Experimental Techniques
Khaled Saad; Andras Lengyel
Abstract
This research presents a parametric three-dimensional finite element study on the effects of closely spaced knots and related fibre deviations on the flexural failure mechanism of wood. The model considers the effects of the position of the knots along the beam's longitudinal and vertical axis. The numerical ...
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This research presents a parametric three-dimensional finite element study on the effects of closely spaced knots and related fibre deviations on the flexural failure mechanism of wood. The model considers the effects of the position of the knots along the beam's longitudinal and vertical axis. The numerical models were validated by bending tests performed on six beams. The actual three-dimensional geometry of knots and related fibre deviations were determined accurately based on an algorithm proposed previously by the authors. The elastic-plastic constitutive law of Nordic Spruce wood was considered based on the Hill anisotropic model. The failures were numerically predicted with the help of the Tsai-Wu failure criterion. The validated numerical models can also be used based on visual inspections. The user needs only to define the position and size of the knots and the space between them. Moreover, the model allows defining different fibre patterns in the knot vicinity. The model considers a fixed knot located in the tension zone at the mid-span of the beam and a moving knot adjusted at horizontal and vertical centre-to-centre distances d and v from the fixed one. Results revealed that regardless of the distance d (where v = 0), the failure will initiate at the same load levels for both knots. However, moving the adjacent knot diagonally (v not equal to 0) causes shear failure between the knots. The part of the clear wood between the knots is ineffective if the knots' centre-to-centre distance is less than three times the knot diameter.
Prabhjot Singh Virdi; Gulab Pamnani
Abstract
Liquefied Petroleum Gases [LPG] are flammable mixtures of gases such as propane and butane mainly which is transported and stored in liquid phase in storage vessels under amply pressure. These industrial processes are of high fire and explosion hazard. When a vessel carrying LPG is damaged, an abrupt ...
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Liquefied Petroleum Gases [LPG] are flammable mixtures of gases such as propane and butane mainly which is transported and stored in liquid phase in storage vessels under amply pressure. These industrial processes are of high fire and explosion hazard. When a vessel carrying LPG is damaged, an abrupt drop in pressure may release colossal quantities of evaporating gas and energy that has a destructive effect on the vessel itself and its surroundings. When comes in contact with ignition source, BLEVE phenomenon is developed. Elevated temperature environment outside the LPG pressure vessel can cause vessel explosion due to the pressure mount inside the tank and drop in strength of the tank walls. This catastrophic rupture will lead to BLEVE phenomenon which when ignited will again lead to a vapor cloud explosion. Most common scenario is when the pressure vessel partially filled with liquid form of LPG is exposed to a fire. The primary focus of the paper is to analyze the LPG storage pressure vessel under thermal loading condition. For this Finite element modeling approach is used and the analysis is carried out in ANSYS TM software.
Prosenjit Das; R. Jayaganthan; I. V. Singh
Abstract
The present work describes an experimental evaluation of yield strength, tensile strength, initiation fracture toughness and Finite element simulations of fracture behaviour for both bulk and ultrafine-grained (UFG) 7075 Al Alloy. The 7075 Al alloy has been rolled for different thickness reductions (40%, ...
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The present work describes an experimental evaluation of yield strength, tensile strength, initiation fracture toughness and Finite element simulations of fracture behaviour for both bulk and ultrafine-grained (UFG) 7075 Al Alloy. The 7075 Al alloy has been rolled for different thickness reductions (40%, 70% and 90%) at cryogenic (liquid nitrogen) temperature, and its mechanical properties and microstructural morphology have been investigated. Rolling of the Al alloy at cryogenic temperature suppresses the dynamic recovery and grain growth, which leads to grain fragmentation. Dislocation cells formed during consecutive rolling passes, transformed into fully formed UFG (600 nm) up to 70% thickness reduction. Grain size gets reduced further when 90% thickness reduction is achieved. Incremental crack growth simulations have been carried out by commercial software ABAQUS under quasi-static loading using deformation plasticity theory based on Griffith energy concept. J-integral, stress along crack path, effect of crack and specimen size over J-integral, stress distribution and plastic dissipation ahead of the crack tip have been investigated for some practical crack problems under mechanical and thermo-mechanical loading. The numerical examples indicates a significant enhancement in crack arrest capabilities of UFG alloys for the same boundary conditions because of decreasing J values with increasing % thickness reduction. This is attributed to the improved mechanical properties (UTS: 625 MPa and YS: 610 MPa) of the cryorolled alloy which hinders the onset of plasticity, results from ultrafine-grain formation.
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