A study of the stress-strain state (SSS) of disc specimens has been conducted when testing specimens with stress concentrators (grooves). The research has shown that the truncation of circular discs along two symmetrical chords makes it possible to change the type (the ratio of principal stresses) of SSS that occurs at the destruction site. Therefore, these specimens can be used to assess the structural strength of materials on standard single-drive testing machines, taking into account the real type of SSS that occurs in the bearing elements of machines. The results of numerical SSS modeling have been used to build the dependences of the SSS type and level on geometric parameters of specimens. Geometrical parameters can be chosen for a certain SSS type to assess both the static and fatigue strengths of materials used in the manufacture of bearing elements.

Large-scale wind turbines mostly use Continuously Variable Transmission (CVT) as the transmission system, which is highly efficient. However, it comes with high complexity and cost too. In contrast, the small-scale wind turbines that are available in the market offer a one-speed gearing system only where no gear ratios are varied, resulting in low efficiency of harvesting energy and leading to gears failure. In this research, an unsupervised machine-learning algorithm is proposed to address the energy efficiency of the automatic transmission system in vertical axis wind turbines (VAWT), to increase its efficiency in harvesting energy. The aim is to find the best adjustment for VAWT while the automatic transmission system is taken into account. For this purpose, the system is simulated and tested under various gear ratios conditions while a centrifugal clutch is applied to automatic gear shifting. The outcomes indicated that the automatic transmission system could successfully adjust the spinning in line with the wind speed. As a result, the obtained level of harvested voltage and power by VAWT with the automatic transmission system are improved significantly. Consequently, it is concluded that automatic VAWTs, equipped with the machine-learning capability can readjust themselves with the wind speed more efficiently.

Polynomial equations in non-dimensional form for various fracture parameters of double-K fracture model for compact tension specimen have been derived and presented in this paper. These equations can be used for computing different double-K fracture parameters of concrete for known material properties and specimen size having relative size of initial crack length of 0.3 without involving much complexity in numerical computations. Values of peak load and corresponding crack opening displacement as necessary to compute the double-K fracture parameters of concrete have been derived from the established fictitious crack model in the present study. A simplified equation in non-dimensional form between peak load and critical crack opening displacement as obtained from a fictitious crack model has also been presented.

Research on shallot planting feeding technology is an integral part of the shallot planter associations in which determines the suitable drop of shallot seeds to the planting mechanism. The shape of shallot seed will affect the process of selecting the feeding mechanism and feeding funnel shape. The dynamics study of shallot seeds in the feeding funnel and their movement (that is dependent on the profile and mass property of seeds) is important for manufacturing and running a good mechanism. The shallots will then be transferred by the feeding mechanism to the planting mechanism with a suitable falling trajectory. In this research, design and calculation of dynamics of the feeding mechanism of the shallot seeds is investigated using dynamics equations and also Autodesk Inventor Professional and Matlab Simulink codes. The suitable ranges of feeding mechanism parameters are obtained for the analyzed shallot seeds in terms of the specific shape, weight and mass center coordinates of the seeds.

This paper presents a Mori-Tanaka-based statistical methodology to predict the effective Young modulus of carbon nanotubes (CNTs)-reinforced composites considering three variables: weight content, reinforcement dispersion and orientation. Last two variables are quantified by two parameters, namely, free-path distance between nano-reinforcements and orientation angle regarding the loading direction. To validate the present methodology, samples of multi-walled CNTs (MWCNTs)-reinforced polyvinyl alcohol (PVA)-matrix composite were manufactured by mixing solution. The MWCNT/PVA Young modulus was measured by nano-indentation, while the MWCNTs Young modulus was quantified by micro-Raman spectroscopy. Both stretched and unstretched composite specimens were fabricated. Transmission electron microscopy (TEM) and in-plane image analysis were used to obtain fitting coefficients of log-normal frequency distribution functions for the free-path distance and orientation angle. It was evidenced that numerical results fit well to measured values of effective Young modulus of MWCNTs and MWCNT/PVA, with exception of some particular cases where significant differences were found. Microstructural heterogeneities, cluster formation, polymer chains alignment, errors associated with the dispersion, orientation and mechanical characterization procedures, as well as idealization and statistical errors, were identified as possible causes of these differences. Finally, using the proposed methodology and the dispersion and orientation distribution functions experimentally obtained, the effective Young modulus is estimated for three kinds of thermoplastic matrices (polyvinyl alcohol, polyethylene ketone, and ultra-high molecular weight polyethylene) with different kinds of nanotubes (single wall, double wall, and multi-walled), at different weight contents, finding the superior mechanical performance for double-walled CNTs-reinforced composites and the lower one for multi-walled CNTs-reinforced ones.

When it comes to engineering, high performance is always a desired goal. In this context, regarding stiffened plates, the search for better geometric configurations able to minimize the out-of-plane displacements become interesting. So, this study aimed to analyze several stiffened plates defined by the Constructal Design Method (CDM) and solved through the Finite Element Method (FEM) using the ANSYS® software. After that, these plates are compared among each other through the Exhaustive Search (ES) technique. To do so, a non-stiffened rectangular plate was adopted as reference. Then, a portion of its steel volume was converted into stiffeners through the ϕ parameter, which represents the ratio between the volume of the stiffeners and the total volume of the reference plate. Taking into consideration the value of ϕ = 0.3, 75 different stiffened plates arrangements were proposed: 25 with rectangular stiffeners oriented at 0°; 25 with rectangular stiffeners oriented at 45° and 25 with trapezoidal stiffeners oriented at 0°. Maintaining the total volume of material constant, it was investigated the geometry influence on the maximum deflection of these stiffened plates. The results have shown trapezoidal stiffeners oriented at 0° are more effective to reduce the maximum deflections than rectangular stiffeners also oriented at 0°. It was also observed that rectangular stiffeners oriented at 45° presented the smallest maximum deflections for the majority of the analyzed cases, when compared to the trapezoidal and rectangular stiffeners oriented at 0°.

Bonded joints have important benefits over conventional joining techniques such as rivets, welding, bolts and nuts in structural applications, particularly for components prepared of composite or polymeric materials. Due to the involvement of many geometric, material and construction variables, and the complex fracture and mechanical modes offered in the bonded joints, a proper consideration of fracture behavior is required to fully achieve their benefits. The fractures in bonded joints are mainly of three types; interlaminar (delamination), adhesive (interfacial) and cohesive crack. For a particular defect, crack propagation may occur in the tensile (mode I), the shear (mode II), and the tear (mode III) and their combinations (mixed mode). This study deals with topics such as theories of bonded composite joints and repairs, finite element analysis and fracture-based analysis and tests of mixed-mode cohesive, interfacial and interlaminar fracture mechanics. By employing geometrical factors extracted from finite element analysis and experimental results obtained from a modified Arcan test fixture, the mixed-mode cohesive, interfacial, and interlaminar fracture toughness are determined and fracture surfaces obtained are discussed.

This paper aims to develop a maintenance optimization model to maintain a high level of efficiency and reliability of the machinery. The methodological approach is based on preventive maintenance through the partial or total replacement of critical components. Although an intermediate intervention control, the focus is on a particular machine that has stopped several times, reducing its operational availability and resulting in a high cost of non-production. This study uses a Weibull model to analyze and optimize the correct maintenance process of the machinery considered. The failure data are then analyzed and scheduled. The final purpose is to standardize the operators' intervention procedures to reduce the time for the same interventions.

One of the major successes in the field of Linear Elastic Fracture Mechanics (LEFM) is the groundwork of the stress intensity factor (SIF) computation. The approaches used to carry out SIF values may be analytical, semi-analytical, experimental or numerical. Each one of the above methods has its own benefits however the use of numerical solutions has become the most frequent and popular. Numerous schemes for the numerical computation of SIF have been developed, the J-integral method being the most popular one. In this article we examine the SIFs of an edge cracked two dimensional (2-D) steel plate subjected to tensile loading. Extended finite element (XFEM) computational scheme has been employed to estimate the values of SIF. The SIF values of cracks with different lengths and inclination angles (different configurations) have been examined by utilizing the domain based interaction integral approach. The effect of crack inclination and crack position on SIFs (KI and KII) has also been studied. The results obtained in this study were compared with those from literature and theoretical values and observed that they are in close agreement.

The incremental launching method (ILM) is an efficient method of bridge construction primarily suited for environmentally sensitive areas. However, during the bridge launching, there are significant contact stresses between the launching system and the steel bridge girders. These substantial contact stresses can cause damage both on, and just under, the girder surface. Although Hertz contact theory solutions may give an insight into the problem, the accuracy is uncertain due to the presence of complex geometries, loads, and material properties. The complicated structural systems need to rely on numerical modeling such as the finite element analysis which are not always available. The primary objective of this study is to estimate the relationship of the maximum contact stress between an I-girder and a roller using a nomogram. The nomogram is built based on a parametric study with various roller dimensions and loads by numerical modeling. The maximum contact stress from the nomogram can be a useful tool in designing a bridge girder on a support roller.