Nowadays CMM machines are widely used in surface measurement and inspection. As inspection results from CMM machine are obtained by the means of measuring surfaces with direct contact, they are more precise than non-contact method (like optical measurement). However, CMM machines give more reliable and accurate results rather than non-contact methods but also these results come with error when outer surface contains porosity spaces. This paper proposes a new method for measuring outer surface of porous objects. In this method the probe will be located above the porous area and doesn’t enter inside. The proposed strategy could be utilized whether CAD model of object is available or not. If CAD drawing of object exists, the probing stylus will not enter into the hole. On the other hand, if the CAD drawing doesn’t exist a perpendicular plane to the surface will be virtually modeled and by this normal plane the outer surface of the object will be estimated. In addition in this research an effort has been made to reduce dependence on CAD drawing. تفاصيل المقالة

In this paper a new method for Nondestructive testing or Nondestructive evaluation is proposed for Glass-Epoxy composite. For this purpose, impact-echo is used to evaluate the properties of composite materials, detecting internal defects and thickness measurement. In the impact-echo method a steel ball impacts on a composite plate and generates stress waves or P-waves which will be transferred into the plate. The results show that impact response of the composite plate for dominant thickness frequency for measuring thickness and locating the defect is in agreement with the normal measurement. Results represent that this method could be used for thickness measurement and flaw detection of Epoxy-Glass composites with a reasonable accuracy. تفاصيل المقالة

In this paper, an Impact-Echo method has been used to numerically simulate low velocity impact of a steel ball on laminated composite plates in order to measure the plate's thickness. For the purpose of simulation, Ls-Dyna finite element code has been employed to express the behaviour of impact between steel ball and composite plates. Furthermore, a single node near the impact area has been chosen and its displacement was demonstrated during the impact time on a graph by the software. After that, displacement-time graph was transformed to amplitude-frequency domain graph by means of Fast Fourier Transform which was done by MATLAB software. The peak frequency was used to calculate the plate's thickness. The calculated thickness was verified by real plate thicknesses and this comparison shows an acceptable agreement between simulation and experimental results. تفاصيل المقالة

In this paper, a circumferential external surface flaw in a metallic round pipe under cyclic bending loading is considered. Because of very rapid changes in the geometrical parameters around the crack front region, the mesh generation of this region must be done with great care. The analysis of the fatigue crack growth is done in accordance with Paris law. The spread lane of the exterior defect is achieved from the graph of “α” vs. “relative crack depth”. The growth of fatigue crack is also analyzed (the comparative crack depth against loading runs diagram) with various initial crack “α” beneath periodic loading. Fatigue shape growth of primarily semi-elliptical peripheral surface flaws is shown. The weight of the Paris exponent (material constant) on fatigue crack propagation is presented as well. Furthermore, the “fatigue crack growth” progression of several specimens is evaluated experimentally by employing a manually-constructed experimental setup. Conclusively, the experimental results achieved by periodic bending loading tests are compared with the numerical results. Fatigue shape development of initially semi-elliptical external surface defects is illustrated. The effect of the Paris exponent (material constant) on fatigue crack propagation is shown as well. Moreover, the fatigue crack growth of several specimens is assessed experimentally using a manually-constructed experimental set up. Finally, the experimental results obtained by cyclic bending loading tests are compared. تفاصيل المقالة

Strength reduction in structures like an aircraft could be resulted as cyclic loads over a period of time and is an important factor for structural life prediction. Service loads are emphasized at the regions of stress concentration, mostly at the connection of components. The initial flaw prompting the service life was expected by using the Equivalent Initial Flaw Size (EIFS) which has been recognized as a powerful design tool for life prediction of engineering structures. This method was introduced 30 years ago in an attempt to study the initial quality of structural details. In this paper, the prediction of life based on failure mechanics in a riveted joint has been addressed through the concept of EIFS. For estimation of initial crack length by EIFS, extrapolation method has been used. The EIFS value is estimated using the coefficient of cyclic intensity (ΔK) and using the cyclic integral (ΔJ), and the results are compared with each other. The simulation results show that the if the coefficient of tension been used in EIFS estimation, which based on the Paris law, the EIFS value will be dependent on the loading domain, while the use of the J-Cyclic integral in the EIFS decrease its dependence on the load domain dramatically. تفاصيل المقالة