Pär A. T. Olsson

• PhD in Mechanics
• Professor (Associate) at Malmö University

In a structural modification problem the mass and stiffness matrices are modified to obtain a desired spectrum. In this paper, this is done by imposing constraints on the structure. The undamped natural vibrations of a constrained linear structure are calculated by solving a generalized eigenvalue problem derived from the equations of motion for th...

The undamped natural vibrations of a constrained linear structure are given by the solutions to a generalized eigenvalue problem derived from the equations of motion for the constrained system involving Lagrangian multipliers. The eigenvalue problem derived is defined by the mass matrix of the unconstrained structure and a non-symmetric and singula...

In this paper, we report the results of a systematic study of the elastic properties of nanosized single-crystal wires and beams of bcc iron. Both tensile and bending stiffnesses have been determined employing molecular statics simulations for specimens of different sizes and three different crystallographic orientations. We also analyze the influe...

In this paper a systematic study of the surface influence on the elastic properties of nanosized iron and tungsten wires and films is performed. Single crystal defect-free nanowires and nanofilms are examined through molecular statics simulations, and the concepts of surface energy and third order elastic constants are used in an attempt to describ...

We have constructed a set of embedded atom method (EAM) potentials for Fe, Ta, W and V and used them in order to study point defect properties. The parametrizations of the potentials ensure that the third order elastic constants are continuous and they have been fitted to the cohesive energies, the lattice constants, the unrelaxed vacancy formation...

The present study focuses on the computation of interfacial excess potential for the cohesive zones through which a brittle crack propagates in tungsten (W) twist grain boundaries (TGBs). Additionally, the influence of phosphorus (P) impurities is investigated. To this end, we have performed classical atomistic modeling of several ⟨110⟩ TGBs in the...

Ni-based superalloys, essential for high-temperature applications, derive strength from coherent second-order precipitates that impede dislocation motion through coherency misfit and elastic mismatch. This study employs multi-component phase-field crystal (PFC) simulations to explore the elastic deformation of such precipitates. Using a binary orde...

We use first-principle density functional theory (DFT) to predict properties for semicrystalline polyvinyl fluoride (PVF) and compare with polyvinylidiene fluoride. We note that the crystalline regions of PVF are complex in the sense that we lack a complete experimental characterization of the detailed atomic organization. We therefore turn to DFT...

Zirconium hydride is commonly used for next-generation reactor designs due to its excellent hydrogen retention capacity at temperatures below 1000 K. These types of reactors operate at thermal neutron energies and require accurate representation of thermal scattering laws (TSLs) to optimize moderator performance and evaluate the safety indicators f...

We investigate how the Re content affects the coefficient of thermal expansion (CTE) of the non-stoichiometric W-based 𝜎 and 𝜒 phases, forming upon neutron irradiation of W, to explore and quantify its mismatch between precipitates (W-Re) and matrix (W). To this end, we have conducted first-principles calculations using two approaches: the Debye-Gr...

We present a new classical interatomic potential designed for simulation of the W-Mo-Nb system. The angular-dependent format of the potential allows for reproduction of many important properties of pure metals and complex concentrated alloys with good accuracy. Special attention during the development and validation of the potential was paid to the...

In the present work, we have used classical molecular dynamics and quantum mechanical density functional theory modeling to investigate the grain size-dependent thermal expansion coefficient (CTE) of nanocrystalline Cu. We find that the CTE increases by up to 20% with a gradually decreasing grain size. This behavior emerges as a result of the incre...

In the present work, we report the results of a systematic ab initio study of the thermo-elastic properties of delta-MH1.5 (M=Zr, Ti). This investigation serves three purposes: (i) Elucidate the fully anisotropic temperature dependent elastic constants of hydrides, (ii) address discrepancies in thermal expansion data reported in the literature and...

To increase the understanding of the role of carbide precipitates on the hydrogen embrittlement of martensitic steels, we have performed a density functional theory study on the solution energies and energy barriers for hydrogen diffusion in orthorhombic M7C3 (M = Cr, Mn, Fe). Hydrogen can easily diffuse into the lattice and cause internal stresses...

In the present work, we have generated a new second-nearest neighbour modified embedded atom method potential (2NN-MEAM) for the W–P system to investigate the impact of P impurity segregation on the strength of symmetric 〈110〉 tilt coincident site lattice grain boundaries (GBs) in tungsten. By incorporating the impurity-induced reduction of the wor...

Tungsten (W) is a leading candidate for plasma-facing materials in fusion reactors. Recently, experiments have shown that during neutron irradiation, W and its transmutation products, mainly rhenium (Re), will form precipitates of the σ and χ types. This study identifies close-packed planes of the σ- and χ-phases in the W-Re system and uses ab-init...

In the present work, we have evaluated the performance of different embedded atom method (EAM) and second-nearest neighbour modified embedded atom method (2NN-MEAM) potentials based on their predictive capabilities for modelling fracture in single- and bicrystalline tungsten. As part of the study, a new 2NN-MEAM was fitted with emphasis on reproduc...

We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O2, with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES...

We present the idea and illustrate potential benefits of having a tool chain of closely related regular, unscreened and screened hybrid exchange-correlation (XC) functionals, all within the consistent formulation of the van der Waals density functional (vdW-DF) method [JPCM 32, 393001 (2020)]. Use of this chain of nonempirical XC functionals allows...

In the present work, the impact of phosphorus impurities on the grain boundary strength of nickel has been investigated by means of density functional theory (DFT) modelling. Owing to different outcomes and trends previously reported in the literature, it is unclear whether P is strengthening or weakening the Ni grain boundary. To address this issu...

The present research front of NbO2 based memory, energy generation, and storage thin film devices is reviewed. Sputtering plasmas contain NbO, NbO2, and NbO3 clusters, affecting nucleation and growth of NbO2, often leading to a formation of nanorods and nanoslices. NbO2 (I41/a) undergoes the Mott topological transition at 1081 K to rutile (P42/mnm)...

We study the adhesion and tensile behaviour of bi-layer interfaces comprising polyethylene, doped with carbonyl and hydroxyl functional groups emanating from ozone treatment, and α-Al 2 O 3 by means of density functional theory and classical atomistic modelling. The results show that the deformations are localized within the polymer and comprise ch...

We investigate the variation of elastic stiffness moduli and the thermodynamic properties of yttrium orthosilicate (Y2SiO5, YSO) under various doping concentrations of Eu3+ ions. The model is based on a low temperature approximation (T<<θD) , and the plane-wave density functional theory (DFT) is used to carry out the calculations. The results show...

We study the stability, magnetic order, charge segregation, and electronic properties of a novel three-layered Fe 3 O 4 film by means of Hubbard-corrected density functional theory calculations. The stable film is predicted to consist of close-packed iron and oxygen layers, comprising a center layer with octahedrally coordinated Fe sandwiched betwe...

We have investigated the structure of an ultrathin iron oxide phase grown on Ag(100) using surface x-ray diffraction in combination with Hubbard-corrected density functional theory (DFT+U) calculations. The film exhibits a novel structure composed of one close-packed layer of octahedrally coordinated Fe²⁺ sandwiched between two close-packed layers...

We study the phase stability and martensitic transformation of orthorhombic and monoclinic polyethylene by means of density functional theory using the nonempirical consistent-exchange vdW-DF-cx functional [Phys. Rev. B 89, 035412 (2014)]. The results show that the orthorhombic phase is the most stable of the two. Owing to the occurrence of soft li...

In the present work we have performed classical molecular dynamics modelling to investigate the effects of different types of force-fields on the stress-strain and yielding behaviours in semi-crystalline lamellar stacked linear polyethylene. To this end, specifically the all-atomic optimized potential for liquid simulations (OPLS-AA) and the coarse...

The fracture mechanics properties of injection-moulded low-density polyethylene (LDPE) sheets were investigated both experimentally and numerically. The total work of fracture was determined experimentally, by means of fracture mechanics testing of sheets of injection-moulded LDPE with side cracks of different lengths. A multi-specimen method, prop...

The formation of a second phase in presence of a crack in a crystalline material is modelled and studied for different prevailing conditions in order to predict and a posteriori prevent failure, e.g. by delayed hydride cracking. To this end, the phase field formulation of Ginzburg–Landau is selected to describe the phase transformation, and simulat...

In the present work we have studied the influence of phosphorus impurities on the grain boundary strength of tungsten by means of quantum mechanical calculations based on density functional theory. As model grain boundary we consider the $\Sigma$5(310)[001] high angle configuration. The results show that by the introduction of a clean (i.e. impurit...

The formation of a second phase, such as a brittle hydride, in presence of a crack is modeled for hexagonal close-packed metals. To this end, the Ginzburg-Landau phase-field formulation which relies on a sixth-order Landau potential is adopted. The crack-induced stress is implicitly included in the phase-field equation through the mechanical energy...

Injection-moulding is one of the most common manufacturing processes used for polymers. In many applications, the mechanical properties of the product is of great importance. Injection-moulding of thin-walled polymer products tends to leave the polymer structure in a state where the mechanical properties are anisotropic, due to alignment of polymer...

We study the stability of twin boundaries and slip in crystalline orthorhombic polyethylene by means of density functional theory (DFT), using a nonempirical, truly nonlocal density function, and by means of classical molecular dynamics (MD). The results show that, in accordance with experimental observations, there is a clear preference to chain s...

Nanoindentation, in combination with scanning probe microscopy, has been used to measure the hardness and Young's modulus in the hydride and matrix of a high burn-up neutron-irradiated Zircaloy-2 cladding material in the temperature range 25–300 °C. The matrix hardness was found to decrease only slightly with increasing temperature while the hydrid...

In this work we have studied transgranular cleavage and the fracture toughness of titanium hydrides by means of quantum mechanical calculations based on density functional theory. The calculations show that the surface energy decreases and the unstable stacking fault energy increases with increasing hydrogen content. This is consistent with experim...

Microstructure evolution in thin Cu films during room temperature self-annealing is investigated by means of a mesoscale level set model. The model is formulated such that the relative, or collective, influence of anisotropic grain boundary energy, mobility and heterogeneously distributed stored energy can be investigated. Density functional theory...

Abstract In this work we report the results of an ab initio study of the influence of hydrogen filled vacancies on the mechanical properties of zirconium. The modelling shows that hydrogen filled vacancies contribute to a lowering of the surface energy and an increase in the unstable stacking fault energy, which implies a reduction in ductility. Th...

In this work we report the results of an ab initio study of the transgranular fracture toughness and cleavage of brittle zirconium hydrides. We use the Griffith–Irwin relation to assess the fracture toughness using calculated surface energy and estimated isotropic Voigt–Reuss–Hill averages of the elastic constants. The calculated fracture toughness...

The purpose of this work is to investigate how well the temperature dependence of the elastic constants of single crystal zirconium, magnesium and gold are reproduced by ab initio density functional theory (DFT). The modelling was conducted via the quasi-harmonic approximation with the exchange–correlation functional based on the local density appr...

We report the results of an ab initio-based density functional theory study of the thermodynamic and structural properties of titanium hydrides. The thermodynamic modelling contains contributions from both vibrational and electronic excitations to the free energy and is conducted using the quasi-harmonic approximation (QHA). The enthalpy, entropy a...

We report the results of a systematic ab initio study of the elastic and thermodynamic properties of -ZrH, - -ZrD, and -ZrD1.5. In addition, pure -Zr as well as the -ZrH2 and -ZrD2 phases are evaluated for reference. The calculations are performed using quantum mechanical density functional theory (DFT) with the frozen core projector augmented wave...

We present a theoretical model to calculate the flexural rigidity of nanowires from three-dimensional elasticity theory that incorporates the effects of surface stress and surface elasticity. The unique features of the model are that it incorporates, through the second moment, the heterogeneous nature of elasticity across the nanowire cross section...

In this work, we present results from atomistic simulations of gold nanowires under axial compression, with a focus on examining the effects of both axial and surface orientation effects on the buckling behavior. This was accomplished by using molecular statics simulations while considering three different crystallographic systems: 〈100〉/{100}, 〈10...

In a previous publication P. A. T. Olsson, J. Appl. Phys. 108, 034318 2010, molecular dynamics MD simulations have been performed to study the resonant properties of gold nanowires. It has been documented in the aforementioned publication that the eigenfrequencies of the fundamental mode follows the continuum mechanically predicted behavior when Be...

In this work, resonant and elastic properties of single crystal gold nanowires have been studied through classical molecular dynamics simulations. The considered nanowires have perfect square cross sections and are oriented with the [100] direction along the wire axis and with {100} side surfaces. Three different sizes were simulated; 4.08×4.08 nm...