جستجوی مقالات مرتبط با کلیدواژه « crack » در نشریات گروه « مکانیک »

Analyzing and modeling damage and crack growth in bodies and structures is one of the important issues in designing methods to prevent crack growth or stop it in order to avoid sudden fracture and increase the lifetime of structures. Extensive research has been performed in the field of modeling fracture, crack growth, and damage in bodies and structures. However, there are still many problems in modeling crack growth and damage in bodies with points of singularity and discontinuities. In recent years, a new theory called peridynamic has been proposed to model and analyze such problems. The formulation framework of peridynamic theory is based on integral equations. In addition, points of singularity and discontinuities and damage in the body and modeling them are another type of deformation and part of the structural equations of this theory. As a result, the peridynamic theory is used directly, without the need for additional relations to model crack growth in problems involving points of singularity and discontinuities. In this paper, a bond-based peridynamic modeling for unidirectional carbon fiber reinforced polymer material(UDCFRP) orthogonal cutting process is proposed, and the corresponding composite material bond failure criterion is also investigated for better revealing the machining mechanism of UD-CFRP machining. From comparing between simulation and experimental results, it can be indicated that the peridynamic modeling is capable for predicting the chip formation and surface crack and damages in UD-CFRP machining.

In this research, an analysis of the stress and stress intensity factor in a cracked plate under thermal and mechanical loading is done. For this purpose, using MATLAB coding, a plate with a center crack was modeled by the isogeometric method (IGA) based on the Bezier extraction operator. In this method, NURBS basis functions are generated as a linear combination of Bernstein polynomials using the Bezier extraction operator. Using this operator Bezier elements with Co continuity (similar to elements of the finite element method) were produced and Bernstein polynomials are defined on these elements. In order to model the crack, the extended isogeometric method (XIGA) was used. In this method, the control points that exist along the crack and at the tip of the crack are identified and extracted using the proper level set functions. Therefore, there is no need to re-meshing or modify the elements. By enriching the extracted control points with appropriate enrichment functions and applying boundary conditions, the analysis process was carried out and the strains and stresses were calculated. Finally, the value of the first mode stress intensity factor was obtained based on the interaction integral method. To check the accuracy of the obtained results, a similar analysis was performed using the finite element method and the results obtained from both methods were compared. These studies showed that the considered isogeometric method provides more accurate solutions with a much smaller number of elements and computational costs.

Bonded repair of cracks by gluing patches in metal structures has been widely used due to high strength and speed, and easiness. Obviously, the efficiency of this repair is affected by the shape of the patch. In this research, the shape of the patch with constant thickness is optimized in the unsymmetric bonded repair of an aluminum plate with a central crack, under uniaxial tension perpendicular to the crack. For this purpose, a topology optimization algorithm based on the strain energy density homogenization has been used. The two-dimensional three-layer finite element model of Naboulsi and Maal has been used to model and analyze the repair system. The results show that the optimal shape efficiency of this algorithm in reducing the strain energy released at the crack tip per unit of crack extension is affected by the dimensions of the design initial geometric space relative to the crack length and its volume relative to the patch material volume. It is a efficiency criterion of repair. Therefore, with the appropriate selection of the initial space, the optimal shape of this algorithm is desirable both from the point of view of the repair efficiency criterion and from the point of view of construction.

The goal of this study is to analyze the interplay of mechanical and thermal properties and the applied thermomechanical cyclic load combined with the fatigue crack numerical simulation of a thick cylinder. The applied boundary conditions are similar to the working gun barrel during continuous firing. Four stress conditions in 25-950°C and 100-400 MPa pressure has been investigated. Conditions include first, without autofrettage and cracking; second, with autofrettage and without cracking; third, without autofrettage and with cracking; and fourth with autofrettage and with cracking has been investigated. A comparison of the results obtained from simulated models of the autofrettaged and non-autofrettaged barrels has information about the evolution of strains and stresses in the barrel at different points under thermo-mechanical loading cycles in both cases. The materials in the barrel were ST50 steel and SiC/Ti-24Al-11Nb metal matrix composite in three different diameter ratios. The results showed that autofrettage softened the inner surface of the barrel. This phenomenon was seen as a decrease in the hardness of the inner surface of the barrel. The maximum stress of thermomechanical cyclic loading there was until 9 mm of depth. This depth is the active length of crack propagation.

Bearings are one of the main components used in the drive-train of electrical machines. Early fault diagnosis and classification of bearing fault for maintenance of electromechanical system are very important. With progresses in measurement and digital systems, extensive range of real-time data can be available in electrical machines. Since fault diagnosis based on signal processing methods from extracted signals may not be possible due to different reasons such as noise level, natural frequencies of system, saturation of core,, severity of fault and load torque, deep learning methods have been considered in recent years. In this paper, time series deep learning method for condition monitoring of bearing in electrical machine for the purpose of detection and classification of fault is considered. Obtained results by means of proposed method have been compared with pervious techniques. Experimental results show that proposed deep learning method can detect and classify bearing fault with accuracy above 90%.

The free and forced vibration analysis of a rotating large flexible structure with a single crack is investigated using the Homotopy Perturbation Method (HPM). The crack is modeled with a torsional spring element on a structure that follows the Euler-Bernoulli theory. The nonlinear equations of motion of the co-rotational system considering centrifugal forces are derived using the calculus of variation and the Assumed Mode Method (AMM). Applying the Galerkin method, the spatial domain is extracted and the time domain is transformed into a second-order nonlinear differential equation. The results of time response, phase plane, and bifurcation diagrams for different functional parameters variations such as base angular velocity, crack position and stiffness have been analyzed. Moreover, it is shown that as the base angular velocity increases, a tensile force appears along the cracked structure axis, stiff it, and shifts the backbone to the right, this can highly affect the nonlinear features of the system.