Forces in mechanics最新文献

Effect of strain rate on the damage behaviour of hydrogen (H)-charged dual phase (DP 780) steel via the in-situ digital image correlation (DIC) technique is investigated in this work. Since stress concentration sites like notches are common in engineering practice, two types of uniaxial tensile tests have been carried out using smooth and notch tensile specimens for detailed analysis. The study reveals the significance of hydrogen embrittlement in DP 780 steel, as no strain rate effect is observed on the mechanical property in the case of an uncharged smooth tensile specimen. However, a significant effect of strain rate is detected after the H-charging. Hydrogen showed a lesser ability to aid the failure process when the applied strain rate is raised, as it could diffuse over a limited distance during the tensile test. The local axial and width strains, along with necking and fracture strains, are quantified for each specimen to understand the strain rate effect better. A centre-line crack is observed in every H-charged specimen's fracture surface owing to the presence of MnS inclusion in DP steel along the central line and its interaction with the atomic hydrogen. Moreover, the degree of hydrogen embrittlement is substantially higher in the notch tensile specimens than in the smooth ones.

Functionally graded materials (FGMs) are high temperature-resistant materials that can simultaneously maintain metallic tenacity and anti-corrosive properties. Nevertheless, using FGMs during a multi-year service life at ultrahigh temperatures is crucial. Hence, the time-dependent creep response of variable-thickness rotating disks made of FGM is investigated. Four different disk profiles of linear, concave, convex, and uniform are considered. The material's creep properties are defined by the Bailey-Norton creep law. Loading is a rotation-based mechanical body force and a uniform temperature throughout the disk. Simultaneous solution of equilibrium, stress-strain, and strain-displacement equations yields a non-homogenous differential equation containing variable and time-dependent coefficients. In an attempt to optimize the computation cost, Bat and Fish algorithms were used to optimize the initial strain presumptions. Semi-analytical solution of this differential equation gives radial and circumferential stress histories and displacement histories. To confirm the solution method, initial thermo-elastic radial stress, and the effective stress history are validated with the existing literature; there is a good agreement between the results. In addition, the finite element software ABAQUS was used to model the FGM disk thermo-elastic behavior, and the result was compared with the semi-analytical solution results. This study emphasizes the significance of accounting for creep effects in the design of FGM rotating disks, as remarkable changes in their displacements and stresses occur over time. This study emphasizes the significance of accounting for creep effects in the design of FGM rotating disks, as notable changes in their displacements and stresses occur over time.

The developed method of processing experimental data from tests performed according to the four-point asymmetric bending scheme made it possible to establish the coefficient of proportionality between the modes of failure I and II, which for structural steels is in the range of 2,5÷3. The established longevity before the appearance of the critical speed according to the developed models is within the limits of the natural dispersion inherent in fatigue failure, which indicates the effectiveness of the developed algorithm and the correctness of the determined indicators of resistance to failure. The problem of the appearance of an oblique crack during tests on four-point asymmetric bending has been solved. It can be assumed that about 90% of the growth of an oblique crack is caused by the contribution of the mode of failure II.

While several theoretical and experimental studies for cracks in piping exist, most pertain to pipelines, equipment, or fittings under pressure conditions or under stress corrosion conditions at welding. Element finite Method models have occasionally supplemented experimental methods, to investigate such operational fails. In this approach we explore technical options to comprehensively understand crack propagations, by first, evaluating the Stress Intensity Factor $\left(K_I\right)$ using ANSYS Parametric design language then, comparing with the Displacement Correlation Technique, for an elliptical base gas piping (20″APL Gr. B) suffering a longitudinal welding-induced crack, under a compression of 1.86 MPa. The $K_I$value for an Electric Resistance Welding crack was calculated for the two-dimensional plane, for a quarter-length of propagated crack along the elliptical front. The $K_I$ value estimates are 0.94x${\left(10\right)}^{-3}$ MPa$\sqrt{m}$ from ANSYS Parametric design language vs. 0.7$0x{\left(10\right)}^{-2}$ MPa$\sqrt{m}$from DCT the two methods are close less than 1. These results were compared with the theorical stress intensity factor for elliptical cracks by Broek¹ David called elementary engineering fracture mechanics where the values were 0.5x${\left(10\right)}^{-1}$ MPa$\sqrt{m}$. We found that the proposed FEM method for estimating $\left(K_I\right)$is the approach that is closest to the theoretical value.

Laser peening without coating (LPwC) is a well-known technique to improve high-cycle fatigue properties by introducing compressive residual stress (RS) near the surface of metal components. In this study, X-ray diffraction (XRD) and flexural fatigue tests were applied to pre-cracked 12 mm thick SM490A welding structural steel specimens that were subjected to LPwC nearly 20 years ago with a pulse energy of 200 mJ, a spot diameter of 0.8 mm and a pulse density of 36 pulse/mm². XRD revealed that the compressive RS has remained stable to date, with approximately 400–500 MPa remaining at the surface and a compressive depth of approximately 0.9 mm from the surface, which is comparable to the data measured by XRD immediately after LPwC. In the flexural fatigue tests with a stress ratio of 0.1 and stress rages of 100, 150 and 200 MPa, LPwC extended the fatigue life by more than 1.6 times, depending on the stress range and individual specimens. Crack restarting cycles were significantly increased by a factor of at least 1.8, and the crack growth rate was suppressed by a factor of about 0.7 or less.

The main goal of this paper is to improve the mixed interpolation of tensorial components triangular (MITC3) by using the edge-based smoothed finite element method (ES-FEM), so-called ES-MITC3, for analyzing the vibration of piezoelectric functionally graded porous (p-FGP) plates subjected to dynamic loading. The material properties of the FGP core vary through thickness with uneven porosity distribution. Besides, the linear relationship between the electric potential and the thickness of the piezoelectric sublayer is taken into account. A closed-loop control algorithm is employed to actively control the vibration of p-FGP plates, through feedback from displacement and velocity. The performance of the proposed method is verified through comparative examples. Finally, the authors hope that the present method can be effectively applied to many smart material models in a multiphysics environment and contribute to understanding texture control by piezoelectric materials through numerical results.

This research paper presents a comprehensive investigation into the response of a 3D finite element model when subjected to 7.62 AP projectiles. The study utilises Hetherington's armour composite equation and incorporates the Johnson-Holmquist material model to analyse the strength and failure criteria of the ceramic and Kevlar/epoxy components, respectively. The results highlight the remarkable resilience of the composite armour, demonstrating its ability to withstand projectile velocities up to 1500 m/s. However, as the ballistic velocity limit increases, the armour experiences significant damage, including projectile erosion and panel delamination. Through numerical simulations and advanced modelling techniques, the paper thoroughly explores the failure modes and energy absorption characteristics of composite armour systems under projectile impact. It investigates key parameters such as velocity, acceleration, kinetic energy, internal energy, pressure distribution, displacement, and damage progression. The analysis reveals a progressive decrease in kinetic energy as the projectile interacts with the armour, underscoring the crucial role of energy absorption in preventing projectile penetration. Moreover, the impact velocity influences the distribution of internal energy within the composite armour, with higher velocities leading to greater energy absorption up to a threshold limit. The study also determines the ballistic limit velocity (V50) using the velocity history approach and validates the findings with existing literature. Overall, the research provides valuable insights into the limitations of composite armour and offers important recommendations for designing and improving materials to achieve superior ballistic protection. It emphasises the significance of reaching the maximum ballistic limit while maintaining a lightweight armour structure by optimising the total armour thickness. This study contributes to the advancement of armour technology and enhances our understanding of the behaviour of composite materials under high-velocity impacts. It offers valuable guidance for the development of more robust armour systems suitable for various defence and protection applications.

The aim of this work is to derive exact partial-wave series expressions for the radiation force of plane compressional progressive waves propagating inside an elastic medium and incident upon an embedded elastic sphere. The analytical modeling is needed to provide fundamental physical understanding of the underlying phenomenon of mode conversion and its contribution to the acousto-elastic radiation force, and in experimental design. In the context of linear elasticity theory, a rigorous derivation for the acousto-elastic radiation force, based on the integration of the time-averaged radial component of the elastodynamic Poynting vector (or power flow density), is presented and discussed. Initially, the elastic scattering problem is determined and subsequently used to derive the mathematical expression for the acousto-elastic radiation force of progressive compressional waves. The method is also verified using the extended optical theorem for elastic compressional plane waves. Extension to the case of elastic plane standing wave is also provided. Particular importance is made on the contributions of elastic mode preservation (P → P) and mode conversion (P → S) to the acousto-elastic radiation force. Numerical computations for the dimensionless radiation force efficiency and its components demonstrate the importance of compressional-to-shear mode conversion in the scattering by the sphere encased in a linearly-elastic medium. The analytical formalism presented here can be used to validate numerical methods, and the results of the simulations can be utilized as a priori knowledge in optimizing and designing acousto-elastic radiation force experiments involving elastic compressional progressive waves on a sphere in acoustically-engineered materials applications, elasticity imaging methods, activation of implantable devices, characterization of biological tissue, and non-destructive evaluation to name some examples.

In view of the recent interest in modifying the surface functionality and esthetics of polymeric materials by sand blasting treatment, a numerical model was developed as a tool to predict the evolution of surface morphology as a function of blasting parameters. The wide range of shot size and shape variations, typical of blasting media, were parametrized based on microscopical observations. Thus, the developed numerical model accounts for the media inhomogeneity and also implements randomness in both the sequence and position of the multiple impacts. To make the model as realistic as possible, the velocity of individual shots was calculated based on their interaction with the airflow. Systematic experiments were performed using Polycarbonate (PC) as the substrate material and Alumina as the blasting media. A comparison of the experimental and numerical results demonstrated the ability of the developed model to successfully predict the surface roughness generated by sand blasting, as the shot arrangement and distribution were varied. This model establishes a potential basis for future studies regarding the performance of the sand blasted surfaces such as wettability using numerical approaches.

In this article, to study the fluid behavior on various specific conditions to improve the heat transfer system and here, analysis on mathematical model of dynamic fluid consist of micropolar fluid has allowed micro rotational effect with laminar flow of Darcy forchheimer model which allow inertia effect has incorporated with heterogeneous and homogenous chemical reaction undergoes heat exchanger system with boundary layer problem has modeled. The mathematical model of fluid mechanic governing equations are in the form of partial differential equation (PDE) and similarity transformation into numerical methods (PC4-FDM) of predictor and corrector technique undergoes discretized mesh point and convergence with fourth order finite difference method and shooting method is also equipped to get better solution. The additions of significant heterogeneous parameter depicts that increasing behavior in fluid concentration and homogeneous parameter depicts that decreasing in fluid concentration by allowed micro rotations leads to collision and on increasing the Eckert number related to viscous dissipation has exhibited that increased fluid velocity and decreased fluid temperature. Micro rotation parameter exhibits that similar increased fluid velocity and slight decreased in temperature of the fluid. Darcy forchheimer parameter which related to inertial effect has depicts that decreased in velocity with increased temperature of the fluid in convection system. Due to Industrialization, the study of convection heat transfer system has enormous scope which has necessity to improving the heating and cooling system of industrial mass machineries like powerplant, waste heat recovery unit, pharmaceutical industries etc.