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In the CCG life assessment for defective structures based on the two-parameter method with considering constraints, the establishment of a correlation equation between the constraint parameter and the CCG rate for a material at a temperature is very important, but it is difficult and costly. For engineering applications, it is desirable to have a unified correlation equation for different materials. In this work, based on a large amount of experimental CCG rate data of different specimens from the literature, combining with the finite element (FE) calculations of a new unified creep constraint parameter Ac ,, a unified correlation equation has been obtained. In the CCG life evaluation for cracked structures based on the C*-Ac two-parameter method, this correlation equation may be used to estimate the constraint-dependent CCG rates for any materials at different temperatures. The correlation equations of eleven materials are also summarised in this paper. [ABSTRACT FROM AUTHOR]

Extensive finite element analyses of cracked pipes with different crack sizes and orientations have been conducted to investigate effects of creep properties of materials on the unified creep constraint parameter Ac. The results show that the constraint parameter Ac is independent on Norton's coefficient A, and it is only affected by the creep exponent n of materials. For a given crack size, with increasing n, Ac decreases and constraint level increases. The Ac of lower constraint cracks is more sensitive to n. The unified correlation equations between Ac and n have been obtained for cracked pipes with a wide range of crack sizes and constraint levels. They may be used to estimate the constraint parameter Ac at different positions along the crack fronts in cracked pipes made of materials with different n values. The two-parameter C*-Ac approach for assessing creep life of cracked pipes has also been discussed. [ABSTRACT FROM AUTHOR]

Fiber-like high-surface-area and natural nanostructure clay mineral palygorskite (or attapulgite, ATP) containing lots of hydroxyl groups is found to efficiently catalyze the ring-opening polymerization (ROP) of ϵ-caprolactone (ϵ-CL). The products are subsequently characterized by FTIR,1H NMR, GPC, DSC, SEM and XPS analysis. The results show that porous PCL with relatively high molecular weight is obtained. A mechanism is proposed to illustrate that ϵ-CL is initiated by the constituent water in ATP and catalyzed by three active centers relate to hydroxyl groups on the surface of ATP. The ATP acts as a proton shuttle via its acidic hydrogen atoms and basic oxygen atoms. Moreover, there exists synergetic catalytic effect between the metal centers and Si centers. [ABSTRACT FROM AUTHOR]

Hybrid materials consisting of polydimethylsiloxane (PDMS) and polycyclohexyl-methylsiloxane (PCHMS) grafted graphene oxide (GO) were obtained by condensation polymerization in toluene. Fourier transform infrared spectroscopy indicates that the composites were synthesized through the formation of Si-O bond. The X-ray diffraction, scanning electron microscopy and thermogravimetric indicate that the hydrolysis polycondensation can accelerate the graft reaction. The hybrid films were prepared by simple filtration of the dispersed system of PDMS/GO/water, PCHMS/GO and PCHMS/GO/water in dimethylformamide. Tensile tests indicate the mechanical properties of the films varied with their structure. The rigid PCHMS/GO/water films have a tensile strength of 17.83 MPa, and the pliant PDMS/GO/water films have an elongation at break of 3.14%. UV-Vis spectra of GO and the hybrids indicate that the addition of polysiloxane caused a red-shift (10–20 nm) of the absorption peak. [ABSTRACT FROM AUTHOR]