Forces in mechanics最新文献

Geo-materials naturally display a certain degree of anisotropy due to various effects such as deposition. Besides, they are often two-phase materials with a solid skeleton and voids filled with water, and commonly known as poroelastic materials. In the past, despite numerous studies investigating the vibrations of strip foundations, dynamic impedance functions for multiple strip footings bonded to the surface of a multi-layered transversely isotropic poroelastic half-plane have never been reported in the literature. They are first presented in this paper. All strip foundations are assumed to be rigid, fully permeable, and subjected to three types of time-harmonic loadings. The dynamic interaction problem is investigated by using an exact stiffness matrix method and a discretization technique. The flexibility equations are established by enforcing the appropriate rigid body displacement boundary conditions at each footing-layered soil interface. Numerical results for dynamic impedance functions of two-strip system are presented to illustrate the influence of various effects on dynamic responses of multiple rigid strip foundations.

Offshore renewable energy structures are subject to harsh environments with loading from wind, wave, and tides which introduce fatigue damage in corrosive and erosive environments. An effective approach that has been found to improve mechanical and fatigue resistance of engineering structures is employment of Additive Manufacturing (AM) technology. However, little research has been conducted for implementation of AM technology in offshore renewable energy structures. This study aims to collate and critically discuss the advantages that AM technology can offer to enhance the lifespan of offshore renewable energy structures. In addition to fatigue life improvement, the potential of AM technology to enhance corrosion and erosion resistance in offshore renewable energy structures has been explored. It has been found in this study that among the existing AM techniques, Wire Arc Additive Manufacturing (WAAM) offers promising potentials for life enhancement of offshore wind turbine and tidal turbine support structures. Early research into the potential of using WAAM to create corrosion resistance coatings and components highlights many benefits achieved from this new emerging manufacturing technology, but further research is required to justify the use of the processes for commercial applications. In terms of erosion and wear resistance even less research has been conducted but initial findings show that AM has the potential to add a great level of resistance compared to the wrought material. This study presents the key advantages that AM technology offers to enhance the design life and integrity of offshore renewable energy structures as a first step towards unlocking the great potentials of AM for consideration and implementation in the energy transition roadmap.

The current computational investigation employs the stochastic extended finite element approach, which the authors have previously developed, to investigate the probabilistic fracture response of double edge cracked orthotropic laminated composite plates under varying stress conditions. The well-known extended finite element method is used to determine the mean and coefficient of variation of stress intensity factors KI and or KII by treating the input parameters as random variables. This is done under the assumption that all of the laminated plate's layers are perfectly bonded to one another and that there is no delamination effect between the layers, the matrix, or the fibres. And it's believed that the plate has through thickness crack. A combination of input random Gaussian variables is used to model the various input factors, such as the lamination angle, the applied loads, and the crack parameters (such the crack length and location). Typical numerical results are shown to investigate the effects of varying degrees of uncertainty in the lamination angle, crack length, crack length to plate width ratio, crack positions, and applied tensile, shear, and combined (tensile and shear) stresses. An excellent agreement arises when the findings generated with the stochastic extended finite element method methodology are assessed against the results found in the published literature through Monte Carlo simulations.

The present work involves experimentally determining the nano-mechanical properties (elastic modulus, hardness, plasticity index, and recovery resistance) of low viscosity (LV) and high viscosity (HV) Poly (methyl methacrylate) (PMMA) bone cement from load-displacement data obtained using Berkovich indenter, and then the effect of indentation parameters on these properties are explored through a validated three-dimensional (3D) finite element (FE) simulation. The 3D FE model includes a specimen with bilinear isotropic elastic-plastic material model. The good agreement between experimental and simulated load-displacement data for both variants of the bone cement emphasizes the applicability of the 3D FE model to predict mechanical behavior at nano scale indentation for both PMMA bone cements. The experimental and numerical analysis yield significantly higher values of elastic modulus, hardness, plasticity index, and recovery resistance for LV compared to that of HV bone cement. The experimentally determined values of elastic modulus, hardness, plasticity index, and recovery resistance for LV bone cement are 5.04±0.21 GPa, 312.33±2.84 MPa, 0.51±0.04, and 258.90±3.34 GPa, respectively, whereas the corresponding values for HV bone cement are found to be 4.45±0.29 GPa, 301.41±3.67 MPa, 0.42±0.01, and 191.63±1.66 GPa. The simulated load-displacement data concludes a remarkable results (elastic modulus, hardness, plasticity index, and recovery resistance), which suggest that the both variants of PMMA bone cement attain higher peak load along with larger hysteresis curve for increased indenter tip radius for a given indentation depth. The friction coefficient along the contact surfaces of specimen with indenter has no pronounced effect on the measurement of mechanical properties of bone cements.

The aim of this research was to investigate on bolted joints characterized by steel screws and aluminum nuts by means of numerical simulation. 2D and 3D CAD/FEM parametric models were developed in order to determine the preload distribution in joints with and without a Wired Threaded Inserts (WTI), so as to compare the trend of the stress distributions and the amount of load applied to each thread. The operating mechanisms and the effectiveness of a WTI were investigated in a parametric study by means of which the most important factors of the joint (materials, class, diameter, Engagement Ratio (ER), tolerance bands) were varied.

Ceramic Matrix Composite (CMC) is an emerging material system that can be a game changer in the aerospace industry, both civil and military. CMCs components are, in fact, lighter and less prone to fatigue failure in a high temperature environment. However, at high temperatures, the diffusion of oxygen and water vapour inside the CMC can have detrimental effects. Therefore, the presence of protective coating is necessary to extend the life of CMC components. In the present work, a three-layers coating, consisting of a silicon bond (BND), adhesively bonded to the CMC, an Environment Barrier Coating (EBC) and a softer layer 3 (LAY3), is investigated for a CMC component. An aero-engine high pressure turbine seal segment was considered. Two design aspects are covered: (i) creep law is determined and calibrated in environment Abaqus from the experimental data of each coating layer available in the open literature, to provide a suitable instrument for the creep relaxation analyses of hot components; (ii) thickness sensitivity study of each layer of the coating is conducted to minimise the interface stresses of coating with substrate in order to mitigate cracking and removal/spalling phenomena when exposed to temperature gradients and to increase their service life. These two different aspects are combined together to predict the coating stress field as a function of service time.

Ultrasonic fatigue tests were carried out under continuous cycling on the maraging 300 steel for the following conditions: (A) solution annealed (as received from supplier), (B) after aging heat treatment of 490 °C for 6 h, (C) after pre-corrosion attack, and (D) specimens loaded at 293 MPa at room temperature without failure until 1.0E+10 cycles. The ultrasonic fatigue strength of the four modalities were compared and discussed in regard the crack initiation inclusion, the heat treatment and the testing conditions. Crack initiation and propagation under this fatigue testing modality was analyzed; revealing that ultrasonic fatigue strength is related to internal TiN-inclusions and its parameters of shape and orientation, in regard the uniaxial applied load. Numerical simulations were carried out to investigate the stress concentration of an ellipsoidal void of 150 mm (longer radius), and a TiN ellipsoidal inclusion of same dimensions. In addition, SEM (Scanning Electron Microscope) analysis was carried out on the fracture surfaces to determine the crack initiation and propagation zones.

In this paper, the mechanical and fatigue behavior of pre-corroded wrought AZ31 magnesium alloy was studied. For this purpose, the standard 3.5 wt.% NaCl corrosive solution was used. The samples were immersed for 3–24 h to characterize the effect of immersion time on the mechanical properties of AZ31 alloy. Standard specimens were also immersed for 1–3 h for the fatigue testing. Results of tensile tests showed that thorough the immersion of 0–24 h, the deviation of ultimate tensile stress and yield stress were less than 4 % and 6 %, respectively. Moreover, the deviation of elastic modulus was less than 20 %. Although, the elongation was deviated by 81 % through the immersion of 0–24 h. A drastic decrease was observed in the fatigue lifetime of pre-corroded alloy compared to the bare alloy. As the immersion time increased, the fatigue lifetime decreased. Maximum reduction in fatigue strength occurred when the immersion time was 3 h and the stress amplitude was 82.5 MPa. Fatigue results also showed that the Levenberg-Marquardt was a good method to find the materials' constants, as the maximum and average relative errors were 10.28 % and 2.78 %, respectively. The fatigue fracture surfaces of pre-corroded specimens indicated the brittle fracture. The Basquin model was used for fatigue lifetime prediction. A new model was proposed with a new parameter, initial virtual crack size, to relate the immersion time to the fatigue lifetime using the Paris equation. The fatigue lifetime of 1–3-h pre-corroded AZ31 magnesium alloy was estimated by the new model with acceptable relative errors.

This paper presents a novel method for analyzing the dynamic response of plane Euler-Bernoulli frames with semi-rigid connections subjected to arbitrary external loads and bending moments. The proposed solution methodology is the Green’s Functions Stiffness Method (GFSM) in the frequency domain. The GFSM is a mesh reduction method closely related with the Finite Element Method (FEM) sharing with it key components such as shape functions, fixed end forces, and stiffness matrices. By capitalizing on the strengths of both FEM and Green’s Functions, the GFSM facilitates the derivation of closed-form solutions for structural analysis. The formulation is initially established in the frequency domain and is later transformed into the time domain using the fast Fourier transform algorithm. To illustrate the applicability of the method, an example involving a one-bay, one-storey plane frame with semi-rigid connections is presented.

During well operations in Mexico, a weight loss incident occurred, accompanied by the detachment of a section of the Bottom Hole Motor (BHM) connected to coiled wellbore tubing. To investigate the cause of the BHM rupture, a comprehensive analysis was conducted, including chemical analysis, metallurgical examination, thickness measurements, hardness, tension, and impact tests, as well as Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS). The results indicated brittle failure, potentially initiated by excessive torque, with evidence of plastic deformation and fatigue. The failure was attributed to weight forces overcoming well-related resistances, generating flexion stresses in the BHM body. Mechanical damages, including scratch marks, and localized deformation areas, indicated that the material is brittle, which is observed in the low elongation values (6 %) and energy impact exhibited. Microscopic analysis revealed predominantly brittle characteristics of the surface fracture. The failure of the BHM occur during attempts to unclog CT due to the material exhibiting low elongation and impact energy, suggesting that the material experienced deformation hardening, and fatigue before reaching failure. Additionally, scratches and excessive torque contributed to the material failing prematurely.