Repairing cracked aerial structures using patches is a common way to restore mechanical properties, strength and extend fatigue life. The performance of such patches can be obtained by comparing the maximum amount of force tolerated by the repaired piece with the unrepaired piece. The shape and dimensions of the patch used to repair the crack and the way the patch is bonded affect the repair quality which are of great importance. Therefore, in this paper, we investigate the factors affecting the diffusion bonding between the patch and the piece. The impact of the shape of the aluminum patch attached on a 10 mm central crack piece and perpendicular to the loading direction (mode I) is studied experimentally and numerically. The optimum conditions for the diffusion connection including the pressure, time and temperature of the connection were obtained experimentally using a composite rotatable centered design and in the connection made under these conditions, the patch shape and aspect ratio was considered as variables of design, and the results were obtained for square, rectangular, circular and elliptical patches. At the end, it was found that the best connection under the pressure conditions of 570 °C, 70 bar and 100 min was formed and the rectangular patch efficiency was greater whereas its extent is more in line with crack than the other modes. At a fixed area, the different patch geometries investigated in this study were able to influence up to 80% of the maximum force tolerated by the repaired parts. Also, there is an acceptable convergence between experimental and numerical results. تفاصيل المقالة

One of the most valid and efficient models of long rod projectile penetration in homogeneous targets is Tate and Alekseevskii’s (A&t) model. Based on Tate’s model, the present research tries to calculate the optimum speeds to achieve the maximum penetration depth in the homogeneous targets. The proposed collision speed-penetration depth diagrams are developed using Tate’s model. In this way, various collision speed-penetration depth diagrams for different projectile dynamic resistances and targets are calculated and the optimum speed envelope is derived. According to Tate’s diagrams, the increase of collision speed is not followed by the increase of penetration depth; instead, it causes erosion phenomenon to happen. The comparison of the resulted optimum penetration speeds and the available data confirms the findings. Speed and rigidity both have a positive impact on the increase of penetration depth. With the increase of speed, the erosion issue finds a higher significance due to the increase of pressure on the projectile tip. Therefore, higher speed and erosion are opposed to each other; for the case of Y>R, there are some maximum points which indicate the optimum reciprocity of the two mentioned factors to obtain a maximum penetration depth. In the present research, an equation is developed indicating the optimum speeds resulting in the maximum penetration rate in the case of Y>R. For the reciprocity of speed and erosion, the target resistance against an erosive projectile should be 4 to 5 fold higher than the same target resistance against a rigid projectile penetration. [1] تفاصيل المقالة