Procedia Structural Integrity最新文献

The aim of this paper is to present a baseline-free method for the identification of slot edges in a square plate. The slots, created by reducing the plate thickness, have different geometries and are placed in several locations. We make use of Savitzky-Golay smoothing and differentiation filters for the computation of modal strains. These modal strains are computed by differentiating the modal displacements (mode shapes), which are obtained by the finite element method. A discussion on the set of Savitzky-Golay filter parameters to obtain the best damage identifications is presented. The influence of noise on the quality of these damage identifications is also studied. The norm of modal strains is found to be very sensitive to the stiffness decrease, allowing the identification of single damage (one slot) and multiple damage (three slots).

Additive manufacturing (AM) technologies are widely used in the fabrication of topologically complex components with thin-walled features, such as lattice structures. In this context, Laser Powder Bed Fusion (L-PBF) is one of the most commonly used AM technologies for producing such components. In order to further expand and justify the application of these components in operation and to model their mechanical behavior, it is necessary to know the mechanical properties of the matrix material from which they are formed. Therefore, there is currently a high interest in studying the behavior of these materials when subjected to monotonic or cyclic loading. However, determining the mechanical properties of the matrix material of thin-walled structures using tensile tests is challenging on the required subsize specimens. As a micro- or even nano-scale technology, nanoindentation can be used to probe a small volume of specimen, thus allowing the mechanical properties such as Young modulus, of thin-walled structures to be determined. In this work, Young's modulus of L-PBF Ti6Al4V alloy produced using different laser power and scanning speed combinations, has been determined on nano and macro scale. By comparing obtained results at both scales, it is evident that Young's modulus values determined at nano scale are higher and more scattered when compared to results determined at macro scale. Furthermore, this study implies that a wider range or a higher number of L-PBF process parameters should be considered to model it's influence on Young's modulus with higher accuracy.

Traditional methods of manufacture require the assembly of individual components to create multi-material structures, leading to increased costs and weight, as well as potentially reduced usable lifetimes. However, there are numerous applications that cannot be realized using conventional manufacturing techniques, as they need a multi-material approach. Additive manufacturing presents a ground-breaking opportunity to fabricate components that combine diverse materials in a single part or incorporate three-dimensional gradient areas throughout the entire cross-section of the component. The utilization of additive manufacturing has transcended its initial prototype phase and has garnered attention for its potential in facilitating low-scale production of products employed across various areas, including underwater field, such as components of the underwater acoustic recorder used by the Brazilian Navy. In this study, the durability of 3D-printed multi-material parts for potential applications in structures exposed to marine environments was investigated. Multi-material sandwich structures with outer layers made of ABS and a PLA core were fabricated using a Fused Deposition Modeling (FDM) 3D printer. Three different configurations were studied, varying the number of ABS layers (one, three and five layers of ABS were used). The ageing process was carried out in seawater for 60 days. Tensile and flexural tests were used to measure the mechanical properties of both unaged (control) and aged specimens. As expected, the highest water absorption was observed in the PLA samples, while the lowest in ABS samples. For the multi-material samples the lower absorption was found for the one layer ABS samples. For the unaged samples, the mechanical properties (tensile and flexural) varied as a function of varying the number of ABS layers, while for the aged samples, a plateau tendency was observed.

High-performance composite materials generally respond in a manner close to that of linear-elastic materials with brittle failure in many cases. However, when the mechanical behaviour of the matrix is predominant, these composites show non-linear elasticity, viscous effects, and plastic deformations before failure. Therefore, these materials should be analysed to understand their response in long-term applications. For this purpose, the mechanical response of a composite reinforced with short carbon fibres and graphene subjected to monotonic tensile tests, as well as cyclic tests at constant load and repeated progressive load will be evaluated. The results showed that this type of composite, and all those with similar behaviour, require a complex model to predict their mechanical behaviour.

Based on advantages of additive manufacturing (AM), this technology is becoming one of the most popular and preferable manufacturing processes in different industries. Although AM was introduced for fabrication of prototypes, it has been used for production of end-use products. Consequently, the mechanical strength of AMed parts has become of significant importance. In the present study, Influence of geometry and thermal aging on the mechanical strength of AMed parts has been investigated. To this aim, polylactic acid material was used to print specimens based on fused deposition modeling process. Since geometry of AMed parts has effect on their mechanical behavior, the specimens with three different geometries are fabricated and examined. Particularly, dumbbell-shaped, smooth, and V-notched specimens were subjected to tensile load under static loading conditions. In addition, in order to evaluate Influence of thermal environment, we carried out an accelerated thermal aging within temperatures of -5°C to 35°C, which is below glass temperature of the examined material. Experimental results showed different fracture behaviors and tensile strength due to the different geometries. Moreover, based on a series of tests, the failure behavior of original and aged specimens are determined. The outcomes of this study confirmed that the geometrical appearance and environmental working conditions of AMed parts must be taken into account in the design of these components.

This research investigated on the tensile properties of Additive Manufacturing (AM) PolyEther Ether Ketone (PEEK) under different printing and post processing conditions, with a focus on providing insights for future fatigue tests. PEEK is a high-performance thermoplastic material with excellent mechanical properties that is widely used in many industries. In this study, the miniFactory Ultra 3D printer, based on Fused Filament Fabrication (FFF) technology, was used to fabricate PEEK specimens so as to assess the influence of printing parameters on the mechanical performances. Three key factors were considered: layer height, infill pattern and annealing as possible post-processing treatment. The variation of layer height and infill pattern aimed at evaluating their effects on the tensile properties, whereas annealing treatment was performed to assess the influence of residual stresses. The results indicated that infill pattern significantly affected the tensile properties, whereas annealing did not improve properties of specimens with triangular infill pattern. This research provides valuable insights for industries such as aerospace, automotive, and healthcare, where AM PEEK components are increasingly utilized.

Regional Technological Institute, the research center of the Faculty of Mechanical Engineering at the University of West Bohemia in Pilsen, operates some technologies for additive manufacturing. This is powder bed fusion technology for metal printing and some technologies for printing composite materials and plastics. The necessary tools for reverse engineering, support calculations, in-service measurements, laboratory tests and material analysis are available. The contribution presents the potential of additive technologies in the maintenance of machines and equipment. Examples of printed spare parts are shown and commented on.

The marine environment poses significant challenges to metallic engineering structures, not only due to the exposure to wave and wind action and logistic challenges related to transport and maintenance, but also due to the constant exposure to seawater, which makes them vulnerable to corrosion. Typically, protective strategies, such as coatings, are used in marine structures, allowing the base material to retain its properties. However, these protections have limited lifespans which can lead to damage of the base material before maintenance. Structural steels with a higher mechanical strength, such as S690 steel, are object of increasing interest for offshore structures applications due to weight reduction advantages. However, its mechanical behaviour in a corrosive medium is not yet well reported in literature. Thus, this work intends to characterize a S690 steel under marine environment conditions. As such, a methodology for inducing accelerated pre-corrosion is developed and applied to quasi static tensile specimens. Its effect on the tensile mechanical properties is evaluated through testing in accordance with the ASTM E8 standard.

The fatigue behavior of the aluminum alloy AlSi10Mg manufactured by laser powder bed fusion for as-build and residual stress relief conditions with different notch geometries will be studied in this work. The fatigue tests (R=0) are carried out, at ambient temperature and in load control mode. The main results showed that the stress relief heat treatment had a slight positive effect on the fatigue strength, and effectively relieved residual stresses. The presence of different notches decreased the fatigue life when compared to the specimens without notches. Also, a model based on SWT parameter was successfully applied to predict fatigue life.

Concrete is one of the most prominent building materials in the construction industry. Further, lightweight concrete has recently emerged, contributing to the sustainable values of modern construction. Many researchers have worked on enhancing the concrete's compressive strength by applying externally bonding fiber-reinforced polymer (FRP) composites via epoxy adhesives. Such FRP materials are very promising due to their lightweight and high tensile strength along with high corrosion, impact, and fatigue resistance. This paper aims to investigate the use of carbon fiber reinforced polymer (CFRP) wraps in enhancing concrete's compressive properties. The study is conducted on strengthened and control normal weight (NWC) and structural lightweight concrete (LWC) cylinders (150 mm x 300 mm). Experimental results show that CFRP wrapping increase the compressive strength and stiffness of both types of concrete. The compressive strength of structural LWC increased by 67.9% and 118.1%, compared to an increase of 46.1% and 105.0% for LWC, using one and two layers of CFRP, respectively. Further, the ductility is significantly enhanced with CFRP wrapping, suggesting increased resilience and ability to absorb energy during deformation. In terms of behavior at failure, LWC exhibited a more favourable response than NWC at failure. Results indicate that LWC has a satisfactory performance in withstanding compressive loads. This underscores the potential for lightweight concrete to serve as a viable structural material and highlights the role of CFRP reinforcement in further elevating its structural capabilities.