Effects of T-tabs and large deflections in DCB specimen tests

A simple strength of materials analysis was developed for a double-cantilever beam (DCB) specimen to account for geometric nonlinearity effects due to large deflections and T-tabs. A new DCB data analysis procedure was developed to include the effects of these nonlinearities. The results of the analysis were evaluated by DCB tests performed for materials having a wide range of toughnesses. The materials used in the present study were T300/5208, IM7/8551-7, and AS4/PEEK. Based on the present analysis, for a typical deflection/crack length ratio of 0.3 (for AS4/PEEK), T-tabs and large deflections cause a 15 percent and 3 percent error, respectively, in the computer Mode 1 strain energy release rate. Design guidelines for DCB specimen thickness and T-tab height were also developed in order to keep errors due to these nonlinearities within 2 percent. Based on the test results, for both hinged and tabbed specimens, the effects of large deflection on the Mode 1 fracture toughness (G sub Ic) were almost negligible (less than 1 percent) in the case of T300/5208 and IM7/8551-7; however, AS4/PEEK showed a 2 to 3 percent effect. The effects of T-tabs G sub Ic were more significant for all the materials with T300/5208 showing a 5 percent error, IM7/8551-7 a 15 percent error, and, AS4/PEEK a 20 percent error

Experimental and analytical investigation on CFRP strengthened glulam laminated timber beams: Full-scale experiments

© 2018 Elsevier Ltd Timber is one of the most appealing and aesthetic construction materials with excellent characteristics compared with other construction materials such as steel, concrete and clay bricks. It is one of the oldest sustainable construction materials and still continues to be a popular choice in modern infrastructure. In recent years, fibre reinforced polymers (FRP) has emerged to improve mechanical properties even further. In this study, results of experimental tests on strengthened glulam beams have been used to investigate potential parameters affecting flexural strength and ultimate load carrying capacity of glulam beams strengthened with externally bonded FRP sheets. Eight full-scale timber beams with and without FRP reinforcement were tested where the bonded length, width, and thickness of the FRP was varied for FRP strengthened beams. The test results pointed out that reduction of stress concentrations can enhance the mechanical performance of the strengthened beams. The ultimate load carrying capacity and flexural strength of reinforced beams improved significantly when bond length and bond width increased. Results of experiments showed that further increase in bond thickness predominantly improves stiffness and ductility of the strengthened timber beams which has a significant enhancement in ultimate deflection and serviceability limit state. An analytical model has been established to determine the ultimate flexural capacity of strengthened timber beam. Satisfactory correlation is achieved between measured and predicted flexural capacity, signifying the capability of the new models

Modelling the bond slip behaviour of FRP externally bonded to timber

Recent studies and applications have demonstrated that Fibre Reinforced Polymer (FRP) has become a mainstream technology for the strengthening and/ or rehabilitation of ageing and deteriorated structures. However, one of the main problems which limit the full utilisation of the FRP material strength is the premature failure due to debonding. This research study presents 1) a review of available FRP-to-timber and FRP-to-concrete bonded interface models, and 2) investigates factors affecting bond strength. A stepwise regression method has then been employed to evaluate the influence of potential factors on the bond strength. The proposed stepwise regression model is based on 195 experimental results of FRP-to-timber bonded interfaces. Results of this stepwise regression analysis are then assessed with results of pull-out tests and satisfactory comparisons are achieved between measured failure loads (R2=0.59) and the predicted loads (R2=0.71, P<0.0001)

South Africa

Since the late 1990s, empirical evidence has strongly suggested a gradual increase in drug-related problems and substance abuse (illicit and prescription) in South Africa. Abuse of alcohol is still the primary issue, but other illegal drugs are a very close in any list of social ills for South Africa As in most parts of the world, issues and social problems associated with substance abuse continue to be exacerbated and perpetuated by socio-economic and developmental factors in South Africa. This issue is made worse by the fact that South Africa is one of the world’s largest producers of some illegal drugs such as marijuana. Many international law enforcement experts offer that this location in Africa is the genesis of much of the cannabis trafficked into the Netherlands and the United Kingdom

Timber type effect on bond strength of frp externally bonded timber

© WCTE 2018 Committee. The performance of FRP composite bonded externally to timber is complex and limited attempts have been made to-date to investigate the bond behaviour of the FRP to timber interface. Furthermore, analytical solutions to determine the interface behaviour of FRP to timber have not been fully investigated and are not covered in current standards. This study investigates the influence of timber type and timber mechanical properties on the bond strength of FRP-to-timber joints. Two different types of timber (LVL and hardwood) have been used and results of experimental tests showed that with the increase of timber tensile strength and modulus of elasticity, the interfacial bond strength increases; however, the failure mode can be brittle. Specimens made from LVL exhibited more ductile behaviour failing gradually; while joints made from hardwood failed suddenly in a brittle manner. It was also observed that the local slip between FRP and timber was higher for joints fabricated from LVL compared to hardwood. Therefore, to achieve a satisfactory bonded joint, the effectiveness of timber mechanical properties is required to be accurately considered

Bond strength model for externally bonded FRP-to-timber interface

© 2018 Elsevier Ltd Despite the large number of studies on externally bonded elements using FRP composites, there is a significant knowledge gap to gain a comprehensive understanding of potential parameters such as bond width, bond length, material properties and geometries that influence bond strength. Behaviour of FRP bonded to concrete has been well investigated and there are a number of experimental and theoretical studies in this area; however, limited attempts have been made to investigate the bond behaviour of the FRP to timber interface. This paper reports an investigation on the behaviour of FRP externally bonded to timber. A novel theoretical model has been developed through stepwise regression analysis of 136 single shear FRP-to-timber joints. This has led to establishing a new predictive model for determination of the bond strength for FRP-to-timber joints. Results of this stepwise regression analysis are then assessed with results of experimental tests, and satisfactory comparisons have been achieved between ultimate applied loads and the predicted loads. Finally, a significant improvement in prediction of bond behaviour has been achieved when results of the proposed analytical model compared with the existing models from the literature, signifying the capability of the new models

Every breath you take: An examination of the natural phenomenon of stalking

Everyone is a potential stalker, given the right set of circumstances. There are a vast number of tools readily available—from social media networking to easily accessible websites that provide background checks for a minimal fee—that allow individuals to observe the life (or lives) of whomever they so desire. But what are the innate, essential traits and characteristics of an individual that extends beyond the more normative expression of romantic interest and the general curiosity that is a natural and accepted occurrence for anyone who has ever been infatuated with another? This paper will consider the intentionality and motivation behind stalking, including cyber-stalking, as well as the general obsessive behavior that acts as a proclivity toward stalking and ultimately conclude that everyone is a potential stalker and, further, that we as a society are being conditioned by the media—particularly social media—to accept stalking as a natural phenomenon

Effect of substrate thermal resistance on space-domain microchannel

In recent years, Fluorescent Melting Curve Analysis (FMCA) has become an almost ubiquitous feature of commercial quantitative PCR (qPCR) thermal cyclers. Here a micro-fluidic device is presented capable of performing FMCA within a microchannel. The device consists of modular thermally conductive blocks which can sandwich a microfluidic substrate. Opposing ends of the blocks are held at differing temperatures and a linear thermal gradient is generated along the microfluidic channel. Fluorescent measurements taken from a sample as it passes along the micro-fluidic channel permits fluorescent melting curves to be generated. In this study we measure DNA melting temperature from two plasmid fragments. The effects of flow velocity and ramp-rate are investigated, and measured melting curves are compared to those acquired from a commercially available PCR thermocycler

Control of CNS midline transcription by asymmetric E-box-like elements: Similarity to xenobiotic responsive regulation

Central nervous system midline cells constitute a discrete group of Drosophila embryonic cells with numerous functional and developmental roles. Corresponding to their separate identity, the midline cells display patterns of gene expression distinct from the lateral central nervous system. A conserved 5 base pair sequence (ACGTG) was identified in central nervous system midline transcriptional enhancers of three genes. Germ-line transformation experiments indicate that this motif forms the core of an element required for central nervous system midline transcription. The central nervous system midline element is related to the mammalian xenobiotic response element, which regulates transcription of genes that metabolize aromatic hydrocarbons. These data suggest a model whereby related basic-helix-loop-helix-PAS proteins interact with asymmetric E-box-like target sequences to control these disparate processes