Forces in mechanics最新文献

In this study, a circular type honeycomb sandwich panel using natural JUCO and synthetic woven glass fiber was fabricated, and the bending properties like bending strength, modulus of rupture (MOR), and modulus of elasticity (MOE) were evaluated. Polyurethane (PU) foam was injected into the core structure to improve the bending strength. The orientation of jute and cotton fiber was varied to investigate the best stiffness and strength. In addition, twill-type JUCO fiber mat and synthetic woven glass fiber were also used to fabricate the circular type honeycomb sandwich panel. Finite element modeling was undertaken to validate the experimental results. Prior to the finite element analysis, a tensile test was carried out to determine the boundary conditions. Injecting polyurethane foam into the honeycomb core does not show any significant impact on bending properties. However, the deformation rate increased considerably by adding PU foam in the core structure. According to the results, honeycomb sandwich panels made of woven glass fiber with PU foam exhibited more homogenous deflection and bending compliance compared with others.

The moment distribution method is considered one of the easiest and most reliable analysis methods. However, little attention has been given to modelling the stiffness of each member separately, as currently only one factor is being used to model all structural members without taking into account the loading conditions and curvature of the member. This can significantly influence the results when modelling columns, since unlike beams, which are usually bent in a single curvature configuration, columns can be bent in either a single or double curvature configuration. This paper presents a new set of stiffness factors to model each structural member separately depending on its boundary conditions and curvature. To validate this modification, an example concrete frame was modelled and analysed using the structural analysis software ETABS, and then the results were compared with that obtained from the standard moment distribution method and the modified moment distribution method. The results have revealed a significant enhancement in the accuracy of the obtained results when using the modified moment distribution method compared with the original moment distribution method, especially the values of the columns’ bending moments.

The improvement of hard machining efficiency has been a growing concern in the production practice while the environmental friendly characteristics have to be guaranteed. The application of nanofluid minimum quantity lubrication (NF MQL) technique was considered to be as a promising approach to obtain the cooling and lubrication effectiveness in the cutting area. In this present study, the MQL hard turning performance using CBN inserts under different cooling lubrication conditions (dry, Al₂O₃ nano cutting oil, and Al₂O₃/MoS₂ hybrid nano cutting oil) was investigated through evaluating the cutting force, tool wear, tool life, and surface roughness. Based on the obtained results, the normal force component F_y has the large values and the increasing rate is closely related to the flank wear, so it can be used as a criterion to evaluate the tool life. In addition, cutting force coefficient $K_F$ not only presents the relative increase of the normal force F_y compared to the tangential force F_z but also can be used for machining performance evaluation. The wear modes are mechanical scratching and chipping, and the wear land on rake and flank faces is concentrated on the main cutting edge, which is the distinguishing feature of hard machining with conventional cutting. In addition to cutting parameters, tool wear was proven to be affected by the cooling lubrication condition. Furthermore, the machined surface roughness was improved and tool life was prolonged under Al₂O₃/MoS₂ hybrid nanofluid MQL condition when compared to those in dry and Al₂O₃ nanofluid MQL due to the cooling and lubrication effectiveness.

This present work uses the phase-field modelings to investigate the influence of interfacial effects on damage and mechanical behavior, as well as the optimal distribution of the inclusion shape within brittle inclusion-matrix structures in various typical cases. These two constituent phases in the structures are assumed to be either isotropic or anisotropic. To achieve these goals, this work will: (i) use the phase-field modelings either considering or neglecting interfacial debonding, and the anisotropic phase-field modeling; (ii) determine and incorporate the strain tensor orthogonal decompositions into each specific phase-field modeling to enhance the accuracy and effectiveness of the simulation methods; (iii) combine the phase-field modelings with the BESO topology optimization algorithm to analyze the influence of interfacial effects on relationship curves and the optimal distribution of the inclusion shape. Through proposed numerical examples, it is demonstrated that the interfacial effects strongly influence crack paths, behavior curves, and optimal material distribution in structures. When considering interfacial effects, cracks are almost unable to penetrate into the inclusion phase. However, when neglecting interfacial effects, cracks propagate into the inclusion phase. This reason makes the structure more difficult to damage than when considering the interfacial effects, as evidenced by greater peak load values in behavior curves and greater total fracture resistance of the material. Especially in the example of inclusion phase optimization, the total fracture resistance value of the case neglecting interfacial effects is more than 107.9% greater than that considering interfacial effects.

The laminated sandwich composites have wide structure-making applications in the automotive and aviation fields due to their lightweight and superior flexural rigidity properties. Making grooves or holes to assemble more than one structure induces crack discontinuities near the stress concentration region in these sandwich structures. The present work examines the effect of crack discontinuities on the mechanical performance and failure process of the sandwich structures under different loading conditions. Phase field method (PFM) has been presented and implemented using in-house developed MATLAB code. The effect of holes, multiple cracks, number of cores, and loading conditions are analyzed for the mechanical and fracture behavior of the structure. Load-carrying capacity, threshold displacement value for crack initiation, crack propagation trajectory, and energy absorption capacity are compared for various crack discontinuities under different loading conditions. Approximately 35% increase in load carrying capacity is observed in equivalent multiple core sandwich structures.

In the past decade, the world has witnessed a new space race, driven by a growing commitment to reducing the environmental impact of space missions. This has led to the widespread adoption of liquid-propellant rocket engines, which offer several advantages over their solid-propellant counterparts. One key advantage is their reusability, which not only helps to reduce the generation of space debris but also makes space exploration cheaper. To further enhance the performance of liquid rocket engines, researchers have been exploring innovative cooling techniques and advanced materials. Among these materials, Ceramic Matrix Composites (CMCs) have shown great potential in reducing the overall engine weight when used instead of high-tech metal alloys, resulting in lower fuel consumption and emissions during launches. This paper focuses on the mass minimization of inner liners made of CMCs in rocket thrust chambers. At this aim, a computationally efficient preliminary design approach, based on an analytical one-dimensional thermo-mechanical model, is proposed. A case study of mass minimization of an inner liner of rocket thrust chamber is also presented and discussed, by considering five different CMC materials.

Ground mobile robots operating in outdoor environments face multiple challenges, being overcoming obstacles on uneven terrain a prominent one. This challenging task has been addressed by numerous researchers who have developed robots employing various strategies, all aimed at efficiently overcoming increasingly higher obstacles. This article describes 108 robots designed for this purpose, incorporating the principle of rolling for locomotion and obstacle overcoming. These robots have been categorized into six major groups based on their operating principle and strategy for overcoming obstacles. After conducting a meticulous review and comparison, it has been determined that both the definition of the strategy robot will use to overcome an obstacle and the optimized robot design from the early stages of its development through clearly established requirements are the elements that hold the greatest significance in enabling a mobile robot to efficiently overcome an obstacle. In this regard, specific requirements and parameters have been identified that must be considered in the design of the robot to fulfill its purpose. Among these, key considerations include dimensional optimization, robustness, adaptability, energy efficiency, sensory capability, and appropriate navigability.

In this study, an external semi-elliptical crack was modeled in a 3D API 5 L X52 pipeline with stress corrosion cracking (SCC). To make the crack, the finite element method (FEM) was used to obtain the failure pressure (P_f) and its mechanical behavior. The longitudinal crack had a constant length (2c) and varied with depth (a). The properties of X52 steel subjected to SCC using the slow strain rate technique (SSRT) were considered. True stress-strain curves were obtained in air and in an NS4 solution with pHs of 3.5 and 9.5 at temperatures of 25 and 50 °C. According to the SCC index calculated from the mechanical properties of the SSRT, the X52 steel is susceptible to SCC at pH 3.5 and 50 °C. The mechanical properties of the tensile test using the stress-strain curves decreased as the pH and temperature changed, compared to those carried out at room temperature. This was due to the corrosion and hydrogen embrittlement produced by the solution on the X52 steel. The failure pressure is sensitive to the stress-strain curve; if the stress-strain curve decreases, the failure pressure also decreases. Corrosion defects, such as longitudinal cracks in X52 steel, which could be susceptible to SCC in an NS4 solution, decrease the failure pressure (P_f) and its capacity to withstand pressures of up to 75 % in pipe-grade steel that transports hydrocarbons.

In this analysis, the creep responses of a non-constant thickness annular plate was presented. The material of disc is assumed functionally graded magneto-electro-elastic (FGMEE) in which the material properties change through the radius. Also, the heat transfer coefficients for convection and conduction are functions of radius and temperature. At first, the equation of heat transfer accounting for thermal gradient, convection boundary conditions, internal heat generation, and solar radiation effects was derived. The differential transformation method (DTM) was used to solve the resulting nonlinear differential equation. The equilibrium equation for the annular plate including creep strain effects was then obtained. Ignoring creep strains, an analytical solution was obtained for the zero-time of this equation. Then, creep strains were introduced using Norton's law and the Prandtl-Reuss relations to find the stress and strain rates under fixed temperature boundary conditions. Next, the equation of strain rates including creep strains was solved analytically. Finally, an iterative approach was used to evaluate the time-dependent redistribution of creep stresses at any time point. Numerical examples highlighted the influences of key parameters like internal heat generation, convective heat transfer, grading index, solar radiation, thickness profile, and angular speed on the stresses, deformations and electric and magnetic potentials.

For the first time, this paper investigates the forced vibrations of a functionally graded (FG) nanobeam with an accelerating moving load in a thermal environment. There is no exact coupling solution for the vibrations of nanobeam with an accelerated moving load, so this paper aims to provide a method to obtain an accurate solution for nanoscale structures with an accelerated moving load. The equations of motion are derived using Timoshenko's beam theory and the nonlocal strain gradient theory (NSGT). The Laplace method has been used to solve the coupling and exact differential equations. Then, by inverting Laplace from the coupled equations, an exact solution of the temporal response for FG nanobeam with constant acceleration and initial velocity in a thermal environment was obtained. The natural frequency was compared with previous works for validity and had acceptable results. Finally, the effect of parameters such as changes in acceleration and velocity of moving force, negative acceleration, power law index of FG material, different temperatures, nonlocal parameter, and longitudinal scale parameter on the maximum dynamic displacement of nanobeam is investigated. These results can be used better to design FG nanostructures with accelerated moving loads. Considering the sensitivity of data analysis in nano dimensions, it is necessary to provide an analytical solution method in these dimensions to reduce the error percentage in nano dimensions to zero. which is presented in this work for the first time.