1. Monitoring surface state of AA7075-T6 during dynamic loading with FBG sensorMarijana Milković, Matej Njegovec, Jožef Predan, Jure Javornik, Denis Đonlagić, Nenad Gubeljak, 2023, izvirni znanstveni članek Opis: The AA7075-T6 material is widely used in aerospace applications due to its favourable strength-to-weight ratio and cost-effectiveness. The material undergoes a process of cold rolling and subsequent stretching to form metal sheets. This process generates residual compressive stresses on the surface of the material. Surface changes in the material are observed at low stress levels, resulting in variations in residual stresses and surface roughness. This article presents an approach to monitor the surface state changes of AA7075-T6 material during dynamic loading using Fiber Bragg Grating (FBG) sensor. Numerical Finite Element Method (FEM) simulations analyse the transfer of deformations from the damaged surface through the adhesive layer to FBG with different cladding thicknesses. Loading induces microcrack-related intensity changes in the FBG optical spectrum and deformation response. The magnitude of the response is greater, when the cladding thickness of the optical fibre is thinner. Experimental results show that the FBG optical spectrum response varies with cumulative number of dynamic cycles.
Ključne besede: AA7075-T6, dynamic loading, Fiber Bragg Grating (FBG) sensor, surface condition
Objavljeno v DKUM: 10.03.2025; Ogledov: 0; Prenosov: 6
 Celotno besedilo (1,20 MB)
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2. Dimensional deviations in Ti-6Al-4V discs produced with different process parameters during selective laser meltingSnehashis Pal, Marijana Milković, Riad Ramadani, Janez Gotlih, Nenad Gubeljak, Radovan Hudak, Igor Drstvenšek, Matjaž Finšgar, Tomaž Brajlih, 2023, izvirni znanstveni članek Opis: When manufacturing complicated products where both material and design play a role, especially thin and curved components, it is difcult to maintain accurate dimensions in Selective Laser Melting. Considering these difculties, this article presents the dimensional errors in the fabrication of Ti-6Al-4V discs and their thermomechanics during manufacturing. Various combinations of laser processing parameters were used to fabricate the 2.00 mm thick discs with a diameter of 5.70 mm. It was found that the thickness shortened and the round shape changed to an oval shape for most of the discs. The thickness decreased along the build-up direction from the bottom to the top and formed a taper that increased with increasing energy density (ED). The horizontal diameter of the discs changed slightly, while the vertical diameters changed remarkably with increasing ED. On the other hand, reducing the laser power resulted in a reduction of the roundness error, while it caused a reduction of the thickness. The hatch spacing signifcantly afected the volume of the melt pool and caused a change in the vertical diameter. The central part of the curved surface of the discs became concave and the concavity increased due to the increasing ED.
Ključne besede: dimension, Ti-6Al-4V, lase power, scanning speed, hatch spacing, selective laser melting
Objavljeno v DKUM: 29.03.2024; Ogledov: 219; Prenosov: 9
Celotno besedilo (4,48 MB)
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3. Razvoj modela za spremljanje degradacije površine materiala med dinamičnim obremenjevanjem : doctoral disertationMarijana Milković, 2023, doktorska disertacija Opis: The study focuses on the behavior of the AA7075-T6 material, widely used in the aerospace industry, under dynamic loadings. The material undergoes processing, including cold rolling and stretching, resulting in residual stress compressive stresses on its surface. The research centers on monitoring changes in the surface condition during dynamic loaidngs using Fiber Bragg Grating (FBG) sensors and numerical simulations.
The dissertation includes experimental testing of AA 7075-T6 material samples, numerical simulations of optical fiber responses to tensile loads, and an investigation of surface condition changes using techniques such as focused ion beam engraving and scanning electron microscope observation.
The study has shown that the surface condition of the material changes even under low dynamic loads, including variations in surface roughness, residual stresses, and FBG response. Despite low load levels, changes in FBG sensor spectra are observable.
The dissertation concludes that the surface condition of the material changes during dynamic loadings, detectable through FBG sensors. It underscores the effectiveness of FBG sensors in monitoring stress levels throughout the material’s service life, particularly on the side lobes of the spectral response.
In summary, the research on the dynamic behavior of the AA7075-T6 alloy offers valuable insight into surface condition changes that can impact the integrity and durability of materials in the aerospace industry.
Ključne besede: fatigue, high cycle load, Fiber Bragg grating
Objavljeno v DKUM: 05.01.2024; Ogledov: 466; Prenosov: 61
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