Papers by Keyword: Damage

Abstract: Bonding metallic structures with composite materials is widely considered to be the most optimal method for joining damaged and fractured structures. This method offers important advantages, such as reducing the stress intensity factor (SIF) and increasing the lifetime of the joined structure. However, hygrothermal aging is a phenomenon that can reduce the lifetime of reinforced structures made of glass fiber-reinforced polymer (GFRP). This study used numerical modeling to investigate a cracked stainless steel pipe operating in a hygrothermal environment and repaired with three patches. The main objective of this work is to determine the effect of adhesive aging due to hygrothermal damage on the repair efficiency of a cracked SA312 type 304 stainless steel pipe. The Finite Element Method (FEM) is used to evaluate the SIF as a function of applied load for different immersion times and at two different temperatures. First, the developed model was validated against literature results. A parametric study was then carried out. The obtained results showed that the adhesive maintains its stiffness for 7.5 months of immersion and that the mechanical properties of the adhesive are acceptable even at temperatures of 90°C or lower and internal pressures less than or equal to 50 bar. However, when the pressure load exceeds 50 bar (p_int > 50 bar), the degradation of the adhesive becomes more significant, and the hygrothermal aging leads to variations in the mechanical properties of the joined structure. It is important to note that these results can contribute to the improvement of the existing composite repair design standard and can provide reliability for the application of GFRP in different humid environments.

Abstract: This article presents a study of the mechanical behavior of tuffeau, a porous building limestone. Previous studies were focused on using strain gauges for mechanical monitoring with some limited success due to the size and the local nature of the measurement. The Digital Image Correlation (DIC) method has proven to be a valuable tool for noncontact, full-field strain measurements in various materials, including rocks which are natural and heterogeneous materials. After a prior phase of optimization involving texture acquisition and lighting conditions, this paper compares several DIC software programs to achieve consistent results on soft limestone specimens. Once the DIC program is chosen, a focus is made on detecting heterogeneities in the stone specimens. The occurrence of such heterogeneities explains why strain gauge measurement sometimes fails when applied to soft and natural materials.

Abstract: The purpose of this research is to develop a vibration isolator using auxetic viscoelastic sheet technology. The procedure for the design and elaboration of the insulator using polymers and by means of fatigue analysis using impacts is exposed, the absorption of energy by cycles is compared and the damage that is produced in the viscoelastic is observed with an optical microscope. This is to compare the variation in the force that the fatigue equipment exerts to deform the sheet in the same magnitude and to be able to establish, through the ratio of absorbed energy and returned energy, criteria on the useful life of the element for future designs.

Abstract: In all implantations into crystalline targets, quite a few ions find a path along a crystal channel or plane, so called channeling, and these ions travel deep into the crystal. This paper treats aluminum (Al) implantation in 4H-SiC and show how the crystal lattice will guide incoming ions deep into the target and modify the final dopant distribution. 4H-SiC samples have been implanted with 100 keV Al-ions, in a “random” direction using the wafer miscut angle of 4°, as well as with the impact beam aligned anti-parallel to the [0001] direction. Aluminium concentration versus depth profiles has been recorded by secondary ion mass spectrometry (SIMS). To track the most probable ion paths during stopping process, SIIMPL, a Monte Carlo simulation code based on the binary collision approximation (MC-BCA) has been used. In addition, the remaining ion energy has been extracted from SIIMPL at various depth along the ion path. Our results show that, independent of the used impact angle, some ions will be steered by crystal planes predominantly into the direction and also along the six directions. The energy loss is smaller along these low index axes. Therefore, at a depth of 1.2 μm, some Al ions along a path may still have kinetic energy, more than 40% of the original 100 keV, and continues to move deep into the SiC sample. The mean projected range of 100 keV ions in 4H-SiC is about 120 nm.

Abstract: The main shaft of shot blasting machine mainly uses cylindrical roller bearing as the supporting part. The influence of stress, strain and temperature on bearing damage was studied by thermal structural coupling analysis of the bearing through finite element simulation. The causes and main damage forms of bearing surface were verified by super depth of field observation and finite element analysis. It is found that there exists pyramidal strain in the contact area between inner and outer raceway and roller, and its distribution form is continuous point distribution. The stress concentration is mainly distributed in the contact area between the roller face and the retaining edge, and the roller temperature is more concentrated in the area near the end face. The maximum length and depth of spalling pit on racetrack surface were 572.2μm and 14.15μm respectively. The maximum width and depth of the scratches on the roller surface are 386.7μm and 10.7μm, and the damage degree of the roller surface is not uniform. The thermo-structural coupling analysis is used to simulate the running state of bearings, which is of guiding significance to analyze the failure forms of bearings and improve the service life of bearings.

Abstract: The paper deals with analysing the causes of damage to the injection mould insert block to produce plastic parts. Mould insert block material has been declared as alloy tool steel for hot working 1.2344 (X40CrMoV5-1). Part of the analysis is also evaluating an attempt to repair a damaged block using welding methods temporarily. However, there was an intense cracking of the welded joint already during the welding process. Therefore, a non-destructive capillary test was used to analyse surface defects. Complex material analysis of the mould insert block was performed using light and electron microscopy methods, the chemical composition was determined based on optical emission spectrometry.

Abstract: Causes of damage occurrence in vital components of welded structures of the bucket-wheel excavator boom (DU1) at the coal landfill of the thermal power plant 'Nikola Tesla A' in Obrenovac (Serbia) are investigated. Bucket-wheel excavator was produced by French company 'Ameco' and it moves along the circular track. Taking into account lack of technical documentation, all tests and were carried out under the assumption that welded structures were made of structural steels S355 and S235. Investigation of causes of damage occurrence are based on results of non-destructive tests (NDT) and tensometric measurements.

Abstract: It is proposed to apply a composite sheet of viscoelastic material encapsulated in ABS plastic to be used in the design of a prototype of vibration isolator in the use of motor bases. The cyclical impact tests presented are carried out with an insulator unit named as a viscoelastic sheet that takes advantage of Hooke's law 3D. Using a vibrating equipment, reproductions of impacts are made to study the ability of the vibration isolator to resist impacts and evaluate its useful life. Through the analysis of force and variation in the response to its natural frequency of vibration, the evaluations and its behavior to the tests are established, and its change to a passive type of isolator. The evolution of the damage in the viscoelastic and the appearance of cracks is also shown.

Abstract: Hysteresis is observed in various mechanical systems. For structural elements, cyclic loads cause deterioration of their characteristics due to cracks opening, yielding and buckling of metal­lic elements, etc. This contribution presents a smooth hysteresis model for reinforced concrete (RC) structural elements that accounts for both damage and pinching effects. The model is based on the Bouc­-Wen differential equation. Deterioration of the mechanical properties is introduced through a damage index that includes energy dissipation and ductility. Pinching is simulated by acting directlyon the stiffness of the system. The parameters of the model have clear physical meanings, which helps in the identification and interpretation of the results. Applications to RC elements show that the model is suitable for describing complex cyclic behaviours involving effects of damage. Being defined by a smooth hysteresis law, the model is a computationally-­effective tool useful for dynamic and stochastic simulations.

Abstract: In this contribution, the modelling of salt crystallization-induced damage in layered porous materials (such as masonry strengthened with composites, glazed earthenware, etc.) is addressed through a staggered multiphysics method. A staggered interchange of data is pursued between a multiphase model (crystallization pressure) and a macro-scale nonlinear mechanical model (material damage). Such method is preliminary applied to layered porous materials through a simple benchmark. Accordingly, the effects of layers with different properties on the crystallized salt distribution and damage pattern are highlighted.