present a procedure for numerical computation of elastic-plastic bending and springback of beams with asymmetric cross-sections. Elastic-nonlinear hardening behavior of the material is assumed and both isotropic and kinematic hardening models are considered. The strains are described as a function of rotation and shift of the neutral axis and the curvature of the beam. Exact geometric expressions for large deflections and large rotations are taken into account during bending process. A complete loading history is taken into account including the effect of the local loading during the monotonic decrease of the load. Numerical examples confirm a strong influence of the load on the final and springback rotation of the neutral axis, its shift, and curvature of the beam for different cross-sections and materials. A custom made forming tool was designed and manufactured in-house to experimentally evaluate the proposed solution procedure. It is shown that relative difference between experimentally and theoretically predicted results of the final radius of curvature of the formed beam is 0.177+/-0.683%, if also the effect of pre-strain on elastic modulus is taken into consideration.
COBISS.SI-ID: 13799963
We present the results of an experimental investigation on the crystallography of the dimpled patterns obtained through wrinkling of a curved elastic system. Our macroscopic samples comprise a thin hemispherical shell bound to an equally curved compliant substrate. Under compression, a crystalline pattern of dimples self-organizes on the surface of the shell. Stresses are relaxed by both out-of-surface buckling and the emergence of defects in the quasi-hexagonal pattern. Three-dimensional scanning is used to digitize the topography. Regarding the dimples as point-like packing units produces spherical Voronoi tessellations with cells that are polydisperse and distorted, away from their regular shapes. We analyze the structure of crystalline defects, as a function of system size. Disclinations are observed and, above a threshold value, dislocations proliferate rapidly with system size. Our samples exhibit striking similarities with other curved crystals of charged particles and colloids. Differences are also found and attributed to the far-from-equilibrium nature of our patterns due to the random and initially frozen material imperfections which act as nucleation points, the presence of a physical boundary which represents an additional source of stress, and the inability of dimples to rearrange during crystallization. Even if we do not have access to the exact form of the interdimple interaction, our experiments suggest a broader generality of previous results of curved crystallography and their robustness on the details of the interaction potential. Furthermore, our findings open the door to future studies on curved crystals far from equilibrium.
COBISS.SI-ID: 13852187
Substructure-decoupling techniques are used to identify a substructure as a stand-alone system while it is coupled to a complex structure. These techniques can be used for various applications, e.g., when the substructure cannot be measured separately from the complex structure, when modal testing methods are not appropriate due to the limits of the measurement equipment and for vibration-control techniques. The complex structure consists of the unknown substructure and the remaining structure. A drawback of the available substructure-decoupling techniques is that they require a model of the remaining substructure. However, when the model cannot be calculated or (experimentally) identified, the substructure-decoupling techniques cannot be used. In this paper a new approach is presented that does not require a model of the remaining substructure, but is based on an experimental identification of the interface forces. The sensitivity of the approach to experimental errors was researched. Numerical and experimental test cases are researched.
COBISS.SI-ID: 13798683
The paper presents a modelling of the laser hardening process by a high-power diode laser (HPDL). Through numerical implementation in to the finite element method (FEM) code ABAQUS, the modelis used in the computer simulation of two case studies of laser hardening selected for experimental validation. In the experiment, 100 x 100 x 15 mm cuboid samples made of 50CrV4 steel were subjected to laser hardening with signi fi cantly different sets of applied technological parameters (laser beam power, laser beam velocity) but still aiming at attaining a comparable maximum temperature on the sample surface. The simulation considers two alternative approaches to microstructure evolution and subsequent material hardness determination: one relying on the heating rate dependent austenitisation temperatures ( Ac 1 and Ac 3 ) governing microstructure transformation kinetics and the other neglecting heating rate dependence. Physical objectivity of the computed results is verified based on the corresponding temperature field measurements on the sample surface during heat treatment process and hardness measurements throughthe thickness of the laser-hardened sample. The experimental validation clearly proves that considering austenite kinetics at a high temperature change rate in computer simulation is de finitely more physically congruent. In the study of the applied process parameters impact, the effect of a higher temperature change rate on austenite kinetics is shown by the temperature shift of austenite and ferrite to austenite start formations. From the investigation of the effect of different heat inputs providing the same maximum temperature on the sample surface it results that deeper area of increased hardness is established when less laser beam power and velocity are applied.
COBISS.SI-ID: 13943323
A modern class of micro aerial vehicles (MAVs) uses deformable membrane wings (DMWs), which comprise rigid or rigidizable structural elements that guarantee stiffness, as well as flexible membranes that provide an aerodynamic shape, all in a compact and lightweight form. To contribute to the body of knowledge about DMWs, this paper presents extensive numerical simulations, accompanied by experiments that substantiate the findings pertinent to the aerodynamics and static aeroelastic behavior of these unconventional wings. The performance characteristics of canonical, untapered, and untwisted rectangular DMWs are studied using a parametric physical-based twodimensional (2D) fluid structure interaction (FSI) model adopting a two-way coupled FSI algorithm. The effect of geometrical, material, and flow properties is investigated, and the results obtained show that the material Young%s modulus is the most influential parameter affecting the aerodynamic characteristics of the studiedDMWs, with their higher rigidity and lower excess length ratio producing a higher lift-to-drag ratio. The validation of the computational modeling is carried out using a dedicated experimental setup tested in a low-speed wind tunnel facility. Numerical investigations show reasonably good agreement with the performed experiments and provide a wealth of information on the aerodynamic and aeroelastic behavior of this class of wings.
COBISS.SI-ID: 14280475