The fatigue failure around rail-end-bolt holes is particularly dangerous since it leads to derailment of trains and consequently to inevitable accidents. It is well-known that the fatigue life of structural holed components, subjected to cyclic load, can be increased by generating compressive hoop stresses around the holes. These beneficial residual compressive stresses significantly reduce the maximum values of the operating tensile stresses arising at the critical points of the components and thus impede the formation of first mode cracks. A new approach to enhancement of fatigue life of rail-end-bolt holes has been developed. The approach involves sequential drilling and reaming through a new combined tool and then slide diamond burnishing by a new device. The technology implementation was carried out on machine tool. The process of creating residual stresses has been studied both experimentally and numerically. The experimental study was conducted by means of a modified split ring method. A reliable finite element modeling approach to the slide diamond burnishing process was developed. On this basis, the process was optimized by means of a genetic algorithm. As a result, the optimal combination of the governing process parameters is established, which ensures both maximum depth of the compressive zone and maximum absolute values of the residual stresses.
In this paper, we have provided hands-on experience in systematic design, implementation and flight test of an atmospheric data acquisition flying vehicle as a standard CanSat telemetry mission. This system is designed for launching from a rocket at a separation altitude about 1000-meter. During its flight, the reusable flying vehicle collects environmental data and transmits it directly to the ground station. The ground station, which is implemented at a pre-defined radio frequency band receives data and plots the respective graphs. The design performs based on a systematic approach, in which the first step is set aside to mission and objectives definition. In the next step, the system requirements are identified and the required main subsystems and elements with their technical requirements will be extracted. The structure analyses were also performed by ABAQUS software to obtain the natural frequency and the mode shape. The wireless communications, onboard microcontroller programming, sensor interfacing and analog to digital conversion describe the basic technologies employed in the system implementation. This flying vehicle in comparison with the other similar ones is more lightweight, has few interface circuits and high precision sensors. According to the flight test outputs, low power consumption, high transmit line up to 2Km despite of limitation in TX power and up to 10g normal acceleration withstanding are important specific characteristics of the implemented flying system.
The effect of first nonsingular stress term of elastic stress field on fracture toughness around bi-material notch tip is studies in this paper. First, a modified maximum tangential stress criterion (MMTS) is proposed for determination of the fracture toughness at the tip of the interface notches. The proposed criterion takes into account the effect of first nonsingular stress term as well as the singular stress terms. Then, the effect of I-stress on determination of the fracture toughness is studied analytically. Finally, the proposed criterion is applied on a finite element (FE) simulated laboratory specimen. A very good correlation was observed between the FE results and theoretical predictions.
Fracture phenomenon in orthotropic materials, generally associates with region called, “damaged zone” in crack tip vicinity. In quasi-brittle materials, this area is known as fracture process zone (FPZ). This area contains a multitude of microcracks, which cause difficulties in analytical process of the region. Also, energy waste in damaged zone can affect the material fracture properties. The characteristics of damaged zone should be considered to figure out the residual strength of composite materials. It also can help to predict the value or even the direction of crack growth of orthotropic materials. So far, several efforts have been made to determine the mechanical properties of this region, but none of them (due to the immense complexity of this region) can express the behavior of this region properly. Moreover, previous approach has not been verified by new experimental and numerical results, yet. In the present study, a new approach “damaged zone simulation (DZS)” is proposed based on the experimental and numerical data, for investigating the orthotropic damaged zone properties. Comparison with existing analytical data shows the capabilities of the presented approach.
This paper presents a perfect analytical solution of the hyperbolic asymmetric heat conduction equation and the related thermal displacement equation within a long hollow cylinder (plain strain condition) exposed to a harmonic boundary condition. The material is assumed to be homogeneous and isotropic with temperature-independent thermal properties. The standard method of separation of variables is used for solving the problem with time-independent boundary conditions and the Duhamel integral is used for applying the time-dependency. The results show the wave behavior of Non-Fourier thermal stresses and higher oscillation amplitude in comparison with Fourier one. The developed analytic answer can be applied for modeling cylindrical shell of nuclear rod and can be applied as a benchmark to validate the other numerical solutions.
Laser forming is a modern metal forming method in which no mechanical force is needed. In this paper, numerical and experimental approaches to this phenomenon on were conducted. Numerical method comprised of couple heat-displacement. In it, heat flux distribution of laser beam was applied on the steel layer in Gaussian form and by using subroutine code writing procedure. Experimental tests were conducted by using Nd: YAG laser with maximum power of 300 watts and on a bi-layer Fe/Al work piece. The result of bending angle at different laser power ranges indicated that bending angle increases occur as this parameter is increased.
In this paper, an analytical method is proposed for calculation of natural frequencies of a delaminated composite beam from both free and constrained mode frequencies. In previous studies, the frequencies of a delaminated composite beam were computed with assumption of occurring open or close delamination during the vibration. According to this assumption, two separated modes, i.e., “free mode” and “constrained mode”, are occurred in vibration of the delaminated beam. In fact, a delamination may breathe (open and close) during the vibration and the assumptions of the free or constrained mode models are not completely correct in the whole of the vibration period. For this reason, a new formulation is proposed for calculation of natural frequencies based on the breathing of delamination. The obtained results are compared with various theoretical and experimental results available in the literature. Thus, the effects of location and size of delamination can be investigated on the natural frequencies of delaminated beams.
In this paper, a simplified method is proposed for deriving equilibrium equations in continuous systems. The new method is indeed the direct applying of Newton’s laws on free body diagram of point. First, by describing the concept of equilibrium equations and investigating the differences between concentrated masses and continuous systems, the physical basis of new method is introduced. It is shown that, using intensive properties simplifies the analysis of continuous systems. For verifying the new method, the governing equations in Cartesian, polar and spherical coordinates systems are derived. We have to consider nonlinear terms due to developing large slopes in system. Hence, nonlinear governing equations in Cartesian system are derived too. Finally by noting to the simplicity of new method and its independency from complicated differential and vector analysis in other methods such as Hamiltonian and classic methods, the interests of new method are emphasized. By knowing concept of physical point, a united process is accessible which is extendable to other governing equations of continuous systems.