Forces in mechanics最新文献

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.

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.

Honeycomb sandwich panels (HSPs) with efficient core design have the potential to enhance blast resistance to tackle increasing blast threats by terrorist attacks. In this work, an innovative vertex-derived approach is introduced to enhance the blast resistance of HSPs. First, a quarter model of regular quadrilateral core HSP structures (RQH) with a cell size of 30.5 mm (10 × 10) was simulated with various amounts of TNT charges(1,2,&3 kg) kept at a height of 100 mm using the CONWEP algorithm available in ABAQUS/Explicit. The results obtained through simulation were validated with the tested results available in the literature. The study was extended by varying the cell sizes of 61 mm (5 × 5), 15.25 mm (20 × 20), and 7.625 mm (40 × 40) for comparison purposes. Further, honeycomb cores were tailored with the vertex-derived approach to enhance the blast resistance characteristics of RQH structures. The explosion resistance was assessed in terms of the deformation of the face sheets and dissipated energy through plastic deformation (PDE) of the face sheets and core. The result proved that the cell size variation and vertex-derived hierarchical core improved the blast resistance and the energy dissipation capacity of the RQH. The obtained results demonstrated that RQH with a 15.25 mm cell size (20 × 20) was found to have a good blast resistance at low and high-intensity blasts compared to other core sizes. The results also proved that the vertex-derived hierarchical topology enhanced the blast resistance of RQH under the same geometric parameters. The results demonstrate that employing vertex-derived hierarchical topology can enhance the blast resistance of HSPs.

In this paper, higher-order closed-form analytical solutions to the static bending and free vibration problems of laminated composite shells with double curvature are obtained using a hyperbolic shear deformation theory. The current theory is a modification of the shape function provided by Soldatos [30] in his well-known hyperbolic theory. The distributions of transverse shear stresses through the thickness of the shell are precisely predicted by the current theory satisfying traction free boundary conditions at the top and the bottom surfaces of the shell. Hamilton's principle serves as the foundation for the development of equations of motion. Navier's method is used for the analysis of simply-supported laminated shells under static and free vibration conditions. Displacements, stresses, and natural frequencies are presented for different shells with double curvature. The results from past investigations are compared to verify the accuracy and efficacy of the present hyperbolic shell theory.

In aerospace acamedic and industrial world, soft impacts are commonly used to replace bird strike tests for the validation of materials and structures as well as the calibration of numerical models. However in general, the analysis reported show only a few part of the experimental information available. In this paper, three laminate composites made of epoxy resin reinforced by glass or carbon fibres are tested under gelatin impact at several velocities up to complete failure. A detailed analysis based on 3D Digital Image Correlation (3D DIC) and visual inspection of the three laminates is provided for a total of 21 tests with impact velocities in the range 60–112 m/s. DIC extraction provides accurate quantitative displacement fields of the rear face in both time and space. Moreover, specific failure scenarios are identified for each laminate. The results obtained provide a suitable database for the development of numerical models. In addition, all experimental data from DIC extractions are opened to the readers on the Recherche Data Gouv website for comparisons with their own tests or numerical models.

Bellows are flexible structures and widely used in different industries to accommodate the internal pressure and deformations. This paper focuses an extensive review on analytical, numerical, and experimental approaches followed by various researchers with respect to the design aspects and applications of metal expansion bellows. The design aspect has been differentiated in three categories as mechanical design, thermal analysis, and forming process of bellows. While, the applications of bellows are categorized as automobile, piping systems, nuclear plant, and power generation units. In this paper, different stresses and deformations with internal and external boundary conditions are discussed. The effect of geometrical parameters on various design aspects will be the key attraction for leading researchers. It is found that various design aspects of bellows are related to deformation and stresses due to internal and external pressure, while a limited research work has been performed on the thermal study of bellows. This work will be useful for the bellows design for different applications.