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This article examines the influence of various factors on the precision of 3D printed objects produced through Fused Filament Fabrication (FFF) using Polylactic Acid (PLA) as the primary material. While PLA is widely chosen for its compatibility with biological applications, it does suffer from limited dimensional accuracy. The study focuses on investigating the effects of four independent parameters, namely layer height, infill density, printing speed, and the number of top and bottom layers, on accuracy along the three axes of length, width, and depth. The research objective is to identify the optimal levels of these parameters that minimize dimensional errors across all axes. However, due to conflicting requirements among different dimensions, determining a comprehensive decision-making methodology presents a significant challenge. To address this issue, three distinct approaches are proposed, each offering a unique perspective and practical application. Interestingly, the outcomes of these approaches converge on a single solution. Among these parameters, printing speed emerges as the dominant factor, while, the number of layers is the least influential. Moreover, consistent shrinkage is observed in the length and width dimensions, with greater errors evident in longer dimensions. Overall, a preference for lower layer height and infill density, along with higher printing speed and increased top and bottom layers, is recommended. The study findings indicate that the most effective parameter selection for reducing errors in all dimensions involves a layer height of 0.2 mm, infill density of 60%, printing speed of 50 mm/s, and the use of four top and bottom layers. [ABSTRACT FROM AUTHOR]

Friction stir welding is a relatively new way to join solid materials without melting using a nonconsumable tool, which has many applications in different industries including automotive, shipbuilding, and aerospace. Destructive testing is an integral part of engineering science, which costs a lot. Reducing the number of destructive tests via numerical calculations to determine the quality of welded parts is valuable. On the other hand, advances in computer technology and embedded sensing systems in different domains have made it possible to collect a variety of data in huge volume at an unbelievable velocity, which provides an opportunity and at the same time a challenge to engineers and practitioners to utilize this rich source of information efficiently. Functional data as a rich form of structured data allows for high dimensionality modeling and analysis of the data. In this paper, we develop a fully functional linear regression model to quantify and predict the quality of the process outputs by reducing the number of destructive tests and presenting a change-point detection model to avoid using the model when a change has occurred in one of the components of the process. Important issues such as autocorrelation and correlation are taken into account in the presented model. The functional variables of the model are solved by polynomial basis function expansions. The results of the experimental tests indicate that the proposed method performs well in detecting out-of-control conditions as well as estimating the change-point location. The obtained value of the multiple correlation coefficient 0.98 and the corresponding F-value equal to 652.95 support these results. [ABSTRACT FROM AUTHOR]

In this work, the fracture toughness of limestone was determined utilizing advantage edge-notched disc (END) type specimens. The normalized Phase I stress high transformational of limestone was calculated using a novel method. The samples’ Mode I (opening)-fracture toughness was accurately calculated using the flexible finite element method (FEM) to develop this helpful formula. The notched Brazilian discs (NBD) were used in a lab experiment to test the accuracy of the END procedure. To recreate these tests numerically and verify the correctness of the fracture toughness measurements, a discrete element analysis of the END tests was also performed. The findings of the numerical simulations and the fracture extension patterns derived from the experimental testing showed excellent agreement. The toughness levels determined by END studies, however, were less than those specified by NBD testing. This is because the notch in the END limestone sample has a uniform tensile stress distribution. [ABSTRACT FROM AUTHOR]

The heterogeneous structure of polymer and aluminum alloy is an effective way to meet the dual technical indicators of structural performance and lightweight design. Friction stir welding (FSW) is a solid-phase welding technology characterized by low temperature and large plastic deformation. It is basically not affected by the crystal structure and physical-chemical properties of materials and can realize polymer and aluminum alloy-specific materials quality connection. This paper presents a comprehensive review of the current advancements in FSW between polymers and aluminum alloys with a focus on optimizing welding parameters, joint formation, defect identification, and mitigation. The results showed that the most important details are that high rotation speed combined with low welding speed that is beneficial to increase welding heat input, improve joint forming and mechanical properties, and form aluminum riveting structure. Welding defects are the main reason for the low FSW performance of polymer and aluminum alloy heterogeneous structures. To improve the forming and load-bearing capacity of heterogeneous structures, welding tool structure design, surface pretreatment, and welding structure optimization can be utilized. [ABSTRACT FROM AUTHOR]

Understanding the cracking resistance of ballast rock materials is key parameter for designing the ballast rock crushing machines or estimating the onset of fracture in the ballast rocks of railway tracks. In this research, mode I fracture toughness (KIc) and mode I fracture energy (GIc) values were determined experimentally for the red andesite ballast rock obtained from the Shahryar mine (Tehran province). Two disc-shaped samples subjected to three-point bending, namely semi-circular bend (SCB) and edge-notched disc bend (ENDB) are selected for conducting the tests and for each specimen 14 replicates were tested. Although a natural scatter was observed for the experimental results the failure probability curves of SCB and ENDB samples showed meaningful difference demonstrating the effect of testing method on mode I fracture behavior. Two- and three-parameter Weibull distribution curves were fitted to the fracture toughness and fracture energy results of andesite ballast rock tested with both specimens. By relating the Weibull distribution curves obtained for the ENDB and SCB samples to their geometries, the statistical fracture behavior curves of SCB were estimated theoretically in terms of the Weibull statistical curves of the ENDB specimen. In addition, the relationship between the statistical fracture toughness and fracture energy data obtained from the tested SCB and ENDB specimens made of andesite ballast rock was examined and it was shown that these two parameters are correlated well to each other as suggested by the framework of linear elastic fracture mechanics. Highlights: Two different mode I configurations were used for rock fracture studies. The effect of specimen geometry on KIc and GIc of andesite ballast rock was studied using Weibull statistical analysis. Two and three-parameter Weibull distribution curves were obtained for the fracture toughness and fracture energy results. The relationship between fracture toughness and strain energy release rate of tested rock samples was investigated statistically. [ABSTRACT FROM AUTHOR]

Polymer concrete is a relatively new type of concrete in which polymer is used as a binder. This paper investigates the effect of compositions on the tensile strength and mode-I fracture toughness of polymer concrete (PC) and fiber-reinforced polymer concrete (FRPC). According to the literature, the range of compounds (in unit weight) is selected 15 to 25% for resin, 0 to 2% for fibers, 45 to 55% for fine aggregates, and 25 to 35% for fine and coarse aggregates. Using a design of experiment software, 198 specimens made of 66 different mixture designs have been designed, prepared, and tested. The results show that reducing the size of aggregates, increasing fiber content, and increasing resin content increase the tensile strength and fracture toughness. Results show that fiber reinforcement effect on mixtures with higher resin and smaller aggregates content is more promising. In addition, the minimum resin content for PC and FRPC materials is about 12.5%. In addition, the results show that the optimal percentage of fiber depends on the percentage of resin; in a mixture with 15%, optimum resin content is equal to 1.5%, and in a mixture, with 25%, optimum resin content is equal to 4.0%. [ABSTRACT FROM AUTHOR]

Concrete, as one of the most widely used construction materials, has brittle behavior. Adding fiber to concrete affects the latter's ductility behavior as well as some of the mechanical properties. Hence, experimental research was conducted to study the effect of fiber type and content on the flexural performance of fiber-reinforced concrete. In this study, the concrete samples were made and evaluated in accordance with ASTM C1609, ASTM C1399 and ASTM C79 standards, with three different types of polymer fibers, including twisted, barchip and fibrillated, and three contents of 0.2, 0.4 and 0.6 volume percentages. The results showed that by adding fibers to concrete samples, the flexural strength and flexural toughness increased by 19.6–81.69% and 3.98–79.89%, respectively. Furthermore, adding the fibers to the concrete sample increased the postcracking flexural strength by 16.63–30.14%. The concrete containing twisted and broken fibers, despite their different fiber types, had similar flexural performance. [ABSTRACT FROM AUTHOR]

This study investigates the effects of tool traverse and rotational speeds in the friction stir back extrusion (FSBE) process on the microstructural and mechanical properties of brass wires produced. The microstructural properties were examined by microscopic tests and the mechanical properties of the wires by hardness and pressure tests. The material flow pattern, temperature history, and strain experienced by the materials were investigated using a numerical model to understand better the effects of tool traverse and rotational speed on the final properties of the wires. Numerical results showed that, on the one hand, the strain experienced by the material in the wire periphery is more than the center of the wire, and on the other hand, the material experiences a lower temperature in the wire periphery. The microstructural results showed that this more significant strain and lower temperature in the perimeter of the wires caused the grain size to be finer than the center of the wire. Moreover, a coarser microstructure is produced by a faster rotation speed or a slower traverse speed. Also, increasing the traverse speed or decreasing the rotational speed increased the hardness of wires produced, so that the sample made with a traverse and rotational speeds of 40 mm/min and 315 rpm had the highest hardness, and the wire made with a rotational speed of 800 rpm and a traverse speed of 25 mm/min had the lowest hardness. [ABSTRACT FROM AUTHOR]

One of the most important challenges of storing fluids in thin walled pressure vessels under internal pressure is preventing crack propagation. At low temperatures, steel shows brittle crack propagation characteristic, which is highly dangerous. In this paper, a new numerical model is presented, in order to investigate the reinforcement of a cracked thin walled pressure vessel by composite patch. The extended finite element method (XFEM) technique is used to model brittle crack propagation through the thickness of a thin-walled pressure vessel utilizing the multi-scaling technique. Crack propagation in the thickness of a pressure vessel was studied utilizing the combination of XFEM approach in fracture mechanics and multi-scaling technique. Then, the critical energy, which is the maximum strain energy that the pressure vessel can absorb before the brittle crack starts to propagate, was calculated using the numerical techniques of XFEM. In order to increase the critical energy, cohesive elements and composite patches with different stacking sequence, which were extracted from previous experimental and analytical studies, were used, and the best stacking sequence was identified using the current XFEM code. Moreover, the optimization was carried out using the traditional optimization technique for reinforcing with composite patches, which was based on the optimum ratio of the increased critical energy to the thickness of the reinforcement. Results obtained show that, keeping constant the reinforcing thickness and changing the stacking angle, the maximum energy capacity is increased by 7-11%. Also, by increasing the thickness of the reinforcement, a significant growth in strain energy capacity (up to 40%) is observed. The Hashin damage criterion was used to ensure that none of the laminas' damage during the crack propagation is critical. [ABSTRACT FROM AUTHOR]

In laboratory fracture toughness studies, the crack growth resistance of rock materials may be influenced by different factors such as specimen geometry, loading conditions, and also the type of pre-notch cut in the test sample. In this paper, a large number of mode I fracture toughness experiments are conducted on an Iranian white rock “Harsin marble” with six different mode I specimens. The selected test specimens are in the shape of cylindrical rod, rectangular beam, and circular Brazilian disk containing either chevron notch or straight crack. The effect of specimen geometry and pre-notch type was investigated statistically, and it was found that the average fracture toughness values of notched specimens were higher than those of the similar specimens but containing straight crack. Meanwhile, the scatters of fracture toughness data for chevron notched specimens were smaller than those for the straight cracked samples. For each set of experimental fracture toughness results, probability of fracture was investigated using two- and three-parameter Weibull statistical distributions. Comparison of the Weibull fitted curves for chevron notched and straight cracked samples with the same geometries demonstrated that the discrepancy between the corresponding curves can be described with a good accuracy by a simple shift factor. In addition, using the extended maximum tangential strain criterion which takes into account the influence of both KI and T-stress terms, the statistical fracture toughness data of chevron notched specimens were predicted in terms of the Weibull distribution parameters of the straight cracked specimens. [ABSTRACT FROM AUTHOR]

A ring shaped specimen is used for studying mixed mode fracture in brittle materials. The ring specimen is subjected to a compressive diametral load and contains two angled central cracks. A series of fracture tests are conducted under various mode mixities using the ring specimen. It is shown that the obtained experimental results are in a very good agreement with theoretical predictions of the modified maximum tangential stress criterion. [ABSTRACT FROM AUTHOR]