Experimental Study of the Relaxation Properties of Carbon Fiber Cloth

In this study, a new method was proposed to study the relaxation properties of carbon fiber reinforced plastics (CFRP) fabric under axial tension. Under the condition of constant temperature and humidity, six groups of 168 h stress relaxation tests were conducted. Considering the influence of the prestress level, the size of CFRP cloth, and the surface coating of CFRP cloth on the relaxation performance, the measures to reduce the relaxation loss were proposed. The relaxation rate calculation model was established based on the test results of the authors and other scholars and was validated through comparisons with the test results. The results indicate that the relaxation rate of CFRP cloth was between 1.92% and 6.1%. When the prestress level was smaller than 0.3 fu, the relaxation rate of CFRP cloth decreased with the increase of prestress level. When the prestress level was greater than 0.3 fu, the relaxation rate increased with the increase of the prestress level. Under the same conditions, the relaxation rate of the CFRP specimens coated with glue was smaller than the uncoated samples by 3.21–6.28%. The calculation model could well estimate the relaxation rate of CFRP cloth.

Improved Water-Tree Resistances of SEBS/PP Semi-Crystalline Composites under Crystallization Modifications

Water-tree resistances of styrene block copolymer/polypropylene (SEBS/PP) composites are investigated by characterizing crystallization structures in correlation with the dynamic mechanical properties to elucidate the micro-structure mechanism of improving insulation performances, in which the accelerated aging experiments of water trees are performed with water-knife electrodes. The water-tree morphology in spherulites, melt-crystallization characteristics and lamella structures of the composite materials are observed and analyzed by polarizing microscopy (PLM), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively. Dynamic relaxation and stress-strain characteristics are specifically studied by means of a dynamic thermomechanical analyzer (DMA) and electronic tension machine, respectively. No water-tree aging occurs in both the highly crystalline PP and the noncrystalline SEBS elastomer, while the water trees arising in SEBS/PP composites still has a significantly lower size than that in low-density polyethylene (LDPE). Compared with LDPE, the PP matrix of the SEBS/PP composite represent a higher crystallinity with a larger crystallization size in consistence with its higher mechanical strength and lower dynamic relaxation loss. SEBS molecules agglomerate as a “island” phase, and PP molecules crystallize into thin and short lamellae in composites, leading to the blurred spherulite boundary and the appreciable slips between lamellae under external force. The high crystallinity of the PP matrix and the strong resistance to slips between lamellae in the SEBS/PP composite essentially account for the remarkable inhibition on water-tree growth.

Electroactive Composites with Block Copolymer-Templated Iron Oxide Nanoparticles for Magnetic Hyperthermia Application

Cancer has been one of the leading causes of human death for centuries. Magnetic hyperthermia is a promising technique to confine and control cancers. However, particles used in magnetic hyperthermia leaking from where the cancers are located could compromise human health. Therefore, we developed electroactive iron oxide/block copolymer composites to tackle the leakage problem. Experimental results show that oleylamine-modified magnetic iron oxide (Fe3O4) particles and electroactive tetraaniline (TA) could be templated in the self-assembled microstructures of sulfonated [styrene-b-(ethylene-ran-butylene)-b-styrene] (S-SEBS) block copolymers. Various amounts of Fe3O4 particles and TA oligomer were incorporated in S-SEBS block copolymer and their electroactive behavior was confirmed by exhibiting two pairs of well-defined anodic and cathodic current peaks in cyclic voltammetry tests. The heating performance of the resultant TA/Fe3O4/polymer composites improved on increasing the added amount of Fe3O4 particles and TA oligomers. Both Fe3O4 and TA can contribute to improved heating performance, but Fe3O4 possesses a greater contribution than TA does. Hence, the main source for increasing the composites’ temperature is Neel relaxation loss from Fe3O4 magnetic particles.

ADHESION OF COMPONENTS OF COMPOSITE STEEL AND CONCRETE CROSS SECTION IN ANALYSIS OF BEAMS WITH CONCRETE ENCASED SECTIONS

A brief overview of the issues of aggregate work of components of the composite steel and concrete section is made. It is presented various options for the layout of the cross-section of beams used in the practice of design. A review of the design of the regulatory documents regarding the issues of adhesion of cross-section el­ements is performed. The characteristic of experimental models is given. The features of destruction of models are shown. The reasons of the destruction are analyzed. The case of the loss of the bearing capacity of the ele­ment due to relaxation (loss) of adhesion at the steel - concrete interaction boundary is considered. Various shear surfaces of the concrete section are given. Calculations of the bearing capacity of the composite steel - concrete beams for each computational surface were performed, the obtained results were evaluated. Conclusions have been made on the question of ensuring aggregate work in case of composite steel - concrete beams with a fully encased steel core.

The Effect of Humidity on Dielectric Properties of PP-Based Nano-Dielectric

Nano-dielectrics are sensitive to humidity and easily degraded in damp environment because of the high surface energy of nanoparticles. In order to study the effect of humidity on the dielectric properties of nano-dielectric, polypropylene (PP) was modified by polyolefin elastomer (POE) and nano-SiO2, and the samples with obvious filling concentration were pre-selected by breakdown strength for damp aging. The aging experiments were carried out in different relative humidity. The dielectric properties of new, hygroscopic saturation and samples after drying were measured and analyzed. It is found that the breakdown strength of hygroscopic saturation nano-dielectrics decreased obviously compared with new samples, and it was difficult to recover after drying. The damp degradation resulted in different changing trends of permittivity of PP and nano-dielectric, but there were relaxation loss peaks of water in both of them. The influence of damp degradation on the trap distribution was studied by thermally stimulated depolarization currents (TSDC), and it was found that the traps level introduced by water molecules was different in PP and nano-dielectrics. All experiment results showed that the performance of nano-dielectrics degraded obviously in humid environment, and it was difficult to recover even after complete drying because of the existence of bounded water molecules in nano-dielectrics.

Relaxation behavior of prestressing basalt fiber-reinforced polymer tendons considering anchorage slippage

Relaxation is a key factor that controls the application of prestressing fiber-reinforced polymer tendons. This paper focuses on the evaluation of the relaxation behavior of newly developed basalt fiber-reinforced polymer tendons through an approach considering anchorage slippage. A series of relaxation tests on basalt fiber-reinforced polymer tendons subjected to three levels of initial stresses (0.4 fu, 0.5 fu, and 0.6 fu, where fu = ultimate strength) were conducted using a specially designed test setup that eliminates the impact of slippage at the anchor zone. An additional group of tests was conducted to validate the enhancement effect of pretension on the relaxation behavior. The relaxation rates at one million hours were predicted based on experimental fitting. Finally, the relaxation rates at 1000 h were predicted using the correlation between the relaxation and creep and were validated with the experimental relaxation rates. The results demonstrate the effectiveness of the proposed setup in measuring the relaxation loss of specimens and reveal that the relaxation rates of untreated basalt fiber-reinforced polymer tendons at 1000 h are 4.2%, 5.3%, and 6.4% at 0.4 fu, 0.5 fu, and 0.6 fu, respectively. Pretension treatment performs effective in relaxation loss controlling. BFRP tendons are recommended to be applied at an initial stress of 0.5 fu after pretension treatment, with one-million-hour relaxation rate equal to 6.7%. Furthermore, the relaxation rate at 1000 h can be predicted accurately based on the creep behavior. The conclusions of this study can provide guidance for the prestressing applications of basalt fiber-reinforced polymer tendons.

Analysis of Locking Value of Anchor Cable in Pile Anchor Supporting Structure

This paper analyses the problem of locking value of anchor cable of pile anchor supporting of a deep foundation pit in the north of Kunming city. There are many influencing factors of locking value of anchor cable such as relaxation loss of anchor cable materials, tensioning system, pre-stress loss caused by anchorage friction, geological conditions and so on. And the author put forward the corresponding treatment measures for achieving the stability of supporting structure.