Procedia Structural Integrity最新文献

Additive manufacturing (AM) technology, particularly for polymers, as versatile technology, becomes increasingly important in various fields, especially in medical and healthcare. The wide usage of 3D printed parts and layer-by-layer nature of them introduces unique considerations for potential fatigue-related issues, therefore, fatigue crack propagation and material failure are significant concerns when it comes to the long-term performance and reliability of such components. In this context, thermography can help identify areas of localized heating that could indicate the initiation and propagation of fatigue cracks. Energy Methods are time-efficient and requires fewer specimens compared to conventional fatigue testing methods which can provide valuable insights to the design and printing parameters to enhance the fatigue performance. In this research, after modelling different types notched dog-bone specimens, they were printed with FDM printer using PLA material and similar setting parameters. After that, 3D printed specimens were subjected to static tensile loading and stepwise fatigue tests monitoring the energy release to assess their fatigue behaviour. Additionally, we employed ACP module in Ansys to model notched specimens, calculating stresses within different layers.

Achieving a mirror-like finish surface quality in plastic injection molds and dies is necessary for the manufacture of optical components in the automotive industry. Any defects present on the mold surface will be evidenced on the injected part, compromising the functionality of the final product. Moreover, the typically employed finishing techniques (milling and polishing) in mould steels can be excessively time-consuming. The identification of machining and polishing combinations that meet the demanding surface requirements while minimizing time and material resources is therefore essential for ensuring the efficiency and cost-effectiveness of the mould-making process. In this work, an experimental study was conducted on the milling of hardened tool steel using a 6 mm two flute ball nose end mill. Distinct configurations of axial and radial depths of cut as well as feed per tooth were considered and their impact on the pre-polishing surface roughness was analysed. A methodology for the parametrization of polishing conditions was developed, ensuring consistency of speed and pressure. Further tests were conducted to evaluate the relation between post-polishing surface quality and the total duration of the combined finishing approach. The polishing stage consisted on submitting the milled samples to SiC paper (800 and 1000 grit) and diamond cloth (6 and 3 µm) polishing. The method provided enhanced control of the polishing operation and revealed milling/polishing improved sequences for attaining surface roughness technical requisites.

The present study aimed to develop a new life prediction model of a Ti-6Al-4V alloy obtained by additive manufacturing (AM). The Selective Laser Melting (SLM) method was used to obtain specimens. This study contemplates four phases. The first phase encompasses an analysis of the manufacturing process, including the raw materials cycle, specimen design, and the cutting process. In the second phase, tensile and fatigue tests are conducted to obtain the elastic and plastic proprieties and fatigue parameters (S-N Curve). The third phase involves an analytical and quantitative study of the manufacturing intrinsic defects of the SLM process, using optical microscopy, micro and nanotomography, and image treatment. The last phase focused on developing a life prediction model for Ti-6Al-4V based on experimental findings from the preceding steps. In conclusion, Ti-6Al-4V alloy obtained by additive manufacturing showed better overall mechanical properties when compared to the same alloy produced by a traditional method, exhibiting robust plastic behaviour and good ductility. Concerning life prediction models, two new models were developed to predict the fatigue limit of a Ti-6Al-4V obtained by additive manufacturing based on two different defect quantification methods.

This study explores the viability of upcycling the metal residues from machining industry into powders for additive manufacturing (AM). It investigates the production of powders from AISI P20+Ni steel chips using two different techniques: vibratory disc milling (VDM) and planetary ball milling (PBM). These powders were then sieved to select specific size ranges for directed energy deposition (DED) and laser powder bed fusion (L-PBF) processes. The study further aimed to optimize milling parameters to improve process efficiency and powder characteristics. The powders produced by VDM had a flaky morphology, while those produced using PBM had a rounded shape. Microstructural and microhardness analyses were conducted to evaluate particle consolidation and work-hardening effects. Despite the non-spherical shape of VDM powders, they were successfully used in the DED process. The deposit bead evaluation and dilution analysis were conducted, and subsequently correlated with the energy density. A multi-layered volume was printed for further microstructural, chemical, and hardness analyses. In conclusion, the study found that upcycled AISI P20+Ni feedstock can be used in DED, but strict atmospheric control during milling and printing is necessary. Further optimization of process is recommended to ensure chemical composition stability in the printed alloy.

The paper describes the progress in the development, manufacturing and qualification of the Support Attachments of the Body Flaps Assembly (BFA) of the ESA funded SPACE RIDER re-entry vehicle, involving innovative Additive Layer Manufacturing (ALM) techniques.

The SPACE RIDER program aims to define and to develop an affordable reusable European space transportation system to be launched by the ESA VEGA-C launcher and able to perform experimentation and demonstration of multiple future application missions in low Earth orbit. The proposed BFA design is based on a hybrid approach: Ceramic Matrix Composite (CMC) control surfaces capable to withstand the harsh environment of re-entry combined with high temperature metallic components allowing the connection of the control surfaces to the cold structure.

In particular, these support attachments have been designed as Ti6Al4V components and due to their geometrical complexity manufactured by using ALM technique.

The paper describes the ALM technology used, that is the Electron Beam Melting (EBM) process, and it is focused on the development activities for the qualification of ALM process and of the components for space applications according to ESA ECSS standards.

Electron Beam Melting (EBM) is a technology that allows to process materials, such as titanium alloys, that require high process temperatures and are difficult-to-machine through traditional manufacturing technologies. The Ti6Al4V alloy, widely used in biomedical, automotive and aerospace applications, relies in the group of the materials that present these requirements and, nowadays, is perhaps the most widely EBM-printed material.

The performance of this material under cyclic loading can be influenced by many factors such as porosities, residual stresses, corrosive environments, building direction, etc. This research aimed at assessing the fatigue crack propagation behavior of TiAl64V specimens made by EBM along different building directions. Tests were carried out using standard 8 mm thick Compact-Tension C(T) specimens in laboratory conditions. The main objective was to study the effects of the building direction on the residual fatigue life of specimens and to understand the fatigue failure mechanisms.

Huge amounts of waste are generated each year in the world. In addition, the construction sector is one of the larger producers of residues and a huge energy consumer. Thus, architects, engineers and other actors of the building sector should give solutions in order to reduce that problem. In that sense, the idea of finding solutions for the end of the service life of materials, in order to promote circularity, has been studied by several researchers. In this study, biomass wood ash has been used as aggregate for the generation of new eco-efficient gypsum plasters, for its application in new buildings and rehabilitation works. In order to conduct an exhaustive characterization of the new composites, an experimental campaign of the plasters has been conducted: dry bulk density and thermal conductivity of the plasters have been measured. The results showed that it was possible to add up to 25% of wood ash without modifying the water/gypsum ratios. Moreover, thermal conductivity of the plasters has improved up to18% when the ash was added to the mixture. Finally, the effects of using the new gypsum composites in the thermal envelope of buildings was analyzed by its usage in a rehabilitation case study simulation.

Additive manufacturing (AM) is a process that can achieve many complexities in the production of parts. The most important aspect of AM is that there is no more material wastage, so costs are reduced. Additive manufacturing is starting to be used in many fields, including medicine, automotive, aircraft, etc. The method of adding layer by layer is used for a wide range of materials: plastics, metals, and ceramics.

This paper investigated the influence of nutshells on shear specimens. To obtain the specimens Prusa 3D printer and PETG filament were used. The specimens were built using Fused Deposition Modeling (FDM) technology. The shear properties were investigated in-plane, where the force was measured with a load cell, and the displacement was measured with Dantec Q400 digital image correlation. The difference between nutshell and without nutshell specimens in the shear strength was investigated. It has been seen that the specimens behave differently when the nutshell exists or not. On the other hand, digital image correlation (DIC) was used to calibrate the strain that appears on the fracture.

Rapid development of additive technologies presents enormous opportunities. associated with the production of complex geometries. For this reason. the field of 3D printing has become an ideal technique for producing cellular structures. The paper addresses the issue. related to the determination of the minimum number of unit cells. at which the structure is characterized by a constant effective Young's modulus. Currently. it is not possible to state unequivocally what number of individual cells is needed. For this reason. the paper proposes an algorithm by which the minimum number of unit cells can be determined. The parameters of the structure. such as the relative density and the topology of a single cell. have an important influence. It is worth noting that the base material also plays an important role. Various methods are used for numerical analysis of cellular structures. such as finite element-based analysis. numerical homogenization and beam-based analysis. Nevertheless. each of them has its own advantages as well as disadvantages. This paper proposes to optimize the numerical homogenization of cellular structures. using models consisting of a minimum number of unit cells and a 3D representation of actual printed models of cellular structures. Based on these optimizations. better agreement with experiment was obtained.

In engineering applications, considering the growing utilization of Polylactic acid (PLA) material manufactured through material extrusion (MEX) additive manufacturing techniques, it becomes imperative to predict its fracture behavior to assess damage thoroughly under various loading scenarios. As an initial step, this study focuses on determining the Mode-I fracture toughness of the PLA material manufactured by MEX in three different print orientations through a three-point (3P) bending fracture test. The raster angle utilized to fabricate the single-edge notch bending (SENB) specimens was chosen as ±45°. Three different print orientations were used to investigate the effects of printing direction (i.e., horizontal, lateral, and vertical) on the fracture properties. The fracture properties were extracted per the standard ASTM D5045-14 on the specimens fabricated in three different print orientations. The values of Mode-I fracture toughness of PLA were respectively obtained as 4.22, 4.18, and 3.56 MPa/m with horizontal, lateral, and vertical print orientation. Then, corresponding fracture energy values were calculated for numerical investigations. A commercial finite element package was utilized to employ the extracted values into the extended finite element method (XFEM) and investigate the crack propagation in the specimens. It was found that the numerical analyses well simulated the crack propagation and peak load (damage initiation point) experienced in the SENB specimens tested under 3P bending loading.