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The focus of this research project is to establish what effect graphitization has on the static mechanical properties of service exposed ASTM A516 Grade 65 steam pipe material, which operated for prolonged periods above 425 ̊C. The research study was conducted on three graphitized service exposed steam pipe weldment samples and on a newly welded and post weld heat treated sample with graphitized service exposed steam pipe material. Macro samples were removed from each of the samples at two positions and these were evaluated with regard to graphite nodule size, nearest neighbour spacing and % planar graphitization in the parent pipe and HAZ regions on either side of the welds. It was found on all of the service exposed samples that the graphite nodules of the HAZ regions have a smaller median nodule size, smaller median nearest neighbour spacing and increased % planar graphitization in comparison to the parent pipe material. The service expose parent pipe material on either side of the weldments of the respective samples was chemically analyzed. This was done with the focus being on the deoxidizing element content (Si and Al) of the respective parent pipe regions and to what extent these elements influenced the development of planar graphitization in these regions. No correlation could be identified between the level of deoxidizing elements and the levels of % planar graphitization in the parent pipe material. Tensile and Charpy impact samples were removed from the respective service exposed samples parent material on either side of the weld and from the HAZ regions on the side with the highest levels of planar graphitization. These samples were tested and the yield and ultimate tensile strength and Charpy impact toughness of the respective samples were then evaluated to establish how these static mechanical properties were influenced by the % planar graphitization. The yield and ultimate tensile strength of the service exposed material did not show a statistically significant correlation with the % planar graphitization. The Charpy impact toughness results did however show a statistically significant negative correlation towards the % planar graphitization. This was clearly evident from the results of the HAZ regions of the service exposed weldments (Samples A-C) which had the highest levels of % planar graphitization and the lowest impact toughness, while the newly welded and post weld heat treated Sample D had no planar graphitization outside the HAZ and the highest impact toughness. This research project not only investigated how planar graphitization affects the static mechanical properties of service exposed pipe material, it also investigated on a microstructural basis, how planar graphitization nucleates and grows. The microstructural investigation showed that the free carbon required for the development of planar graphitization originated from the regions outside the HAZ, which were formed when the pearlite bands were dissolved during the welding of the steam pipe. The heat input from the welding sensitized this region for the development of planar graphitization, probably due to the formation of a “carbon-rich” matrix due to the partial dissolution of the cementite precipitates. All the carbide precipitates in this region consisted of M3C. aluminium-rich precipitates were found inside newly nucleated graphite nodules, indicating its role as a possible heterogeneous nucleation site. Growth of newly formed graphite nodules showed a preference towards high-angle grain boundaries and regions with dislocations for the initial growth stages of the graphite nodules. The microstructure of the region outside the HAZ of the newly introduced seam weld on the service exposed steam pipe material (with graphitization), was also investigated using advanced electron microscopy methods and it yielded no evidence of the development of planar graphitization.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2009. / Materials in almost all components are subjected to some kind of loading that must be correctly predicted to produce reliable designs. The understanding of a material's properties significantly impacts appropriate selection for a structure. This kind of material characterization is also important in the development of improved or new materials for high strength and novel applications. There are numerous metallurgical variables (composition and process parameters) that influence the physical and mechanical properties of materials. The aim of this work has been to study the influence of microstructure on mechanical properties of steel, specifically the effect of grain sizes within solid phase mixtures. Parameters for simple models of the variation of material properties with grain size can be determined. These models can then be incorporated in the material data sets of Finite Element Analysis programs which will then allow for structural analysis with zones in a material having different grain sizes. The deformation and damage behaviour of EN 8 steel have been stUdied with emphasis on the effects of grain size on the elastic-plastic response of the material. For that purpose, EN 8 specimens with a range of microstructures (grain size and phase) were prepared by heat treatment The microstructural features were carefully characterized using two different experimental surface microscopy techniques; Light Optical Microscope and Scanning Electron Microscope. The deformation and hardness characteristics have been studied with the help of tensile and hardness tests. The mechanical properties were determined as a function of microstructure (grain size and phase). The yield stress followed the classical Hall-Petch relation. The results indicated that tensile strength and hardness increases with decrease in grain size while elongation decreases. The main philosophy behind this research has been the study of the microstructure and information from the iron-carbon phase diagram together with numerical analysis of stress-strain data, in order, to understand the influence of grain size on mechanical behaviour of EN8 steel. This combination was then used to make general conclusions on mechanical behaviour of EN 8 based on heat treatment history.

The study of mechanical properties of perpendicular to the grain research is important regarding connections within mass paneling and other wood connections. Research on wood properties perpendicular to grain and the effect of decay on this direction is needed. Brown-rot fungi are a major contributor in having to replace or repair wooden members; therefore, the objectives of this study were to study the effect brown-rot decay has on the mechanical properties of perpendicular to the grain over different periods of exposure; and to evaluate the efficacy of various methods on assessing decay on wood. The methods evaluated in this study were mass loss (ML), moisture content (MC), density, time of flight, modulus of elasticity in tension (ET) and ultimate tensile strength (UTS). In this study, low mean values of ML occurred but due to fungal activity, MC of specimens were highly affected. Among all methods tested, time of flight showed the highest significant correlations with ET and UTS. Neither initial or final time of flight correlated with MC, concluding NDT was the most consistent method in identifying early decay on mechanical properties of wood.

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Yes / Mechanical properties of 2-4% manganese PM steels were determined in tension and in bending following laboratory sintering in dry, hydrogen rich atmospheres. Young's modulus determined by an extensometric technique was about 115 GPa; when measured by an ultrasonic method it was about 153 GPa, in accordance with the 'law of mixtures'. The microstructures, significantly devoid of oxide networks, were predominantly pearlitic, but frequently with variability for specimens similarly processed, resulting in appreciable variations in the stresses for macroscopic yielding and fracture. The majority of the experiments were conducted on 3 and 4Mn-0·6C alloys and for these R0·1 was in the range 275-500 MPa, tensile strength (TS) 300-600 MPa, and (apparent) transverse rupture strength (TRS) 640-1260 MPa. Statistical techniques were employed to analyse the data. When careful control of processing was maintained, the Weibull modulus was highest, at about 17, for TS of furnace cooled specimens, and lowest, about 6, for TRS of the rapidly cooled specimens. In order to interpret the significant differences between the TRS and the TS values, both apparently measuring the critical stress for cracking after strains of up to 7%, a two stage normalising technique for TRS was adopted. By taking account of the plastic strains preceding failure, the elastic 'strength of materials' formula was modified to allow true fracture stresses to be calculated. It was also postulated that failure was initiated from a population of flaws of variable size and then the 'normalised' bend strengths, smaller than TRSs, were shown to correspond well with TSs. It is suggested that this combined plasticity correction and Weibull analysis approach, which has a sound scientific basis, should be employed to interpret bend test data in preference to empirical correlations between TS and TRS.

Studies have investigated and dismissed the effect of freeze-thaw cycles on both skeletal muscle and on trabecular bone, but have failed to properly address the effects of these storage methods on the integrity of articular cartilage. Preventing cartilage injury is important in minimizing the long term debilitating effects of osteoarthritis. Accurate subfracture injury prediction must take into account the possible effects that freeze thaw cycles may have on the mechanical properties of cartilage tissue. This paper addresses this concern with matched pair testing of various low temperature storage techniques against fresh control groups. Controlled mechanical indention tests were performed on bovine articular cartilage-on-bone specimens to compare stiffness, peak stress, and loading energy of the cartilage. Findings showed that a slow freeze thaw or flash freeze cycle caused cartilage stiffness to decrease by 37% and 31% respectively. Compressive stress at this strain was also lowered by 31% with a single freezing process. These results may be indicative of a weakened extracellular matrix structure caused by the freeze-thaw process. It is still unclear whether these changes in mechanical properties will result in a change in injury susceptibility for articular cartilage. / Master of Science

Yes / Melt blending of polyolefin/carbon nanotube (CNT) composites always leads to serious agglomeration of CNTs and hence inferior properties. Thus, well-dispersed CNTs within matrix are urgently required during processing. In this work, effective breakage of CNT agglomerates was achieved by solid-phase die drawing at a temperature below but near to the melting temperature of the matrix. Experimental results indicate that the incurred extensional stress provides a high orientation degree on the polypropylene (PP) matrix and consequently helps rupture CNT agglomerates, leading to improved alternating current（AC） conductivity by ~5–6 orders in magnitude. The reduced agglomerate ratio, the altered CNT networks (3D→2D), and the improved interfacial morphology between CNT and matrix are suggested to be responsible for the viscoelasticity variation of the composite melt and the improved property of PP/multiwalled CNTs (MWCNTs) composite. The initial loss of tensile ductility by the incorporation of MWCNTs is recovered by nearly 100%, which was attributed to the low agglomeration rate and improved interfacial morphology. This article provided the potential inspiration for the melt blending of polymer melt and CNTs. / China Scholarship Council. Grant Number: 201806465028

The tensile strength of the fiber/matrix interface was determined through the development of an innovativetest procedure.Aminiature tensile coupon with a through-thickness oriented, embedded single fiberwas designed. Tensile testing was conducted ina scanning electron microscope (SEM)while the failure process could be observed.Finite element stress analysis was conducted to determine the state of stressat the fiber/matrix interface in the tensile loaded specimen, and the strength of the interface.Test specimensconsistingof dry E-glass/epoxy and dry and seawater saturatedcarbon/vinylester510Awere preparedand tested.The load at the onset of debondingwascombined withthe radial stressdistributionnear thefree surface of the specimento reducethe interfacial tensile strength. For glass/epoxy, was 36.7±8.8MPa.For the dryand seawater saturated carbon/vinylester specimensthetensilestrengthsof the interface were 23.0±6.6 and 25.2±4.1MPa, respectively.The difference is not significant. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection