Experimental evaluation of the plane stress fracture toughness for ultra-fine grained Al/Al specimens prepared by accumulative roll bonding process. Materials Science and Engineering A.
In this study, ultrafine grained Al5052/Cu multilayered composite has been produced by accumulative roll bonding (ARB) and fracture properties have been studied using plane stress fracture toughness. The fracture toughness has been investigated for the unprocessed specimens, primary sandwich and first, second, and third cycles of ARB process by ASTM E561 and compact tension (CT) specimens. Also, the microstructure and mechanical properties have been investigated using optical microscopy, scanning electron microscopy, uniaxial tensile tests, and microhardness measurements. The value of plane stress fracture toughness for the ultrafine grained Al5052/Cu composite increased by increasing the number of ARB cycles, continuously from the primary sandwich to end of the third cycle. The maximum value of 59.1 MPa m1/2 has been obtained that it is about 2.77 and 4.05 more than Al5052 and pure Cu (unprocessed specimens). This phenomenon indicated that ARB process and the addition of copper to aluminum alloy could increase the value of fracture toughness to more than three times. The results showed that by increasing the ARB cycles, the thickness of copper layers reduced and after the fifth cycle, the excellent uniformity of Cu layers achieved. By increasing the number of ARB cycles, the microhardness of both aluminum and copper layers have been significantly increased. The tensile strength of the sandwich has been enhanced continually, and the maximum value of 566.5 MPa has been achieved.
In the notched structures, to achieve maximum buckling resistance in comparison with structural weight, the optimal design of a stiffener is very important. In this research, after a review of the existing literature, nonlinear buckling behavior of composite plates containing the cutout with three different designs of stringer was investigated. The considered stiffeners are planer, longitudinal, and ring types. The buckling experiments were carried out on the stiffened plates containing a circular notch. Moreover, to achieve an efficient prediction of the buckling in the stiffened laminate with the hole, a finite strip method is developed based on the Airy stress function and von Karman’s large deformation equations. Studies show that there is a good agreement between the postbuckling behaviors derived from developed finite strip method with experimental results. Fast convergence of the considered finite strip method compared with the finite element results shows its efficiency for prediction of buckling behavior in laminated composites. The results show that the buckling load-bearing capacities of perforated plates with a longitudinal and planer stiffener are higher compared with the other stiffener, respectively. The detailed parametric study on the effects of thickness of the plate and stiffener and opening diameter on buckling behavior was performed using experiments and modeling.
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