Necar Merah

Fatigue Life Estimates in Woven Carbon Fabric/Epoxy Composites at Non-Ambient Temperatures

The influence of temperature on fatigue resistance of Plain Weave Woven CFRP isexamined. The 8-ply laminateswere obtained from epoxy resin prepreg fabric layers stacked in two different sequences, producing unidirectional [0]8 and angle plied [0, 0, 45, −45]s orientations. The fatigue tests were carried out at −20, 0, 24, 100 and 150°C. It wasfound that there wasno change in sequence of damage eventsbut duration of each event and hence cumulative damage rateswere different at different temperatures. The fatigue life at elevated temperature was found to decrease with increasing temperature but decreasing temperature below ambient conditions caused an increase in fatigue life for both classes of woven laminates. An analytical model based on stiffness degradation during cyclic loading, which isused in fatigue life prediction of CFRP at ambient temperature conditions has been successfully employed to estimate fatigue lives of WCFRP at non-ambient temperatures. A parameter D critical, which isa function of testing temperature, and represents the least stiffness value in modulus degradation curve, was introduced. Estimates of fatigue lives were compared with experimentally determined fatigue lives. Reasonably good correlation has been obtained between calculated and experimentally determined values of fatigue at all test temperatures considered in the present investigation.

Detecting and measuring flaws using electric potential techniques

The electric potential techniques are of two types: the direct current potential drop method (DCPD) and the alternating current potential drop method (ACPD). While the latter can be used mainly to detect surface defects, the first is more appropriate for detecting the initiation of cracks and monitoring their growth. One of the advantages of the ACPD is that it can be easily employed as a non‐destructive inspection tool. The DCPD has been used mainly in the laboratory environments under various conditions of loading including high gross inelastic deformations where subsurface flaws are present. Both these techniques have high accuracy and can be used as tools to detect defects in manufactured parts such as flaws in welds. Their findings are very useful in preventive maintenance; the inspectors and engineers use them to take decisions for scheduling maintenance. The present paper presents a review of the evolution in the design of ACPD and DCPD systems, with their advantages, disadvantages and fields of application. It is shown that ACPD and DCPD have comparable sensitivity and are widely used for surface crack measurement. The relatively new AC field measurement technique will be described. Its performance will be compared to that of ACPD. The use of DCPD in applications involving high temperature and gross inelastic strains will be stressed. The results obtained in low cycle fatigue conditions show that by including a special reference potential ratio, the DCPD yields a good estimation of the average surface and subsurface crack lengths. The method also allows an accurate detection of crack initiation in these conditions.

Optimizing the Curing Process of Epoxy-Clay Nanocomposites

Epoxy resin is one of the most applied thermoset polymers as a matrix for Glass Fiber Reinforced Pipes (GFRP). Curing process of epoxy resin is important for the integrity of the GFRP. The present work has been conducted to determine the proper pre-curing and post-curing temperatures and duration to develop epoxy-clay nanocomposite. During this study a differential scanning calorimeter (DSC) was used to determine the glass transition temperature and hence the degree of curing. Several samples of epoxy were prepared at different pre-curing and post-curing temperatures and durations. Pre-curing temperatures ranging from 80 to 150°C and post-curing temperatures ranging from 150 to 200°C were studied. The results show that the optimum pre-curing and post-curing temperatures are 100 and 170°C, respectively. Regarding the effect of curing duration, several specimens were prepared at the same pre-curing and post-curing temperatures with different curing durations of 1, 2, and 3 hours. It was observed that beyond one hour curing, the changes in the Tg and the degree of crosslinking were negligible. Using these optimum conditions samples of epoxy-clay nanocomposites were prepared using ultrasonication. The results showed that the addition of nonoclay to epoxy resulted in a reduction of the Tg.

The Effects of Clay Content and Sonication Time on Water Uptake in Epoxy-Organoclay Nanocomposites

The effects of clay loading and the extent of sonication time on water uptake in epoxy-organoclay based nanocomposites have been investigated as a function of exposure time in 3.5% NaCl at room temperature. Three clay loadings (2%, 4%, and 5wt.%) were dispersed in the epoxy resin by 10 and 60 minute sonication. The weight gains in the neat epoxy and the nanocomposites with 2 wt.% and 4 wt.% clay loadings showed a common asymptotic saturation value of 0.72 wt.% after 1000 hours of exposure. The saturation value was independent of sonication time. Nanocomposite with 5% clay loading and 60 minutes sonication exhibited a unique behavior and did not show saturation after 1000 hours of exposure. Scanning electron microscopy of tensile fractured nanocomposite specimens revealed the presence of organoclay aggregates, the size and number of which increased with an increase in clay loading. The Glass transition temperatures (Tg) for the nanocomposites decreased by approximately 20-25C° after 1000 hours of exposure in 3.5% NaCl solution.

Variation of Mechanical Properties of Epoxy-Clay Nanocomposite with Sonication Time and Clay Loading

Epoxy-clay nanocomposites have recently gained considerable attention due to their interesting physical, thermal and mechanical properties. These properties, however, depend on a number of parameters such as the clay type, clay modifying agent, polymer matrix and the adopted mixing process. In the current work, epoxy-clay nanocomposites were prepared from Araldite GY6010 CRS and Nanomer I.30E nanoclay using different sonication (mixing) periods (5 to 60 minutes) and different concentrations of clay (2 to 5%wt). The effect of sonication time and clay loading on the tensile and hardness properties of the resulting nanocomposites were investigated. The results showed that the ultimate strength and fracture strain of the nanocomposites were below that of the neat epoxy, but the elastic modulus was generally enhanced by the addition of the nano-clay content. Increasing the sonication time enhanced the tensile strength on the expense of reducing the modulus of elasticity. Hardness of the nanocomposites did not show significant change with either the addition of clay or processing under different sonication times.

Effect of pin tool profile on mechanical and metallurgical properties in friction stir spot welding of pure copper

In this paper, the influence of thread feature on mechanical and metallurgical properties of friction stir spot weldments is studied. Two pin tools, plain cylindrical and threaded cylindrical, having the same size are used to produce lap joints by friction stir spot welding (FSSW) of commercially pure copper. All experiments have been performed under the same welding parameters. The results revealed that joints produced with threaded pin tool have more than double the tensile shear strength of those produced by plain cylindrical pin. Moreover, the samples that were FSS welded with threaded pin tool failed in a plug failure mode, which is a desirable ductile failure mode. On the other hand, the weldments that were produced using plain cylindrical pin tool failed in interfacial failure mode or shear fracture mode. Effective upper sheet thickness analysis showed upward hook formation and less effective upper sheet thickness, which indicate better material mixing in the case of threaded pin tool. Furthermore, the transition bonding region was found to be very narrow in the case of plain tool while that of the threaded pin tool showed a transition region that is almost equal to complete bonding region, indicating gradual change from unbonded to complete bond; resulting in the above observed higher strength. Scanning electron microscopy analysis of the hook formation region revealed that, contrary to the weldments performed by plain pin tool, which showed the presence of large voids around the hook region, weldments performed with threaded pins were free of defects.

Effect of Sonication Time and Clay Loading on Nanoclay Dispersion and Thermal Property of Epoxy-Clay Nanocomposite

The development of nanoclay-epoxy nanocomposite material requires a suitable blending process to be employed. Amongst blending techniques, sonication has been one of the promising means for polymer-clay nanocomposite fabrication. In this study, epoxy-clay nanocomposites with 2, 4 and 5% clay loadings were fabricated using different sonication periods ranging from 5 to 60 minutes. The effect of sonication time and clay loading on the nanocomposite structure was investigated using Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), Scanning Electron Micropscope (SEM) and Energy Dispersive Spectroscopy (EDS). Differential Scanning Calorimetry analysis indicated that while clay loading reduced the glass transition temperature (Tg), sonication time did not alter Tg significantly. Upon examining the structure of the resulting nanocomposites both exfoliation and intercalation structures were present, yet, neither structure was fully achieved; evident by the XRD patterns. Nonetheless, the predominant structures for most of the nanocomposites were intercalation. Intergallery spacing of the nanocomposites were enhanced with increased sonication time mainly at 2%wt loading; whereas further increase in nano-clay loading resulted in a reduction of the d-spacing. SEM analysis showed that clay agglomerates were present in the nanocomposites irrespective of the sonication time. However, the analysis revealed that dispersion of clay was better in the nanocomposite fabricated at higher sonication time. From the EDS analysis, the different sites in the nanocomposites’ microstructure were identified which were then correlated with the observation made in the fractographic analysis.

Crude Oil and Outdoor Temperature Effects on the Tensile and Creep Properties of Glass Fiber Reinforced Vinylester Composite Pipes

Composites are overtaking their traditional counterpart materials by prooving themselves to be superior alternatives even for their application in harsh environmental conditions. The technological innovations and developments in manufacturing processes, which lead to a wide range of new composite products, have made them attractive candidates for applications in oil & gas industry, with their application ranging from oil production to transportation. Lack of enough data regarding their long-term environmental and mechanical durability has been a major hinderance in their full-fledge application. This paper investigates the effect on the tensile and creep strength of filament wounded E-glass/vinylester composite pipes (GFRV) exposed to a combination of crude oil and outdoor temperature conditions of Dhahran. The variation in the tensile and creep properties is considered for exposure periods of 6, 12 and 24 months. The combined crude oil filled GFRV pipes exposed to outdoor environmental conditions for a periods of 6, 12 and 24 months have shown a constant increase in the tensile and creep strengths respectively, when compared with the as-received GFRV samples. This increase in the tensile and creep strengths may be attributed to the dual curing of the GFRV pipes i.e both the outer side and inner side of the pipes due to outdoor temperature and crude oil respectively. Microscopic analysis of fractured surfaces using optical microscope and SEM is used to characterize the failure mechanisms responsible.

Nanoclay enhancement of flexural properties and water uptake resistance of glass fiber-reinforced epoxy composites at different temperatures

In this study, glass fiber-reinforced epoxy-nanoclay composite plates, with I.30E clay contents ranging between 0 and 5 wt.%, were manufactured by hand layup with hot pressing. Flexural strength of unexposed fiber-reinforced epoxy-nanoclay reached an optimum improvement of 11% for 1.5 wt.%. Scanning electron microscope analysis showed that at this clay loading, better interfacial adhesion of clay with glass fibers was achieved. At higher clay loadings, clay agglomeration and presence micro-voids led to less strength improvement. The maximum water uptake was found to decrease with increasing clay loading and moisture diffusion at 80℃ was about 80% higher than that at room temperature. Post exposure flexural tests revealed a behavior similar to that of unexposed samples with nanoclay loading of 1.5 wt.% leading to optimal flexural properties. Exposure to moisture resulted in degradation of fiber-reinforced epoxy-nanoclay flexural properties with about 36% reduction in strength for 80℃ and 8% for room temperature.

Premature Failure of an Industrial Mixer Timing Gears

A systematic and practical methodology was adopted to determine the root cause(s) of the premature failure of a pelletizer mixer timing gear. The investigation activities covered all possible causes of failure and included field examination, interview of engineers and operators, lubrication analysis, metallurgical examination. Fracture surfaces and microstructure of gear material were examined, and hardness profiles were developed. Analyses of shaft misalignment and teeth profiles were performed and found to be within acceptable limits. Results clearly indicate the surface hardness deficiencies in many locations specifically at center of the driven gear, area of severe pitting. The developed hardness profile for all locations is lower than that specified by the manufacturer. Fractographic analysis revealed that failure occurred by pitting followed by crack propagation. A number of cracks are seen to branch in different directions indicating the presence of high contact stresses combined with weak surface strength. Bending fatigue and pitting fatigue stress calculations revealed that the safety factor under contact is well below the desired value.