Transient analysis of layered beams subjected to steady heat supply and mechanical load

Zhong Zhang,Ding Zhou,Jiandong Zhang,Hai Fang,Huixuan Han 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.1

In this study, an analytical model is developed for the analysis of transient temperature, displacements, and stresses in simply supported layered beams. The beam is suddenly heated from the top and bottom surfaces by external steady heat sources and is subjected to a mechanical load. The temperature in each layer is variable along the thickness and follows the one-dimensional (1-D) transient heat transfer equation. The Laplace transform approach is used to obtain the transient temperature field in the beam. The thermoelastic constants of the beam are temperature-dependent. Dividing every layer into a series of thin slices, the temperature and the thermoelastic constants for each slice can be considered uniform. The two-dimensional (2-D) thermoelasticity theory is adopted to derive the governing equations of displacements and stresses in each slice. The transfer matrix method is applied to obtain the displacement and stress solutions for the beam. As an example, the distributions of transient temperature, displacements, and stresses in a three-layer beam are studied. The effects of the temperature dependent thermoelastic constants on the mechanical behavior of the beam are discussed in detail.

Mechanical Behavior of Composite Beams Considering Nonlinear Shear Stiffness of Clustered Studs

Duo Liu,Ding Zhou,Bohai Ji,Wenqin Deng,Shang Zha,Jiandong Zhang 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.4

Clustered studs are suitable for use in prefabricated steel-concrete composite beams. As a kind of shear connector, clustered studs have a non-negligible influence on the mechanical behavior of structures. Based on the theory of elasticity, prefabricated composite beams investigated via laminated plane stress problem. The load-slip curves of the shear connectors are linearly processed, and through iterative calculations, the displacement and stress distribution functions of prefabricated composite beams are obtained. Then, a model test is carried out on the positive bending moment section of prefabricated composite beams. A sampling method with front segments controlled by the load and back segments controlled by the slip is adopted. This method provides a better rate of convergence and higher accuracy than those of other methods. The test results show that when the load is small and the composite beam is in the elastic stage, the slope of the load-slip curve can be used as the shear stiffness of the clustered studs. When the load is large and the composite beam enters the plastic stage, the nonlinear shear stiffness of the studs must be considered to obtain a high-precision solution.

In vitro Degradation and Protein Release of Transparent and Opaque Physical Hydrogels of Block Copolymers at Body Temperature

Lin Yu,Jiandong Ding,Zheng Zhang 한국고분자학회 2012 Macromolecular Research Vol.20 No.3

Poly(D,L-lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(D,L-lactide-co-glycolide) (PLGA-PEGPLGA)triblock copolymers were synthesized at 130 and 160 oC. The concentrated aqueous solutions of both specimens underwent reversible sol-to-(transparent gel)-to-(opaque gel) transitions upon heating but exhibited different critical gelation concentrations and transition temperatures, possibly due to the minor sequence differences between D,L-lactide (LA) and glycolide (GA) in the PLGA blocks. Aqueous solutions (20 wt%) of the copolymers synthesized at 130 and 160 oC spontaneously formed an opaque gel and a transparent gel at body temperature, respectively. The resulting hydrogels displayed similar in vitro degradation profiles in phosphate buffer saline solutions at 37 oC. Nevertheless, the late-stage releases of bovine serum albumin from the physical hydrogels differed. The present study reveals for the first time that transparent vs. opaque thermogel state influences some of their biomaterialrelated properties via the “overheat degree” of the thermogelling systems at a given working temperature, usually 37 oC.

Gas-phase dehydration of glycerol to acrolein over different metal phosphate catalysts

Tianlin Ma,Jianfei Ding,Xueli Liu,Gangling Chen,Jiandong Zheng 한국화학공학회 2020 Korean Journal of Chemical Engineering Vol.37 No.6

We conducted a comparative study of gas phase dehydration of glycerol to acrolein over aluminium phosphate, iron phosphate and nickel phosphate catalysts prepared by a simple replacement reaction method (AlP, FeP and NiP). The textural properties, acid amounts, acid types, and coke contents of the samples were studied. The results showed that all metal phosphate catalysts remained in an amorphous state. The glycerol conversion was proportional to the acid amount of metal phosphate catalyst in the glycerol dehydration reaction. Higher value of B/L was more likely to produce acrolein. Among the metal phosphate catalysts, FeP showed superior performance due to its suitable textural and acid properties. After 2 h on stream, high glycerol conversion (96%), acrolein selectivity (82%) and acrolein yield (79%) were achieved on the FeP catalyst at 280 oC. The catalyst deactivation was ascribed to carbon deposition on the catalyst surface blocking the active sites during the glycerol dehydration reaction.

Vulnerability of East Asian bumblebee species to future climate and land cover changes

Naeem, Muhammad,Liu, Meijuan,Huang, Jiaxing,Ding, Guiling,Potapov, Grigory,Jung, Chuleui,An, Jiandong Elsevier 2019 Agriculture, ecosystems & environment Vol.277 No.-

<P><B>Abstract</B></P> <P>Pollinators play a key role in agricultural and natural ecosystems, but their biodiversity is highly vulnerable to the impact of environmental changes. Here, we evaluated the distributional responses of 29 bumblebee species endemic to East Asia to future (2050s and 2070s) climate and land cover changes, and 17–27 (59–93 %) of the species exhibited range contraction. A decrease in species richness from 25 to 19 species in the highest region of central China was also detected due to range shifts of 17 km to 574 km. Furthermore, one (3.44%), three to five (10–17 %), and two to eight (7–28 %) of the 29 bumblebee species were predicted to become critically endangered, endangered and vulnerable in the future, respectively. Our study highlights the strong impact of environmental changes on species distributions, and we suggest strategies for the conservation of vulnerable species that include protecting the regions of high species richness and the most dominant land covers within the current range to mitigate the threat of environmental changes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pollinators are under threat from climate and climate-induced land cover changes. </LI> <LI> Distributional responses were predicted for 29 bumblebee species in East Asia. </LI> <LI> Of the studied species, 59–93 % experienced range loss in the future. </LI> <LI> Species richness declined within central mainland China and northeastern Asia. </LI> <LI> Conserving regions with high species richness and dominant land covers is needed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Design of Molecular Parameters to Achieve Block Copolymers with a Powder Form at Dry State and a Temperature-Induced Sol-Gel Transition in Water without Unexpected Gelling Prior to Heating

Lin Yu,Wenjia Sheng,Dicheng Yang,Jiandong Ding 한국고분자학회 2013 Macromolecular Research Vol.21 No.2

Thermogelling block copolymers composed of polyester and polyether are faced with a dilemma of achieving powder form in order to easily handle the samples in the bulk state and avoid unexpected ahead-of-time gelling of the corresponding polymer aqueous solution below the thermogelling temperature due to the spontaneous crystallization of some polymer segments in water. In order to resolve this dilemma, we synthesized amphiphilic poly(ε-caprolactone-co-glycolide)-poly(ethylene glycol)-poly(ε-caprolactone-co-glycolide) (PCGA-PEG-PCGA) triblock copolymers with a series of ratios regarding caprolactone (CL) and glycolide (GA). The different polymer morphologies from powder to sticky paste were obatined by altering the ratios to adjust the ability of crytallization for the PCGA blocks. All of the copolymers reported in this paper were able to dissolve in water, and their aqueous solutions underwent a sol-gel transition upon heating. The polymer with an appropriate CL/GA ratio not only exhibited the powder form in the bulk state, but also achieved the sol stability in water. The triblock copolymers formed micelles in water and the micellar aggregation occurred with increasing temperature, resulting in physical gelation upon the percolation of micelles. The injectability and gellability of the copolymer-water systems were confirmed both in vitro and in vivo. Consequently, this study provides a promising injectable biomaterial, and also affords a new successful case of the molecular design of functional polymers, based upon common monomers.

Polyetheretherketone implants with hierarchical porous structure for boosted osseointegration

Zhiyong Chen,Yu Chen,Yang Wang,JiaJia Deng,Xin Wang,Qingqing Wang,Yuehua Liu,Jiandong Ding,Lin Yu 한국생체재료학회 2023 생체재료학회지 Vol.27 No.00

Background Good osseointegration is the key to the long-term stability of bone implants. Thermoplastic polyetheretherketone (PEEK) has been widely used in orthopedics; however, its inherent biological inertia causes fibrous tissue to wrap its surface, which leads to poor osseointegration and thus greatly limits its clinical applications. Methods Herein, we developed a facile yet effective surface modification strategy. A commonly used sulfonation coupled with “cold pressing” treatment in the presence of porogenic agent formed a three-dimensional hierarchical porous structure on PEEK surface. Subsequently, the effects of porous surface on the in vitro adhesion, proliferation and differentiation of rat bone marrow-derived mesenchymal stem cells (BMSCs) were evaluated. Finally, the osteoinduction and osseointegration of surface-porous PEEK implant were examined in the rat distal femoral defect model. Results In vitro results showed that the surface modification did not significantly affect the mechanical performance and cytocompatibility of PEEK substance, and the porous structure on the modified PEEK substrate provided space for cellular ingrowth and enhanced osteogenic differentiation and mineralization of BMSCs. In vivo tests demonstrated that the surface-porous PEEK implant could effectively promote new bone formation and had higher bone-implant contact rate, thereby achieving good bone integration with the surrounding host bone. In addition, this modification technique was also successfully demonstrated on a medical PEEK interbody fusion cage. Conclusion The present study indicates that topological morphology plays a pivotal role in determining implant osseointegration and this facile and effective modification strategy developed by us is expected to achieve practical applications quickly.