Materials Science Forum Vol. 726

Abstract: Effects of variables related to design and production of riveted lap joints representative of longitudinal sheet connections for a pressurized transport aircraft fuselage were experimentally investigated. The specimens from an aircraft Al alloy D16 Alclad sheets of three different thicknesses (1.9, 1.2 and 0.8 mm) were assembled under load control using round head rivets and rivets with the compensator from a P24 Al alloy. For the joints from 1.9 mm thick sheets fatigue tests indicated a dependency of the crack initiation site and crack path on the squeeze force level and on the rivet type. At the same time, increasing the squeeze force led to improved fatigue properties of the joints, specimens assembled using the rivets with the compensator showing fatigue lives consistently longer than joints with the round head rivets. All observed trends have been explained based on hole expansion and load transfer measurements. For thin sheets connected using the round head rivets, local deformations and indentations under the driven rivet head promoted crack initiation and failure in the adjacent sheet. Fatigue test results indicated that the detrimental effect of this type imperfections could outweigh the benefits associated with a decrease in secondary bending due to thinning the sheets. The rivets with the compensator were observed to cause significant local imperfections beneath the manufactured head, which adversely affected the joint fatigue performance.

Abstract: In the paper method of displacement analysis in the cracking zone based on digital image correlation and advanced multi-processor graphic cards procedures was presented. The basic assumption for the discussed displacement and strain measurement method under time variable loads was obtaining high measurement sensitivity by simultaneously minimizing the measurement time consumption. The developed digital procedures for correlation of images has been used for an example of displacement analysis in the crack propagation testing in airplane riveted joints.

Abstract: The authors of this article have presented a hybrid method for inspection in the visible and infrared bands. A model of a test stand equipped with a monochromatic CCD and thermovision cameras which enable execution of tests in the field of active and passive thermography has been presented. Application of two vision channels provides the possibility of observing the defects caused by cracks and non-uniformity of a material structure, in the subsurface layer. An analysis of experimental tests performed on selected objects has been presented. Images from both channels, effects of the image overlapping and profiled charts along characteristic lines in thermograms have been shown.

Abstract: The article presents a dual-camera vision system for fatigue monitoring composed of a vision unit, a camera positioning set and a computer unit. Vision modules are mounted onto the 4DOF positioning sets, which allows for an easy determination of the position of the camera in relation to the sample. The application of motorized measurement lenses with changeable configuration, thanks to the alteration of the distance of observation and the vision angle, enables the adaptation of the system to different scales of observation of the fatigue processes in the specimen surface. Automatic focus setting is realised with the use of the implemented algorithm. The software developed allows for the analysis of fatigue fracture for two 2D images or the 3D stereovision image.

Abstract: The paper discusses issues related to the damage accumulation and cracking in steels. Special attention is paid to the selection of appropriate methods in the modeling of progressive damage development. In special cases, the accumulation of damage and crack propagation may lead to the brutal destruction of machine parts. In addition, some attention was drawn to the conditions that can lead to this brutal destruction.