The homogeneous dispersion of nanofillers and filler–matrix interfacial interactions are important factors in the development of high‐performance polymer materials for various applications. In the present work, a simple solution‐mixing method was used to prepare multi‐walled carbon nanotube (MWCNT)–graphene (G) (3:1, 1:1, 1:3) hybrids followed by their characterization through wide‐angle X‐ray diffraction, transmission electron microscopy and thermogravimetric analyses. Subsequently, MWCNT–G (1:1) hybrid was used as reinforcing filler in the formation of silicone rubber (VMQ) nanocomposites by solution intercalation, and their morphology and properties were investigated. Our findings showed that MWCNT–G (0.75 wt%)/VMQ composite exhibited significant improvements in tensile strength (110%) and Young's modulus (137%) compared to neat VMQ. The thermal stability of MWCNT–G (1 wt%)/VMQ was maximally improved by 154 °C compared to neat VMQ. Differential scanning calorimetry demonstrated the maximum improvement of glass transition temperature (4 °C), crystallization temperature (8 °C) and melting temperature (5 °C) for MWCNT–G (1 wt%)/VMQ nanocomposite with respect to neat VMQ. Swelling measurements confirmed that the crosslink density and solvent resistance were a maximum for hybrid nanocomposites. Such improvements in the properties of MWCNT–G/VMQ nanocomposites could be attributed to a synergistic effect of the hybrid filler. © 2013 Society of Chemical Industry

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A three-dimensional finite element analysis has been developed to compute the out-of-plane normal (known as peel stress) and shear stresses in an adhesively bonded single lap joint (SLJ) with laminated FRP composite plates which, in comparison to other analytical methods for bonded joint analysis, is capable of handling more general situations related to initiation of damages and its growth. Other analytical methods, such as Hart-Smith’s (Hart-Smith, L. J. (1973). Adhesive-Bonded Single Lap Joints, NASA-CR-112236.), are 1-D and mainly focus on obtaining adhesive stresses, while generally ignoring stresses in laminated adherends, particularly interlaminar stresses which are known to be the key contributors to the failure. Unlike the Volkersen’s (Volkersen, O. (1938). Die Niektraftverteilung in Zugbeanspruchten mit Konstanten Laschenquerschritten. Luftfahrtforschung, 15: 41-47.) and Goland-Reissener’s (Goland, M. and Reissner, E. (1944). The Stresses in Cemented Joints, Journal of Applied Mechanics, 11: 17-27.) analysis, the free rotation of the overlap region and adherends are considered in the present analysis. Joining of composite structures using adhesive bonding has always been a concern to the designers because the performance of the joint is severely influenced by the characteristics of the laminated composite adherends, which usually have low inter-laminar strengths. The present method computes local 3D stress fields in the most critical region, which vary along the overlap length. Adhesive layer is a linearly elastic material whereas the adherend materials are orthotropic. Thus an accurate evaluation of 3D local stress fields will enable the failure criterion to be employed effectively to predict joint strength and initiation/propagation of damages. The analysis consists of four steps. In the first step a complete three dimensional stress analysis is carried out with a special importance for the evaluation of out-of-plane stresses. Failure indices at different surfaces are calculated in the second step. The third step identifies the location of damage initiation based on the value of the failure indices. The failure index for the adhesive layer is calculated using quadratic failure criterion (QFC), whereas the Tsai-Wu’s coupled stress quadratic failure criterion is used for the interface of adherend and adhesive. Subsequently, damage propagation is analyzed by fracture mechanics based strain energy release rate (SERR) approach using virtual crack closure technique (VCCT). It is seen that the three-dimensional effects exist in the joint. The stress distributions in the joint overlap region near the free surface are quite different from those occurring in the interior. Also, it is found that the peel stresses are extremely sensitive to this three-dimensional effect, but the shear stresses are not. The value of the failure index at the interface of the loaded adherend (top) and adhesive along the free edge is the highest which indicates the location of the possibility of damage initiation. Such type of damage is considered as an adhesive failure. The propagation of such damage is governed by SERR. It is observed that the individual mode of SERR remains constant over the damage front irrespective of the damage length except at the free edge. Moreover, it is found that contribution of SERR in mode II is prominent compared to the mode I and mode III for the damage propagation due to the adhesive failure in the SLJ.

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Interference-fit pin connections have wide applications ranging from aerospace structures to electric hardware systems and the telephone industry. In order to derive the maximum benefit by the use of interference-fit pin in all such applications, a complete understanding of their behavior in the regions of joints is essential. This paper deals with the study of various beneficial effects of interference-fit pin-loaded FRP composite laminates. Three-dimensional finite element models have been created to simulate interference-fit pin-loaded joints in various composite laminates. Non-linear contact analyses have been performed to study the effects of interference for different material cases on (a) circumferential edge stresses, (b) stresses across the weakest section (i.e., net-tension plane), and (c) the out-of-plane stresses around the hole periphery. It is observed that interference with specific value for each material case and laminate configuration is beneficial for better load carrying capabilities. Suitable interference for improved performance has been evaluated and recommended for each case. It is also emphasized that by interference-fit fatigue life of the joint can be improved.

A new two-noded shear flexible curved beam element which is impervious to membrane and shear locking is proposed herein. The element with three degrees of freedom at each node is based on curvilinear deep shell theory. Starting with a cubic polynomial representation for radial displacement (w), the displacement field for tangential displacement (u) and section rotation ( ) are determined by employing force-moment and moment-shear equilibrium equations. This results in polynomial displacement field whose coefficients are coupled by generalized degrees of freedom and material and geometric properties of the element. The procedure facilitates quartic polynomial representation for both u and for curved element configurations, which reduces to linear and quadratic polynomials for u and , respectively, for straight element configuration. These coupled polynomial coefficients do not give rise to any spurious constraints even in the extreme thin regimes, in which case, the present element exhibits excellent convergence to the classical thin beam solutions. This simple C element is validated for beam having straight/curved geometries over a wide range of slenderness ratios. The results indicates that performance of the element is much superior to other elements of the same class.

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Welding process parameters and joint fit-ups significantly affect angular distortion patterns. By using constraints at proper positions the angular distortion can be minimized. In the present work the effect of constraints in the form of tack welds to minimize angular distortion in one-sided fillet welds has been analysed. It has been observed that proper positioning of tacks plays an important role in controlling angular distortion. The process was modelled using the three-dimensional finite element technique. Three-dimensional transient thermal analyses were done for predicting temperature distributions by considering a moving heat source. The element birth and death technique was used for simulating filler material deposition. The fillet welds were sectioned and microstructure zones were measured. The thermal model was verified by comparing the temperatures obtained from the thermal analysis with experimental results. Transient thermal and non-linear structural analyses were carried out in order to predict angular distortions.