China
Africa
Explore chapters and articles related to this topic
Turn performance and flight maneuvers
Published in Mohammad H. Sadraey, Aircraft Performance, 2017
Based on Equation 9.195, as the airspeed increases, the maximum load factor will increase proportional to V2. However, nmax cannot be allowed to increase indefinitely. It is constrained by the structural strength (structural limit load factor). The top horizontal line denotes the positive limit load factor in the V-n diagram.
Plastic Deformation
Published in Abdel-Rahman Ragab, Salah Eldin Bayoumi, Engineering Solid Mechanics, 2018
Abdel-Rahman Ragab, Salah Eldin Bayoumi
The linear relation between stress and strain, which describes the behavior of an elastic solid under load, holds up to a certain limit. Beyond this limit the deformation is not fully recovered upon load removal, indicating that the solid has undergone plastic deformation. Most engineering constructions are designed to support service loads within the elastic regime of the materials used. Nevertheless, the analysis of plastic deformation is required in several engineering applications, as indicated by the following: Although machine and structural components are designed to behave elastically, localized plastic deformation does occur at locations where stress concentrations are inevitably encountered. At holes, notches, supports, etc. contained plastic deformation is observed.Plastic deformation is utilized to produce favorable residual stresses in many mechanical parts to improve the elastic stress distribution and, hence, increase the load-carrying capacity, e.g., autofrettage of gun barrels.In the analysis of components, which inevitably contain preexisting crackslike defects, the elasticity theory predicts infinite stresses at the crack tip. However, this cannot be physically feasible and the material will yield in a small zone ahead of the crack tip. This constitutes the subject of elastoplastic fracture mechanics.In components subjected to cyclic loads, limited plastic deformation can be allowed to occur during the first few cycles of load. Such behavior, which ensures cessation of plastic deformation in the long term, is known as elastic shakedown, and is utilized in the design of many critical components, e.g. in the nuclear power industry, in thermal power generation, and in the aeronautical and aerospace industries. The phenomenon of accumulated plastic deformation due to reversed cyclic loading has to be studied. This is essential for a proper design against low-cycle fatigue failures (i.e., life less than 103 to 104 load cycles).Analysis of ductile failure of components requires the determination of the maximum load sustained before fracture. This is often taken as the load at which the material becomes fully plastic, and such loads are termed limit loads.The assessment of material behavior by conventional tests requires good understanding of plastic deformation. Ultimate tensile strength, hardness numbers, creep strength, low cycle fatigue, etc. are determined by testing materials within the plastic deformation regime.The analysis and design of metal-forming processes such as forging, extrusion, rolling, drawing, etc. cannot be worked out rationally unless the plastic behavior of metals is thoroughly understood.
Effect of weld geometry on the limit load of a cracked specimen under tension
Published in Mechanics Based Design of Structures and Machines, 2023
Sergei Alexandrov, Elena Lyamina, Yeau-Ren Jeng
The assessment of the remaining load capacity of structures with a crack is commonly based on analytical flaw assessment procedures. A comprehensive review of such procedures has been provided in Zerbst and Madia (2018). A typical methodology of using flaw assessment procedures for practical applications is described in detail in Cicero et al. (2008). Independently of the procedure and methodology, the limit load is an essential input parameter. The accuracy of limit load solutions is of particular interest for welded structures (Kim and Schwalbe 2001a). It is known that an accurate estimate of the limit load for such structures is difficult due to strength mismatch and geometric effects (Yan et al. 2021). A large amount of finite element analyses is required to reveal these effects (Chen et al. 2022). Analytical and semi-analytical solutions are an alternative to lengthy finite element solutions. Such solutions provide a formula or a simple numerical procedure for calculating the limit load for a given set of parameters. Accurate analytical and semi-analytical solutions are possible if the boundary value problem possesses some features that allow for reliable assumptions to be used. Typical features used in recent publications are the small thickness of structural components (Huang et al. 2021), geometries allowing for generalized stress variables to be used (Orynyak, Bai, and Mazuryk 2022), and the geometries allowing for piece-wise constant stress fields to be used (Picon and Canas 2009; Hasegawa, Li, and Shimomoto 2013; Hasegawa et al. 2022). The present article utilizes such features of highly undermatched welded joints as the small thickness of the weldment and the localization of plastic deformation within it.
The upper bound shakedown analysis of strip footing on cohesive slopes under repeated vertical–horizontal loads
Published in European Journal of Environmental and Civil Engineering, 2022
Mohammad Mojallal, Orang Farzaneh, Faradjollah Askari
The behaviour of a structure under repeated loads depends on the intensity (amplitude) of the load and can vary from purely elastic to non-restricted or progressive plastic flow behaviour. If the intensity of the load is such that plastic strains occur during the initial cycles, but after a number of load cycles drop to lower amounts and cease to develop further, the structure is considered to have reached the shakedown status (Kachanov, 1971). The maximum load that causes a structure to reach shakedown is known as the shakedown limit. This limit load can be used as the design load.