DAMAGE CHARACTERIZATION AND REHABILITATION OF FIBER-REINFORCED-POLYMER (FRP) COMPOSITE PIPES UNDER LOW VELOCITY IMPACT. PhD thesis, King Fahd University of Petroleum and Minerals.

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Arabic Abstract

الأنابيب المصنوعة من الالياف المعززة بالبوليمرات تحل تدريجيا محل الأنابيب التقليدية المصنوعة من الحديد في التطبيقات الصناعية بسبب خصائصها الميكانيكية والحرارية المتفوقة. ومع ذلك، فإن الفشل المتكرر من هذه الأنابيب الناجمة عن الأضرار الميكانيكية هي واحدة من الجوانب الهامة التي تحتاج إلى معالجة. ويمكن أن يعزى الفشل الهيكلي لخطوط الأنابيب هذه إلى عدة أسباب، مثل الانفجار، الاصطدامات، والثقب، والإفراط في ضغط التشغيل، والاجهادات والكسر. هذه الأنابيب غالبا ما تكون عرضة لتأثير جسم غريب أثناء الخدمة. هذه الأضرار يمكن أن تكون جداً خطره بسب كونها غير مرئية وخاصة في الاصطدامات التي تكون على سرعات منخفضة. يمكن أن تؤدي هذه الاصطدامات إلى أضرار كامنة كبيرة على سبيل المثال، تكسر الألياف او ضعف او انكسار الربط بين الألياف والبوليمرات. وليس من المعقول عموماَ تغيير خطوط الأنابيب بأخرى جديدة، اذ لم يكن هناك أي تسريب، بسبب التكاليف المرتفعة للتغيير ولأسباب تقنية وتشغيلية. بدلاً من ذلك من المهم التحقق من كفاءة وسلامة هذه الانابيب وإعادتها للخدمة عن طريق تأهيليها وإصلاح عيوبها اعتمادا على طبيعة وشدة الضرر. ولذلك، تم إجراء بحوث شاملة، بشأن القضايا المتعلقة بتصميم هذه الانابيب المصنوعة من الالياف وتصنيف وتوصيف أنواع الضرر الممكن حدوثها لها. لذلك فأن الهدف الرئيسي من هذه الرسالة هو وضع مبادئ توجيهية لتصميم الألواح والانابيب المعززة بالألياف. ولهذا الغرض، تم النظر في تصاميم جديده باستخدام بوليمرات مختلفة ذات سّماكات متفاوتة. علاوة على ذلك، تم توصيف وتصنيف الأضرار باستخدام المجهر الضوئي والتصوير الحراري والتصوير المقطعي المحوسب، وغيرها من التقنيات المتاحة، لتصنيف الأضرار في هذه الالواح والأنابيب المركبة تحت تأثير الاصطدامات منخفضة السرعة. كان الهدف الرئيسي ايضاً التركيز على قضايا الجودة ذات الصلة أثناء تصميم الالواح والأنابيب المصنوعة من الألياف الزجاجية وكذلك أفضل أساليب تقييم الجودة. أجريت مجموعة من الدراسات التجريبية للتحقق من صحة النماذج العددية المتقدمة. تم دراسة تأثير عوامل كثيرة تدخل في تصنيع هذه الالواح والأنابيب المصنوعة من الالياف على أدائها (مثل سماكة الطبقة المركبة وأنواع البوليمرات المستخدمة وأنواع الألياف وما إلى ذلك).

English Abstract

Composite pipes are gradually replacing the conventional pipes in the industrial applications because of their superior mechanical and thermal properties. However, the frequent failure of composite pipes caused by the mechanical damages is one of the important aspects that need to be addressed. These pipes are often very susceptible to foreign object impact during service. These damages can be vulnerable and can go unseen especially in case of low velocity impacts since these are not visually observable. A small dent caused by such impacts can lead to significant underlying damages for example, delamination, cracking of matrix, breakage of fiber and de-bonding between fiber and matrix interfacial. It is not generally desirable to replace the pipeline with such no leaking failures because of cost and technical reasons; rather it is important to check its fitness for service. The fitness for service could possibly incorporate remedy of a pipeline containing defects. The judgement is made on the nature and severity of the damage. Therefore, comprehensive research was done, on issues related to composite design, impact damage, damage classification, damage characterization, and rehabilitation. The objective of this Ph.D. work was to develop a design guideline for Fiber-Reinforced-Polymer (FRP) plates and pipes. For this purpose, new FRP composite plates and pipes using different resins and thicknesses was considered to develop a methodology for the designs that fulfill the static internal pressure testing (for the case of fiberglass pipe) and improved impact resistance. The methodology is based on experimental and computational studies. The finite element (FE) models for both plate and pipe have been validated by the results of the conducted experimental work for the manufactured plates and for the existing high-pressure pipes designed per API-15HR. The developed FE model is capable to predict the behavior of high-pressure fiberglass pipes under low velocity impact with acceptable accuracy. Effects of major parameters, such as composite layer thickness, resin types and fiber types on composite design performance were investigated to formulate guidelines related to the design of the composite system. It was found that, for plate testing, the amount of energy absorbed (impact performance) varies significantly for the variations in the thickness of a single layer, number of layers and stacking sequence. Carbon-fiber/epoxy composite plate has better impact resistance compared to glass-fiber/epoxy composite plate due to the higher measured absorbed energies of the carbon-fiber/epoxy. The experimental test data showed an increased energy absorption for the composite plates made with phenolic resin. The effect of the carbon fiber plies location for the mixed plates was not exceptionally pronounced. The stacking sequence with [90/0/45/-45] was better than [60/45/-45/-60]s in term of impact resistance as concluded from the simulated cases. For pipe design, the incorporation of rings within the fiberglass pipe with different fiber materials or orientation can improve the impact resistance of the pipe as well as the mechanical strength under internal static loading. These designs with rings among all the simulated cases, meet and exceed durability requirements necessary to provide the desired impact resistance for the pipeline structures. Moreover, damage characterization was done utilizing, Optical Microscopy, Thermography Imaging, Computed Tomography (CT) scan, and other available techniques, to classify the damages in composite plates and pipes under low velocity impact. Visual inspections showed a large extent of damage on the polyester and epoxy resins plates when they are compared with same plates made with phenolic resin. Infrared (IR) Thermography Imaging was used to provide additional information on the initiation and development of deferent damage mechanisms due to impact. The experimental apparatus and approach using mid-wave IR thermography camera with continuous heat source are reliable methods which can be applied to determine damage inside composite materials in real time. It was possible to obtain a 3D image of the delamination which was in good agreement with physical observations using the measured temperature gradients across the thickness of different manufactured composite plates. The study also demonstrates that it is possible to assess the thinning severity experienced by the composite materials through inferred thermal imaging. The impact damage morphology of API-15HR fiberglass pipe sections, rated at 1500 psi, were studied at different impact energies. X-ray Computed Tomography (CT) scan was used to assess and examine the extend of the induced damage within the wall thickness of the fiberglass pipe. Statistical analysis (a histogram depth trace for each slice as well as a continuous histogram map for the whole length) and the visual analysis (both slice and vertical/horizontal reconstructed slab images) are analyzed. It is concluded that CT scanning is an effective way of damage characterization for fiberglass pipes with some discussed limitations. The CT results have been validated by comparison of the results from optical microscopy taken at the center of the impacted areas and through the pipe wall thickness as a reference. Good interfacial adhesion between fiber glass and epoxy resin is optically observed for low energy impacted samples whereas delamination is seen for specimens impacted at 210J indicating that the fiber—matrix interface is completely removed. The usage of the medical CT scanner in this study proves that the resultant photos are only for visual quality and descriptive assessment. The joint utilization of x-ray computed tomography and optical microscopy was tried and proved to offer a powerful methodology for impact damage identification. Finally, Artificial Neural Network (ANN) was adopted to find the best model that can be used for predicting the thinning severity. The simulation results included predictions, model plots, formulae and accuracy metrics. Accurate approach for the thinning estimation in composite plates using thermal imaging as well as ANN models was developed. The use of thermography testing data along with ANN models seems more viable than other non-destructive tools as they are together can describe different damage on composite. The estimation of thinning parameters is accurate with less than 1% error where the overall absolute error for untrained data, is less than 8%.

Item Type:	Thesis (PhD)
Subjects:	Mechanical
Department:	College of Engineering and Physics > Mechanical Engineering
Committee Advisor:	AbulFazal, Arif
Committee Co-Advisor:	Al-Athel, Khaled
Committee Members:	Al-Suliman, Faleh and Yilbas, Bekir and Merah, Necar
Depositing User:	Ahmed Alomari (g199702860)
Date Deposited:	30 Oct 2017 11:28
Last Modified:	31 Dec 2020 08:28
URI:	http://eprints.kfupm.edu.sa/id/eprint/140486