1,721,014 research outputs found
Fdm layering deposition effects on mechanical response of tpu lattice structures
Full text linkNowadays, fused deposition modeling additive technology is becoming more and more popular in parts manufacturing due to its ability to reproduce complex geometries with many different thermoplastic materials, such as the TPU. On the other hand, objects obtained through this technology are mainly used for prototyping activities. For this reason, analyzing the functional behavior of FDM parts is still a topic of great interest. Many studies are conducted to broaden the spectrum of materials used to ensure an ever-increasing use of FDM in various production scenarios. In this study, the effects of several phenomena that influence the mechanical properties of printed lattice structures additively obtained by FDM are evaluated. Three different configurations of lattice structures with designs developed from unit cells were analyzed both experimentally and numerically. As the main result of the study, several parameters of the FDM process and their correlation were identified as possible detrimental factors of the mechanical properties by about 50% of the same parts used as isotropic cell solids. The best parameter configurations in terms of mechanical response were then highlighted by numerical analysis
Microstructure-based RVE modeling of the failure behavior and LCF resistance of ductile cast iron
Full text linkIn this work the failure behavior of ductile cast iron microstructure subjected to tensile and low-cycle fatigue loadings is simulated by a 3-D, FE Reference Volume Element approach. A fully ferritic matrix is considered as representative of the low-hardness, high-ductility material class of nodular cast irons. Plastic flow potential rule, ductile and low cycle fatigue damage models are implemented at the micro-scale for the matrix constituent in conjunction with nonlinear cyclic hardening laws, and periodic boundary conditions are imposed over the RVE at the meso-scale. Different values of triaxiality are imposed. Numerical results confirm experimental findings of the behavior at the meso-scale and correctly predict the LCF lifetime, driving the interpretation of inner strain distribution, voids interaction and triaxiality effects on failure mechanisms
A method for the correlation of accelerometric data acquired in different locations and times
No full textIn this work a new method for the time and space superposition of data acquired in the dynamical testing of large structures is presented and discussed. The method consists in the integration of sets of measurements taken at different times and the integration of sets of measurements taken at different places of the tested structure. The latter is a very useful feature when dealing with huge structures, like big buildings comprising a number of different architectural details.
The method is even validated, presenting a case study consisting of many dynamical tests performed on an ancient castle
Microstructural, multilevel simulation of notch effect in ferritic ductile cast iron under low cycle fatigue
Full text linkTriaxiality of stress affects damage and failure of ductile metals. In mechanical components, triaxiality increases in the proximity of a notch, or, at the microstructural level, due to inclusions or voids. In this work, the effect of triaxiality on the LCF of ductile cast iron is investigated by a multilevel approach, homogenizing the response of a microstructural model which feeds a notched specimen. Moving from micro- to macro-scale, results indicate that triaxiality shorten the fatigue life. Thus, the notch effect on fatigue life of cast iron can be explained in terms of the combined effects of microstructure and applied triaxiality
Micromechanical modeling of the effect of stress triaxiality on the strain to failure of ductile cast iron
No full textThis paper presents modeling of the tensile and failure behavior of different nodular cast iron microstructures under variable stress triaxialities. The model is based on a Representative Volume Element (RVE) approach, which reproduces periodic stochastic distributions of nodules within a 3-D cell. Three cast iron matrices, from fully ferritic to fully pearlitic, are considered as representing the various nodular cast iron classes in relation to strength and ductility. Ductile damage and shear damage models are used for ferrite and pearlite, respectively. Several values of stress triaxiality are applied within the RVE. It is found that numerical results support experimental findings in relation to the local strain distribution and damage initiation and accumulation, reproducing macroscopic tensile responses with good approximation. As highlighted by experiments, triaxiality is found to have a strong effect on material ductility and void volume fraction growth
Mechanical characterization and constitutive modeling of tensile behavior of bovine aorta
No full textAn experimental campaign consisting in uniaxial tensile tests is conducted on several bovine aorta specimens with the aim of developing and calibrating a hyperelastic model for the tissue. Bovine aorta partially reflects the behavior of human aorta, which will be tested soon. This kind of biological materials present hyperelasticity, strain-rate dependency, relaxation, Mullins-like unloading effect and, eventually, anisotropy due to collagen fibers that are evenly dispersed in the structure. Mechanical tests show quite a high dispersion. The modeling approach, based on the Holzapfel’s skin constitutive equation and expressed in terms of invariants, demonstrates to be adequate in describing the nonlinear-hyperelastic behavior
Mechanical stress and deformation analyses of pressurized cylindrical shells based on a higher-order modeling
Full text linkIn this research, mechanical stress, static strain and deformation analyses of a cylindrical pressure vessel subjected to mechanical loads are presented. The kinematic relations are developed based on higher-order sinusoidal shear deformation theory. Thickness stretching formulation is accounted for more accurate analysis. The total transverse deflection is divided into bending, shear and thickness stretching parts in which the third term is responsible for change of deflection along the thickness direction. The axisymmetric formulations are derived through principle of virtual work. A parametric study is presented to investigate variation of stress and strain components along the thickness and longitudinal directions. To explore effect of thickness stretching model on the static results, a comparison between the present results with the available results of literature is presented. As an important output, effect of micro-scale parameter is studied on the static stress and strain distributio
CRACK DETECTION IN TENSIONING TIE-RODS BY DYNAMIC ANALYSIS
Full text linkSo-called “tie-rods” are metal beams used in a wide range of civil constructions. The main purpose of these structural elements is to provide support for masonry arches and vaults in ancient buildings, like churches, cathedrals and castles, which are known to lurch and founder in course of time. Tie-rods are subjected to axial tension and, thus, help the building resist lateral loads exerted by walls and facades.
Indeed, over the years, deformations of masonry walls and eventual displacements in the building may cause significant changes in the axial loads of tie-rods. In the extremes, this can lead to either of two scenarios: failure in structural integrity of tie-rods (damages and cracks), or loss of loads and subsequent performance decline – a phenomenon referred to as the “laziness” of tie-rods. Both of the scenarios are dangerous for the safety and integrity of buildings and can lead to irretrievable harm to the precious historical heritage of the human race. For this reason regular monitoring of tie-rods’ condition is of a great importance.
Health monitoring of tie-rods includes two major steps. The first one is identification of axial load and the second one is damage identification. As for the first one, multiple methods have been developed to accomplish this task, even some from the present authors [1-4]. However, the knowledge of axial load is not enough to assess the condition of structural tie-rods, because it does not contain any information on possible damages inside them, as for example that one shown in Figure 1. As for the damage identification, it definitely requires a more deep inspection of beams and a more careful analysis of experimental data, especially when tie-rods are ancient and hand-made. Such experimental techniques should be as less invasive as possible and at the same time should provide sufficient data on the beam condition, in one word non-destructive
Electro-magneto-mechanical formulation of a sandwich shell subjected to electro-magneto-mechanical considering thickness stretching
No full textThickness stretching included formulation of a multi-layered doubly curved shell in small scale is studied in the present work. Out-of-plane normal strain is accounted in our formulation based on a higher-order theory. Based on this theory, the total transverse deflection is divided into three portions named as bending, shear and stretching parts. Transient formulation of the nanoshell is derived using Hamilton’s principle and nonlocal formulation. The natural frequencies of the nanoshell are obtained in terms of main input parameters, such as initial electric and magnetic potentials, nonlocal parameters, aspect ratio, radii ratio and foundation parameters
- …
