Papers by Bernard C . Ogazi-Onyemaechi
Technical Papers, Regional Technical Conference - Society of Plastics Engineers, 2008
Polymers and Polymer Composites, 2009
The accurate prediction of scientific and statistical parameters depends, largely, on the functio... more The accurate prediction of scientific and statistical parameters depends, largely, on the functional correlation between the variables involved, as well as their definite and predictable behaviour around the line of best fit (the regression line). Hence, an accurate and reliable prediction of the fracture toughness and mechanical properties of glass fibre reinforced polypropylene (GFPP) composites is very important in order to prevent sudden failure of components fabricated from them. It also gives the opportunity to save cost on experimentation. Three grades of polypropylene (PP) of different molecular weights (MW) had glass fibre reinforcements each. The incorporation of maleic anhydride grafted PP (MA-g-PP) into the composites was for compatibilisation between the matrix and reinforcements. There was tensile testing on both the un-notched and notched dumbbell samples. The use of J-Integral analysis was to investigate the fracture toughness of the composites. There was an evaluati...
所属：大学院工芸科学研究科博士後期課程先端ファイブロ科学専攻；取得大学：京都工芸繊維大学 ; 取得学位：博士（学術）; 学位授与年月日：2010-09-24 ; 証書番号：博甲第５８３号 The... more 所属：大学院工芸科学研究科博士後期課程先端ファイブロ科学専攻；取得大学：京都工芸繊維大学 ; 取得学位：博士（学術）; 学位授与年月日：2010-09-24 ; 証書番号：博甲第５８３号 The prevention of catastrophic failures in engineering components depends largely on the accurate prediction of their fracture mechanism. Much research efforts have been made to understand the fracture toughness of polymeric materials and composites but these are limited to investigations conducted on samples introduced with single-depth standard V-notches. However, there is inadequate understanding on the notch sensitivity of injection moldings especially when a hierarchical skin-core structure is present. Therefore, this thesis focused on characterizing the fracture toughness of injection molded polyethylene terephthalate (PET) and glass fiber reinforced polypropylene (GFPP) composites, both of which are known for being notch sensitive. Chapters 3 and 4 of this thesis were dedicated to understanding the effects of standard V-notch and sharper hairline cracks, respectively, on the fracture...
The effect of notches was investigated by introducing single-edge hairline cracks and V-shaped no... more The effect of notches was investigated by introducing single-edge hairline cracks and V-shaped notches of different depths on dumbbell samples to ascertain the fracture behavior at the skin and core parts of virgin and recycled poly(ethylene terephthalate), (V-PET/R-PET), injection-moldings. Investigation shows that the fracture behavior of the materials responded differently to both hairline crack and V-shaped notch. Results revealed that a mere 5μm deep critical hairline crack caused a drastic change in the fracture behavior of the materials. In contrast, a standard V-shaped notch would only cause drastic change in toughness at a much higher critical notch depth of 600μm. V-shaped notch also provided a gradual transition in fracture behavior from the skin to the core regions, which suggests that the fracture behavior can be dependent on the skin and core sizes of PET injection moldings.
During tensile loading, the temperature of notched materials is correlated to the applied stress ... more During tensile loading, the temperature of notched materials is correlated to the applied stress and its resultant strain. At crack propagation, the strain energy that is released, or work done during deformation, affects the temperature at the crack tip and the yielding axis. The intensity of the temperature is seen to depend on the notch depth and stress intensity at the notch root. In this investigation, an infrared camera was used to monitor the temperature distribution around the crack axis during the tensile loading of notched PET specimens. The correlations between the temperature distributions at the crack-tip, notch sensitivity and essential work of fracture were established. Results reveal that the one of the major fracture mechanism that increases temperature is a mixed mode fracture. This occurs when crazing precedes semiductile/brittle fracture. It was observed that the highest change at the notch root temperature occurred in samples where the notch depths are located a...
Polymer Journal, 2010
Polyethylene terephthalate (PET) is often thought to be extremely notch sensitive, as other amorp... more Polyethylene terephthalate (PET) is often thought to be extremely notch sensitive, as other amorphous or slow-crystallizing polymers. However, our previous studies demonstrated three distinct fracture modes during tensile loading of PET when notch depth was gradually increased, namely ductile, semiductile and brittle. Therefore, the notch sensitivity of PET is thought to depend on its morphology and notch depth, whereas linear elastic fracture mechanics would be inadequate to characterize the fracture toughness of PET, especially when the material is injection molded and possesses the characteristic skin-core structure. This study revealed that the temperature at the crack tip significantly increased because of local plastic deformation when the crack tip was situated within the skin region. As such, full ligament yielding was obtained, which allowed characterization of the fracture toughness of PET using the principles of essential work of fracture (EWF). However, no significant temperature increase occurred when specimens fractured in a brittle manner as the notch penetrated through the skin and into the core. At this point, the material is said to be notch sensitive and is no longer able to undergo any plastic deformation before failure.
Journal of Applied Polymer Science, 2010
Ogazi-Onyemaechi, BC, Leong, YW and Hamada, H.(2010), Crack propagation behavior and toughness of... more Ogazi-Onyemaechi, BC, Leong, YW and Hamada, H.(2010), Crack propagation behavior and toughness of V-notched polyethylene terephthalate injection moldings. Journal of Applied Polymer Science, 116: 132141. doi: 10.1002/app. 31496
Polymer Journal, 2010
Hairline cracks are microscopic defects found in most injection-molded components. The effects of... more Hairline cracks are microscopic defects found in most injection-molded components. The effects of such hairline cracks on the fracture modes of injection moldings, especially polyethylene terephthalate (PET), are still not well understood. The slow crystallizing nature of PET results in a distinct skin-core structure when it is injection molded. By controlling the hairline crack depth, the crack tip can be situated within the skin region of the moldings. The fracture behavior of hairline-cracked PET specimens during tensile loading was found to be dependent not only on the crack depth but also on the region in which the crack tips were situated. In contrast to our previous studies on a standard v-notch, very shallow hairline cracks resulted in catastrophic fracture of PET components. Crystallinity distribution along the skin core was found to affect the notch sensitivity of the materials. Annealing the specimens in hot oil was expected to create a crystallized outermost skin (referred to as the pseudo-skin) in the samples and remove internal stresses. This was intended to alter the skin-core ratio to evaluate its effect on the toughness of hairline-cracked specimens. The results revealed that annealing created a pseudo-skin layer and improved the toughness of the materials.
Contemporary Digital Forensic Investigations of Cloud and Mobile Applications, 2017
Recovering deleted or hidden data is among most important duties of forensics investigators. Exte... more Recovering deleted or hidden data is among most important duties of forensics investigators. Extensive utilisation of smartphones as subject, objects or tools of crime made them an important part of residual forensics. This chapter investigates the effectiveness of mobile forensic data recovery tools in recovering evidences from a Samsung Galaxy S2 i9100 Android phone. We seek to determine the amount of data that could be recovered using Phone image carver, Access data FTK, Foremost, Diskdigger, and Recover My File forensic tools. The findings reflected the difference between recovery capacities of studied tools showing their suitability in their specialised contexts only.
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Papers by Bernard C . Ogazi-Onyemaechi