جستجوی مقالات مرتبط با کلیدواژه "آزمون غیرمخرب" در نشریات گروه "مکانیک"

In recent years, considerable efforts have been deducted to evaluate the quality of various products. In this regard, quality control of products fabricated by the additive manufacturing methods has become a new interest. In the 3D printing industry, Defect detection could have a vital role in the final evaluation of products. In this study, artificial defects are located in PLA samples printed with different infills via the Fused Deposition Modeling (FDM) method. In order to detection of the mentioned defects in these parts, the Active IR Thermography was employed. Thermal stimulation was selected as excitation method. Two different excitation formation including transmission and reflection mode are used. In order to validate the results, the temperature-pixel diagram for each sample were illustrated. The effect of Gaussian filter on thermal images was also investigated to facilitate the identification of the obtained images. The experimental results indicated the capability of thermally stimulated thermographic inspection in detection of defects in FDM printed parts.

Shearography is one of the advanced methods of non-destructive techniques based on the interference of laser beams that have been reflected from the surface of the specimen. This method, which has high speed and accuracy, can evaluate the displacement derivative on the sample surface at once. In this paper, the possibility of sub-surface cracks detection with different lengths and angles in composite samples was investigated by shearography method and thermal stimulation system. For this purpose, in composite samples, controlled cracks were created with different lengths and angles. After calibration of the performance of the shearography setup, two heat sources of radiation were used to load samples. Loading quantity, the amount and direction of the shear, the cracks length, and their angles were chosen as the studied parameters. The results of this paper showed that the optimum loading amount plays a more critical role in the quality of the results than shear amount, and this value is related to the materials of the samples. To achieve the best results in crack detection on the selected specimens, optimum thermal loading was obtained between 12 and 15 seconds from in front of the specimen. Also, the optimum shear amount in the composite specimens was estimated at about 0.1 image width recorded by the camera. With the optimized values, all sub-surface cracks were identified.

Thermal image analysis can be used to identify and detect patch defects in the interface between multilayer sheets. Specimens made for testing were carbon fiber and glass fiber patches on aluminum sheets that were embedded in composite patch layers, for interlayer separation, in different metal-patch joints. The defect pattern was designed so that the bugs at the edge and center of the patch were tested simultaneously. In this study, the effects of depth and dimension of separation faults with pulsed heat treatment were identified and investigated. Then, the factors affecting the accuracy of the identified defect size were investigated. In the thermal images obtained, almost all the defects can be identified by pulsed thermography and with increasing the size of the defect the thermal difference with the sound areas increases. It was found that the defects in the carbon fiber field were up to an average of 1°C, there was a greater thermal difference than that of glass fiber field. However, the results showed that the accuracy of the measurement of defects in glass fiber was 2 times higher than that of carbon fiber.

Nowadays, the use of a non-contact digital imaging system for non-destructive testing on composite materials has received much attention because of its advantages. In this research, the shape, position and area of ​​the breakdown region in glass/epoxy samples with blind holes and different depths under tensile loading have been investigated using a non-contact digital imaging system. Specimens with a 10 mm diameter blind, depths of 0.5, 1 and 1.5 mm, and an average thickness of 4 mm have been subjected to the tensile loading. Lateral strain contours for all three samples have been obtained at different loads. By increasing the lateral strain loading, it focuses on an area on the surface of each specimen that corresponds to the position of the blind hole. Then the lateral strain is measured separately in length and width for each specimen. Increasing the amount of loading and the depth of the breakdown have resulted in greater strain concentration in the breakdown area as well as increasing the accuracy of the digital images correlation system. The position, shape, area, and diameter of the blind hole measured by digital image correlation method have been compared with real values, which considering the acceptable consistency of the results of the digital image correlation method with the features of each sample, It can be used as an efficient method for detecting and evaluating failures in composite structures.

In this paper, the evaluation of infrared thermography has been done to detect subsurface defects of polymer composite pipes made by filament winding method. In this method, in order to stimulate the test specimen, the heat flux is applied over the surface of the specimen and the thermal response is processed to detect defects. Experimental investigation was applied by hot air, optical pulse, and modulated stimulation on specimens were made with common controlled defects in composite materials. Interpretation of the results were utilized in the calculation of defects’ size and location, it was observed that in specimen with 4 mm thickness dry fiber defect with a minimum size of 3040 mm, delamination and inclusion defects with a minimum size of 25*25 mm clearly is detected and is measured. The evaluation of thermal stimulation techniques shows in the examined samples, according to the type of cylindrical structure and ability of applying thermal fluid to its internal side, the method of hot air stimulation by the blower is a reliable method and provides trusted results.

In certain cases, the presence of residual stress reduces the strength of parts, hence, its detection and estimation is of great importance. Ultrasonic waves have the potential to be employed in nondestructive tests to do this task. The analysis is based on the acoustoelasticity properties of the material that studies changes in wave velocity when passing through a stressed medium. To derive the equations of motion for a particle in a stressed elastic solid, it is supposed that the displacement vector consists of two parts: a static part, which may be developed by a residual or applied stress field, and a dynamic part, which is produced due to wave propagation and is considered a small amplitude harmonic motion. The finite displacement theory is employed to derive the general form of the non linear equations of motion in three dimensions for an incident wave at various angles, which are made linear by the Taylor expansion method. Various components of the wave velocity are computed from linear equations as an eigenvalue problem. Relative velocity changes versus one dimensional stress and strain in an aluminum block, and the effect of wave incidence angle on the propagation velocity are established and plotted. It is shown that the speed of wave in a stressed elastic solid depends not only on the material properties of the solid, but, also, on the wave incidence angle and the propagation and particle displacement direction relative to the stress direction. From the presented diagrams, it is revealed that if the direction of incidence and propagation of the wave coincides with the direction of normal stress, then, the velocity of the longitudinal mode will decrease in tension and increase in compression. On the other hand, the velocity of shear wave will increase in tension and decrease in compression. These conclusions agree with the results in other references. Comparing the slope of relative velocity diagrams in a stressed body, we conclude that the velocity of longitudinal waves that are incident along the normal stress component, is greater than other wave modes, although the magnitude of this change is very small for either modes; say, about 0.6 percent for longitudinal waves at 70 MPa tension in aluminum. Therefore, precise measurement of the flight time of the wave is necessary.