of underground caverns and slope engineering under the condition of thermo-hydro-mechanical coupling with rheological deformation.

Printability during projection-based 3D bioprinting

Since projection-based 3D bioprinting(PBP)could provide high resolution,it is well suited for printing delicate structures for tissue regeneration.However,the low crosslinking density and low photo-crosslinking rate of photocurable bioink make it difficult to print fine structures.Currently,an in-depth understanding of the is lacking.Here,a research framework is established for the analysis of printability during PBP.The gelatin methacryloyl(GelMA)-based bioink is used as an example,and the printability is systematically investigated.We analyze the photo-crosslinking reactions during the PBP process and summarize the specific requirements of bioinks for PBP.Two standard quantized models are established to evaluate 2D and 3D printing errors.Finally,the better strategies for bioprinting five typical structures,including solid organs,vascular structures,nerve conduits,thin-wall scaffolds,and micro needles,are presented.

INVESTIGATION ON THE GELATION BEHAVIOR OF BIODEGRADABLE POLY(BUTYLENE SUCCINATE) DURING ISOTHERMAL CRYSTALLIZATION PROCESS

The early stage of polymer crystallization may be viewed as physical gelation process,i.e.,the phase transition of polymer from liquid to solid.Determination of the gel point is of significance in polymer processing.In this work,the gelation behavior of poly（butylene succinate）（PBS） at different temperatures has been investigated by rheological method.It was found that during the isothermal crystallization process of PBS,both the storage modulus（G′） and the loss modulus（G″） increase with time,and the rheological response of the system varies from viscous-dominated（G′G″） to elastic-dominated （G′G″）,meaning the phase transition from liquid to solid.The physical gel point was determined by the intersection point of loss tangent curves measured under different frequencies.The gel time（t_c） for PBS was found to increase with increasing crystallization temperature.The relative crystallinity of PBS at the gel point is very low（2.5%-8.5%） and increases with increasing the crystallization temperature.The low crystallinity of PBS at the gel point suggests that only a few junctions are necessary to form a spanning network,indicating that the network is＂loosely＂connected,in another word,the critical gel is soft.Due to the elevated crystallinity at gel point under higher crystallization temperature,the gel strength S_g increases, while the relaxation exponent n decreases with increasing the crystallization temperature.These experimental results suggest that rheological method is an effective tool for verifying the gel point of biodegradable semi-crystalline polymers.