Hasil Pencarian  ::  Simpan CSV :: Kembali

"Untuk mengetahui kekuatan struktur doubler dalam menahan terjadinya kegagalan akibat retakan yang disebabkan oleh cyclic loading, diperlukan suatu analisis tersendiri yang tidak terdapat pada panduan Structural Repair Manual (SRM). Cyclic loading dapat mengurangi kekuatan skin doubler secara bertahap (fatigue) hingga mencapai kegagalan (fracture). Pada penelitian ini akan dilakukan analisis crack growth rate dan jumlah siklus pembebanan yang dibutuhkan untuk memunculkan retakan dengan panjang tertentu (fatigue cycle) terhadap struktur doubler fuselage skin pesawat Boeing 737-900 Extended Range dengan station number 360-380 di antara stringer 6L-7L pada setiap panjang retakan dan ketinggian terbang simulasi. Analisis dilakukan menggunakan pendekatan numerik dengan metode Modified Virtual Crack Closure Integral (MVCCI) untuk mendapatkan nilai Stress Intensity Factor (SIF) melalui software berbasis metode elemen hingga. Melalui nilai yang diperoleh dapat diketahui bahwa nilai crack growth rate dan fatigue cycle berbanding lurus terhadap variasi panjang retakan dan ketinggian terbang simulasi yang diberikan. Nilai crack growth rate paling rendah terjadi pada struktur doubler dengan panjang retakan 8,5 mm dan kondisi terbang 5000 feet yaitu sebesar 2,964 mm/cycle, dan nilai tertinggi sebesar 5,471 mm/cycle terjadi pada struktur doubler dengan panjang retakan 51 mm dan kondisi terbang 40000 feet. Sedangkan, nilai fatigue cycle paling rendah terjadi pada struktur doubler dengan panjang retakan 8,5 mm dan kondisi terbang 40000 feet yaitu sebesar 2,540 cycle, dan nilai tertinggi sebesar 5,470 cycle terjadi pada struktur doubler dengan panjang retakan 51 mm dan kondisi terbang 5000 feet."

"In considering Composite Material Systems, the Markov Model is important for studying the behavior of composite materials. The monitoring of crack growth is suggested as the basis for this study. In fact, crack growth strongly impacts Composite Material Systems. Crack growth may lead to system failure, especially if we cannot prevent the various kinds of risk states and if we do not take necessary actions to maintain this system while in operation. In order to analyze risk states for steel materials, in the Moroccan National Railway Office, the Markov Model of a unit jump is chosen to analyze the crack growth of a composite material. This model is defined by a transition vector and a state vector, with a calculation of the averages and the extensions of the crack. Using these parameters, the jump of each extension of the crack and the number of the crack extensions are considered. A mathematical calculation helps us to find the formula for the transition probability, based on the average. An algorithm allows us to estimate the value of the crack jump. These estimations indicate the level of risk for each system state and values of the crack extension. The obtained results show that more the unit jump approximates to zero, the more the system is maintained in an acceptable operation, despite any disruptions that may influence the results."

"Sebagian besar jaringan pipa bawah laut di Indonesia dipasang dengan menggunakan metode S-Lay, dengan menggunakan kapal tongkang yang dilengkapi dengan mooring spread, tensioner dan stinger. Selama pemasangan pipa bawah laut, beban statis terjadi dikarenakan bentuk konfigurasi pipa dari atas kapal sampai di dasar laut, dimana pipa akan mengalami tegangan aksial (axial tension) dan momen lentur (bending moment) di dua area kritis, yaitu overbend dan sagbend. Selain itu beban fatik juga terjadi pada saat pemasangan pipa bawah laut dikarenakan beban lingkungan (seperti arus dan gelombang). Cacat yang terjadi pada proses pengelasan akan mengalami pertumbuhan retak (crack growth) dikarenakan beban fatik.Analisa retak dengan pendekatan fracture mechanics atau yang lebih dikenal dengan Engineering Critical Assessment (ECA) dilakukan dengan mempertimbangkan beban fatik akibat variasi ketinggian gelombang signifikan (wave height significant) untuk 0.5m, 1.0m dan 1.8m. BS 7910 digunakan sebagai acuan dalam menentukan kriteria cacat yang diperbolehkan baik untuk cacat diluar dinding pipa (external flaw) dan cacat didalam dinding pipa (internal flaw), dimana kedalaman cacat disimulasikan dari kedalaman (a) 1mm – 3mm.Dari hasil analisa ditemukan bahwa panjang cacat (2c) yang diperbolehkan mengalami penurunan sebesar 12.7% - 25.0% dari ketinggian gelombang 0.5m ke 1.8m untuk cacat diluar dinding pipa, sementara untuk cacat didalam pipa ditemukan bahwa panjang cacat (2c) yang diperbolehkan mengalami penurunan sebesar 5.9% - 13.6% dari ketinggian gelombang 0.5m ke 1.8m. Hasil ini dapat menjadi dasar bagi kontraktor instalasi pipa bawah laut untuk melakukan sensitivitas beban fatik dalam optimisasi untuk menentukan cacat yang diperbolehkan berdasarkan aktual beban gelombang yang terjadi.

---

Most of the subsea pipelines in Indonesia are installed using the S-Lay method with pipelay barges equipped with mooring spreads, tensioners, and stingers. During the installation of subsea pipelines, static loads occur due to the pipeline configuration from the firing line of the pipelay barge up to seabed. Where the pipe will experience with axial tension and bending moment in two critical areas, which are overbend and sagbend. In addition, fatigue loads also occur during the installation of subsea pipeline due to environmental loads (i.e., currents and waves). Defects that found after welding will growth due to this fatigue loads.

Crack analysis with a fracture mechanics approach or known as Engineering Critical Assessment (ECA) is carried out by considering the fatigue load due to significant wave height variations for 0.5m, 1.0m, and 1.8m. BS 7910 is used as a standard reference in order to determine the allowable defects criteria for an external flaw and internal flaw, where the depth of the defect (a) is simulated from a depth of 1mm – 3mm.

From the analysis found that the allowable defect length (2c) decreased by 12.7% - 25.0% from a significant wave height of 0.5m to 1.8m for an external flaw. While for an internal flaw, it is found that the allowable defect length (2c) decreased by 5.9% - 13.6% from a significant wave height of 0.5m to 1.8m. These results can be used as a basis for subsea pipeline installation contractors to perform fatigue load sensitivity to optimize the allowable defects based on the actual wave load that occurs at site."

"Aluminum alloys, such as A6061-T6, are widely used in engineering components. However, detailed knowledge is needed to understand the way they respond to a fracture due to mechanical loading. Fractures occur in the structural component from crack propagation, and it is important to understand the mixed mode fracture behavior of crack growth. In this research, mixed mode fracture testing was conducted on the aluminum alloy A6061-T6 by employing a compact tension shear specimen. Crack growth behavior was investigated by applying a quasi-static loading at a constant cross-head speed using a Servopulser universal testing machine. The crack growths were observed by a Keyence digital microscope, and the critical stress intensity factors of the material were examined. Results showed that the shear type of crack initiation preceded the opening-type fracture. The dimple-type fracture on the fracture surface occurred under mode I and mixed mode with a loading angle of about 60o and 75o, respectively. The transition of crack initiation behavior from the opening-type fracture to the shear-type fracture occurred at a loading angle from 15o to 30o. The experimental data followed the maximum hoop stress criterion under mode I and mixed mode at a loading angle 60o and 75o, respectively, for the compact tension shear specimen. Crack propagation behavior with three small holes occurring in a zigzag pattern ahead of the crack tip showed that crack initiation and propagation occurred only in the opening-type fracture. The experimental data followed the maximum hoop stress criterion under mode I and mixed mode with a lower mode II component at a loading angle of 75o. When the small holes occured inline, there were two types of fractures occurring: an opening fracture at crack initiation and then crack propagation caused by shear fracture."

"This book provides a state-of-the-art review of the fail-safe and damage tolerance approaches, allowing weight savings and increasing aircraft reliability and structural integrity.The application of the damage tolerance approach requires extensive know-how of the fatigue and fracture properties, corrosion strength, potential failure modes and non-destructive inspection techniques, particularly minimum detectable defect and inspection intervals. In parallel, engineering practice involving damage tolerance requires numerical techniques for stress analysis of cracked structures. These evolved from basic mode I evaluations using rough finite element approaches, to current 3D modeling based on energetic approaches as the VCCT, or simulation of joining processes. This book provides a concise introduction to this subject."

"This book provides a concise discussion of fatigue crack growth (FCG) failure and lifing analysis methods for metallic aircraft structures and components. After a reasonably concise historical review, surveys are made of (i) the importance of fatigue for aircraft structural failures and the sources of fatigue nucleation and cracking, (ii) contemporary FCG lifing methods, and (iii) the Quantitative Fractography (QF) required for determining the actual FCG behaviour. These surveys are followed by the main part of the book, which is a discussion, using case histories, of the applicabilities of Linear Elastic Fracture Mechanics (LEFM) and non-LEFM methods for analysing service fatigue failures and full- and sub-scale test results. This discussion is derived primarily from the experiences of the Defence Science and Technology Group in Melbourne, Australia, and the Netherlands Aerospace Centre, Marknesse, the Netherlands."

"This volume contains the proceedings of the XIX International Colloquium on Mechanical Fatigue of Metals, held at the Faculty of Engineering of the University of Porto, Portugal, 5-7 September 2018. This International Colloquium facilitated and encouraged the exchange of knowledge and experiences among the different communities involved in both basic and applied research in the field of the fatigue of metals, looking at the problem of fatigue exploring analytical and numerical simulative approaches.Fatigue damage represents one of the most important types of damage to which structural materials are subjected in normal industrial services that can finally result in a sudden and unexpected abrupt fracture. Since metal alloys are still today the most used materials in designing the majority of components and structures able to carry the highest service loads, the study of the different aspects of metals fatigue attracts permanent attention of scientists, engineers and designers."