560 research outputs found
Simulations of a top-hat section subjected to axial crushing taking into account material and geometry variations
No full textAbstractSimulations of top-hat thin-walled sections of dual-phase steel DP800 subjected to axial crushing have been performed taking into account process history and measured geometric imperfections, thickness variations and material variations. The simulations were based on experiments performed by Fyllingen et al. [Fyllingen, Ø., Hopperstad, O.S., Langseth, M., 2008. Robustness study on the behaviour of top-hat thin-walled high-strength steel sections subjected to axial crushing. International Journal of Impact Engineering, in press, doi:10.1016/j.ijimpeng.2008.03.005], who investigated the robustness of a top-hat section subjected to axial crushing. The geometry variation and spatial strain hardening variation were mapped onto the model. The fracture parameter and strain-rate sensitivity were based on values obtained from one of the batches. It was emphasised to use an element type, element size, a fracture criterion and a spot-weld model typically used by the industry. Compared to nominal models especially the thickness variations, geometric imperfections and material failure criterion influenced the behaviour. The material batch variation resulted in large differences in the batch means of the mean crushing forces and the variation in the geometric imperfections and thickness resulted in variation in the mean crushing force within each batch. Compared to the experiments the model generally under-predicted the mean crushing force
Laminated Beam Analysis by Polynomial, rigonometric, Exponential and Zig-Zag Theories
No full textA number of refined beam theories are discussed in this paper. These theories were obtained by expanding the unknown displacement variables over the beam section axes by adopting Taylor's polynomials, trigonometric series, exponential, hyperbolic and zig-zag functions. The Finite Element method is used to derive governing equations in weak form. By using the Unified Formulation introduced by the first author, these equations are written in terms of a small number of fundamental nuclei, whose forms do not depend on the expansions used. The results from the different models considered are compared in terms of displacements, stress and degrees of freedom (DOFs). Mechanical tests for thick laminated beams are presented in order to evaluate the capability of the finite elements. They show that the use of various different functions can improve the performance of the higher-order theories by yielding satisfactory results with a low computational cost
System Analysis – Cross Sectional and Structural Behaviour
No full textin "Rotational Capacity of Aluminium Beams - Final Report", Eds. M. Langseth, O.S. Hopperstad, F.M. Mazzolani, Norwegian University of Science and Technology (NTNU), University of Naples Federico II, Hydro Aluminium Maritme
Deformation and rupture of armour grade steel under localised blast loading
No full textA series of 30 blast experiments were conducted on monolithic steel panels of two armour grade steels. The two steels evaluated were a high hardness armour (HHA) and a rolled homogenous armour (RHA). Tests were conducted at two standoff distances using a fixed charge diameter. The charge weight was varied to produce specific magnitudes of blast loading and to isolate the rupture threshold of each material. The results indicated that the HHA steel, generally reserved for ballistic protection, outperformed a more ductile RHA steel in terms of both its deformation resistance and rupture threshold. Optical and scanning electron microscopy was utilised for fractographic analysis of the ruptured plates. The failure of the steels in this investigation was found to be initiated by slant shear fracture with little to no localised thinning. This is in contrast to the tensile instability and ductile tearing predicted by established theories of plate rupture for mild steels under blast loading. The deformation and rupture of the candidate steels was analysed for all experimental conditions and compared to current empirical models based on a non-dimensional impulse parameter. While deformation behaviour is well predicted, the blast rupture threshold of the armour grade steels is poorly captured by current empirical modelling approaches. The identified shear fracture mode leads to lower energy absorption capabilities of the material compared to more ductile tensile failure
Impact behaviour of the high-strength aluminium alloy AA7075-T651
No full textIn this study, the mechanical properties of 20 mm thick rolled plates of AA7075-T651 are determined based on a number of material tests. The obtained data are used to calibrate a modified version of the Johnson-Cook constitutive relation and the Cockcroft-Latham fracture criterion. Component tests using 20 mm diameter, 197 g mass projectiles with various nose shapes are carried out in a compressed gas-gun to reveal the alloy's resistance to ballistic impact. The results are compared to preliminary FE simulations using LS-DYNA and the calibrated material model. Even though the simulations are not able to describe the quasi-brittle failure process of the aluminium plates in full detail, reasonable agreement between experimental and predicted results is obtained
Stress–strain behaviour of aluminium alloys at a wide range of strain rates
No full textAbstractThe stress–strain behaviour of extruded AA6xxx and AA7xxx aluminium alloys in T6 temper was studied at a wide range of strain rates. Tensile tests at low to medium strain rates were performed in a standard tensile test machine, while a split-Hopkinson tension bar was used to carry out tests at high rates of strain. Extruded aluminium alloys have anisotropic mechanical properties, and tests were therefore done in three directions with respect to the extrusion direction. It is found that the AA6xxx alloys exhibit no significant rate sensitivity in the stress–strain behaviour, while moderate rate sensitivity was found for the AA7xxx alloys. There seems to be no significant difference between the rate sensitivity in the three tensile directions. The experimental data were used to identify the parameters of a thermo-viscoplastic constitutive relation for the extruded alloys, which includes the effects of strain hardening, strain-rate hardening, thermal softening and plastic anisotropy
Ductile Failure Predictions Using Micromechanically-Based Computational Models
No full textThree different micromechanically-based computational models for fracture in porous ductile solids are compared and assessed. Model A is a unit cell model of a porous ductile solid comprising a uniform periodic distribution of voids subjected to normal macroscopic loading. Models B and C, on the other hand, are unit-cell type models that represent an imperfection band governed by a doubly periodic array of voids separating two non-porous outer blocks. The outer blocks have a finite size in Model B and are semi-infinite in Model C. The non-porous material surrounding the voids, and the material of the outer blocks in Model B and Model C, are considered as an elasto-plastic isotropic material. Numerical simulations are performed for a wide range of macroscopic stress states. For each model, various criteria for determining the onset of ductile failure are evaluated to demonstrate their impact on the failure predictions. The results show that the failure loci strongly depend on the computational model and failure criterion employed. Thus, these three models cannot be used interchangeably – neither to investigate failure mechanisms nor to develop or calibrate fracture models – and an unambiguous failure criterion must be chosen. © 2022 The Author(s)The authors gratefully appreciate the financial support from NTNU and the Research Council of Norway through the FRIPRO programme , Project No. 250553 (FractAl).Norges Teknisk-Naturvitenskapelige Universitet, NTNU; Norges Forskningsråd: 25055
Cyclic stress-strain behaviour of alloy AA6060, part I: Uniaxial experiments and modelling
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Optimum design for energy absorption of square aluminium columns with aluminium foam filler
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