Search results

Friction stir welding (FSW) is simple, clean and cost effective joining technology which allows high‐quality joining of materials that have been traditionally troublesome to weld conventionally without distortion, cracks or voids such as high‐strength aluminium alloys. Since FSW has been identified as “key technology” for primary aerospace structures, the recent FAR regulations for damage tolerance and fatigue evaluations of aircraft structures require fatigue life predictions for this specific joint type also in the presence of corrosion. The purpose of this paper is to give an overview of the prediction of small coupon fatigue lives of thin section friction stir welded butt and T‐joints.

Particularly, as a special application, widespread fracture mechanics software will be used to predict the fatigue life of FSW joints and to obtain SN curves. The engineering approach will start from an easy definition of the damage affecting the fatigue life of any of the previously mentioned cases (inclusions, tool markings, corrosion pits) and will move through affordable fracture mechanics solutions. Particularly, a first step in predicting the fatigue life of complex friction stir welded structures will be taken by combining the FEM code with the fracture mechanics software in the prediction of the FSW T‐joints.

The calculations are in very good agreement with the experimental results once the following basic assumptions are done: the welded material is treated as base material; particle inclusions and welding imperfections are treated as initial flaws while predicting the life of polished and un‐polished (including the T‐joints) FSW material, respectively, and the entire fatigue life was comprised of crack propagation; pitting and inter‐granular corrosion are treated as a single corrosion damage source and the model surface crack comprehends this damage; and the several corrosion‐damaged areas of the specimen surface are simulated with a single semi elliptical surface crack having the dimensions of the deepest and the widest corrosion damage area.

A simple engineering approach which is based on a relatively solid background and which is checked against fatigue test data for various FSW test specimens was developed: it may provide a practical and reliable basis for the analysis of fatigue tests of integral structures in the presence of corrosion attack, by using widespread fracture mechanics principles.

This study aims to uncover the multiscale relations among geometry, surface finish, microstructure and fatigue properties of curved-surface AlSi10Mg parts fabricated by powder bed fusion (PBF) additive manufacturing.

This paper investigated the high-cycle tensile and bending fatigue behaviors of PBF-built AlSi10Mg parts with curved surfaces. Besides, the surface finish, porosity and microstructure around various curvatures were characterized. Meanwhile, the stress distributions of the fatigue specimens with curved surfaces under the dynamic tensile/bending loading were analyzed via theoretical analysis and ANSYS simulation.

The results showed that the as-built specimens with the smallest curvature exhibited the best surface quality, smallest grain sizes and thinnest grain boundaries. In addition, the tensile fatigue fracture occurred around the largest curvature position of fatigue specimens, which was consistent with the simulated fatigue safety factor results. Moreover, the bending fatigue specimens with the largest curvature presented the shortest fatigue life due to the highest bending and shear stresses along the loading direction.

So far, most studies have focused on the fatigue behavior of as-built AlSi10Mg parts with planar structures only. The investigation on fatigue properties of as-built AlSi10Mg parts with curved surfaces remains unexplored. This study provides new insights into the characterization and quantification of the fatigue performance of PBF-built metal parts with complex geometries, the knowledge of which can promote their adoption in real industries.

The main purpose of this work is to explore the erosion wear characteristics of additively manufactured aluminium alloy. Additive manufacturing (AM), also known as three-dimensional (3D) manufacturing, is the process of manufacturing a part designed in a computer environment using different types of materials such as plastic, ceramic, metal or composite. Similar to other materials, aluminum alloys are also exposed to various wear types during operation. Production efficiency needs to be aware of its reactions to wearing mechanisms.

In this study, quartz sands (SiO₂) assisted with oxide ceramics were used in the slurry erosion test setup and its abrasiveness on the AlSi10Mg aluminum alloy material produced by the 3D printer as selective laser melting (SLM) technology was investigated. Quartz was sieved with an average particle size of 302.5 µm, and a slurry environment containing 5, 10 and 15% quartz by weight was prepared. The experiments were carried out at the velocity of 1.88 (250 rpm), 3.76 (500 rpm) and 5.64 m/s (750 rpm) and the impact angles 15, 45 and 75°.

With these experimental studies, it has been determined that the abrasiveness of quartz sand prepared in certain particle sizes is directly related to the particle concentration and particle speed, and that the wear increases with the increase of the concentration and rotational speed. Also, the variation of weight loss and surface roughness of the alloy was investigated after different wear conditions. Surface roughness values at 750 rpm speed, 10% concentration and 75° impingement angle are 0.32 and 0.38 µm for 0 and 90° samples, respectively, with a difference of approximately 18%. Moreover, concerning a sample produced at 0°, the weight loss at 250 rpm at 10% concentration and 45° particle impact angle is 32.8 mg, while the weight loss at 500 rpm 44.4 mg, and weight loss at 750 rpm is 104 mg. Besides, the morphological structures of eroded surfaces were examined using the scanning electron microscope to understand the wear mechanisms.

The researchers verified that this specific coating condition increases the slurry wear resistance of the mentioned steel. There are many studies about slurry wear tests; however, there is no study in the literature about the quartz sand (SiO₂) assisted slurry-erosive wear of AlSi10Mg alloy produced with AM by using SLM technology. This study is needed to fill this gap in the literature and to examine the erosive wear capability of this current material in different environments. The novelty of the study is the use of SiO₂ quartz sands assisted by oxide ceramics in different concentrations for the slurry erosion test setup and the investigations on erosive wear resistance of AlSi10Mg alloy manufactured by AM.

The purpose of this study is to explore the applications of 3D printing in space sectors. The authors have highlighted the potential research gap that can be explored in the current field of study. Three-dimensional (3D) printing is an additive manufacturing technique that uses metallic powder, ceramic or polymers to build simple/complex parts. The parts produced possess good strength, low weight and excellent mechanical properties and are cost-effective. Therefore, efforts have been made to make the adoption of 3D printing successful in space so that complex parts can be manufactured in space. This saves a considerable amount of both time and carrying cost. Thereof the challenges and opportunities that the space sector holds for additive manufacturing is worth reviewing to provide a better insight into further developments and prospects for this technology.

The potentiality of 3D printing for the manufacturing of various components under space conditions has been explained. Here, the authors have reviewed the details of manufactured parts used for zero-gravity missions, subjected to onboard international space station conditions and with those manufactured on earth. Followed by the major opportunities in 3D printing in space which include component repair, material characterization, process improvement and process development along with the new designs. The challenges like space conditions, availability of power in space, the infrastructure requirements and the quality control or testing of the items that are being built in space are explained along with their possible mitigation strategies.

These components are well comparable with those prepared on earth which enables a massive cost saving. Other than the onboard manufacturing process, numerous other components as well as a complete robot/satellite for outer space applications were manufactured by additive manufacturing. Moreover, these components can be recycled onboard to produce feedstock for the next materials. The parts produced in space are bought back and compared with those built on earth. There is a difference in their nature, i.e. the flight specimen showed a brittle nature, and the ground specimen showed a denser nature.

This review discusses the advancements of 3D printing in space and provides numerous examples of the applications of 3D printing in space and space applications. This paper is solely dedicated to 3D printing in space. It provides a breakthrough in the literature as a limited amount of literature is available on this topic. This paper aims at highlighting all the challenges that additive manufacturing faces in the space sector and also the future opportunities that await development.

The purpose of this paper is to consider an approximate model of accumulation of microdefects in a material under repeated loading which makes it possible to define theoretical parameters of the fatigue failure (durability, fatigue limit, etc.). The model is involving the relevant law of distribution of ultimate (yield) stresses in the material of these members in combination with the basic characteristics of main mechanical properties of a material (ultimate and yield stresses and associated standard deviations).

The model of fatigue failure of brittle and elastoplastic materials based on the use of the structural-probabilistic approach and up-to-date ideas on the mechanism of material fracture is proposed. The model combines statistical fracture criteria, which are expressed in terms of damage concentrations, with the approximate model of microcrack accumulation under repeating loading of the same level. According to these criteria, the fatigue failure begins with the accumulation of separation- or shear-type microdefects up to the level of critical values of their density.

The failure mechanism is associated with the accumulation of dispersed microdamages under repeated loading. The critical value of the density of the microdamages, which are identified with those formed either by separation or shear under static loading in consequence of simple tension, compression or shear, is accepted as the criterion of the onset of fatigue failure. The fatigue being low-cycle or high-cycle is attributed to accumulation of shear microdamages in the region of plastic deformation in the former case and microdamages produced by separation under elastic deformation in the latter one.

The originality of the paper consists in the following. The authors theoretically define parameters of the fatigue failure (durability, fatigue limit, etc.) using the model in combination with the statistical failure (yield) criteria appearing in the damage measures. The constructed fatigue diagram has discontinuities on the conditional boundary dividing domains with the shear-type and separation-type fractures of structural elements. Such results are supported by the experimental results.

This study aims to introduce a novel approach in form of a comprehensive software suite to help understanding and optimizing the build orientation toward maximizing the fatigue lifetime of complex geometries. The objective is to find an optimized build orientation under a given in-service loading state, which brings on smoother surfaces in stressed regions, mitigated roughness-induced stress concentration and deferred crack initiation stage. The solution addresses scenarios that no post-build surface treatment can be applied.

To account for the surface topography, the staircase induced surface roughness is registered as a function of build angle using the white light interferometry characterization, based on which the stress concentration factor (k_t) is calculated. Thereafter, the developed module in “Fatlab toolbox” is used to find the optimum build angle, considering the integrated surface orientations and stress analysis under a given loading condition.

Surface topography creates local stress concentrations upon loading, directly influencing the fatigue lifetime. It is a well-established fact that the conditions of the staircase geometry and surface roughness affect the magnitude of the stress concentration upon loading, which is influenced by the build orientation of the component. The proposed solution suggests the best build orientation that mitigates staircase-related surface roughness.

The suggested numerical approach assists the designers with positioning of the part on the build plate to minimize the build orientation-induced surface roughness and improve the as-built fatigue lifetime of the component.

The thermal behavior at the interfaces (of the deposited strands) during fused filament fabrication (FFF) technique strongly influences bond formation and it is a time- and temperature-dependent process. The processing parameters affect the thermal behavior at the interfaces and the purpose of the paper is to simulate using temperature-dependent (nonlinear) thermal properties rather than constant properties.

Nonlinear temperature-dependent thermal properties are used to simulate the FFF process in a simulation software. The finite-element model is first established by comparing the simulation results with that of analytical and experimental results of acrylonitrile butadiene styrene and polylactic acid. Strand temperature and time duration to reach critical sintering temperature for the bond formation are estimated for one of the deposition sequences.

Temperatures are estimated at an interface and are then compared with the experimental results, which shows a close match. The results of the average time duration (time to reach the critical sintering temperature) of strands with the defined deposition sequences show that the first interface has the highest average time duration. Varying processing parameters show that higher temperatures of the extruder and envelope along with higher extruder diameter and lower convective heat transfer coefficient will have more time available for bonding between the strands.

A novel numerical model is developed using temperature-dependent (nonlinear) thermal properties to simulate FFF processes. The model estimates the temperature evolution at the strand interfaces. It helps to evaluate the time duration to reach critical sintering temperature (temperature above which the bond formation occurs) as it cools from extrusion temperature.

The purpose of this study is to investigate the efficiency of applied vibration in improving the forming quality (mechanical property and dynamics characteristics) of fused filament fabrication (FFF) parts.

A vibrating FFF three-dimensional printer was set up, with which the samples fabricated in different directions were manufactured separately without and with vibration applied. A series of experimental tests, including tensile tests, dynamics tests and scanning electron microscopy (SEM) tests, were performed on these samples to experimentally quantify the effect of applied vibration on their forming quality.

It has been found that the applied vibration can significantly increase the tensile strength and plasticity of the samples built in Z-direction, and obviously decrease the orthogonal anisotropy. It can also significantly change the sample’s natural frequency, decrease the resonant response and increase the modal damping ratio, thus improve the anti-vibration capability of FFF samples. In addition, the SEM analysis confirmed that applying vibration into FFF process could improve the forming quality of the fabricated part.

Future research may be focused on investigating the efficiency of applied vibration in improving the forming quality of parts fabricated by the other additive manufacturing techniques.

This study helps to improve the reliability of FFF parts and extend the application range of FFF technology.

A novel method to improve the forming quality of FFF parts is provided and the available information about the performance of dynamics characteristics.

Process parameters in Fused Filament Fabrication (FFF) can affect mechanical and surface properties of printed parts. Numerous studies have reported parametric studies of various materials using full factorial and Taguchi design of experiments (DoEs). However, a comparison between the two are not well-established in literature. The purpose of this study is to compare full factorial and Taguchi DoEs to determine the effects of FFF process parameters on mechanical and surface properties of Nylon 6/66 copolymer. In addition, perform in-depth failure mechanism analysis to understand why the process parameters affect the responses.

A full factorial DoE was used to determine the effects of FFF process parameters, such as infill density, infill pattern, layer height and raster angle on responses, such as compressive strength, impact strength, surface roughness and manufacturing time of Nylon 6/66. Micro-computed tomography was used to analyse the impact test samples before and after impact and scanning electron microscope was used to understand the failure mechanism of infill and top layers. Differential scanning calorimetry (DSC) scans of infill and top layers were then taken to determine if a variation in crystallinity existed in different regions of the build.

Analysis of variance and main effects plots reveal that infill density has the greatest effect on mechanical and surface properties while manufacturing time is most affected by layer height for the polymer used. A 20% reduction in infill increased impact strength by 19% on average, X-ray images of some of the samples before and after impact tests are presented to understand the reason behind the difference. Moreover, DSC revealed a difference in the degree of crystallinity between the infill and top layers for 80% infill density samples. In addition, Taguchi DoE is realized to be a more efficient technique to determine optimum process parameters for responses that vary linearly as it reduces experimental effort significantly while providing mostly accurate results.

To the author’s knowledge, no published paper has reported a comparison between predictive DoE method with full factorial DoE to verify their accuracy in determining the effects of FFF process parameters on properties of printed parts. Also, a theory was developed based on DSC results that as the infill is printed faster, it cools slowly compared to the top layers, and hence the infill is in a less crystalline state when compared to the top layers. This increased the ductility of the infill (of 80% infill samples) and thus improved impact absorption.

The purpose of this study was to introduce three-dimensional printing (3DP) of functionally graded sandwich foams (FGSFs). This work was continued by predicting the mechanical buckling and free vibration behavior of 3DP FGSFs using experimental and numerical analyses.

Initially, hollow glass microballoon-reinforced high-density polyethylene-based polymer composite foams were developed, and these materials were extruded into their respective filaments. These filaments are used as feedstock materials in fused filament fabrication based 3DP for the development of FGSFs. Scanning electron microscopy analysis was performed on the freeze-dried samples to observe filler sustainability. Furthermore, the density, critical buckling load (P_cr), natural frequency (f_n) and damping factor of FGSFs were evaluated. The critical buckling load (P_cr) of the FGSFs was estimated using the double-tangent method and modified Budiansky criteria.

The density of FGSFs decreased with increasing filler percentage. The mechanical buckling load increased with the filler percentage. The natural frequency corresponding to the first mode of the FGSFs exhibited a decreasing trend with an increasing load in the pre-buckling regime and an increase in post-buckled zone, whereas the damping factor exhibited the opposite trend.

The current research work is valuable for the area of 3D printing by developing the functionally graded foam based sandwich beams. Furthermore, it intended to present the buckling behavior of 3D printed FGSFs, variation of frequency and damping factor corresponding to first three modes with increase in load.