Closed-form solution for a mode-III interfacial edge crack between two bonded dissimilar elastic strips

A closed-form solution is obtained for the problem of a mode-III interfacial edge crack between two bonded semi-infinite dissimilar elastic strips. A general out-of-plane displacement potential for the crack interacting with a screw dislocation or a line force is constructed using conformal mapping technique and existing dislocation solutions. Based on this displacement potential, the stress intensity factor (SIF, K_III) and the energy release rate (ERR, G_III) for the interfacial edge crack are obtained explicitly. It is shown that, in the limiting special cases, the obtained results coincide with the results available in the literature. The present solution can be used as the Green’s function to analyze interfacial edge cracks subjected to arbitrary anti-plane loadings. As an example, a formula is derived correcting the beam theory used in evaluation of SIF (K_III) and ERR (G_III) of bimaterials in the double cantilever beam (DCB) test configuration.     

Unexpected selective monoadduct formation from 2-methyl-3-butyn-2-ol and α,ω-diiodoperfluorobutane

Radical chain addition of α,ω-diiodoperfluorobutane to 2-methyl-3-buten-2-ol and 2-methyl-3-butyn-2-ol has been studied. The Huang sulfinatodehalogenation system, used as initiator, gave satisfactory conversion yields of the starting diiodide when compared to more classical initiators (AIBN, Fe, triethylborane). Addition to the alkenol yields classically the bis-adduct with variable amounts of the monoadduct. On the contrary the alkynol leads exclusively to the monoadduct formation, in high yield. Some considerations are proposed for interpreting this result. The monoadduct selectively obtained constitutes a powerful intermediate for synthesis.     

Initiation mechanism of ultrasonically irradiated emulsion polymerization

The emulsion polymerization of some monomers can occur without the conventional free radical initiators under ultrasonic irradiation. However, the initiation mechanism is still under controversy. In this paper, the sources of free radicals arising from ultrasonically initiated emulsion polymerization were investigated. Experimental results show that ionic surfactants play a very important role in obtaining a high polymer yield. While monomer conversion is very low in the absence of surfactants or in the presence of nonionic surfactants, it increases significantly upon addition of a little amount of ionic surfactant. FTIR and a radical trapping experiment confirm that the free radicals involved in the irradiation process originate from the decomposition of the ionic surfactants. Under ultrasonic irradiation, ionic surfactants undergo bond scission between the alkyl and ionic group, where the bond is the weakest along the chain. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2617–2624, 2005     

Circular crack in a transversely isotropic piezoelectric space under point forces and point charges

In this paper, two kinds of circular crack including external circular crack and penny-shaped crack in a transversely isotropic piezoelectric space are considered. Firstly, we obtain the solution to the problem of an external circular crack in a transversely isotropic piezoelectric space subjected to antisymmetric normal point forces and point charges. Based on this, the solution of one-sided loading of an external circular crack is constructed. Secondly, the real shape of an external circular crack and the opening displacement of a penny-shaped crack under an arbitrary point force and point charge are further obtained. At last, the results are presented in a graphical form. The project supported by the National Natural Science Foundation of China (19872060 and 69982009) and the Postdoctoral Foundation of China     

Comparative Properties of Styrene-Butadiene Rubbers (SBR) Containing Pyrolytic Carbon Black,Conventional Carbon Black,and Organoclay

To evaluate the reinforcing potential of pyrolytic carbon black, styrene-butadiene rubber (SBR) was filled with pelletized pyrolytic carbon black (pCB_p), N660 industrial CB, their blend in a 1/1 ratio, and the latter also in the absence and presence of additional organoclay (OC). The Shore A hardness of the filled SBR gums was 65 ± 2°. Effects of the compositions on the filler dispersion, cure behavior, dynamic mechanical thermal parameters (including the Payne effect), tensile mechanical (including the Mullins effect), and fracture mechanical (making use of the J-integral concept) properties were studied and discussed. Though pCB_p had a higher specific surface weight than CB, the latter proved to be a more active filler with respect to the tensile strength. The opposite tendency was found for the tear strength and fracture mechanics characteristics (J-integral at crack tip opening, tearing modulus, and trouser tear strength). This was traced to an enlargement in the crack tip damage zone supported by the dispersion characteristics of the pCB_p. The performance of pCB_p was similar to that of CB with respect to some other properties. OC supported the filler networking which positively affected the resistance to crack initiation.     

一维正方准晶沿准周期方向穿透的抛物线裂纹问题

利用广义复变函数方法研究了一维正方准晶材料中周期平面的抛物线裂纹问题,通过建立广义保角映射,将物理平面的抛物线裂纹外映射到数学平面里的单位圆内.得出了声子场和相位子场的应力分量在像平面下的复表示,并且得到了抛物线裂纹尖端的应力强度因子.并在特殊情况下,所得结果与Griffith裂纹的结果一致.     

用边缘荷载格林函数方法计算含裂纹Reissner型有限板的弯曲

本文在文献[1]所得到的受边缘荷载格林函数基本解方法基础上,利用叠加原理,通过边界积分方程的方法,分析了含裂纹Reissner型板的弯曲断裂问题。计算表明方法正确,便于应用。     

Influence of specimen geometry on the slow crack growth testing of HDPE for pipe applications

The majority of field failures in piping are attributable to slow crack growth (SCG) fractures. These fractures are characterized by the stable growth of a crack with little deformation in the plastic material. Slow crack growth (SCG) testing involves accelerating the growth mechanism through elevated temperature, concentrated stress, constrained geometry, surfactants or some combination of these factors. Some of these accelerated tests, Pennsylvania Edge-Notch Tensile (PENT) and Full Notch Creep Tests (FNCT), have been designed specifically to promote the SCG failure by stress concentration. However, the development of new polymeric materials used in pipes for transportation, has greatly increased the time required to happen SCG failure through these accelerated tests. Recently, new specific geometries for specimens to promote the failure by SCG have been analyzed, such as the Circumferentially Deep Notched Tensile (CDNT) sample.In this work, the reliability of the CDNT specimen to promote SCG failure on two types of ethylene copolymers was studied. The ligament surfaces after failure were analyzed to identify the SCG. The failure times were compared with those obtained on the same materials tested with a PENT geometry.     

Hierarchical Nacre Mimetics with Synergistic Mechanical Properties by Control of Molecular Interactions in Self‐Healing Polymers

Designing the reversible interactions of biopolymers remains a grand challenge for an integral mimicry of mechanically superior biological composites. Yet, they are the key to synergistic combinations of stiffness and toughness by providing sacrificial bonds with hidden length scales. To address this challenge, dynamic polymers were designed with low glass‐transition temperature T_g and bonded by quadruple hydrogen‐bonding motifs, and subsequently assembled with high‐aspect‐ratio synthetic nanoclays to generate nacre‐mimetic films. The high dynamics and self‐healing of the polymers render transparent films with a near‐perfectly aligned structure. Varying the polymer composition allows molecular control over the mechanical properties up to very stiff and very strong films (E≈45 GPa, σ_UTS≈270 MPa). Stable crack propagation and multiple toughening mechanisms occur in situations of balanced dynamics, enabling synergistic combinations of stiffness and toughness. Excellent gas barrier properties complement the multifunctional property profile.     

Three-dimensional analysis of a spheroidal inclusion in a two-dimensional quasicrystal body

This paper deals with the three-dimensional problem of a spheroidal quasicrystalline inclusion, which is embedded in an infinite matrix consisting of a two-dimensional quasicrystal subject to uniform loadings at infinity. Based on the general solution of quasicrystals in cylindrical coordinates, a series of displacement functions is adopted to obtain the explicit real-form results for the coupled fields both inside the inclusion and matrix, when three different types of loadings are studied: axisymmetric, in-plane shear and out-of-plane shear. Furthermore, the present results are reduced to the limiting cases involving inhomogeneities including rigid inclusions, cavities and penny-shaped cracks.