Forces in mechanics最新文献

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.

In this article, the deflection profile and response characteristic of axially prestressed continuous beam under the actions of load travelling at non-uniform velocity is explored. To achieve this, The governing equation is transformed using weighted residual method to obtain a set of coupled second-order Ordinary Differential Equations (ODEs) governing the amplitude factors of the beam-mass system. This set of ODEs is further simplified by applying a modified asymptotic method of Struble. Impulse response function is finally employed to obtain solutions representing the responses of this structural member to accelerating masses. Dynamic time history is carried out. Deformation and responses due to the stress in the structure are evaluated for different parameters. Dynamic effects of decelerating, accelerating and uniform velocity-type of motions on the dynamic amplification factor (DAF) and response characteristics are extensively studied for various vital structural parameters such as the beam span length, foundation stiffness, prestress, rotatory inertia correction factor, load position and velocity. The values of the amplification factors (DAF) against various pertinent parameters are presented in plotted curves for the pinned-pinned beam. It is found that, for accelerating, decelerating and constant velocity-type of motion, the value of the dynamic amplification factor increases as the values of axial force, foundation subgrade, and rotatory inertia factor increase. Various useful results in perfect agreement with existing studies are presented. It is further established that variations of the various structural parameters of interest significantly alter the response characteristics of the vibrating system.

Permanent tooth avulsion is a common but extremely serious dental injury that can negatively affect both economic output and lifestyle. Even though it is not a disease, no one is ever completely safe from the possibility of suffering from these disastrous injuries. Dental implants play a vital role in the treatment of such injuries (tooth loss). This work was focused on to find the effects of two different platform switched abutment-implant assembly on hard tissues (Cortical and cancellous) bone. Materialized Mimics Medical Software was used for processing clinical imaging (CBCT) data of mandibular bone and micro-CT data of implant (5.5 × 9.5 mm), Abutments (Pt. sw. I and Pt. sw. II) and final 3D model of all parts were obtained by Fusion 360 CAD software and implanted into a right mandible bone block. Implant-Abutment with different switching assembly as platform switched-I (Pt. Sw. I) Ø5.5-mm implant and Ø3.8-mm abutment and the platform switched-II (Pt. Sw. II) Ø5.5-mm implant and Ø4.5-mm abutment were compared. Each model was subjected to 50 N, 100 N and 150 N longitudinal and lateral loads at occlusal surface of the abutment to evaluate the mechanical parameters. ANSYS 2020R1 was used to conduct the computational analysis. Mechanical characteristics such as von-Mises stresses and total deformation were measured in the hard tissues using finite element modelling. Under the application of different loads the cancellous bone experiences maximum von misses stress 4.7 MPa and 5.4 MPa for Pt. Sw. I and Pt. Sw. II respectively under longitudinal load and 7.4 MPa and 8.7 MPa for Pt. Sw. I and Pt. Sw. II respectively under lateral load. Similar trends were observed for cortical bone. While maximum total deformation of 2.1 µm (Pt. Sw. I) and 2.2 µm (Pt. Sw. II) under longitudinal load and 4.4 µm and 4.6 µm in cancellous bone and cortical bone under longitudinal load and 4.4 µm (Pt. Sw. I) and 4.6 µm (Pt. Sw. II) under lateral load in cancellous and 7.5 µm (Pt. Sw. I) and 8 µm (Pt. Sw. II) in cortical bone were recorded. The analysis may help to prevent the progression of marginal bone loss (MBL) because lower results for these variables indicated for higher platform switching in marginal bone. The findings of computational frameworks can help clinicians and other medical professionals make more informed decisions when selecting a treatment strategy from the many options available.

This paper investigates the undrained behaviour of granular clumps after isotropic and K_o-consolidation paths using a three-dimensional discrete element method (3D-DEM). Four randomly chosen clumped particles with a wide range of densification indexes, I_D, and mean confining stresses, p' were considered. The specimens were sheared to the deviatoric strain, ${\epsilon }_q$ of 40 % to reach the critical state (CS) conditions. It was found from the results that a unique critical state line (CSL) was achieved, irrespective of consolidation paths. The micro-mechanical quantities such as the average coordination number (CN) and von Mises fabric in terms of the second invariant of deviatoric fabric, F_vM, also reached CS values. Irrespective of the consolidation paths, unique relationships were found between $e-\log \left(p^{\prime }\right)$and $CN-\text{log}\left(p^{\prime }\right)$. The stress-fabric joint invariant, K_F established a unique relationship with $p^{\prime }$and e, which forms a relationship in the $K_F-p^{\prime }-e$ space and the projection of this relationship in the $e-\log \left(p^{\prime }\right)$ plane confirms the classical CSL. Moreover, the flow potential (u_F), stress ratio at instability (${\eta }_{IS}$), and average coordination number at instability (CN_IS) showed no dependency on the consolidation paths, while a dependency was observed for the second-order deviator fabric, F_vM.

The phase field model - a powerful tool - has been well established to simulate the fatigue crack evolution behavior. However, it is still hard to understand how each energy component in the phase field model contributes to crack evolution since the phase field method is based on an energetic criterion. In this work, we borrow the concept of configurational forces and show a straightforward way to examine the energetic driving forces in the phase field fatigue model. Results show that different parts of the configurational forces provide different energetic contributions during crack propagation.

In order to effectively mitigate the risk of bird strikes, it is imperative that radomes situated in areas prone to such incidents possess the capability to endure the impact loads caused by bird collisions. Additionally, these radomes must maintain their electromagnetic transparency. Therefore, glass fibre reinforced polymer (GFRP) with Nomex honeycomb sandwich material is used for radome structural design. The current research is intended to examine the dynamic behavior of sandwich composite panels in order to determine the penetration velocity by testing them at three distinct bird impact velocities, such as 88 m/s, 135 m/s, and 153 m/s. It is necessary to find the velocity at which the bird will penetrate / rupture the radome for the safety of Antenna / Electronic units mounted behind the radome. Finite element explicit code LS-DYNA simulates all three impacts. Extension of the simulation estimated the threshold bird impact velocity to be 146 m/s at which it penetrates the sandwich panel under fixture-controlled boundary condition.

Employing innovative kinematic function, a new inverse trigonometric shear deformation theory (nITSDT), variationally suitable, is developed to acquire pertinent data on the bending of sandwich plates subjected to transverse loads with variable aspect ratios(S). This nITSDT eliminates the need for shear correction factors since the transverse shear stress is directly determined by constitutive relations on the two extreme faces of sandwich plate satisfying the shear stress free surface circumstances. The governing equations and boundary conditions of the nITSDT are obtained by applying the dynamic version of the virtual work principle. For sandwich plates with simplly supports, solution is given by MATLAB code using Finite Element (FE) based on nITSDT. The findings of displacements and stresses are supported by those of more comprehensive theories, and the exact solution serves to highlight the viability of the proposed theory.