Archives of Civil and Mechanical Engineering最新文献

This article performs a complex analysis of the production of ceramic roof tiles from a plastic mass based mainly on clay with additions, subjected to the successive stages of the process, in order to ultimately obtain a roof tile to be used in roofings. It discusses the most important aspects and parameters of production which affect the abrasive and tribological wear of the machine elements. Particularly the key elements of those devices on the roof tile production lines which are in direct contact with the extruded material have to be especially resistant to abrasive wear, which occurs as a result of contact with the extruded clay band. The wear of tools of this type is affected by many, often opposing, factors and physic and chemical phenomena. This makes the analysis of their wear difficult and complex, at the same time demonstrating the difficulties in a detailed analysis of such processes as well as the key technological parameters, especially in terms of the possibilities of applying numerical modeling. This article also performs a review of the materials used for the production of machine elements for roof tiles and their optimization in the aspect of a continuous development of the production technology. A special attention is mostly paid to the wear of machines and devices used for band extrusion as well as the possible directions of further development of the ceramic industry.

Forging is accompanied by high temperatures, which results in oxidation of the charge material’s and the forging tools’ surface. Microscopic tests realized on the surfaces of post-service life tools demonstrated the presence of stick-ons originating from the forging material, which were accompanied by oxidation products. Their presence on the tools’ surfaces translates to their physico-chemical properties, which directly affect the tribological properties of the pair: tool-processed stock. The study presents the results of tribological tests performed on four hot work tool steels. The investigations were realized at the temperatures of 400 and 480°C with the use of the “ball-on-disc” test. In the case of the steels tested at 400°C, the recorded wear was higher than at the higher temperature. The wear resistance tests were complemented with microscopic tests of the friction face. It was stated that the presence of an oxide layer on the surface increases the steel’s resistance to sliding wear as well as affects the friction coefficient. This is connected with tribo-oxidation taking place at high temperatures as a result of mechanical forces (friction). The presence of oxides on the tool surfaces decreases the zone exposed to plastic deformations, which translates to the steel’s higher wear resistance. This oxide scale acts as a solid lubricant, protecting the contact surfaces from wear, which demonstrates the importance of preheating the dies before forging. On the other hand, we should consider the antagonistic impact of oxides, which can work as an abradant, leading to a possible damage of the forging surface and making it difficult to maintain its dimensional tolerances. The selection of steel for the forging tools should thus be based on a compromise between these two opposing phenomena.

This research experimentally analyses the fabrication, testing, and development of cement mortar incorporating Polyvinyl Alcohol (PVA) fiber at concentrations of 1%, 2%, and 3% by volume of the total cementitious matrix. PVA fiber geometry with a length of 8 mm and a diameter of 40 µm, specifically the RECS 15/8 mm type, was utilized due to its optimal balance between mechanical performance and workability. Mechanical tests, including three-point bending, were conducted to assess the load–deflection behavior, ultimate strength, and energy absorption capacity of the reinforced beams. The scope of this study encompasses tensile strength, elastic modulus in four-point bending with un-notched specimens, fracture energy in three-point bending with notched specimens, and compressive strength tests. The addition percentages of PVA fibers (1%, 2%, and 3%) were selected to investigate the effect of fiber concentration on mechanical properties systematically and to identify the optimal reinforcement level for enhancing performance. Tensile strength values exhibited a clear enhancement with increasing PVA fiber content, recording 1.96 MPa, 3.17 MPa, and 5.12 MPa for 1%, 2%, and 3% PVA fiber, respectively. The Elastic Modulus, determined through four-point bending with un-notched specimens, demonstrated a notable increase in stiffness, with values of 26.17 GPa, 53.63 GPa, and 67.7 GPa for 1%, 2%, and 3% PVA fiber, respectively. Three-point bending tests with notched specimens revealed improved energy absorption capabilities, as indicated by Fractured Energy values of 1.33 N.mm/mm², 2.98 N.mm/mm², and 3.91 N.mm/mm² for 1%, 2%, and 3% PVA fiber. Furthermore, compressive tests yielded increased strengths, with values of 46.8 MPa, 57.2 MPa, and 73.9 MPa for 1%, 2%, and 3% PVA fiber, respectively. The goal of this research is to explore and quantify the benefits of adding PVA Fibers to cement mortars, focusing on enhancing mechanical properties such as tensile strength, elastic modulus, fracture energy, and compressive strength. The findings are particularly beneficial for developing auxetic cementitious materials, offering applications in advanced structural components, earthquake-resistant structures, protective barriers, flexible pavements and runways, and innovative architectural designs. The results highlight the potential of PVA fibers to significantly enhance the performance and durability of construction materials, paving the way for advanced and resilient building components.

Single point incremental forming (SPIF) is a low-cost, low-volume forming technique that has gained the attention of researchers over the past two decades. However, it has primarily been utilized for ductile materials such as aluminum and steel alloys and has yet to be extensively explored for hard-to-form materials such as magnesium (Mg) alloys, which are widely used in aviation and automotive industries. The hexagonal close-packed structure of these alloys makes it challenging to deform at room temperature. Studies have shown that the formability of Mg alloys can be increased under warm forming conditions. The analytical model needs to be developed to understand the effect of temperature on material properties and process parameters and their dependencies on each other. The present work proposes an analytical thermal model to predict in-plane strains during the warm SPIF process of magnesium (AZ31B) alloy. A coupled thermo-mechanical numerical simulation model was developed using ABAQUS/EXPLICIT^® software to estimate in-plane strains and thickness distribution. The Johnson–Cook model was applied to define the fracture criterion and the constitutive model. The predictions of the analytical and numerical models developed in this study were compared with experimental results. Further, the study investigated the impact of step depth, tool diameter, and wall angle on formability and thickness distribution. The predictions from the model developed in this study take significantly less computational time than numerical simulation analysis with an accuracy within 3% of the numerical model.

In the present work, ZrO₂, HA, and Y₂O₃ hybrid reinforced AZ91D alloy surface composites were fabricated using multi-passes friction stir processing (FSP) route. Consequently, microstructure, microhardness, tensile, and corrosion behavior were thoroughly examined on processing passes. The FSP passes increased coarse-shaped grains which were gradually refined into finer equiaxial grains due to severe plastic deformation and equal dispersion of reinforcements. Microhardness values successfully increased with the incorporation of hybrid reinforcements and increasing FSP passes. Tensile tests demonstrated decreased ultimate tensile strength as compared to substrate materials but an increase compared to 1 pass to 3 passes. Due to grain arrangements, grain dislocations decreased between surface matrices. Corrosion rate increases with the number of days; however, when FSP passes rise, compared to FSP passes, corrosion rate also increases due to the formation of secondary surface layers on the surface.

For the first time, a new method has been introduced to address the optimal design problem of large and complex steel structures with a focus on minimizing weight. The structures considered in this study represent typical steel factory structures with nonprismatic sections of columns and rafters. The process of simulating this structure, from its geometric representation to a finite-element (FE) model, poses significant challenges using conventional methods. To overcome these challenges, a program was developed using the Open Application Programming Interface (OAPI) in the SAP2000 software and MATLAB to establish a new FE model updating technique. The weight optimization process is performed using a newly devised optimization algorithm named KODE. This algorithm combines the advantages of two existing algorithms, namely the K-means clustering optimizer (KO) and the Differential Evolution algorithm (DE). The primary innovation of KODE lies in its ability to generate additional movement directions, ensuring a better balance between the ability of exploitation and exploration compared to the original KO algorithm. To demonstrate the effectiveness of KODE compared to the other algorithms, 23 classical benchmark functions and CEC2005 benchmark functions are employed as initial numerical examples. Subsequently, KODE is applied to optimize objective functions, which is established based on the AISC360-05 design standard (American Institute of Steel Construction 360-05), for optimal weight in a steel factory structure. The results in this study show the efficiency of KODE in solving optimization problems. In particular, KODE has demonstrated high effectiveness and reliability when combined with FE model updating to design optimization for large-scale steel structures.

The pursuit of cement-based materials with enhanced mechanical performance in the construction industry involves formulating numerous mixtures with varied contents of raw materials. However, the scarcity or contamination of these materials demands optimization methods to minimize the number of trials required. Response Surface Methodology (RSM) is a statistical experimental optimization method with which relations between sets of factors and responses can be established. This systematic review aims to analyze the existing literature on RSM models developed to achieve optimum levels in cementitious mixes. Over 100 papers were analyzed in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) format. A comprehensive review of the RSM analyses in those studies and their effectiveness is conducted, through the evaluation of their optimized factors and responses, the selection of their design models, their use of ANalysis Of VAriance (ANOVA), and the determination of their coefficients of determination (R²). Factors such as water/cement ratio and binder content prevailed in most models, the predominant responses of which were, respectively, compressive strength and workability. Although the use of ANOVA is commonly used to demonstrate the validity of the models, the studies replicating the mix with optimal levels of all factors are necessary to validate the results. On the basis of this review and depending on the responses that need to be maximized or minimized, the application of RSM can clearly be very crucial when quantifying the effects of new raw materials, whether recovered waste or natural resources, on mix behaviour.

The present research performed a static and free vibration analysis of a flexoelectric micro-beam with bending–torsion coupling for the first time. Microbeams are used in various microstructures, such as micro-sensors, micro-actuators, and micro-switches. Hence, a study of the static and free vibration behavior of flexoelectric micro-beams with bending–torsion coupling seems necessary. In this study, the governing equations were obtained based on the non-classical size-dependent flexoelectric theory using Hamilton’s principle. Furthermore, the Laplace transform technique was employed to solve the problems in the static case. Additionally, the generalized differential quadrature (GDQ) method was used to solve for the vibration response. Subsequently, the impact of various parameters, such as the size effect, on the static response under direct and inverse flexoelectric effect and the free vibration response were discussed. To validate the results, they were compared to data from previous studies, whereby a good agreement.

Advanced remanufacturing by additive manufacturing is challenging in aerospace due to the minimization of material costs, preparation times and metal waste. This study analyzed a 40HM low-alloy steel ring as a demo tooling used to produce aircraft engine components. The possibility of using laser cladding with powder process with the additive material NiCrBSi alloy powder was analyzed. Optimal parameters of the process were selected in terms of the assumed structural requirements (geometrical parameters of the clad, its hardness and the size of the heat-affected zone) for the remanufactured surfaces, ultimately obtaining a crack-free multilayer coating with a thickness of 2 mm and a hardness of above 700 HV1. The remanufacturing process was performed on three representative surfaces: flat face, cylindrical external, and internal. This approach allowed an analysis of the possibilities of finishing the laser-deposited layers with the machining methods used in the actual tooling department of the aerospace company: turning, milling, grinding, and center grinding. During chip processing, the defects (holes, cracks) made machining difficult and ineffective, mainly due to accelerated tool wear. Single cracks were observed after the grinding operation, which may reduce the durability of the remanufacturing layer. Both the changes in the microstructure of the demo component and the phases present in the cladding were analyzed. The deposition process was found to form a martensitic structure in the substrate at the cross-section in proximity to the remanufactured surfaces. This was also confirmed by an increase in average hardness from 402 HV1 to 605 HV1 for the analyzed substrate areas.

Cement and asphalt (CA) mortar is a key structural material for high-speed railway slab ballastless tracks. To investigate the deformation property of CA mortar in the range of − 20–60 °C, a DIL402C thermal expansion instrument and a self-designed thermal deformation tester were used in this paper, and the thermal deformation mechanism was revealed by combining the dynamic thermal analysis technology, the relationship between the deformation and mass under cyclic temperature variation, and the microstructural testing. The results indicated that the thermal expansion deformation of CA mortar decreased as the moisture content increased. Under vacuum-drying, air-drying, and water saturation state, the thermal expansion strain ranges of CA mortar specimens with different sizes were 1.0248–1.4340 × 10^–3, 0.4438–1.3669 × 10^–3, and − 2.1815–0.5571 × 10^–3, respectively. The smaller the specimen size, the more significant the thermal shrinkage deformation caused by the increased humidity. The thermal expansion coefficient of CA mortar increased gradually during the initial heating process and then changed in a complicated manner with changes in the humidity. As a porous material with asphalt as the continuous phase, when the temperature increases, the volume expansion of ice, the melting of ice into water, the migration and evaporation of water, the phase change of asphalt, and the volume expansion of cement mortar jointly affect the overall deformation property of CA mortar.