Residual stress evaluation in friction stir welding of aluminum plates by means of acoustic emission and ultrasonic waves

© Faculty of Mechanical Engineering, Belgrade. The residual stress assessment in structures is essential for optimization of the structures' design. The attention of this paper is focused on how acoustic emission signals caused by tensile loading of the friction stir welded aluminum plates are expected to vary depending upon the residual stress. To this aim, the distribution of residual stresses in two friction stir welded aluminum specimens was firstly evaluated by ultrasonic stress measurement. AE signals were then produced during tensile tests and captured using AE sensors. The obtained AE signals were analyzed using statistical features including crest factor, cumulative crest factor and sentry function. It was found that the crest factor could be used to identify the presence of the residual stresses and that the trends of sentry function are in good agreement with the results of crest factor and cumulative crest factor

Effect of the drilling process on the compression behavior of glass/epoxy laminates

Composite materials have been widely used in various industries due to their superior mechanical properties. Drilling is a very common machining operation to install fasteners for assembly of laminates. Delamination, however, is a serious concern in the drilling of fiber reinforced composite materials, because it reduces their compressive residual strength. This paper studies the effects of drilling parameters on the thrust force, adjusted delamination factor and compressive residual strength of uni-directional glass/epoxy resin. The design of the experiment was based on the Taguchi method. The results highlight the importance of the feed rate for maximizing the compressive residual strength of drilled laminates. The Acoustic Emission (AE) technique was also used to monitor both drilling process and compression test. The objective was to establish a correlation between AE parameters and mechanical characteristics. The results reveal that root mean square (RMS) can be used for monitoring thrust force and AE energy for compression force