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1.
The structures' durability is an engineering concern for a long time but has been increased in the last years. Lightweight aggregate concrete (LWAC) combined with glass fibre reinforced polymer bars allows to create structures with high performance in terms of durability. The glass fibre reinforced polymer (GFRP) bars have different ribs from those of steel bars, and consequently, its bond to concrete is affected. Moreover, the Young's modulus of GFRP is much below compared with that of steel, and this influences significantly the behaviour of structural elements reinforced with this material. This paper presents an experimental study focused on bond between LWAC and reinforcing bars of GFRP. Thirty‐six pull‐out tests were carried out using steel and GFRP bars. These reinforcements were combined with three types of concrete, all with the same design density 1900 kg m?3 but with different values of compressive strength: 35, 55 and 70 MPa. Furthermore, 12 reinforced ties were tested, combining different types of bars (steel and GFRP), two different diameters (12 and 16 mm) and the three types of LWAC. Based on experimental results, several relations were established to understand the behaviour of LWAC structures reinforced with GFRP bars, mainly in the serviceability conditions. These results point out that ties deformation and crack width are very affected by the reduced Young's modulus of GFRP: deformations and crack width of ties reinforced with GFRP are significantly higher, approximately three times greater, compared with those of ties reinforced with steel. The tension stiffening effect was also analysed in detail, and it was found that it is slightly influenced by the concrete compressive strength but is highly dependent of the Young's modulus of the reinforcing material. 相似文献
2.
An acrylate polymer network was submitted to thermomechanical shape memory cycles. The set of experiments characterized the material stress-free strain recovery and the strain-constrained stress recovery in uniaxial tension. Experimental parameters like temperature of strain fixation, amount of strain and heating rate, were varied in order to provide a relatively complete set of experimental data. A model combining the amorphous polymer viscoelasticity and its time–temperature superposition property was used to predict the shape memory behavior of the acrylate polymer network. All the model parameters were characterized using classical tests for mechanical characterization of polymers, which do not include shape memory tests. Model predictions obtained by finite element simulations compared very well to the experimental data and therefore the model relevance for computer assisted application design was assessed. 相似文献
3.
A Carbonyl Compound‐Based Flexible Cathode with Superior Rate Performance and Cyclic Stability for Flexible Lithium‐Ion Batteries 下载免费PDF全文
A sulfur‐linked carbonyl‐based poly(2,5‐dihydroxyl‐1,4‐benzoquinonyl sulfide) (PDHBQS) compound is synthesized and used as cathode material for lithium‐ion batteries (LIBs). Flexible binder‐free composite cathode with single‐wall carbon nanotubes (PDHBQS–SWCNTs) is then fabricated through vacuum filtration method with SWCNTs. Electrochemical measurements show that PDHBQS–SWCNTs cathode can deliver a discharge capacity of 182 mA h g−1 (0.9 mA h cm−2) at a current rate of 50 mA g−1 and a potential window of 1.5 V–3.5 V. The cathode delivers a capacity of 75 mA h g−1 (0.47 mA h cm−2) at 5000 mA g−1, which confirms its good rate performance at high current density. PDHBQS–SWCNTs flexible cathode retains 89% of its initial capacity at 250 mA g−1 after 500 charge–discharge cycles. Furthermore, large‐area (28 cm2) flexible batteries based on PDHBQS–SWCNTs cathode and lithium foils anode are also assembled. The flexible battery shows good electrochemical activities with continuous bending, which retains 88% of its initial discharge capacity after 2000 bending cycles. The significant capacity, high rate performance, superior cyclic performance, and good flexibility make this material a promising candidate for a future application of flexible LIBs. 相似文献
4.
G. Bertolino P. Arneodo Larochette E.M. Castrodeza A. Baruj H.E. Troiani 《Materials Letters》2010,64(13):1448-1450
The mechanical properties of martensitic Cu-Zn-Al foams produced through molten metal infiltration of a leachable bed of silica gel were investigated. The novel porous shape memory alloy almost reversibly absorbs compression deformations up to 4%. Intergranular fracture occurs in the material along the test, similar to what is observed in polycrystalline solid samples. Despite its tendency to fracture at localized regions, the material is highly resilient, being able to stand several compression cycles. The Cu-Zn-Al foams showed excellent shape recovery after deformation (95%). This previous fact establishes it as a very promising candidate for interesting applications. 相似文献
5.
Fatigue crack propagation behavior of RC beams strengthened with CFRP under cyclic bending loads 下载免费PDF全文
Dongyang Li Peiyan Huang Xinyan Guo Xiaohong Zheng Jiaxiang Lin Zhanbiao Chen 《Fatigue & Fracture of Engineering Materials & Structures》2018,41(1):212-222
A fatigue crack propagation equation of reinforced concrete (RC) beams strengthened with a new type carbon fiber reinforced polymer was proposed in this paper on the basis of experimental and numerical methods. Fatigue crack propagation tests were performed to obtain the crack propagation rate of the strengthened RC beams. Digital image correlation method was used to capture the fatigue crack pattern. Finite element model of RC beam strengthened with carbon fiber reinforced polymer was established to determinate J‐integral of a main crack considering material nonlinearities and degradation of material properties under cyclic loading. Paris law with a parameter of J‐integral was developed on the basis of the fatigue tests and finite element analysis. This law was preliminarily verified, which can be applied for prediction of fatigue lives of the strengthened RC beams. 相似文献
6.
A Polymer Encapsulation Strategy to Synthesize Porous Nitrogen‐Doped Carbon‐Nanosphere‐Supported Metal Isolated‐Single‐Atomic‐Site Catalysts 下载免费PDF全文
Aijuan Han Wenxing Chen Shaolong Zhang Maolin Zhang Yunhu Han Jian Zhang Shufang Ji Lirong Zheng Yu Wang Lin Gu Chen Chen Qing Peng Dingsheng Wang Yadong Li 《Advanced materials (Deerfield Beach, Fla.)》2018,30(15)
A novel polymer encapsulation strategy to synthesize metal isolated‐single‐atomic‐site (ISAS) catalysts supported by porous nitrogen‐doped carbon nanospheres is reported. First, metal precursors are encapsulated in situ by polymers through polymerization; then, metal ISASs are created within the polymer‐derived p‐CN nanospheres by controlled pyrolysis at high temperature (200–900 °C). Transmission electron microscopy and N2 sorption results reveal this material to exhibit a nanospheric morphology, a high surface area (≈380 m2 g?1), and a porous structure (with micropores and mesopores). Characterization by aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy and X‐ray absorption fine structure confirms the metal to be present as metal ISASs. This methodology is applicable to both noble and nonprecious metals (M‐ISAS/p‐CN, M = Co, Ni, Cu, Mn, Pd, etc.). In particular, the Co‐ISAS/p‐CN nanospheres obtained using this method show comparable (E1/2 = 0.838 V) electrochemical oxygen reduction activity to commercial Pt/C with 20 wt% Pt loading (E1/2 = 0.834 V) in alkaline media, superior methanol tolerance, and outstanding stability, even after 5000 cycles. 相似文献
7.
Paakinaho K Heino H Pelto M Hannula M Törmälä P Kellomäki M 《Journal of materials science. Materials in medicine》2012,23(3):613-621
This study reports of the novel water-induced shape-memory of bioabsorbable poly(d,l-lactide). We have developed an orientation-based programming process that generates an ability for poly(d,l-lactide) to transform its shape at 37°C in an aqueous environment without external energy and to adapt to a predefined stress
level by stress generation or relaxation. In this orientation-programming process, polymer material is deformed and oriented
at an elevated temperature and subsequently cooled down while retaining its deformed shape, tension, and polymer chain entanglements.
At body temperature and in an aqueous environment, the shape-memory is activated by the plasticizing effect of water molecules
diffused into the polymer matrix causing an entropy-driven directed relaxation of oriented and preloaded polymer chains. This
plasticizing effect is clearly seen as a decrease of the onset glass transition temperature by 10–13°C. We found that γ-irradiation
used for sterilizing the orientation-programmed materials strongly affected the shape-recovery rate, but not the recovery
ratio. Both non-γ-irradiated and γ-irradiated sample materials showed excellent shape-recovery ratios during a ten-week test
period: 94 and 97%, respectively. The orientation-programmed materials generated a predefined load in a 37°C aqueous environment
when their shape-recovery was restricted, but when external tension was applied to them, they adapted to the predefined level
by stress relaxation. Our results show that functionality in terms of shape-memory can be generated in bioabsorbable polymers
without tailoring the polymer chain structure thus shortening the time from development of technology to its utilization in
medical devices. 相似文献
8.
Massimo Messori Micaela Degli Esposti Katia Paderni Stefano Pandini Simone Passera Theonis Riccò Maurizio Toselli 《Journal of Materials Science》2013,48(1):424-440
The thermally activated shape memory response of polymeric materials results from a combination of the material molecular architecture with the thermal/deformational history, or ‘programming’. In this work, we investigate the shape memory response of systems based on poly(ε-caprolactone) (PCL) so as to explore the adoption of proper chemical and thermomechanical tailoring routes. Cross-linked semicrystalline PCL-based materials are prepared by different molecular architectures starting from linear, three- and four-arms star PCL functionalized with methacrylate end groups, allowing to tune the melting temperature, T m, ranging between 36 and 55 °C. The materials’ ability to display the shape memory is investigated by the application of proper thermomechanical cycles on specimens deformed at two different temperatures (23 and 65 °C, i.e. below and above the T m, respectively). The shape memory response is studied under dynamic thermal conditions in thermally activated recovery tests, to identify the typical transformation temperatures, and under isothermal conditions at given recovery temperatures, to monitor shape recovery as a function of time. All the specimens are capable of full recovery on specific thermal ranges influenced by both melting and deformation temperatures. Specimens deformed above T m are able to recover the whole deformation in a very narrow temperature region close to T m, while those deformed at room temperature display broader recovery processes, those onset at about 30 °C. Isothermal tests reveal that when the deformed material is subjected to a constant recovery temperature, the amount of recovered strain and the time required strongly depend on the particular combination of melting temperature, deformation temperature and recovery temperature. 相似文献
9.
Migration of di‐(2‐ethylhexyl)adipate (DEHA) and acetyl tributyl citrate (ATBC) plasticizers from PVC film into the food stimulant of isooctane 下载免费PDF全文
V. Lajqi‐Makolli M. Kerolli‐Mustafa I. Malollari J. Lajqi 《Materialwissenschaft und Werkstofftechnik》2015,46(1):16-23
Chemical migration from food packing is influenced by several factors such as nature of chemicals, complexity of food, temperature, packing material used and properties of the migrating substances. Chemical compounds that are incorporated within polymeric packaging materials may interact with food components during processing or storage and migrate into the food by jeopardizing the food safety. This migration is higher if food remains in contact with packing material for extended time. Polyvinyl chloride (PVC) film such as di‐(2‐ethylhexyl) adipate (DEHA) and acetyl tributyl citrate (ATBC) are still widely used as a food packing material due to its flexibility, transparency and low water permeability. The present study covers the main migration phenomena of both plasticizers (di‐(2‐ethylhexyl) adipate (DEHA) and acetyl tributyl citrate (ATBC)) from PVC‐film into isooctane food stimulant using a direct gas chromatographic method. An exposure period of 48 h at 30 °C and 4 °C was used. The obtained results showed DEHA levels ranging of 7.2 mg/dm2 while, no ATBC migration from PVC‐film was observed. Results are discussed in relation to EU legislation proposed upper limit for DEHA specific migration (18 mg/L or 3 mg/dm2) and overall migration limit (OM) of 10 mg/dm2. 相似文献
10.
Ultrahigh‐Water‐Content,Superelastic, and Shape‐Memory Nanofiber‐Assembled Hydrogels Exhibiting Pressure‐Responsive Conductivity 下载免费PDF全文
Yang Si Lihuan Wang Xueqin Wang Ning Tang Jianyong Yu Bin Ding 《Advanced materials (Deerfield Beach, Fla.)》2017,29(24)
High‐water‐content hydrogels that are both mechanically robust and conductive could have wide applications in fields ranging from bioengineering and electronic devices to medicine; however, creating such materials has proven to be extremely challenging. This study presents a scalable methodology to prepare superelastic, cellular‐structured nanofibrous hydrogels (NFHs) by combining alginate and flexible SiO2 nanofibers. This approach causes naturally abundant and sustainable alginate to assemble into 3D elastic bulk NFHs with tunable water content and desirable shapes on a large scale. The resultant NFHs exhibit the integrated properties of ultrahigh water content (99.8 wt%), complete recovery from 80% strain, zero Poisson's ratio, shape‐memory behavior, injectability, and elastic‐responsive conductivity, which can detect dynamic pressure in a wide range (>50 Pa) with robust sensitivity (0.24 kPa?1) and durability (100 cycles). The fabrication of such fascinating materials may provide new insights into the design and development of multifunctional hydrogels for various applications. 相似文献
11.
Xiang Liu Wenjian Kuang Haibin Ni Zhi Tao Jianhua Chang Qinquan Liu Junxiang Ge Chi Li Qing Dai 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(22)
The monolithic integration of light‐emission with a standard logic transistor is a much‐desired multifunctionality. Here, a high‐efficiency light‐emitting transistor (LET) employing an inorganic quantum dots (QDs) emitter and a laser‐annealed vertical metal–oxide heterostructure is reported. The experimental results show that the peak efficiency and luminance of this QDs LET (QLET) are 11% and 8000 cdm?2, respectively at a monochromatic emitting light wavelength of 585 nm. As far as it is known, these are among the highest values ever achieved for LETs. More importantly, the QLET exhibits an ultrahigh electron mobility of up to 25 cm2 V?1 S?1, a lower efficiency roll‐off (7% at high 3000 cdm?2), and excellent stability with long‐duration gate stress switching cycles. Additionally, this approach is compatible with those used in conventional large‐area silicon electronic manufacturing and can enable a scalable and cost‐effective procedure for future integrated versatile displays and lighting applications. 相似文献
12.
Felicia Nkem Ihunegbo Claas Wagner Kim H. Esbensen Maths Halstensen 《Particulate Science and Technology》2014,32(1):70-79
Reliable on-line/at-line prediction of particle size fractions of biomass material is a process monitoring concern owing to inherent variation in particle size and difficulty in sampling of pneumatically ducted biomass material. A feasibility study on application of acoustic chemometrics for at-line prediction of size fractions of biomass material has been performed, with all models subjected to independent test set validation. This study serves as a platform for at-line characterization of biomass samples from a sampling device extracting biomass samples from pneumatic conveying systems (based on theory of sampling). A prestudy using complex biomass/plastic pellets mixtures was used to test reliability and robustness of the experimental setup. Promising prediction results were achieved (slope, relative root mean square error of prediction (RMSEPrel), and correlation coefficient (r2) were 1.08, 24.94%, and 0.90, respectively). The same experimental setup was adapted for quantitative prediction of coarse versus fine biomass mixtures (the main objective) with satisfactory results; slope = 0.96, r2 = 0.97, RMSEP(rel) = 11%. A case study was also performed showing the adverse effect of using nonrepresentative coarse versus fine biomass samples for calibration. It is concluded that acoustic chemometrics is a viable technique for at-line prediction of size fractions of representative biomass materials. 相似文献
13.
This paper focuses on understanding the tension-tension fatigue behavior of woven glass fiber reinforced polymer laminates at cryogenic temperatures. Tension-tension fatigue tests at frequencies of 4 and 10 Hz with a stress ratio of 0.1 were conducted at room temperature, 77 and 4 K. The fatigue stress versus cycles to failure (S-N) relationships and fatigue limits for 106 cycles were obtained. Fractured specimens tested under fatigue tests were also examined with optical microscope. 相似文献
14.
In this study, the thermomechanical behavior of a shape memory polymer (SMP) based syntactic foam under three-dimensional (3-D) confinement was investigated through strain-controlled programming and fully confined shape recovery tests. The 3-D confinement was created by encasing the foam in circular confining tubes and subjecting the foam cylinder to uniaxial compression. The parameters investigated included two programming temperatures, three types of confining tubes with varying lateral confinements, three prestrain levels, and one fully-confined recovery condition. A three-layer plane-stress analytical model was also developed to estimate the volume change of the specimen by prestressing. It is found that the stress recovery ratio is the highest with rubber liner and the recovered stress is the highest with nylon liner. The stress recovered in the foam specimen which is confined by the nylon liner is as high as 26 MPa, making it possible as actuators. While volume reduction during programming is the key for the foam to self-close cracks, the volume reduction must be within a certain limit; otherwise, the foam loses its shape memory functionality. 相似文献
15.
Thomas Guillemet Jean‐Marc Heintz Bruno Mortaigne Yongfeng Lu Jean‐François Silvain 《Advanced Engineering Materials》2018,20(1)
16.
17.
As a new kind of smart materials, shape memory polymer composites (SMPCs) are being used in large in-space deployable structures. However, the recovery force of pure SMPC laminate is very weak. In order to increase the recovery force of a SMPC laminate, an alloy film was bonded on the surface of the laminate. This paper describes the post bulking behavior of the alloy film reinforced SMPC laminate. The energy term associate with this in-plane post buckling have been given .Based on the theorems of minimum energy, a mathematical model is derived to describe the relation between the strain energy and the material and geometry parameters of the alloy film reinforced SMPC laminate. The finite element model (FEM) is also conducted to demonstrate the validity of the theoretical method. The relation between the recovery force and the material geometry parameters were also investigated. The presented analysis shows great potential in the engineering application such as deployment of space structures. 相似文献
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19.
Sunhye Yang Kamrun Nahar Fatema Ick-Jun Kim Jihyeon Ryu Sang Eun Shim Won-Chun Oh 《Advanced Powder Technology》2021,32(4):1116-1126
This paper reports the synthesis of various molar concentrations of manganese (Mn)-doped Ultra-High Surface area Activated Carbon (USAC) additives and their efficient use as cathode materials for supercapacitors. We synthesized the nanoparticles via a novel and facile dip-coating process and characterized them in detail by various analytical techniques. The SEM, EDAX, and XPS results showed that the Mn ions were successfully substituted on the USAC additives’ layered structure without any structural changes. The long cyclic stability of the as-prepared Mn-doped USAC additives was tested as a cathode material for supercapacitors at different current densities. The detailed experimental results showed that the Mn dopant content crucially determines the electrochemical performances of the USAC additives. Electrochemical measurements showed that the MnCEP-S600HTT with 0.10 mol% molar concentration of Mn dopant gives the best cycling performances. It delivers a discharge capacity of 262.9 mAh g?1 after 100 cycles. Further increasing the current density to 1000 mA g?1 allowed it to still maintain 253.6 mAh g?1 after 200 cycles. We confirmed that the structure of Mn-doped USAC additives is an important pole to improve the structural stability and electrochemical properties. 相似文献
20.
Xiaoming Chen Meng Zheng Cheol Park Changhong Ke 《Small (Weinheim an der Bergstrasse, Germany)》2013,9(19):3345-3351
Understanding the interfacial stress transfer between carbon nanotubes (CNTs) and polymer matrices is of great importance to the development of CNT‐reinforced polymer nanocomposites. In this paper, an experimental study is presented of the interfacial strength between individual double‐walled CNTs and poly(methyl methacrylate) (PMMA) using an in situ nanomechanical single‐tube pull‐out testing scheme inside a high‐resolution electron microscope. By pulling out individual tubes with different embedded lengths, this work reveals the shear lag effect on the nanotube–polymer interface and demonstrates that the effective interfacial load transfer occurs only within a certain embedded length. These results show that the CNT–PMMA interface possesses an interfacial fracture energy within 0.054–0.80 J/m2 and a maximum interfacial strength within 85–372 MPa. This work is useful to better understand the local stress transfer on nanotube–polymer interfaces. 相似文献